close

Вход

Забыли?

вход по аккаунту

?

s00710-017-0540-0

код для вставкиСкачать
Miner Petrol
DOI 10.1007/s00710-017-0540-0
ORIGINAL PAPER
Evaluation of magma mixing in the subvolcanic rocks
of Ghansura Felsic Dome of Chotanagpur Granite Gneiss
Complex, eastern India
Bibhuti Gogoi1 · Ashima Saikia1 · Mansoor Ahmad2 · Talat Ahmad1 Received: 21 June 2016 / Accepted: 16 October 2017
© Springer-Verlag GmbH Austria 2017
Abstract The subvolcanic rocks exposed in the Ghansura
Felsic Dome (GFD) of the Bathani volcano-sedimentary
sequence at the northern fringe of the Rajgir fold belt in the
Proterozoic Chotanagpur Granite Gneiss Complex preserves
evidence of magma mixing and mingling in mafic (dolerite), felsic (microgranite) and intermediate (hybrid) rocks.
Structures like crenulated margins of mafic enclaves, felsic
microgranular enclaves and ocelli with reaction surfaces
in mafic rocks, hybrid zones at mafic-felsic contacts, backveining and mafic flows in the granitic host imply magma
mingling phenomena. Textural features like quartz and titanite ocelli, acicular apatite, rapakivi and anti-rapakivi feldspar
intergrowths, oscillatory zoned plagioclase, plagioclase with
resorbed core and intact rim, resorbed crystals, mafic clots
and mineral transporting veins are interpreted as evidence of
magma mixing. Three distinct hybridized rocks have formed
due to varied interactions of the intruding mafic magma with
the felsic host, which include porphyritic diorite, mingled
rocks and intermediate rocks containing felsic ocelli. Geochemical signatures confirm that the hybrid rocks present
in the study area are mixing products formed due to the
interaction of mafic and felsic magmas. Physical parameters
like temperature, viscosity, glass transition temperature and
Editorial handling: A. R. Chakhmouradian
Electronic supplementary material The online version of
this article (https://doi.org/10.1007/s00710-017-0540-0) contains
supplementary material, which is available to authorized users.
* Ashima Saikia
[email protected]
1
Chatra Marg, Department of Geology, University of Delhi,
Delhi 110007, India
Rajabazar, Patna 800020, India
2
fragility calculated for different rock types have been used
to model the relative contributions of mafic and felsic endmember magmas in forming the porphyritic diorite. From
textural and geochemical investigations it appears that the
GFD was a partly solidified magma chamber when mafic
magma intruded it leading to the formation of a variety of
hybrid rock types.
Keywords Chotanagpur Granite Gneiss Complex ·
Bathani volcano-sedimentary sequence · Magma mixing
and mingling · Mineral-transporting veins · Felsic ocelli
Introduction
Interaction between mafic and felsic magmas may occur at
different crustal levels leading to the formation of a variety
of hybrid magmas (Annen et al. 2006; Bonin 2004; Kemp
et al. 2007; Pietranik and Koepke 2009). Understanding the
process of magma interaction is very essential to tracing the
evolutionary history of hybrid rocks. Constraining some of
the important physical properties of magmas can significantly contribute toward understanding magma mixed systems, as magma mixing plays a significant role in magma
diversification and also it is considered one of the dominant
mechanisms triggering volcanic eruptions. Direct evidence
of mingling observed in the field includes structures like
crenulated margins of enclaves, back-veining, reaction surfaces and hybrid zones at mafic-felsic contacts, indicating
thermal disequilibrium and comingling of two contrasting
magmas after injection of relatively hotter mafic magma into
a colder felsic magma chamber (Dorais et al. 1990; Waight
et al. 2001; Tepper and Kuehner 2004; Kumar and Rino
2006; Pietranik and Koepke 2009). Textural features like
quartz and titanite ocelli, acicular apatite, resorbed crystals,
13
Vol.:(0123456789)
B. Gogoi et al.
complex zoning in minerals and rapakivi texture are considered reliable petrographic indicators of magma mixing
(Hibbard 1991; Kuşcu and Floyd 2001; Baxter and Feely
2002; Gioncada et al. 2005; Pal et al. 2007; Burda et al.
2011). Detailed analysis of mixing structures and textures
can significantly contribute toward understanding the complex mechanisms governing magmatic interactions, which
in turn can enhance our knowledge on magma dynamics in
particular and magmatic systems as a whole. This paper discusses in-depth field and petrographical observations carried
out on the GFD, where mixing of mafic and felsic magmas
has led to the formation of a variety of hybrid rocks, i.e.,
porphyritic diorite, mingled rocks and intermediate rocks
containing felsic ocelli. Emphasis is placed on the petrogenesis of the intermediate rocks containing abundant felsic
microgranular enclaves (FME) or felsic ocelli. Furthermore,
the fine-grained nature of the rocks helped to understand
the veining mechanism occurring on a micro-scale in the
mingled rocks in our study area. These veins played a key
role in facilitating the mixing process by transferring crystals
between the mafic and felsic phases.
This paper also showcases the reliability of two experimentally derived magma mixing models that uses physical
properties of the magmas involved in the mixing process.
The conventional mixing model of Fourcade and Allégre
(1981) and two experimental magma mixing models based
on the physical properties of the magmas involved in the
mixing process and developed by Giordano et al. (2008)
were applied to test for the geochemical evidence of magma
mixing and to calculate the relative contributions of the
mafic and felsic magmas in forming the hybrid rocks of
GFD. The results of this modeling enabled us to constrain
the physical properties of the interacting mafic and felsic
magmas and their resultant hybrid product.
Fig. 1 Geological map of the Chotanagpur Granite Gneiss Complex
(modified after Acharyya 2003). Abbreviations: DL- Daltonganj,
DM- Dumka, DVB- Dalma Volcanic Belt, D- Dudhi, J- Jirgadandi,
MGB- Makrohar Granulite belt, NPSZ- North Purulia Shear Zone,
PR- Purulia, RJ- Rajmahal Hills, RN- Ranchi, R- Rihand - Renusagar Area, SMGB- Son Mahanadi Gondwana Basins, SPSZ- South
Purulia Shear Zone, SSZ- Singhbhum Shear Zone, SONA- Son Narmada Lineament, M- Munger, VB- Vindhyan Basin, BVSs- Bathani
Volcanic and Volcano-sedimentary Sequence, An- Anorthosite, B-
Bankura. The inset shows location of CGGC along with other Proterozoic mobile belts of India including Central India Tectonic Zone
(CITZ), Eastern Ghats Belt (EGB), Shillong Meghalaya Gneissic
Complex (SMGC), North Singhbhum Mobile Belt (NSMB) and
Aravalli Delhi Mobile Belt (ADMB). Four Archean cratonic nuclei
of India, namely Singhbhum (SC), Bastar (BC), Bundelkhand (BuC)
and Dharwar (KC) are also shown (modified after Chatterjee and
Ghosh 2011)
13
Geological setting
Generalities
The GFD is part of the Bathani volcano-sedimentary
sequence (BVSs), located on the northern fringe of the Chotanagpur Granite Gneiss Complex (CGGC) of eastern India
(Fig. 1). The CGGC is a Proterozoic metamorphic complex
covering ca. 80,000 km2 in the eastern part of the ENEWSW trending Central Indian Tectonic Zone (CITZ). It is
bounded by two mobile belts, namely the North Singhbhum
Mobile Belt to the south and the folded Mahakoshal Mobile
Belt to the north (Fig. 1a). The CGGC essentially consists
of granitoid gneisses and migmatites with minor high-grade
Evaluation of magma mixing in the subvolcanic rocks of Ghansura Felsic Dome of Chotanagpur Granite…
metamorphosed pelitic, calcareous and psammitic sedimentary rocks. These rocks display varying degrees of metamorphism and tectonic deformation which occurred at 1.87,
1.66 − 1.55, 1.2 − 0.93 and 0.87 − 0.78 Ga (Chatterjee et al.
2008, 2010; Maji et al. 2008; Singh and Krishna 2009; Karmakar et al. 2011; Sanyal and Sengupta 2012 and references
therein). Acharyya (2003) has included the CGGC into the
extensive CITZ.
The BVSs is exposed at the northern fringe of CGGC
(Ahmad and Wanjari 2009). The sequence extends over a
distance of ca. 40 km with the type area located at Bathani
village (24°59.5′N, 85°16′E) of Gaya district, Bihar, India.
Field investigations suggest that the belt is composed of several fault-bounded litho-tectonic sequences, including garnetmica schist, tuff/tuffaceous phyllite, banded iron formation
(BIF), banded carbonate chert (BCC) and a differentiated volcanic suite comprising basalt with or without pillow-andesitedacite-rhyolite and mafic volcanoclastic rocks (Ahmad and
Dubey 2011; Ahmad and Paul 2013) (Fig. 2). The metavolcanic and volcanogenic rocks are followed by an alternating sequence of phyllite and two stratigraphically distinct
quartzite horizons. The alternating sequence of phyllite and
quartzite is well known as the folded Rajgir metasediments
(Rajgir Group). On the basis of recent mapping, Ahmad
and Paul (2013) divided the belt into three lithologically
distinct domains: Northern, Central and Southern (Fig. 2).
Each domain is characterized by a distinct lithological association and intensity of deformation. The Northern domain
comprises granitoids intrusive into the volcano-sedimentary
sequence of the Central domain. The Central domain, confined at present to a small exposure, area, preserves volcanic
and sedimentary features, including pillows in basalt, pillow
breccia, heterogeneous volcanic breccia/agglomerate, BIF
and BCC. The Southern domain includes the folded Rajgir
metasediments. However, there is no detectable stratigraphic
break between the Central and Southern domains.
Field relations of the study area
The GFD occurs in the Southern domain as a small microgranitic unit emplaced in the BVSs at Ghansura village near
Bathani. At the outcrop scale, the GFD preserves good evidence of magma mixing and mingling (Fig. 2). In the study
area, many individual hybridized zones formed due to varying degrees of interaction between a mafic magma and its
felsic host. In some zones, the mafic rocks contain angular
clasts of the microgranite, indicating that solidification had
already begun in the host magma chamber when the invading magma disrupted it. Elsewhere, the mafic rocks contain
flows of the host microgranite manifesting back-veining
(Hallot et al. 1996). Well-defined reaction zones can be seen
at the mafic-felsic contacts in these zones (Fig. 3a). Some
zones are composed entirely of microgranite that remained
isolated from the mafic intrusion and is relatively fresh, and
close to the composition of the felsic host prior to the intrusion of mafic magma. A significant portion of our study area
is occupied by a porphyritic intermediate rock of dioritic
composition. The porphyritic diorite is characterized by the
presence of abundant rapakivi-textured feldspars (Fig. 3b).
There are zones in which the mafic rocks contain
abundant FME and felsic ocelli with reaction surfaces.
