Field Evidence of Magma Mixing from Microgranular Enclaves Hosted in Palaeoproterozoic Malanjkhand Granitoids, Central India

Kumar, Santosh; Rino, Vikoleno; Pal, Amit

doi:10.1016/s1342-937x(05)70804-2

Cited by 93 publications

(48 citation statements)

References 54 publications

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“…Their contacts with their host are sharp, rounded or irregular, and big enclaves have diffusive contacts without deformation, a characteristic that can be attributed to the undercooling and mingling of hybrid MME globules formed by a mixture of mafic and felsic magmas (e.g., Perugini et al 2003). The degree of thermal, rheological and compositional contrast of co-existing mafic and felsic magmas governs the hybridization levels, preserving the megascopic features (mafic microgranular enclaves) relevant to the magma mixing (e.g., Kumar et al 2004). The MMEs show magmatic textures similar to the poikilitic-equigranular textures of basic igneous rocks.…”

Section: Mafic Microgranular Enclavesmentioning

confidence: 99%

“…For a more mafic end-member, the SCLM-derived magma seems less likely because of the relatively low initial Sr-Nd isotopic ratios of the hybrid granitoid rocks. The MMEs from the pluton, with their finer grain sizes attributed to the undercooling of a mafic magma in a cooler, felsic magma (e.g., Vernon 1984;Wiebe 1991;Barbarin and Didier 1992;Perugini and Poli 2000;Kumar et al 2004), have mineral assemblages, chemical relationships and isotopic compositions similar to their host rocks. The MMEs contain large, rounded plagioclase phenocrysts, which are Pb for the selected samples from the plutons.…”

Section: Source Featuresmentioning

confidence: 99%

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Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harşit Pluton, Eastern Turkey

Karslı

Dokuz

Uysal

et al. 2010

Contrib Mineral Petrol

147

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We present elemental and Sr-Nd-Pb isotopic data for the magmatic suite (*79 Ma) of the Harşit pluton, from the Eastern Pontides (NE Turkey), with the aim of determining its magma source and geodynamic evolution. The pluton comprises granite, granodiorite, tonalite and minor diorite (SiO 2 = 59.43-76.95 wt%), with only minor gabbroic diorite mafic microgranular enclaves in composition (SiO 2 = 54.95-56.32 wt%), and exhibits low Mg# (\46). All samples show a high-K calc-alkaline differentiation trend and I-type features. The chondrite-normalized REE patterns are fractionated [(La/Yb) 83. These geochemical data rule out pure crustalderived magma genesis in a post-collision extensional stage and suggest mixed-origin magma generation in a subduction setting. The melting that generated these high-K granitoidic rocks may have resulted from the upper Cretaceous subduction of the Izmir-Ankara-Erzincan oceanic slab beneath the Eurasian block in the region. The back-arc extensional events would have caused melting of the enriched subcontinental lithospheric mantle and formed mafic magma. The underplating of the lower crust by mafic magmas would have played a significant role in the generation of high-K magma. Thus, a thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower part of the crust. In this scenario, the lithospheric mantle-derived basaltic melt first mixed with granitic magma of crustal origin at depth. Then, the melts, which subsequently underwent a fractional crystallization and crustal assimilation processes, could ascend to shallower crustal levels to generate a variety of rock types ranging from diorite to granite. Sr-Nd isotope modeling shows that the generation of these magmas involved *65-75% of the lower crustal-derived melt and *25-35% of subcontinental lithospheric mantle. Further, geochemical data and the Ar-Ar plateau age on hornblende, combined with regional studies, imply that the Communicated by G. Moore. Electronic supplementary material 123Contrib Mineral Petrol (2010) 160:467-487 DOI 10.1007 Harşit pluton formed in a subduction setting and that the back-arc extensional period started by least *79 Ma in the Eastern Pontides.

