Magnetic susceptibility and biotite composition of granitoids of Amritpur and adjoining regions, Kumaun Lesser Himalaya

Kumar, Santosh; Singh, Brajesh; Joshi, C Mahesh; Pandey, Abhishek

doi:10.3126/hjs.v2i4.869

Cited by 2 publications

(2 citation statements)

References 3 publications

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“…550–500 Ma) formed during the Pan‐African Orogeny decipher not only the melting characteristics of the crust but also show a transition from I‐type to A‐type felsic magmatism (Kumar, Pundir, et al, 2022). Cambro‐Ordovician (500 ± 25 Ma) granitic magmatism not only provides a comprehensive perspective of the heterogeneous melting of the crust but also the interplay between mafic and felsic magmas during this time (Kumar, Singh, et al, 2022). The intense mylonitization of the Palaeozoic granites is commonly associated with Himalayan Orogeny (Le Fort, 1983; Singh, 2003; Singh et al, 2002; Singh & Jain, 1996).…”

Section: Introductionmentioning

confidence: 99%

Structural and geochemical studies of the Palaeozoic granites from Dalhousie region of Himachal Himalaya: Implications on petrogenesis and deformation of strongly peraluminous S‐type granites

et al. 2022

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The Palaeozoic granites forming the Dalhousie pluton occur as an elongated body intruded into the core of an antiform in Salkhala metasedimentary rocks and are referred to herein as Dalhousie granites (DG). The studied mesoscopic structures, for example, well‐developed and randomly distributed megacrysts of K‐feldspar at the core part of massif, show undeformed porphyritic nature, whereas augen along with the mylonitic foliation and parallelly aligned feldspar megacrysts are dipping towards north‐north‐east (NNE) in the marginal part. The presence of aplite veins is evidence of final stage crystallization, where these rocks rapidly crystallized from siliceous residual fluids/solutions that escaped along fractures in the granites. Moreover, the granites show intrusive as well as thrusted contact with the Chamba metamorphics. The microscopic study from the marginal parts shows the dynamic recrystallization of quartz along with the fractures filled with secondary material oriented opposite to the top‐to‐the‐SW. Whereas euhedral quartz grains with undeformed grain boundaries, compositional zoning in plagioclase, and magmatic (perthite) texture of K‐feldspar are present in the core of Dalhousie pluton. In addition, a new whole‐rock geochemical dataset of DG is presented and investigated to elucidate the petrogenesis and tectonic environment. The geochemical data shows that DG (dominantly monzogranites) are formed from a pelitic source‐derived, (molar Al2O3/CaO + Na2O + K2O > 1.1) strongly peraluminous (S‐type) calc‐alkaline magma. This magma was generated by muscovite vapour absent dehydration melting. Harker bivariate plots indicate that fractional crystallization was a dominant process during the evolution of these granites. The tectonic discrimination diagrams suggest that DG were generated in syn‐collisional setting. Exceptionally high Pb in DG occurred due to primary melt generation at low‐temperature during partial melting (low‐degree melting) of the pelitic source rock. Trace and rare earth elements characteristics, such as positive anomaly of Zr show a notable amount of zircon as one of the accumulating phases. A pronounced negative Eu anomaly (EuN/Eu* = 0.04–0.66), along with high silica content and highly varied trace element ratios in these rocks, show that these are fairly evolved granites.

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Section: Introductionmentioning

confidence: 99%

Structural and geochemical studies of the Palaeozoic granites from Dalhousie region of Himachal Himalaya: Implications on petrogenesis and deformation of strongly peraluminous S‐type granites

et al. 2022

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“…Takahasi et al 1980), which most likely represent a modified composition because of assimilation enroute, magma mixing, and/or later tectonic processes acted upon them significantly affecting their original magnetic property (e.g. Takagi, 2004;Kumar et al 2005Kumar et al , 2006Singh and Kumar, 2005;Singh, 2008, Kumar andPathak, 2009). MS values combined with whole rock geochemical features of anorogenic (A-type) granites have been used to make further distinction between oxidized A-type magnetite series and reduced A-type ilmenite series granites (Dall'Agnol et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Magnetic susceptibility mapping of felsic magmatic lithounits in the central part of Bundelkhand Massif, central India

et al. 2010

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Late Archaean to Palaeoproterozoic felsic magmatic lithounits exposed in the central part of the Bundelkhand massif have been mapped and their redox series (magnetite vs ilmenite series) evaluated based on magnetic susceptibility (MS) data. The central part of Bundelkhand massif comprises of multiple felsic magmatic pulses (~2600-2200 Ma), commonly represented by coarse grained granite (CGG-grey granite, CPG-pink granite), medium grained pink granite (MPG), fine grained pink granite (FPG) , grey and pink rhyolites and granite porphyry (GP). However, the pink colour of these felsic rocks is the result of hydrothermal fluid-flushing leading to potassic alteration of grey granites. MS values of CGG vary from 0.058 to 14.75×10 -3 SI with an average of 6.35×10 -3 SI, which mostly represent oxidized type, magnetite series (73%) granites involving infracrustal (igneous) source materials. CPG (av. MS=3.95×10 -3 SI) is indeed a pink variety of CGG, the original oxidizing nature of which must have been similar to the bulk of CGG, but has been moderately to strongly reduced because of distinctly more porphyritic nature together with partial assimilation of metapelitic (supracrustal) materials, surmicaceous enclaves, carbonaceous material included in the source materials, and to some extent, induced by hydrothermal and later deformational processes. MPG (av. MS= 1.15×10 -3 SI) as lensoidal stock-like bodies intrudes the CPG and represent both magnetite series (18%) and ilmenite series (82%) granites, which are probably formed by heterogeneous (mixed) source rocks. GP (av. MS=6.26×10 -3 SI) occur as dykes (mostly trending NE-SW) intrudes the MPG, CPG and migmatites and bears the nature similar to oxidized type, magnetite series granite. FPG (av. MS= 0.666×10 -3 SI) trending NE-SW occur as lensoid bodies including a large outcrop, is intrusive into both CPG and MPG, and is moderately to very strongly reduced type, ilmenite series granites, which may be derived by the melting of metapelitic crustal sources. FPG hosting microgranular (mafic magmatic) enclaves commonly exhibit high MS values (7.31-10.22×10 -3 SI), which appear induced by the mixing and mingling of interacting felsic and mafic magmas prevailed in an open system. Grey (av. MS=10.30×10 -3 SI) and pink (av. MS=6.72×10 -3 SI) rhyolites represent oxidized type, magnetite series granites, which may have been derived from infracrustal (magmatic) protoliths. Granite series evaluation of felsic magmatic rocks of central part of Bundelkhand massif strongly suggests their varied redox conditions (differential oxygen fugacity) mostly intrinsic to magma source regions and partially modified by hydrothermal and tectonic processes acting upon them.

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Magnetic susceptibility and biotite composition of granitoids of Amritpur and adjoining regions, Kumaun Lesser Himalaya

Cited by 2 publications

References 3 publications

Structural and geochemical studies of the Palaeozoic granites from Dalhousie region of Himachal Himalaya: Implications on petrogenesis and deformation of strongly peraluminous S‐type granites

Structural and geochemical studies of the Palaeozoic granites from Dalhousie region of Himachal Himalaya: Implications on petrogenesis and deformation of strongly peraluminous S‐type granites

Magnetic susceptibility mapping of felsic magmatic lithounits in the central part of Bundelkhand Massif, central India

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