The variably-sized felsic components are embedded
within a fine-grained mafic groundmass. These enclaves
range from 1 mm to a few cm in size (Fig. 3c, d), and are
mostly ellipsoidal in shape. Occasionally, felsic ocelli are
stretched out to thin streaks. The felsic ocelli are comparatively finer-grained than their host mafic rocks. Some
of the felsic ocelli are showing diffused contacts. These
Fig. 2 Geological map of the
Bathani volcano-sedimentary
sequence showing the disposition of various litho-units. The
GFD is marked as G (modified
after Ahmad and Paul 2013)
13
B. Gogoi et al.
Fig. 3 Field photographs of
rocks of GFD displaying: a
reaction surface at mafic-felsic
contact; b porphyritic diorite
containing rapakivi-type feldspars (inset shows a magnified
feldspar crystal); c FME/felsic
ocelli, mostly ellipsoidal in
shape, of various sizes within
mafic rock; d felsic ocelli
stretched out to thin streaks
(reaction surfaces are distinctly
visible around the ocelli); e
alignment of felsic ocelli and
vesicles in the mafic rock;
f occurrence of veins in the
mingled rocks
ocelli show reaction surfaces probably due to chemical
interaction with the mafic melt (Fig. 3d). The host mafic
groundmass is highly vesicular. The vesicles as well as
ocelli have been aligned to form a preferred orientation
(Fig. 3e). Their alignment is possibly due to flow of the
invading mafic magma. Moreover, the elongation of the
ocelli in the direction of their alignment indicates that
distortion occurred due to magma flow and may indicate
localized conduit mixing (Vernon et al. 1988). All degrees
of coalescence were observed among the ocelli. The ocelli
may be juxtaposed, they may merge, or multiple ocelli
may coalesce into domains up to 20 cm in size. The ocelli
do not show zonation, or display any radial internal structure. Their color ranges from white to light grey. Borders
between ocelli and their mafic host vary from sharp to
gradational.
13
An interesting feature observed at the outcrop scale is
the occurrence of veins in the mingled rocks (Fig. 3f). No
such feature was observed in the mafic and felsic rocks, or
in the hybrid intermediate rocks of GFD. The veins act as
conduits for exchange of material between the two intermingling magmas trying to attain chemical equilibrium.
Veins are also observed in thin sections of these rocks.
Analytical methods
Mineral analyses were performed using a CAMECA SX
100 electron probe micro-analyser (EPMA). The data were
obtained using an accelerating voltage of 15 kV, beam current of 10 nA and a beam diameter of ca. 1 μm. Calibrant
materials used include wollastonite for Si and Ca, periclase
Evaluation of magma mixing in the subvolcanic rocks of Ghansura Felsic Dome of Chotanagpur Granite…
for Mg, rhodonite for Mn, albite for Na, corundum for Al,
hematite for Fe, orthoclase for K, apatite for P, metallic Zn,
Cr and Ti, halite for Cl, fluorite for F and barite for Ba. For
all the elements K α lines have been analyzed with a peak
counting time of 10 s and background counting time of 5 s.
The PAP correction was applied to the raw data (Pouchou
and Pichoir 1987).
Major oxides and trace elements were analysed using X-ray
fluorescence (Bruker S8 Tiger Sequential X-ray Spectrometer with an Rh excitation source) following the procedure of
Saini et al. (1998, 2000) and rare earth elements (REE) were
measured using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) (Perkin Elmer made SCIEX quadrapole type
ICP-MS, ELAN DRC-e). Operating conditions for the major
oxides were: no filter, vacuum path, 20/40 kV; for trace elements: no filter, vacuum path, 55/60 kV. The relative standard
deviation (RSD) was < 5% for the major and minor oxides,
and < 12% for the trace elements. The average precision is
better than 2% (Purohit et al. 2006; Saini et al. 2007). Sample
solutions were introduced for REE analysis into the argon
plasma using a peristaltic pump and a cross flow nebulizer.
The procedures adopted for sample digestion and preparation
of solutions were that of Balaram et al. (1990). Several United
States Geological Survey (BHVO-1, AGV-1 and RGM-1) and
Geological Survey of Japan (JG-2) samples were used as rock
standards to minimize matrix effects. The RSD for most of the
samples was < 10%.
Results
Petrography
The rocks from the GFD display good textural evidence
for the interaction of mafic and felsic magmas during their
genesis. Textural features observed in thin section, namely
mineral transporting veins, quartz ocelli, rapakivi and antirapakivi feldspars, acicular apatite, titanite ocelli, oscillatory zoned plagioclase, plagioclase with dissolved core and
undissolved rim, resorbed crystals and mafic clots, can be
explained in terms of magma mixing and mingling. The
rocks from the study area can be classified into three categories: (1) mafic units, comprising doleritic rocks; (2) microgranite, representing a felsic magma; (3) hybrid intermediate
rocks, resulting from the mixing and mingling of mafic and
felsic end-members. The hybrid rocks include porphyritic
diorite, mingled rocks and intermediate rocks containing
felsic ocelli.
Mafic rocks
The doleritic rocks consist of augite, plagioclase, Ti-Fe
oxide as major phases and amphibole, biotite, Fe oxide as
accessory phases. The rocks show holocrystalline texture. A
few of the samples contain phenocrysts of augite giving the
rock a porphyritic texture. Plagioclase laths are partially or
completely engulfed within augite representing sub-ophitic
and ophitic texture (Fig. 4a).
Intermediate rocks
Ocellar hybrid rocks contain felsic microgranular enclaves
or ocelli, which exhibit two types of microzones: one distinctly felsic and the other with a composition ranging
from mafic to intermediate. The felsic zones occur as small
enclaves/ocelli in mafic matrix/host (Fig. 4b). The FME are
essentially fine-grained and comprise a complex mineral
assemblage of quartz, K-feldspar and biotite along with significant amount of coarser epidote, amphibole, titanite and
Fe oxide. Amphiboles mostly occur only at the boundary of
the enclaves where the latter are in contact with the mafic
zone. The FME show a very distinct leucocratic margin and
comparatively darker core. The ocelli are elongated in the
direction of alignment of the grains with aspect ratios up to
1:10 (Fig. 4b). The elongation of the enclaves indicates that
distortion has been accomplished due to magmatic flow and
may indicate local mixing within the conduit. The mafic
zone comprises amphibole, epidote, titanite, plagioclase,
Fe oxide, quartz and K-feldspar. Epidote, titanite and Feoxide seemingly formed by decomposition of amphibole
and biotite. Quartz and K-feldspar are not evenly distributed in the matrix, but are rather concentrated in patches.
Mineral preferred orientation in the direction of elongation
of enclaves is suggestive of magmatic flow. Accumulation
and flow alignment of K-feldspar crystals was observed in
this zone (Fig. 4c).
Mingled rocks are compositionally intermediate hybrid
rocks formed by comingling of the mafic and felsic magmas.
The rocks are fine- to medium-grained and are composed of
amphibole, biotite, calcite, quartz, plagioclase, K-feldspar,
Fe oxide, epidote and titanite. Three distinct microzones
can be identified in thin sections for this particular hybrid
rock: (a) medium-grained mafic zone, which consists essentially of amphibole (hereafter referred to as amphibole-rich
microzones or ARM); (b) fine-grained felsic zone consisting
of quartz, K-feldspar, Fe oxide, biotite and minor amounts
of amphibole and epidote; and (c) biotite-rich intermediate zone. These three distinct zones are in contact with one
another. The amphiboles occurring in the interior and exterior of the ARM are optically different. The interior areas are
composed of a pale green to colorless amphibole, whereas
the exterior areas show a dark green color (Fig. 4d). Quartz
and titanite ocelli are common in these rocks. Sometimes,
mafic clots may be found engulfed in the fine-grained felsic
groundmass.
13
B. Gogoi et al.
Fig. 4 Photomicrographs of rocks of GFD displaying: a ophitic texture
in the mafic rocks showing plagioclase laths engulfed in augite grains;
b felsic ocelli within mafic matrix. Felsic ocelli are fine grained, ellipsoidal in shape with crenulated margin comprising dominantly of quartz
and K-feldspar. Mafic minerals within felsic ocelli are very similar to
the mafic host; c disequilibrium pair of microcline and amphibole in
mafic matrix hosting felsic ocelli. The K-feldspar has migrated from
the felsic zones into the mafic zones via mineral transporting veins; d
ARM in contact with a felsic zone. The amphiboles present at the interior and exterior of the mafic zone are optically different. The interior
amphiboles are pale green to colorless (actinolite), while the exterior
amphibole are green colored (hornblende). A transporting mineral vein
is seen emerging out of the ARM into the felsic zone. Note that near to
the ARM, amphibole constitutes the vein rather than biotite and as it
moves away from the ARM into the felsic zone amphibole is replaced
by biotite; e titanite (in liquid form) migrating from the mafic zone into
the felsic zone; f individual veins of biotite and iron-oxide transporting
these mineral phases from one zone to another; g amphibole vein in felsic
groundmass h Felsic vein containing minor titanite in hybridized rock; i
an oscillatory zoned plagioclase in porphyritic diorite suggesting disequilibrium in melt during the process of crystallization; j acicular apatite in
hybrid diorite; k plagioclase displaying synneusis in the porphyritic diorite; l CPL view of the microgranite. Mineral abbreviations: am, amphibole; ap, apatite; aug, augite; bt, biotite; fsp, feldspar; hbl, hornblende;
Kfs, K-feldspar; ms, muscovite; pl, plagioclase; qtz, quartz; ttn, titanite
An important feature of the mingled rocks is the presence of numerous veins. Veins composed of titanite and
Fe-oxide were observed to emanate from the mafic zones
into the felsic zones and apparently were the source of
these mineral phases in the latter (Fig. 4e, f). These veins
appear to have formed due to decomposition of amphibole
and biotite in the mafic zones. Furthermore, veins consisting of amphibole and biotite were found to serve as the
13
Evaluation of magma mixing in the subvolcanic rocks of Ghansura Felsic Dome of Chotanagpur Granite…
apparent source of these mineral phases in the felsic zones
(Fig. 4d, f, g). As a result of this, felsic zones are increasingly abundant in amphibole, biotite, titanite and Fe oxide.
In their turn, felsic veins consisting of quartz, K-feldspar
and titanite appear to be re-distributing material from the
felsic zones into the mafic zones (Fig. 4h). These veins are
interpreted as conduits along which minerals were transported, which is a viable mechanism to attain chemical
equilibrium between the mafic and felsic domains in the
mingled magma system.
Porphyritic diorite appears to be a homogenous hybrid
product formed by the blending of the mafic and felsic
magmas. Phenocrysts of plagioclase, quartz and biotite
are present in a fine- to medium-grained groundmass of
quartz, plagioclase, K-feldspar, biotite, calcite, apatite and
Fe oxide with plagioclase and biotite containing numerous
inclusions giving rise to a poikilitic texture. Some biotite
grains contain sagenitic titanite needles. Titanite is also
present as inclusions that have formed due to the alteration
of biotite. A number of other textures, such as quartz and
calcite ocelli, rapakivi and anti-rapakivi feldspars, feldspars
with a dissolved core and an undissolved rim, oscillatory
zoned plagioclase (Fig. 4i) and acicular apatite (Fig. 4j),
were observed that are consistent with the interpretation
that this rock has formed by the mixing of mafic and felsic
magmas.