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Section: Mafic Microgranular Enclavesmentioning

confidence: 99%

Section: Source Featuresmentioning

confidence: 99%

Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harşit Pluton, Eastern Turkey

Karslı

Dokuz

Uysal

et al. 2010

Contrib Mineral Petrol

147

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“…The enclaves are ellipsoidal or lenticular, and are noticeably finer-grained than the host felsic rocks. Mafic enclaves are variably elongated without solid-state deformation (Figure 2(b)), which suggests enclaves and host rocks represent compositionally distinct magmas [22,23] . This idea is supported by the alignment of hornblende, biotite and elongate laths of plagioclase (Figure 3(a)) without signs of solidstate deformation, because such a preferred dimensional orientation of crystals was apparently formed in a medium in which enough melt is present to allow extensive rotation of crystals.…”

Section: Field Relations and Petrological Descriptionsmentioning

confidence: 99%

“…Figure 3(a) shows a plagioclase megacryst from an enclave, with a compositionally homogeneous, embayed core (An [31][32][33][34] ). The core is mantled by a euhedral, An-rich plagioclase (An 54-58 ) that is, in turn, mantled by a relatively sodium-rich plagioclase (An [22][23][24][25], and the boundaries between different zones are straight and sharp. Figure 3(b) shows a plagioclase megacryst from the host rock, having an irregular, calcium-rich core (An 53-57 ), surrounded by a relatively Ab-rich rim (An 20-38 ), and the compositional change between the two is abrupt.…”

Section: Field Relations and Petrological Descriptionsmentioning

confidence: 99%

“…As shown in Figure 3(b), plagioclase megacrysts often have an abnormally calcium-rich, irregular core (An 53-57 ), which is abruptly mantled by a relatively sodium-rich plagioclase (An [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] ). This is apparently different from the "normal" compositional zoning of plagioclase.…”

Section: Crystal Exchange Between Enclaves and Host Magmasmentioning

confidence: 99%

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Petrogenesis of mafic enclaves from the north Taihang Yanshanian intermediate to felsic plutons: Evidence from petrological, geochemical, and zircon Hf-O isotopic data

Chen

2009

Sci. China Ser. D-Earth Sci.

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We report the zircon Hf-O isotopic data for mafic enclaves from the Taihang Yanshanian intermediate to felsic plutons, and use them, along with the petrological, whole-rock chemical and Nd-Sr isotopic data, to reveal the petrogenesis of mafic enclaves. Mafic enclaves show magmatic textures and are finer-grained than host rocks. In places they are highly elongated due to stretching within the partially crystallized, convective felsic magma, but show no solid-state deformation. These data suggest that mafic enclaves and host rocks were co-existing, but compositionally distinct magmas. The mafic enclaves contain abundant hydrous minerals such as hornblende and biotite, with pyroxene relict being surrounded by hornblende reaction rim. Plagioclase xenocrysts from mafic enclaves show a complicated compositional and textural disequilibrium. Comparison between mafic enclaves and the immediate host rocks suggests that the two rock units are compositionally correlated. The ε Nd values of mafic enclaves are generally higher than the host rocks, though the Sr isotopic ratios of the two rock units are indistinguishable. Zircons from a single enclave sample show a significant variation in Hf isotopic compositions, with ε Hf = −10-−22, suggesting an origin through magma mixing between mafic and felsic magmas. This is supported by the relatively large variation of zircon O isotopic ratios (δ 18 O = 5.5‰-7.8‰) of the mafic enclaves. The petrogenesis of mafic enclaves could be described as below. Evolved basaltic magma (via fractionation of olivine and pyroxene) first mixed with crustally derived granitic melts in depths, forming a hybrid magma; then the hybrid magma broke up into discrete lumps upon entering the above felsic magma. Subsequently, the enclave-forming magma experienced a double mechanical transfer of plagioclase, and inward chemical transfer of fluid and Na, P, Y, Nb and Pb at the contacts with host felsic magmas. mafic enclaves, compositional zoning, Nd-Sr isotopes, zircon Hf-O isotopes, magma mixingThe petrogenesis of mafic enclaves has been an issue of controversy for long. Models for the origin of mafic enclaves include: (1) mafic enclaves are formed as cognate fragments of cumulate minerals from a mafic magma [1,2] , (2) mafic enclaves represent recrystallized, refractory and residual phase assemblage derived from a granite source [2,3] , and (3) mafic enclaves are formed through hybridization between mafic and felsic magmas [4][5][6][7][8][9][10] .More and more studies suggest that most enclaves are formed by magma mixing between mantle-and crustle-derived melts. However, the mechanisms of magma

