Mineralogy and geochemistry of granitoids from Kinnaur region, Himachal Higher Himalaya, India: Implication on the nature of felsic magmatism in the collision tectonics

Journal of Earth system science

Masao Ban2²  Kazuo Nakashima2²  Santosh Kumar1¹  Brajesh Singh1¹ 

[1] Department of Geology, Kumaun University, Nainital 263 002, Uttarakhand, India.$$;Department of Earth and Environmental Sciences, Yamagata University, 990 8560, Yamagata, Japan.$$

关键词: Mineralogy;    geochemistry;    petrogenesis;    granitoids;    Himachal Higher Himalaya;   

DOI  :  

学科分类：天文学(综合)

来源: Indian Academy of Sciences

【 摘 要 】

Felsic magmatism in the southern part of Himachal Higher Himalaya is constituted by Neoproterozoic granite gneiss (GGn), Early Palaeozoic granitoids (EPG) and Tertiary tourmaline-bearing leucogranite (TLg). Magnetic susceptibility values ($lt$3 ×10$^{−3}$ SI), molar Al$_2$O$^3$/(CaO+Na$_2$O+K$_2$O) ($geq$1.1), mineral assemblage (bt–ms–pl–kf–qtz ± tur ± ap), and the presence of normative corundum relate these granitoids to peraluminous S-type, ilmenite series (reduced type) granites formed in a syncollisional tectonic setting. Plagioclase from GGn (An$_{10}$–An$_{31}$) and EPG (An$_{15}$–An$_{33}$) represents oligoclase to andesine and TLg (An$_2$–An$_{15}$) represents albite to oligoclase, whereas compositional ranges of K-feldspar are more or less similar (Or$_{88}$ to Or$_{95}$ in GGn, Or$_{86}$ to Or$_{97}$ in EPG and Or$_{87}$ to Or$_{94}$ in TLg). Biotites in GGn (Mg/Mg+Fe$^t$ = 0.34–0.45), EPG (Mg/Mg+Fe$^t$ = 0.27–0.47), and TLg (Mg/Mg+Fe$^t$ = 0.25–0.30) are ferribiotites enriched in siderophyllite, which stabilised between FMQ and HM buffers and are characterised by dominant 3Fe$ightleftarrows$2Al, 3Mg$ightleftarrows$2Al substitutions typical of peraluminous (S-type), reducing felsic melts. Muscovite in GGn (Mg/Mg+Fe$^t$ = 0.58–0.66), EPG (Mg/Mg+Fe$^t$ = 0.31−0.59), and TLg (Mg/Mg+Fet = 0.29–0.42) represent celadonite and paragonite solid solutions, and the tourmaline fromEPG and TLg belongs to the schorl-elbaite series, which are characteristics of peraluminous, Li-poor, biotite-tourmaline granites. Geochemical features reveal that the GGn and EPG precursor melts were most likely derived from melting of biotite-rich metapelite and metagraywacke sources, whereas TLg melt appears to have formed from biotite-muscovite rich metapelite and metagraywacke sources. Major and trace elements modelling suggest that the GGn, EPG and TLg parental melts have experienced low degrees (∼13, ∼17 and ∼13%, respectively) of kf–pl–bt fractionation, respectively, subsequent to partial melting. The GGn and EPG melts are the results of a pre-Himalayan, syn-collisional Pan-African felsicmagmatic event, whereas the TLg is a magmatic product of Himalayan collision tectonics.

【 授权许可】

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