An important petrographic feature observed in the porphyritic diorite is smaller-sized plagioclase grains assembled
together to form crystal clusters (Fig. 4k). The crystals in
these clusters have “fused” together to form larger grains.
This aggregation process is called synneusis, the term introduced by Vogt (1921). From petrographic observations it
was inferred that the aggregation of plagioclase grains has
been followed by dissolution of their grain boundaries to
form discrete phenocrysts. The degree of coalescence
between plagioclase grains involved in synneutic relationship varies significantly. Some of the crystals assembled
together with their grain boundaries still intact, but in other
cases, there is complete dissolution of grain boundaries to
form a larger grain. It is inferred that when the crystal-rich
mafic magma intruded the felsic magma chamber, crystals derived from the former were dispersed into the felsic
melt. The crystal-poor nature of the felsic melt allowed the
injected plagioclase crystals to float and undergo synneusis, resulting in an intermediate hybrid rock of porphyritic
nature.
Felsic rocks
The felsic rock is microgranite consisting of quartz, K-feldspar, muscovite, tourmaline and Fe oxide. The rock shows a
holocrystalline texture with the mineral grains mostly ranging from subhedral to anhedral in shape (Fig. 4l).
Major element whole‑rock data and Harker variation
diagrams
A total of 23 whole-rock samples were analyzed for their
major and trace element compositions (Table 1). The measured compositions plotted on Harker variation diagrams
show linear to near-linear, negatively correlated trends
for ­Fe2O3(total), MnO, ­TiO2, MgO and CaO against ­SiO2
(Fig. 5). However, the A
­ l2O3, ­Na2O, ­K2O and P
­ 2O5values
plotted against ­SiO2 exhibit a greater scatter and lack detectable correlation (Fig. 5). In a magma mixing scenario, the
whole-rock compositions of hybrid products are average of
those belonging to the end-member parental magmas (Koyaguchi 1986; Frost and Mahood 1987; Foster and Hyndman
1990). The observed near-linear trends suggest that the
intermediate rocks resulted from the mixing of mafic and
felsic magma end-members in various proportions (Kumar
and Rino 2006). The intermediate rocks plot closer to the
mafic end-member for all the major oxides, indicating that
the contribution of the mafic magma is larger in forming
the hybrid intermediate rocks in comparison to that of the
felsic magma. Furthermore, the trace element plots show
near-linear, negatively correlated trends (Fig. 5), which suggests that the mafic and felsic magmas interacted to form the
hybrid intermediate rocks occurring in the GFD. The total
alkali versus S
­ iO2 plot (Middlemost 1994) illustrates that the
mafic end-member plots in the gabbro field, the hybrid rocks
fall in the fields of monzogabbro, monzodiorite, gabbroic
diorite and diorite, whereas the felsic end-member falls in
the field of granite (Supplementary Fig. 1).
Trace and rare earth element data
Mafic rocks Chondrite-normalized rare earth element
(REE) and primitive mantle-normalized multi-element
patterns (Fig. 6a, b) show enrichment in incompatible elements and especially light rare earth elements
(LREE) and large-ion-lithophile elements (LILE). The
high LILE/HFSE and LREE/HREE (HFSE = high-fieldstrength elements; HREE = heavy REE) ratios are a
distinctive feature of magmas generated in arc tectonic
settings (Murphy 2007). The mafic samples show a
tholeiitic trend and are clearly divisible into two groups:
one group relatively enriched in REE and lacking Eu
anomaly (Eu/Eu* = 0.94–1.06), and the other one with
less REE-enriched patterns and positive Eu anomalies
(Eu/Eu* = 1.14–1.49) possibly indicating plagioclase
accumulation. The sub-parallel REE patterns of the
mafic rocks suggest variations in the degree of partial
melting of their peridotitic source. The eight dolerite
samples are characterized by marked positive anomalies
for Pb indicating a crustal contribution in the magma
composition. Samples RJ20, R12 and R16 show positive
13
B. Gogoi et al.
Table 1 XRF and ICP-MS analysis data of mafic, felsic and hybrid rocks of the GFD
Sample no.
Rock type
R01
Dolerite
R12
Dolerite
R16
Dolerite
Major oxides (XRF results; all values in wt%)
SiO2
45.1
49.4
47.3
1.56
0.83
1.07
TiO2
13.8
11.8
12.3
Al2O3
13.9
11.6
14.4
Fe2O3
MnO
0.19
0.18
0.2
MgO
8.23
10.0
9.35
CaO
9.31
12.1
9.58
2.47
1.51
1.93
Na2O
0.57
0.11
0.13
K2O
0.28
0.07
0.06
P2O5
LOI
2.75
0.55
2.06
Total
98.3
98.3
98.5
Trace elements (XRF results; all values in ppm)
Ba
206
41
75
Cr
228
61
349
V
223
252
246
Co
51
59
60
Ni
96
264
112
Cu
39
9
33
Zn
106
74
96
Ga
20.8
13.3
16.8
Pb
10.7
4.8
221
Th
3.52
BDL
BDL
Rb
24
3
9
Sr
272
186
279
Y
30
13
16
Zr
147
51
53
Nb
12.8
2.49
6.8
Sc
28
39
33
U
0.4
0.1
0.2
Rare earth elements (ICP-MS results; all values in ppm)
La
14.8
3.8
5.8
Ce
34.7
9.3
12.4
Pr
4.9
1.5
1.7
Nd
20.8
6.6
7.5
Sm
5.09
2
2.11
Eu
1.82
1.02
1.11
Gd
5.37
2.36
2.48
Tb
0.88
0.43
0.43
Dy
5.12
2.61
2.63
Ho
1.06
0.56
0.56
Er
2.84
1.49
1.47
Tm
0.42
0.23
0.22
Yb
2.7
1.48
1.45
Lu
0.41
0.22
0.22
13
R17
Dolerite
RJ4
Dolerite
RJ16
Dolerite
RJ18
Dolerite
RJ20
Dolerite
48.2
2.29
11.3
16.6
0.21
5.21
11.9
1.86
0.55
0.24
0.62
99.1
43.9
1.37
9.80
18.7
0.26
7.96
13.3
0.43
0.85
0.14
1.65
98.5
47.6
2.49
11.9
16.7
0.20
5.62
10.5
2.14
0.79
0.25
1.06
99.4
45.6
1.84
13.8
14.5
0.19
7.66
9.77
2.11
0.96
0.23
2.00
98.7
45.5
0.89
13.1
14.1
0.20
9.84
10.9
2.08
0.17
0.06
1.63
98.7
145
253
407
49
80
18
128
17.6
8.05
2.12
15
204
37
156
14.1
44
0.4
59
259
268
52
94
42
114
19.5
25.4
1.38
14
60
32
82
7.7
43
0
223
306
430
61
89
113
138
20.5
4.7
2.25
32
226
48
173
18.0
46
0
201
265
263
58
99
90
110
21.4
12.0
1.28
53
275
37
124
12.4
34
0.0
68
427
228
67
172
145
112
17.4
24.8
BDL
3
229
19
39
7.8
42
0.0
16.1
37.8
5.3
22.8
5.88
2.13
6.59
1.11
6.59
1.41
3.7
0.56
3.59
0.52
7.5
19.9
2.8
12.4
3.29
1.09
3.84
0.68
4.11
0.88
2.35
0.37
2.47
0.38
16.2
39.3
5.5
24.2
6.25
2.14
7.06
1.17
7.03
1.48
3.89
0.58
3.75
0.56
12.2
28.9
4.1
17.9
4.38
1.52
4.74
0.75
4.51
0.92
2.42
0.36
2.25
0.34
5.1
11
1.5
6.4
1.8
0.75
2.27
0.4
2.58
0.55
1.48
0.22
1.46
0.22
Evaluation of magma mixing in the subvolcanic rocks of Ghansura Felsic Dome of Chotanagpur Granite…
Table 1 (continued)
Sample no.
Rock type
RJ05
R04
Hybrid rocks Porphyritic
with FME
diorite
RJ24
Mingled
rocks
Major oxides (XRF results; all values in wt%)
SiO2
52.3
55.8
53.8
1.27
0.88
0.99
TiO2
13.5
15.4
14.1
Al2O3
9.70
8.39
9.31
Fe2O3
MnO
0.18
0.12
0.14
MgO
7.17
6.16
5.19
CaO
12.04
5.74
6.40
1.68
2.25
1.84
Na2O
1.76
4.01
4.05
K2O
0.13
0.37
0.36
P2O5
LOI
1.25
2.31
2.88
Total
101
101
99
Trace elements (XRF results; all values in ppm)
Ba
156
714
746
Cr
356
140
63
V
284
159
181
Co
109
20
52
Ni
73
17
16
Cu
38
81
114
Zn
70
90
106
Ga
15
17
20
Pb
24
15
16
Th
0.4
21
14.5
Rb
21
200
181
Sr
155
291
322
Y
18
23
38
Zr
66
158
170
Nb
6
13
14
Sc
55
18.5
41
U
1.0
4.9
1.2
Rare earth elements (ICP-MS results; all values in ppm)
La
7.4
37.8
37.4
Ce
17
77.7
76.7
Pr
2.5
8.8
9.3
Nd
11.4
36.3
34.3
Sm
3.15
6.99
6.75
Eu
1.1
0.79
1.66
5.32
6.55
Gd
3.58
Tb
0.6
0.79
0.86
Dy
3.64
4.93
4.64
Ho
0.76
0.81
0.9
Er
1.9
2.24
2.41
Tm
0.28
0.34
0.36
Yb
1.75
2.35
2.38
Lu
0.26
0.4
0.37
RJ22B
Mingled
rocks
R02C
Mingled
rocks
TBR
Mingled
rocks
RJ22A
Mingled
rocks
R02A
Mingled
rocks
RJ23B
Mingled
rocks
55.5
1.53
15.6
7.87
0.13
4.86
6.07
2.98
2.44
0.12
1.15
98
56.3
1.32
13.4
9.83
0.16
6.52
8.62
0.70
2.16
0.07
0.95
100
61.7
0.50
10.9
14.8
0.10
5.08
1.30
0.41
2.13
0.04
2.17
99
55.4
1.13
12.1
9.44
0.20
7.21
12.41
0.89
0.84
0.05
1.88
101
50.3
1.73
17.7
10.0
0.14
4.45
6.39
2.42
4.15
0.14
1.46
99.0
47.9
1.90
15.9
10.3
0.16
7.05
8.43
1.41
3.62
0.11
1.15
98.0
135
481
381
146
138
113
87
20
143
< 1.0
38
106
18
71
7
50
1.1
144
290
318
78
63
205
96
16
14
1.5
31
79
16
69
7
58
1.1
189
374
118
36
82
418
129
18
20.1
9.72
62
35
33
76
8.2
16
0
86
264
280
99
65
9
59
15
11
< 1.0
10
89
11
59
6
53
1.1
12
483
328
93
44
145
108
21
125
1.8
59
90
25
84
7.6
49
1.2
510
409
449
57
69
8
61
23
11
1.5
52
184
25
98
10
78
1.0
6.6
16.2
2.3
10.1
2.74
1.1
2.99
0.5
3
0.62
1.58
0.23
1.49
0.22
6.4
16.2
2.3
10.1
2.7
1.02
2.8
0.48
2.86
0.59
1.5
0.23
1.53
0.23
33.7
64.5
6.8
25.1
4.5
1.11
3.53
0.55
3.27
0.73
1.94
0.26
1.77
0.3
4.7
11.5
1.7
7.3
2.03
0.89
2.22
0.38
2.24
0.47
1.21
0.18
1.24
0.18
6.8
17.5
2.6
11.7
3.27
1.19
3.61
0.58
3.35
0.69
1.71
0.25
1.53
0.23
12
30.1
4.3
18.4
4.5
1.65
4.57
0.7
4.16
0.85
2.22
0.34
2.23
0.34
13
B. Gogoi et al.
Table 1 (continued)
Sample no.