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The Early Carboniferous Xiaomiaogou granite porphyry dykes in the northern margin of the North China Craton: implication for crust–mantle interaction and intraplate magmatism

Wang

Lei³

et al. 2016

Geological Journal

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The age, petrogenesis and geodynamic implication of Xiaomiaogou granite porphyry dykes in the northern margin of the North China Craton were investigated using geochronology, geochemistry and Sr–Nd–Pb–Hf isotopic data. LA‐MC‐ICP‐MS zircon U–Pb dating yielded the concordant 206Pb/238U weighted mean age of 350.4 ± 1.4 Ma for the dykes, suggesting they were the productions of the Early Carboniferous magmatism in the northern margin of the North China Craton. The granite porphyries display the pronounced A‐type affinities: apart from higher zircon saturation temperature, they are high‐K calc‐alkaline and metaluminous, with high concentrations of K2O + Na2O varying from 7.93 to 8.55 wt.%, incompatible elements (e.g. Zr, Y, Nb and Ce), REEs and 10 000 Ga/Al ratios but less obvious LREE and HREE fractionation. With the lower initial 87Sr/86Sr ratios (0.7055 to 0.7070), negative values of εNd(t) (−7.1 to −4.9) and εHf(t) (−11.2 to −8.0) and old Nd (1505 to 1681 Ma) and Hf (1861 to 2061 Ma) model ages, all the rocks exhibit the similar geochemical compositions to the melts obtained in experimental studies by dehydration melting of meta‐basalts, implying a lower continental crust origin. However, the high Mg# values (47.53 to 53.60) and subcontinental lithospheric mantle‐like εNd(t), εHf(t) and Pb isotopic compositions ((206Pb/204Pb)i = 17.296–17.766, (207Pb/204Pb)i = 15.460–15.490 and (208Pb/204Pb)i = 37.097–37.568) indicate the involvement of melts from subcontinental lithospheric mantle. Combined with the special features of mafic microgranular enclaves occurring within the granite porphyries, mixing of the lower crust and subcontinental lithospheric mantle of the North China Craton is proposed for the genesis of granite porphyry dykes in this study. During the hybrid magma ascending, pronounced fractional crystallization and crustal assimilation may have also occurred. Based on geochemical criteria, the Xiaomiaogou granite porphyries can be classified into A1 group. Characterized by the compositional features of anorogenic granites, an intraplate setting is envisaged for the formation of Xiaomiaogou granite porphyry dykes. Such a tectonic environment may be related to the northward drift of the North China Craton during rifting away from East Gondwana. Copyright © 2016 John Wiley & Sons, Ltd.

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Field Evidence of Magma Mixing from Microgranular Enclaves Hosted in Palaeoproterozoic Malanjkhand Granitoids, Central India

Cited by 93 publications

References 54 publications

Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harşit Pluton, Eastern Turkey

Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harşit Pluton, Eastern Turkey

Petrogenesis of mafic enclaves from the north Taihang Yanshanian intermediate to felsic plutons: Evidence from petrological, geochemical, and zircon Hf-O isotopic data

The Early Carboniferous Xiaomiaogou granite porphyry dykes in the northern margin of the North China Craton: implication for crust–mantle interaction and intraplate magmatism

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