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Cenozoic Adakite‐type Volcanic Rocks in Qiangtang, Tibet and Its Significance
Author(s) -
Shen LIU,
Ruizhong HU,
Caixia FENG,
Xiaoguo CHI,
Cai LI,
Rihong YANG,
Tianwu WANG,
Wei JIN
Publication year - 2003
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.2003.tb00561.x
Subject(s) - geochemistry , adakite , partial melting , fractional crystallization (geology) , geology , crust , lile , basalt , oceanic crust , subduction , tectonics , paleontology
Volcanic rocks in the study area, including dache, trachyandesite and mugearite, belong to the intermediate‐acid, high‐K calc‐alkaline series, and possess the characteristics of adakite. The geochemistry of the rocks shows that the rocks are characterized by SiO 2 >59%, enrichment in Al 2 O 3 (15.09–15.64%) and Na 2 O (>3.6%), high Sr (649–885 μg/g) and Sc, low Y contents (<17 μg/g), depletion in HREE (Yb<1.22 μg/g), (La/Yb) N >25, Sr/Y>40, MgO<3% (Mg # <0.35), weak Eu anomaly (Eu/Eu*=0.84‐0.94), and lack of the high field strength elements (HFSE) (Nb, Ta, Ti, etc.). The Nd and Sr isotope data ( 87 Sr/ 86 Sr=0.7062‐0.7079, 143 Nd/ 144 Nd=0.51166‐0.51253, εNd = −18.61‐0.02), show that the magma resulted from partial melting (10%‐40%) of newly underplated basaltic lower crust under high pressure (1–4 GPa), and the pedogenesis is obviously affected by the crust's assimilation and fractional crystallization (AFC). This research will give an insight into the uplift mechanism of the Tibetan plateau.