Rock type
R03
Microgranite
RJ23C
Microgranite
Major oxides (XRF results; all values in wt%)
SiO2
73.9
80.7
0.91
0.38
TiO2
13.2
9.19
Al2O3
4.55
2.26
Fe2O3
MnO
0.04
0.03
MgO
1.45
0.50
CaO
0.68
1.80
1.59
2.46
Na2O
3.74
0.99
K2O
0.02
0.03
P2O5
LOI
1.42
0.83
Total
101
99.2
Trace elements (XRF results; all values in ppm)
Ba
151
343
Cr
1311
72
V
132
103
Co
14
163
Ni
35
21
Cu
23
32
Zn
35
15
Ga
14
13
Pb
7
61
Th
5
8
Rb
46
17
Sr
25
81
Y
8
11
Zr
60
45
Nb
8
6
Sc
11.6
13
U
1.2
1.2
Rare earth elements (ICP-MS results; all values in ppm)
La
12.7
12.7
Ce
24.9
23.3
Pr
2.6
2.4
Nd
9.9
9.4
Sm
1.61
1.94
Eu
0.27
0.54
Gd
1.26
1.52
Tb
0.19
0.22
Dy
1.25
1.2
Ho
0.22
0.26
Er
0.67
0.69
Tm
0.11
0.09
Yb
0.76
0.63
Lu
0.13
0.1
BDL below the detection limit, LOI loss on ignition
13
RJ25A
Microgranite
RJ25B
Microgranite
RJ28
Microgranite
RJ26
Microgranite
81.3
0.70
8.48
3.01
0.03
0.43
0.71
0.51
2.14
0.02
0.95
98.2
83.4
0.81
8.15
1.86
0.02
0.23
0.93
1.35
1.46
0.03
0.50
98.7
80.2
0.11
6.08
2.84
0.07
2.29
4.85
0.39
1.22
0.04
0.57
98.7
70.4
0.26
14.8
3.40
0.04
1.45
2.94
5.24
1.19
0.08
0.68
100.5
384
74
80
127
12
48
24
12
40
4
35
17
12
32
6
8
2.3
404
92
118
100
12
8
18
13
22
1
19
37
11
40
4
10
1.2
320
247
8
5
13
15
28
7
14
10
13
58
18
129
25
5.8
3.4
541
263
27
9
10
12
28
18
13
6
35
183
6
149
11
8
3.3
8.8
16.9
1.7
6.3
1.29
0.25
1.04
0.17
0.97
0.22
0.56
0.08
0.53
0.08
1.7
4
0.6
2.4
0.57
0.27
0.61
0.1
0.62
0.14
0.36
0.05
0.32
0.05
38.7
109
9.1
36.1
7.25
0.95
6.24
1.08
7.29
1.72
4.47
0.6
3.85
0.62
29
45.5
4.4
15.1
2.4
0.68
1.89
0.24
1.18
0.23
0.56
0.06
0.41
0.07
Evaluation of magma mixing in the subvolcanic rocks of Ghansura Felsic Dome of Chotanagpur Granite…
Fig. 5 Harker variation diagrams for the felsic, mafic and
hybrid/intermediate rocks of
BVSs showing variation in (a)
major oxides; (b) trace elements
as a function of silica content. Symbols represent: solid
squares - mafic rocks; solid
diamonds - hybrid intermediate
rocks; solid circles - felsic rocks
13
B. Gogoi et al.
Fig. 6 Chondrite normalized rare earth element plots and Primitive
mantle normalized multi-element patterns for the representative rock
samples of the BVSs- (a), (b) mafic rocks; (c), (d) hybrid intermedi-
ate rocks; (e), (f) felsic rocks. Normalizing values of Primitive mantle
are after Sun and McDonough (1989) and those of Chondrite are after
Boyton (1984)
Sr and Eu anomalies, while moderate to small negative
Sr anomalies were observed in samples RJ4, RJ16 and
R17 indicating plagioclase fractionation.
plagioclase fractionation. On the multi-element variation
diagram (Fig. 6d), they show moderately to highly fractionated patterns characterized by Nb depletion and Pb enrichment. Negative anomalies for Nb reflect a crustal signature
and may be related to crustal contamination. In our scenario,
the contamination has been possibly brought about by the
felsic magma. Moderate to slight negative anomalies are
observed for Ba, Th, Sr, P, Ti and Zr indicating the removal
of phases like feldspar, biotite, apatite, titanite, ilmenite, zircon and/or allanite from the melt, which is consistent with
petrographic observations.
Intermediate rocks These samples show moderate to
strongly fractionated REE patterns (Fig. 6c) characterized
by relative enrichment in LREE and nearly flat HREE distributions ­(LaN/YbN = 2.53–12.73, ­LaN/SmN = 1.28–4.62, ­GdN/
YbN = 1.43–2.19). The intermediate rocks are characterized
by variable Eu anomalies (Eu/Eu* = 0.38–1.28). Most of the
samples show slightly positive to flat Eu patterns, with one
sample (R04) showing a negative Eu anomaly indicating
13
Evaluation of magma mixing in the subvolcanic rocks of Ghansura Felsic Dome of Chotanagpur Granite…
Felsic rocks All the calc-alkaline microgranitic samples (Fig. 6e) are characterized by moderate to strongly
fractionated REE patterns ­(LaN/YbN = 3.55–47.30,La N/
SmN = 1.84–7.46), slightly positive to negative Eu anomalies (Eu/Eu* = 0.42–1.40) and nearly flat HREE distributions
­(GdN/YbN = 1.29–3.67). On the primitive mantle-normalized
variation diagram (Fig. 6f), the felsic rocks exhibit strongly
negative Nb, Sr, Eu and P anomalies and positive anomalies for Pb. The negative Sr, Eu and P anomalies may be
explained by plagioclase and apatite fractionation, or the
presence of these minerals in the restite. The negative Nb
anomalies together with the positive Pb anomalies are interpreted as a crustal signature.
Mineral chemistry
Mineral analyses were performed on four major mineral
phases, i.e., pyroxene, amphibole, biotite and plagioclase.
Since these mineral phases are not present in the felsic endmember, mineral chemistry for the microgranite is not presented in this work. Mineral analyses were carried out on
specific major mineral phases from the mafic and hybrid
intermediate rocks with a view to understand the mixing
phenomenon that occurred in the GFD.
Pyroxene is found exclusively in the mafic rocks. The
formulae of pyroxene were calculated on the basis of six
oxygen atoms (Morimoto et al. 1988), and ferric and ferrous iron values were calculated according to Droop (1987).
Representative analyses of pyroxene are reported in Supplementary Table 1. The pyroxene is identified as augite
(Supplementary Fig. 2).
Plagioclase occurs in the mafic and hybrid intermediate rocks. The compositions of plagioclase from the mafic
samples, listed in Supplementary Table 2, plot in the fields
of andesine and labradorite (Supplementary Fig. 3a).Among
the hybrid intermediate rocks, plagioclase compositions
were determined for the porphyritic diorite. Representative
data are provided in Supplementary Table 2, which include
analyses across individual grains evidencing oscillatory zoning. The compositions of plagioclase from the porphyritic
diorite range from bytownite to oligoclase (Supplementary
Fig. 3b, c) and are characterized by jagged zoning patterns
(Supplementary Fig. 4a, b) indicative of disequilibrium conditions associated with magma mixing.
Amphibole occurs as a major phase only in the mingled
rocks. It is also present as an alteration product of clinopyroxene in the mafic end-member. However, the analyses
of this amphibole (actinolite) were omitted from this work
because they are irrelevant to further discussion. The formulae of amphibole were calculated on the basis of 23 oxygens,
and amphibole identifications based on the classification of
Leake et al. (1997). The compositions of amphiboles were
mostly determined for the ARM in the mingled rocks with
a view to understand the genesis of these monomineralic
zones. Representative analyses of amphiboles are presented
in Supplementary Table 3. Amphiboles show compositional
variation from the interior to the exterior of ARM. Those in
the interior are actinolite, whereas those in the exterior zones
are hornblende (Supplementary Fig. 5).
The ARM have been reported in a number of magma
mixing studies (Castro and Stephens 1992; Janoušek et al.
2000b; Choe and Jwa 2004; Martin 2007; Ubide et al.
2014). These textures are usually zoned such that amphiboles in their rims are hornblende, whereas those in the
cores are actinolite. The earlier works on ARM have all
concluded that these monomineralic zones form by solid
state reaction of precursor clinopyroxene crystals. In our
interpretation, the amphiboles constituting the ARM are
pseudomorphs after earlier-crystallized pyroxene crystals.
The pyroxene crystals were derived from the mafic magma
that carried large phenocrysts of augite. The presence of
only one type of pyroxene in the mafic magma further supports our interpretation of the origin of ARM, as it is much
easier to replace clinopyroxene by amphibole in comparison with orthopyroxene. Replacement of orthopyroxene by
amphibole requires considerably larger-scale mass transfers
than the clinopyroxene-amphibole replacement (Ubide et al.
2014).
Biotite occurs as a major phase in the hybrid intermediate
rocks. Compositions of biotite from the mingled rocks and
porphyritic diorite are available in Supplementary Table 4.
The formulae of biotite were calculated on the basis of 11
oxygen atoms. In the mingled rocks, the compositions of
biotite were determined across the amphibole-biotite veins
and the fine-grained felsic zones which these veins are traversing. On the classification diagram of Speer (1984), biotite from the veins and the groundmass plots in the field of
siderophyllite on the A
­ liv versus Fe# (Fe/Fe + Mg) classification diagram (Supplementary Fig. 6a, b). The indistinguishable compositions of biotite samples from the veins
and felsic zones suggest their similar origin. This mineral
has been spread throughout the felsic zones via the veining.
