| Citation: |
WANG Xiaoxian, ZHANG Jinjiang, YANG Xiongying. Geochronology, Geochemistry and Formation Mechanism of Malashan Granite in Tethyan Himalaya[J]. Northwestern Geology, 2015, 48(4): 70-87.
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Geochronology, Geochemistry and Formation Mechanism of Malashan Granite in Tethyan Himalaya
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Abstract
The Malashan granite was exposed in the west of the Tethyan Himalayan sedimentary sequence(THS).It is characterized by gneissic texture and the assemblage of quartz, K-feldspar, muscovite and biotite.LA-MC-ICP-MS zircon U-Pb dating results indicated that the granite recorded two episodes of anatexis at(28.0±0.5) Ma and(18.4±0.3) Ma, respectively.The age of(18.4±0.3) Ma represents the final crystallized time of Malashan granite.Geochemical data show that these samples are characterized by high SiO2(72.36%-72.51%), Al2O3(15.22%-15.37%), CaO(1.64%-1.66%) and high value of K2O/Na2O(0.97-1.05) and A/CNK(1.15-1.20), and the enrichment in Rb, Th, U and K, the depletion in Ba, Nb, Sr and Zr, weak negative Eu anomalies(δEu=0.80-0.89), and strong fractionation between LREE and HREE((La/Yb)N=7.09-19.68).These features suggest that they are high potassium calc-alkaline and peraluminous granites.The relatively low Rb/Sr ratios(0.90-1.10)and high CaO/Na2O ratios(0.44-0.46)imply that the magma source was probably psammitolite.The(87Sr/86Sr)I(0.742522-0.744097) and εNd(t)(-14.5--13.7) can compare well with those of the metasedimentary rocks in the Greater Himalaya Crystalline complex(GHC), so these granite wasgenerated from partial melting of the GHC metasedimentary rocks.The features of relatively low(87Sr/86Sr)i and high Sr content,and the constant Rb/Sr ratios relative to large variations in Ba concentrations approve that, the Malashangranite wasderived from fluxed melting of the GHC metasedimentary rocks,possibly associated tightly with the E-W extension along the North-South trend rift system(NSTR).-
Keywords:
- Malashan granite /
- geochronology /
- geochemistry /
- formation mechanism /
- Tethyan Himalaya
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References
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WANG Xiaoxian, ZHANG Jinjiang, YANG Xiongying. Geochronology, Geochemistry and Formation Mechanism of Malashan Granite in Tethyan Himalaya[J]. Northwestern Geology, 2015, 48(4): 70-87.
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