Biotite compositions were also determined for the porphyritic diorite. The compositions of this biotite plot in the field
of siderophyllite (Supplementary Fig. 6c).
Temperature estimates
Generalities
Three distinct geothermometers were used to calculate
magma temperatures for the three principal rock types, i.e.,
dolerite, microgranite and porphyritic diorite. Although our
study area is a metamorphic terrain, locally the imprint of
deformation is negligible. Magmatic features like ophitic
texture are a common feature in the mafic rocks. In places,
13
B. Gogoi et al.
pyroxene is altered to actinolite along the grain boundaries. However, in most cases, the pyroxene crystals appear
unaltered and fresh. The compositions of such unaltered
pyroxene were selected for T calculations. In the porphyritic diorite, magmatic features like oscillatory zoning in
plagioclase and acicular apatite are observed, which indicates that these rocks have not been affected by the regional
metamorphism. The calculated temperatures are then used
to calculate magma viscosities for the three different rock
types. These physical properties are further used to evaluate
the process of magma mixing in our study area.
Clinopyroxene‑liquid thermobarometer
Estimates of crystallization temperature and pressure of
the mafic magma were made using the thermobarometer
developed by Putirka et al. (2003). In this method, the compositions of clinopyroxene and coexisting residual magma
are used to determine the pressure and temperature (P-T)
at which these two phases were last in equilibrium. The
model estimates pressures to ± 1.7 kbar and temperatures
to ± 33 °C.
A crucial issue which needs to be addressed for this geothermobarometer is the selection of the residual liquid, i.e.,
whether to take the bulk rock, matrix/glass or some other
composition (e.g., composition obtained by removing the
mass fraction of the observed phenocryst phases from the
bulk rock composition) as representative of the liquid with
which clinopyroxene phenocrysts equilibrated. Walker
(1957, p. 1) stated that “in tholeiitic suites both pyroxene
and plagioclase started to form at a very early stage and
continued to crystallize in ophitic relationship and in fairly
constant proportions throughout the cooling history”. The
dominance of clinopyroxene and plagioclase at minor concentrations of Ti-Fe oxide in our mafic samples indicates
that both pyroxene and plagioclase have crystallized simultaneously with definite proportions.
Table 2 Zr saturation
thermometry data calculated for
microgranites of GFD
Crystallization of phenocryst phases changes the composition of the liquid in equilibrium with pyroxene. The
occurrence of such phases should be dealt with cautiously
to obtain correct P-T estimates. It is almost impossible to
determine what combination of phenocrysts and groundmass
should be taken to account for the composition of liquid in
equilibrium with pyroxene. Moreover, it is also difficult to
ascertain what percentage of phenocrysts crystallized before,
during and after pyroxene crystallization.
Our dolerite sample contains phenocrysts of pyroxene
and plagioclase with plagioclase phenocrysts accounting
for 30 wt% of the rock sample. As the two phases are in
ophitic relation with each other, it implies that plagioclase
has crystallized either before or simultaneously with pyroxene. If both these phases have crystallized simultaneously
the bulk rock composition can be used as the composition
of the liquid in equilibrium with pyroxene. On the contrary,
if plagioclase had crystallized before pyroxene, the composition of the liquid in equilibrium with pyroxene can be
determined by subtracting the chemical composition of plagioclase from the whole-rock chemical composition. We
obtained P-T estimates by deducting 10, 20 and 30 wt% of
plagioclase phenocrysts from the whole-rock compositions.
The P-T estimates were based upon six point analyses of
unzoned pyroxene grains in sample R01 (Table 2).
The estimated average temperature and pressure of pyroxene crystallization for the dolerite sample are 1227 °C and
9.6 kbar, respectively, when we consider the whole-rock
composition as the composition of the liquid in equilibrium
with pyroxene. On removing 10, 20 and 30 wt% of plagioclase phenocrysts from the whole-rock compositions, the
calculated temperatures increase to 1254, 1291 and 1366 °C,
respectively, whereas the pressures increase by 2, 5 and 14
kbar, respectively. The increase in temperature and pressure
reflects a decrease in Na concentration in the model liquid
due to sequestration of this element in the plagioclase.
Sample no.
R03
RJ28
RJ26
RJ23C
RJ25A
RJ25B
Cation fractions
(apfu)
Na2O
Al2O3
SiO2
K2O
CaO
Zr (ppm)
M
T (K)
0.03
0.16
0.75
0.05
0.01
60
0.79
1020
0.01
0.08
0.85
0.02
0.05
129
2.10
993
0.10
0.17
0.69
0.01
0.03
149
1.50
1046
0.05
0.11
0.81
0.01
0.02
45
1.13
976
0.01
0.10
0.85
0.03
0.01
32
0.62
983
0.03
0.10
0.85
0.02
0.01
40
0.8
988
*Cation fractions in (afpu) of five major oxides, Zr concentration in (ppm), calculated values of M
[M = (Na + K + 2*Ca) / (Al*Si)] and calculated values of T ­[TZr = 12,900 / [2.95 + 0.85M + ln (496,000 /
­Zrmelt)] in degree kelvin (Watson and Harrison 1983; Miller et al. 2003)
13
Evaluation of magma mixing in the subvolcanic rocks of Ghansura Felsic Dome of Chotanagpur Granite…
Prediction of the actual composition of the liquid in
equilibrium with pyroxene is a difficult task. Going by
the statement of Walker (1957), we can assume that in our
scenario, both pyroxene and plagioclase have crystallized
simultaneously. Thus, the values calculated by taking the
whole-rock composition as the composition of the liquid
in equilibrium with pyroxene can be regarded as the best
P-T estimates for our samples. As a result, we opted to
take the uncorrected whole-rock composition rather than
the corrected one and consider the thermobarometric data
obtained for the observed sample as the lower P-T limit
of clinopyroxene crystallization.
Titanium‑in‑quartz geothermometer (TitaniQ)
Titanium-in-quartz thermometry was applied to the
porphyritic diorite sample (R04) in which Ti content of
quartz is used to unveil the thermal history of this rock.
Wark and Watson (2006) have proposed an experimental
calibration for a new Ti-in-quartz thermometer (TitaniQ)
which is based on the temperature dependence of Ti solubility in quartz.
[ (
)
]
T[K] = −3765 ± 24∕ log TiQtz ppm/aTiO2 − 5.69 ± 0.02
(1)
The thermometer was calculated using quartz equilibrated with a pure ­TiO2 phase (rutile). For rutile-present
conditions, ­aTiO2 = 1. However, the diorite sample lacks
rutile. This thermometer can also be applied to rutile-poor
rocks provided that T
­ iO2 activity of the system is known.
Under such conditions, 0 < aTiO2<1.
The ­TiO2 activity of a system which is unsaturated or
devoid of rutile is difficult to estimate. However, Ghent
and Stout (1984) from their experiments have calculated
­aTiO2 = 0.6 for some metabasites, whereas for metapelites
the values remain close to 1. For silicic igneous rocks,
like granites, which do not have rutile as a stable phase,
activities of 0.5 or higher are more realistic. Though sample R04 contains minor Fe-Ti oxides, it is unlikely that the
­TiO2 activity of the hybrid magma was close to 1. Taking
into consideration all the above facts, a ­TiO2 activity of
0.6 was assumed for the sample. The major advantage of
this thermometer is that activity uncertainties of the order
of ± 0.2 result in an error of ± 10 °C (Kohn and Northrup
2009; Spear and Wark 2009). A total of 15 point analyses were carried out to measure the Ti content in quartz
grains from the porphyritic diorite. The average Ti concentration was found to be approximately 240 ppm. Using
the Ti-in-quartz thermometer and assuming ­a TiO2 = 0.6,
the average crystallization temperature obtained for the
porphyritic diorite is 946 °C.
Zircon saturation geothermometer
Zircon saturation thermometry, which provides good estimates of magma temperature during zircon crystallization,
is calculated from bulk rock compositions (Watson and
Harrison 1983; Miller et al. 2003). This method is based
on the following relationship among zircon solubility, temperature, and major-element composition of melt:
ln DZr,
zircon/melt
= {−3.8 − [0.85(M-1)]} + 12, 900∕T
(2)
where, ­DZr,zircon/melt is the ratio of Zr concentration (ppm)
in zircon (476,000 ppm) to that in the saturated melt; M
is a compositional factor that accounts for the dependence of zircon solubility on ­SiO2 and alumina saturation
index of the melt [(Na + K + 2*Ca) / (Al*Si), expressed in
molar terms]; and temperature, T, is in Kelvin. Rearranging the equation (Eq. 2) yields the temperature of zircon
saturation:
[
(
)]
TZr =12, 900∕ 2.95 + 0.85M + ln 496,000/Zrmelt
(3)
By using this geothermometer, temperatures of the microgranites from Ghansura, i.e., samples R03, RJ28, RJ26,
RJ23C, RJ25A and RJ25B were found to be 747, 720, 773,
703, 710 and 715 °C, respectively, yielding an average temperature of 728 ± 24 °C (Table 2). The lower zircon saturation temperatures for the microgranitic samples indicate that
zircon is undersaturated in these melts, which is consistent
with petrographic observations.
Viscosity calculation
Viscosity of magmas plays a major role in controlling their
transport and emplacement style. Giordano et al. (2008)
has put forth a model that predicts the non-Arhenian Newtonian viscosity of silicate melts as a function of their
temperature and composition. The advantage of this model
is that it uses a single computational strategy independent of whether melts are hydrous or anhydrous, strong or
fragile and, thus, is mathematically continuous in the T-X
space, making it applicable to a wide range of compositions found in naturally-occurring silicate melts.
This model was used to calculate the viscosities of magmas corresponding to the three principal rock types from
our study area, i.e., dolerite, microgranite and porphyritic
diorite (samples R01, R03 and R04, respectively). Samples
R01 and R03 represent the mafic and felsic end-members,
respectively, which have not been modified by mixing or
mingling and in their composition, approach primary magmas. Sample R04 represents a hybrid intermediate rock
formed by mixing of two contrasting magmas similar to
R01 and R03.
13
B. Gogoi et al.
The viscosity of magma is calculated using the VogelFulcher-Tammann (VFT) equation (Vogel 1921; Fulcher
1925; Tammann and Hesse 1926):
(4)
where η is viscosity, T temperature in Kelvin, A an adjustable parameter constant for all melts (i.e., independent of
composition), and B and C are adjustable parameters determined from bulk rock compositions (refer to Giordano et al.
2008 for further details). This model uses the concentrations
of the major oxides and volatile species ­H2O and F to determine the compositionally dependant parameters B and C.
However, due to analytical constraints we were unable to
measure the concentrations of H
­ 2O and F separately. Hence,
we considered the total volatile content present in the rock
samples as H
­ 2O. Despite of these limitations, the results
obtained from the viscosity model are considered reliable.
The viscosities of magmas represented by samples R01
log η = A + B∕T(K) − C
Table 3 Calculated values of the three parameters (A, B and C), log
ƞ, ­Tg and m for mafic, felsic and hybrid rock of GFD
Sample no.
Rock type
R01
Basalt
R04
Porphyritic
andesite
R03
Rhyolite
(Wt. %)
SiO2
TiO2
Al2O3
FeO(t)
MnO
MgO
CaO
Na2O
K2O
P2O5
LOI
A
B
C
T (K)
Log ƞ (Pa s)
Tg (K)
m
45.1
1.56
13.8
13.9
0.19
8.23
9.31
2.47
0.57
0.28
2.75
− 4.55
5189.2
448.35
1500
0.38
762
40.21
55.8
0.88
15.4
8.39
0.12
6.16
5.74
2.25
4.01
0.37
2.31
− 4.55
6810.65
340.12
1219
3.2
752
30.22
3.91
0.91
13.2
4.55
0.04
1.45
0.68
1.59
3.74
0.02
1.42
− 4.55
10433.86
214.21
1020
8.4
845
22.17
LOI loss on ignition
a
The viscosity of magma is calculated using the Vogel-Fulcher-Tammann (VFT) equation (Vogel 1921; Fulcher 1925; Tammann and
Hesse 1926): log η = A + B/T(K) – C where, η is viscosity, T temperature in Kelvin, A an adjustable parameter constant for all melts (i.e.,
independent of composition), and B and C are adjustable parameters
determined from bulk rock compositions (refer to Giordano et al.
2008 for further details). The T
­ g (Glass Transition temperature) value
are calculated using the equation C + (B/12-A) (Angell 1985; Dingwell et al. 1993; Giordano et al. 2008). The “m” (fragility) value can
be obtained from the equation B/Tg{1-(C/Tg)}2 (Giordano et al. 2008)
13
(mafic), R03 (felsic) and R04 (intermediate) a­ re100.38 Pa s
at 1227 °C, 1­ 08.4 Pa s at 747 °C, and 1­ 03.2 Pa s at 946 °C,
respectively (Table 3).
Mixing models
Linear trends on binary diagrams and linear correlation mixing
test involving both mafic and felsic magmas to form hybrid
magmas are used to decipher magma mixing. The availability
of only a few conventional geochemical models, like the majorelement based mixing test of Fourcade and Allègre (1981) and
least-squares linear fit mixing test of Janoušek et al. (2004),
is insufficient to evaluate the complex process of magma
interaction. Moreover, linear arrays on binary diagrams can
be generated by other petrogenetic processes, such as crystal fractionation, assimilation of non-restitic solids and restite
unmixing (DePaolo 1981; Chappell et al. 1987; Wall et al.
1987; Albarède 1995; Janoušek et al. 2004). In this work, we
used two recently developed experimental models of Giordano
et al. (2008), that use physical properties like temperature (T),
viscosity (η), glass transition temperature ­(Tg) and fragility
(m) of the interacting magmas and their corresponding hybrid
product, to evaluate the feasibility of magma mixing in our
study area. The results derived from the newly developed
experimental models were compared with those obtained from
one of the conventional models for a robust conclusion.
Fourcade and Allègre mixing test
The porphyritic diorite and the mingled rocks have formed
due to the interaction of both felsic and mafic magmas. The
relative contributions of both the magmas in forming the
hybrid rocks have been estimated using linear correlation
major-oxides mixing test of Fourcade and Allégre (1981).
According to the model if mixing occurs, each element would
be affected by the process and we can write for each element:
(
)
Ci i - Ci f = m Ci m − Ci f
(5)
where ­Cii is the concentration of i element in intermediate
hybrid magma, C
­ if is the concentration of i element in feli
sic magma, ­C m is the concentration of i element in mafic
magma and m being the fraction of mafic magma in the
mixture. The plot of C
­ im – C
­ if versus C
­ ii – C
­ if would result
in a straight line whose slope gives the mass proportions
of the mixture.
For this model samples R01 and R03 have been taken as
the mafic and felsic end members respectively. These samples are assumed to have been least affected by mixing and
mingling and other post-crystallization alteration processes
and hence best fit the model. Good linear correlations have
been obtained for the porphyritic diorite and mingled rocks
with ­R2 > 0.967 (Fig. 7). The slopes obtained for each of the
Evaluation of magma mixing in the subvolcanic rocks of Ghansura Felsic Dome of Chotanagpur Granite…
Fig. 7 Major-oxides mixing
test of Fourcade and Allégre
(1981) for the porphyritic
diorite and the mingled rocks.
Samples are (a) RJ23B (b) R04
(c) RJ22B (d) R02C. Cf = concentration of an element in felsic magma, Cm = concentration
of an element in mafic magma,
Ci = concentration of an element
in hybrid magma, m = fraction
of mafic magma in the mixture,
R2 = correlation coefficient
observed samples give the fraction of mafic magma involved
in the mixture. The fraction obtained for the porphyritic
diorite (sample R04) is 0.61 and varies from 0.61 to 0.87
for the mingled rocks.
Temperature‑viscosity mixing test
The porphyritic diorite (R04) has formed by the mixing
of 61% mafic magma (R01) and 39% felsic magma (R03),
as deduced from Fourcade and Allégre’s mixing test.
Giordano et al. (2008) has given a binary mixing model
of felsic and mafic melts to ascertain the relative contribution of individual magmas. In this binary mixing model,
viscosities of the two end-member magmas are plotted
against various temperatures. The plotted points give rise
to viscosity curves for the individual magmas. It is obvious
that the viscosity curve obtained for the hybrid product
should lie in between the two curves of the mafic and felsic
end-members. Moreover, the viscosity curve of the hybrid
product should lie closer to the viscosity curve of the parent end-member whose relative contribution is greater in
forming the hybrid. In our case, the viscosity curve of
sample R04 lies closer to the curve of sample R01, indicating that the contribution of the mafic phase in forming the
hybrid is greater in comparison to that of the felsic phase.
Moreover, in accordance with Fourcade and Allégre’s mixing test, the viscosity curve of R04 indicates a contribution
of ca. 60% of the mafic end-member (Fig. 8).
Glass transition temperature‑fragility mixing test
Transport properties of silicate melts such as ­Tg and m can
be independently used to determine the relative contribution
Fig. 8 Comparison of measured values of viscosity for mafic, felsic and hybrid melts to temperature (T) dependent curves (Giordano
et al. 2008). The 100% felsic and 100% mafic curves represent T
dependant viscosity curves for end-member compositions. The 50%
mafic-felsic curve represents viscosity curve for melt formed from
equal contributions from both the end-member magmas. The T
dependent viscosity curve for the porphyritic diorite indicates a ca.
60% contribution from the mafic end-member for 10,000/T (K) < 9.
For lower temperatures (10,000/T (K) > 9), viscosity of the hybrid
melt moves towards the mafic magma
Fig. 9 Plot of calculated glass transition temperature versus fragility
for mafic, felsic and hybrid melts (after Giordano et al. 2008). The
Tg-m plot also indicates a relative contribution of 61% from the mafic
magma in forming the porphyritic diorite
13
of both mafic and felsic end-members in forming the hybrid
(Giordano et al. 2008). The ­Tg value can be calculated using
the equation C + (B / 12-A) (Angell 1985; Dingwell et al.
1993; Giordano et al. 2008). The m value can be obtained
from the equation B / ­Tg{1-(C / ­Tg)}2 (Giordano et al. 2008).
The calculated m values plotted against T
­ g for samples R01,
R03 and R04 show that sample R04 plots on a mixing curve
between the two end-members (Fig. 9). In accordance with
the other mixing models, this model also shows a relative
contribution of 61% from the mafic phase in forming the
porphyritic diorite.
Discussion
Genesis of the hybrid intermediate rock with felsic
ocelli
The hybrid rock with felsic ocelli contains abundant FME
preserved in a mafic groundmass. The FME are essentially
fine-grained and resemble the microgranitic rocks of the
GFD. A large number of ocelli show reaction surfaces suggesting chemical interaction with the surrounding mafic
phase. The nature of interaction between the FME and mafic
phase is limited to chemical diffusion and mechanical transfer of crystals. The felsic and mafic domains are very well
preserved in the hybrid rock suggesting magma mingling
rather than mixing. Most of the FME are elongated with
aspect ratios up to 1:10.
From textural observations it appears that the felsic
magma was partly solidified when the mafic magma intruded
it. The intrusion disrupted the already solidified portion of
the felsic magma chamber and produced abundant felsic
clasts. These clasts were assimilated by the intruding mafic
magma and are now preserved as the FME. After incorporation of felsic clasts in the hotter mafic magma, the temperature of the latter altered the rheological behavior of the clasts
from brittle to ductile. The change in rheological behavior
facilitated the mechanical transfer of crystals from the mafic
magma to the felsic clasts. Moreover, the ductile nature of
the felsic clasts caused them to deform in the direction of
magma flow ultimately forming felsic ocelli.
Veining mechanism
The rocks of the GFD display a number of structures/textures on the outcrop and smaller scales related to magma
mixing and mingling. Transporting veins have played a
very important role in facilitating the mixing process in
our study area. These veins dominantly occur in the mingled rocks showing a considerable variation in size ranging
from microscopic to macroscopic. They transported minerals from the mafic phase to the felsic phase and vice versa.
13
B. Gogoi et al.
The re-distribution of mineral phases through these veins
occurred to attain chemical equilibrium in the disequilibrated mingled system. Through these conduits, either a
single mineral phase (monomineralic) or multiple phases
(polymineralic) could be transported.
From experimental work, it has been predicted that volatiles, K, P, Ba, Rb, Sr, Zr, Nb and light REE migrate rapidly from the felsic towards the mafic phase during magma
mingling (Watson and Jurewicz 1984; Johnston and Wyllie
1988; Baker 1990). On the contrary, cations like Ti, Fe, Mg,
Ca and V migrate from the mafic to the felsic phase (Seaman and Ramsay 1992). Such exchange of chemical components in the form of transported mineral phases is very
well illustrated by the hybrid rocks of the GFD. Mineral
phases like amphibole and biotite were transported from the
mafic to the felsic domain, while quartz and K-feldspar were
transferred in reverse. Thus, mineral-transporting veins can
be an important mechanism to attain chemical equilibrium
in a magma mixing and mingling scenario, in addition to
other mechanisms, such as diffusion and mechanical transfer of crystals (Frost and Mahood 1987; Christiansen and
Venchiarutti 1990; Neves and Vauchez 1995; Tate et al.
1997).
Mixing models
Near-linear trends on Harker variation diagrams displayed
by the rocks of the GFD for most of the major oxides suggest the occurrence of magma mixing. This has been further corroborated by major-oxides mixing tests with linear
correlations greater than 0.96 for all the plots (Fig. 7). The
major oxide linear correlations also enabled us to calculate
the relative contributions of the end-member magmas in
forming the hybrid products. However, the major drawback associated with the conventional models, viz., the
linear correlation test (Fourcade and Allégre 1981) and
least-squares linear fit test (Janoušek et al. 2000a, 2004) is
that they are based solely on the chemical compositions of
the interacting magmas. We also used two recently developed experimental mixing models that are based on the
physical properties of the interacting magmas, including
T, η, T
­ g and m. The calculated physical characteristics of
magmas involved in the mixing process have been used
in the recently developed experimental mixing models
by Giordano et al. (2008). The models confirm that the
porphyritic diorite of the GFD is indeed a hybrid product formed by the interaction of mafic and felsic magmas.
We have chosen the porphyritic diorite for these models
because they require mixing between crystal-poor magmas.
The presence of synneusis in the porphyritic diorite and its
homogenous nature indicate that this rock has formed due
to the mixing of crystal-poor magmas. The relative contributions of the mafic and felsic magmas in forming the
Evaluation of magma mixing in the subvolcanic rocks of Ghansura Felsic Dome of Chotanagpur Granite…
porphyritic diorite have been obtained through these models (Figs. 8 and 9). The results of the recent experimental
mixing models are corroborating those obtained with the
conventional models. These models also work in constraining some of the important physical properties of magmas
involved in the mixing process. Constraining these physical properties will greatly help to understand the nature
of interaction between disparate magmas and the complex
process of magma mixing.
Implications for regional geology
This paper reports the occurrence of magma mixing and
mingling for the first time in the CGGC. Our study area
(i.e., the GFD) is a part of the BVSs located on the northern
fringe of the CGGC. An island arc, subduction-related setting has been proposed for the BVSs by Saikia et al. (2014).
Island arcs are considered to be complex regions marked by
the presence of mafic-intermediate-felsic rocks. Such a wide
variety of rocks in arc systems may have evolved through
interplay of processes like fractional crystallization, crustal assimilation, magma mixing and source heterogeneities
(Murphy 2007).
The BVSs constitutes a bimodal volcanic suite (Saikia
et al. 2014) in which mixing of mafic and felsic magmas
has led to the generation of intermediate rocks. From the
available field, mineralogical and geochemical evidence,
the microgranite does not appear to be fractional crystallization products of the parental mafic magma forming
the dolerite. The mafic magma was probably generated
by volatile-induced partial melting of the mantle wedge
in this subduction zone setting. The mafic magma then
ascended as a network of dykes. During its ascent, some
amount of magma was entrapped in the lithosphere at
crustal levels. The possible presence of subsurface intrusive basic igneous rocks was highlighted by an anomalous NE-SW trending Bouger gravity high adjacent to the
BVSs (Das and Patel 1984). The ponding of mafic magma
caused partial melting of the overlying crust producing
discrete felsic magma pools. One such shallow level felsic
magma pool was intruded by ascending mafic magma
leading to magma mixing and mingling presently exemplified by the GFD.
Conclusions
(1) The rocks of the GFD show a good number of textural
and structural features related to magma mixing and
mingling. Veining mechanism has played a significant
role in facilitating the mixing process. Thus, veins transporting chemical components or mineral phases can be
an important mechanism of attaining chemical equilibrium in magmas undergoing mixing and mingling.
(2) The relative contribution of mafic magma in forming
the porphyritic diorite at the GFD is 61%. This has been
evaluated through the conventional major-oxide mixing
test, as well as recently developed experimental mixing
models.
(3) We propose that volumetrically small dioritic arc magmas produced in the BVSs are hybrid products generated by mixing of mafic mantle-derived melts and
crustal melts produced by mafic underplate-induced
melting of its overlying crust.
(4) In a regional geological context, it is the first report on
the occurrence of magma mixing and mingling in the
CGGC. The BVSs is the first composite magmatic suite
of rocks from the CGGC of the eastern Indian shield.
Acknowledgements Constructive reviews by Erwan Hallot and
an anonymous expert, and comments of journal editor Anton R.
Chakhmouradian are gratefully acknowledged. A.S. acknowledges the
CSIR grant vide Project no. 24(0317)/12/EMR-II, and B.G. acknowledges CSIR JRF/SRF fellowship no. 09/045(1146)/2011-EMR1.
References
Acharyya SK (2003) The nature of Mesoproterozoic central Indian
tectonic zone with exhumed and reworked older granulites. Gondwana Res 6(2):197–214
Ahmad M, Dubey J (2011) Report on prospecting for gold and silver
mineralization in Munger Rajgir group of rocks in Nalanda District, Bihar. P(ii), Unpublished report, Geological Survey of India
(F.S.: 2008-09, 2009-10, 2011-12)
Ahmad M, Paul AQ (2012) Tectono-stratigraphic constraints of the
Bathani volcano-sedimentary, volcanic sequences and associated rocks, Chotanagpur Granite Gneiss Complex, Gaya district Bihar. NEWS, Geological Survey of India, Eastern Region
33(1&2):13–15
Ahmad M, Paul AQ (2013) Investigation of volcano-sedimentary
sequence and associated rocks to identify gold and base metal
mineralization at Gere – Kewti area of Gaya District, Bihar (G4),
Unpublished report., Geological Survey of India (F.S.: 2012-13)
Ahmad M, Wanjari N (2009) Volcano-sedimentary sequence in the
Munger-Rajgir metasedimentary belt, Gaya district, Bihar. Indian
J Geosci 63(4):351–360
Albarède F (1995) Introduction to geochemical modeling. Cambridge
Univ. Press, Cambridge
Angell CA (1985) Strong and fragile liquids. In: Ngai KL, Wright
GB (eds) Relaxations in complex systems. U.S. Department of
Commerce National Technical Information Service, Springfield,
pp 3–11
Annen C, Blundy JD, Sparks RSJ (2006) The genesis of intermediate and silicic magmas in deep crustal hot zones. J Petrol
47(3):505–539
Baker DR (1990) Chemical interdiffusion of dacite and rhyolite: anhydrous measurements at 1 atm and 10 kbar, application of transition state theory to diffusion in zoned magma chambers. Contrib
Mineral Petr 104:407–423
13
Balaram V, Saxena VK, Manikyamba C, Ramesh SL (1990) Determination of rare earth elements in Japanese rock standards by
inductively coupled plasma mass spectrometry. Atom Spectrosc
11(1):19–23
Baxter S, Feely M (2002) Magma mixing and mingling textures in
granitoids: examples from the Galway Granite, Connemara, Ireland. Miner Petrol 76:63–74
Bonin B (2004) Do coeval mafic and felsic magmas in postcollisional
to within-plate regimes necessarily imply two contrasting, mantle
and crustal, sources? A review. Lithos 78(1–2):1–24
Boyton WV (1984) Cosmochemistry of the rare earth elements: Meteorite studies. In: Henderson P (ed) Rare earth element geochemistry. Elsevier, Amsterdam, pp 63–114
Burda J, Gawęda A, KlÓ§tzli U (2011) Magma hybridization in the
Western Tatra Mts. granitoid intrusion (S-Poland, Western Carpathians). Miner Petrol. 10.1007/s00710-011-0150-1
Castro A, Stephens WE (1992) Amphibole-rich polycrystalline clots
in calc-alkaline granitic rocks and their enclaves. Can Mineral
30:1093–1112
Chappell BW, White AJR, Wyborn D (1987) The importance of
residual source material (restite) in granite petrogenesis. J Petrol
28:571–604
Chatterjee N, Ghosh NC (2011) Extensive early neoproterozoic highgrade metamorphism in North Chotanagpur Gneissic Complex of
the central Indian tectonic zone. Gondw Res 20:362–379
Chatterjee N, Crowley JI, Ghose NC (2008) Geochronology of the
1.55 Ga Bengal anorthosite and Grenvillian metamorphism in the
Chotanagpur Gneissic Complex, eastern India. Precambrian Res
161:303–316
Chatterjee N, Banerjee M, Bhattacharya A, Maji AK (2010) Monazite
chronology, metamorphism-anatexis and tectonic relevance of the
mid-Neoproterozoic Eastern Indian tectonic zone. Precambrian
Res 179:99–120
Choe WH, Jwa YJ (2004) Petrological and geochemical evidences for
magma mixing in the Palgongsan Pluton. Geosci J 8(4):343–354
Christiansen EH, Venchiarutti DA (1990) Magmatic inclusions in rhyolites of the Spor Mountain Formation, Western Utah: limitations
on compositional inferences from inclusions in granitic rocks. J
Geophys Res 95:17717–17728
Das B, Patel NP (1984) Nature of the Narmada–Son lineament. J Geol
Soc India 25:267–276
DePaolo DJ (1981) Neodymium isotopes in the Colorado Front
Range and crust–mantle evolution in the Proterozoic. Nature
291:193–196
Dingwell DB, Bagdassarov NS, Bussod GY, Webb SL (1993) Magma
rheology. Experiments at high pressures and application to the
earth’s mantle. Mineral Assoc Canada Short Course Handbook
21:233–333
Dorais MJ, Whitney JA, Roden MF (1990) Origin of mafic enclaves in
the Dinkey Creek Pluton, Central Sierra-Nevada Batholith, California. J Petrol 31:853–881
Droop GTR (1987) A general equation for estimating ­Fe3+ concentrations in ferromagnesian silicates and oxides from microprobe
analyses using stoichiometric criteria. Mineral Mag 51:431–435
Foster DA, Hyndman DW (1990) Magma mixing and mingling
between synplutonic mafic dikes and granite in the Idaho-Bitterroot Batholith. In: Anderson JL (ed) The nature of cordilleran
magmatism, vol 174. Geol Soc Am Mem, pp 347–358
Fourcade S, Allégre CJ (1981) Trace elements behaviour in granite
genesis; a case study: the calc-alkaline plutonic association from
the Quérigut complex (Pyrénées, France). Contrib Mineral Petr
76:177–195
Frost TP, Mahood GA (1987) Field, chemical, and physical constraints
on mafic-felsic magma interaction in the Lamarck Granodiorite,
Sierra Nevada, California. Geol Soc Am Bull 99:272–291
13
B. Gogoi et al.
Fulcher GS (1925) Analysis of recent measurements of the viscosity
of glasses. J Am Ceram Soc 8:339–355
Ghent ED, Stout MZ (1984) T
­ iO2 activity in metamorphosed pelitic
and basic rocks; principles and applications to metamorphism
in southeastern Canadian Cordillera. Contrib Mineral Petr
86:248–255
Gioncada A, Mazzuoli R, Milton AJ (2005) Magma mixing at
Lipari (Aeolian Islands, Italy): Insights from textural and
compositional features of phenocrysts. J Volcanol Geotherm
Res 145:97–118
Giordano D, Russell JK, Dingwell DB (2008) Viscosity of magmatic
liquids: a model. Earth Planet Sci Lett 271:123–134
Hallot E, Davy P, Bremond d’Ars J, Auvray B, Martin H, Damme
HV (1996) Non-Newtonian effects during injection in partially
crystallised magmas. J Volcanol Geotherm Res 71(1):31–44
Hibbard MJ (1991) Textural anatomy of twelve magma-mixed granitoid systems. In: Didier J, Barbarin B (eds) Enclaves and granite petrology. Developments in petrology. Elsevier, Amsterdam,
pp 431–444
Janoušek V, Bowes DR, Rogers G, Farrow CM, Jelínek E (2000a)
Modelling diverse processes in the petrogenesis of a composite
batholith: the Central Bohemian Pluton, Central European Hercynides. J Petrol 41:511–543
Janoušek V, Bowes DR, Braithwaite CJR, Rogers G (2000b) Microstructural and mineralogical evidence for limited involvement of
magma mixing in the petrogenesis of a Hercynian high-K calcalkaline intrusion: the Kozarovice granodiorite, Central Bohemian
Pluton, Czech Republic. Trans R Soc Edinb Earth Sci 91:15–26
Janoušek V, Braithwaite CJR, Bowes DR, Gerdes A (2004) Magma
mixing in the genesis of Hercyniancalc-alkaline granitoids: an
integrated petrographic and geochemical study of the Sazava
intrusion, Central Bohemian Pluton, Czech Republic. Lithos
78:67–99
Johnston AD, Wyllie PJ (1988) Interaction of granitic and basic magmas: experimental observations on contamination processes at 10
kbar with ­H2O. Contrib Mineral Petr 98:352–362
Karmakar S, Bose S, Basu AS, Das K (2011) Evolution of granulite
enclaves and associated gneisses from Purulia, Chhotanagpur
Granite Gneiss Complex, India: evidence for 990 – 940 Ma tectonothermal event(s) at the eastern India cratonic fringe zone. J
Asian Earth Sci 41(1):69–88
Kemp AIS, Hawkesworth CJ, Foster GL, Paterson BA, Woodhead JD,
Hergt JM, Gray CM, Whitehouse MJ (2007) Magmatic and crustal
differentiation history of granitic rocks from Hf–O isotopes in
zircon. Science 315:980–983
Kohn MJ, Northrup CJ (2009) Taking Mylonites’ Temperatures. Geology 37(1):47–50
Koyaguchi T (1986) Evidence for two-state mixing in magmatic inclusions and rhyolitic lava domes on Nijima Island, Japan. J Volcanol
Geotherm Res 29:7–98
Kumar S, Rino V (2006) Mineralogy and geochemistry of microgranular enclaves in Palaeoproterozoic Malanjkhand granitoids, central
India: evidence of magma mixing, mingling, and chemical equilibration. Contrib Mineral Petr 152(5):591–609
Kuşcu GG, Floyd PA (2001) Mineral compositional and textural evidence for magma mingling in the Saraykent volcanics. Lithos
56:207–230
Leake BE, Woolley AR, Arps CES, Birch WD, Gilbert MC, Grice JD,
Howthorne FC, Kato A, Kisch HJ, Krivovichev VG, Linthout K,
Laird J, Mandarino (1997) Nomenclature of amphiboles. Report
of the subcommittee on amphiboles of the International Mineralogical Association: commission on new mineral names. Mineral
Mag 61:295–321
Maji AK, Goon S, Bhattacharya A, Mishra B, Mahato S, Bernhardt HJ
(2008) Proterozoic polyphase metamorphism in the Chotanagpur
Evaluation of magma mixing in the subvolcanic rocks of Ghansura Felsic Dome of Chotanagpur Granite…
Gneiss Complex (India), and implications for trans-continental
Gondwana correlation. Precambrian Res 162:385–402
Martin RF (2007) Amphiboles in the igneous environment. Rev Mineral Geochem 67:323–358
Middlemost EAK (1994) Naming materials in the magma/igneous system. Earth Sci Rev 37:215–224
Miller CF, McDowell SM, Mapes RW (2003) Hot and cold granites?
Implications of zircon saturation temperatures and preservation
of inheritance. Geology 31:529–532
Morimoto N, Fabries J, Ferguson AK, Ginzburg IV, Ross M, Seifert FA, Zussman J, Aoki K, Gottardi G (1988) Nomenclature of
pyroxenes. Miner Petrol 39:55–76
Murphy JB (2007) Igneous rock associations 8. Arc magmatism II:
geochemical and isotopic characteristics. Geosci Can 34(1):7–35
Neves SP, Vauchez A (1995) Successive mixing and mingling of magmas in a plutonic complex of Northeast Brazil. Lithos 34:275–299
Pal T, Mitra SK, Sengupta S, Katari A, Bandopadhyay PC, Bhattacharya AK (2007) Dacite–andesites of Narcondam volcano in the
Andaman sea — an imprint of magma mixing in the inner arc
of the Andaman–Java subduction system. J Volcanol Geotherm
Res 168:93–113
Pietranik A, Koepke J (2009) Interactions between dioritic and granodioritic magmas in mingling zones: plagioclase record of mixing,
mingling and subsolidus interactions in the Gęsiniec Intrusion, NE
Bohemian Massif, SW Poland. Contrib Mineral Petr 158:17–36
Pouchou JL, Pichoir F (1987) Basic expressions of PAP computation
for quantitative EPMA. Proceedings of ICXOM 11, Ontario,
249–253
Purohit KK, Mukherjee PK, Saini NK, Khanna PP, Rathi MS (2006)
Geochemical survey of stream sediments from upper parts of
Alaknanda, Mandakini, Bhilangana and Bhagirathi Catchments,
GarhwalHimalaya. Himal Geol 27(1):31–39
Putirka KD, Mikaelian H, Ryerson F, Shaw H (2003) New clinopyroxene-liquid thermobarometers for mafic, evolved, and volatilebearing lava compositions, with applications to lavas from Tibet
and the Snake River Plain, Idaho. Am Mineral 88:1542–1554
Saikia A, Gogoi B, Ahmad M, Ahmad T (2014) Geochemical constraints on the evolution of mafic and felsic rocks in the Bathani
volcano-sedimentary sequence of Chotanagpur Granite Gneiss
Complex. J Earth Syst Sci 123(5):959–987
Saini NK, Mukherjee PK, Rathi MS, Khanna PP, Purohit KK (1998)
A new geochemical reference sample of granite (DG-H) from
Dalhousie, Himachal Himalaya. J Geol Soc India 52:603–606
Saini NK, Mukherjee PK, Rathi MS, Khanna PP (2000) Evaluation of
energy-dispersive X-ray fluorescence spectrometry in the rapid
analysis of silicate rocks using pressed powder pellets. X-Ray
Spectrom 29(2):166–172
Saini NK, Mukherjee PK, Khanna PP, Purohit KK (2007) A proposed
amphibolite reference rock sample (AM-H) from Himachal
Pradesh. J Geol Soc India 69:799–802
Sanyal S, Sengupta P (2012) Metamorphic evolution of the Chotangapur Granite Gneiss Complex of the East Indian shield: current status. In: Mazumder R, Saha D (eds) Paleoproterozoic of
India geological society, vol 365. Geol Soc London Spec Publ,
pp 117–145
Seaman SE, Ramsay PC (1992) Effects of magma mingling in the
granites of Mount Desert Island, Maine. J Geol 100:395–409
Singh Y, Krishna V (2009) Rb-Sr geochronology and petrogenesis of
granitoids from the Chotanagpur Granite Gneiss Complex of Raikera-Kunkuri region, Central India. J Geol Soc India 74:200–208
Spear FS, Wark DA (2009) Cathodoluminescence imaging and titanium thermometry in metamorphic quartz. J Metamorph Geol
27(3):187–205
Speer JA (1984) Micas in igneous rocks. In: Bailey SW (ed) Micas.
Rev Mineral, vol 70.Miner Soc Am, pp 299–356
Stein H, Hannah J, Zimmerman A, Markey R (2006) Mineralization
and deformation of the Malanjkhand terrane (2,490–2,440 Ma)
along the southern margin of the Central Indian Tectonic Zone.
Miner Deposita 40:755–765
Sun SS, McDonough WF (1989) Chemical and isotopic systematics
of oceanic basalts: implications for mantle composition and processes. In: Saunders AD, Norry MJ (eds) Magmatism in ocean
basins, vol 42. Geol Soc London Spec Publ, pp 313–345
Tammann G, Hesse W (1926) The dependence of viscosity upon
the temperature of supercooled liquids. Z Anorg Allg Chem
156:245–257
Tate MC, Clarke DB, Heaman LM (1997) Progressive hybridisation
between late Devonian mafic-intermediate and felsic magmas in
the Meguma Zone of Nova Scotia, Canada. Contrib Mineral Petr
126:401–415
Tepper JH, Kuehner SM (2004) Geochemistry of mafic enclaves and
host granitoids from the Chilliwack Batholith, Washington: chemical exchange processes between coexisting mafic and felsic magmas and implications for the interpretation of enclave chemical
traits. J Geol 112:349–367
Ubide T, Gale C, Larrea P, Arranz E, Lago M, Tierz P (2014) The relevance of crystal transfer to magma mixing: a case study in composite dykes from the central Pyrenees. J Petrol 55(8):1535–1559
Vernon RH, Etheridge MA, Wall VJ (1988) Shape and microstructure
of microgranitoid enclaves: indicators of magma mingling and
flow. Lithos 22:1–11
Vogel DH (1921) Temperaturabhängigkeitsgesetz der Viskosität von
Flüssigkeiten. Phys Z 22:645–646
Vogt JHL (1921) The physical chemistry of the crystallization and
magmatic differentiation of igneous rocks. J Geol 28:318–350
Waight TE, Maas R, Nicholls IA (2001) Geochemical investigations
of microgranitoid enclaves in the S-type Cowra Granodiorite,
Lachlan Fold Belt, SE Australia. Lithos 56:165–186
Walker F (1957) Ophitic texture and basaltic crystallization. J Geol
65(1):1–14
Wall VJ, Clemens JD, Clarke DB (1987) Models for granitoid evolution
and source compositions. J Geol 95:731–749
Wark DA, Watson EB (2006) TitaniQ: a titanium-in-quartz geothermometer. Contrib Mineral Petr 152:743–754
Watson EB, Harrison TM (1983) Zircon saturation revisited: temperature and compositional effects in a variety of crustal magma types.
Earth Planet Sci Lett 64:295–304
Watson EB, Jurewicz SR (1984) Behavior of alkalies during diffusive interaction of granitic xenoliths with basaltic magma. J Geol
92:121–131
Wilson M (1989) Igneous petrogenesis. Chapman and Hall, London
13
Документ
Категория
Без категории
Просмотров
9
Размер файла
3 096 Кб
Теги
017, s00710, 0540
1/--страниц
Пожаловаться на содержимое документа