TY - JOUR
T1 - Southern Tibetan Oligocene-Miocene adakites
T2 - A record of Indian slab tearing
AU - Zhang, Li Yun
AU - Ducea, Mihai N.
AU - Ding, Lin
AU - Pullen, Alex
AU - Kapp, Paul
AU - Hoffman, Derek
N1 - Publisher Copyright:
© 2014 Elsevier B.V.
PY - 2014/12/1
Y1 - 2014/12/1
N2 - Oligocene-Miocene granitoids exposed within the 1500-km-long Gangdese arc of southern Tibet exhibit adakitic compositions. Five plutonic samples from the southeastern Lhasa terrane near Namche Barwa area were analyzed to determine their geochemical characteristics and to better understand the geodynamic evolution of the eastern Himalayan syntaxis orogen. The samples, yielded U-Pb zircon ages in the range of 30-26Ma, are intermediate to silicic in composition and have elevated K2O (1.5-8.9), Th/La ratios (0.14-1.10), low MgO (<2%) and Mg# (<50), as well as high initial 87Sr/86Sri (0.7062-0.7103) and low εNd(t) (-10.9 to -1.0) isotopic compositions. In addition, these granitic and granodioritic rocks have high Sr/Y (66-306) and La/Yb (25-312) ratios, a characteristic of adakitic rocks. In-situ zircon εHf(t) isotopic compositions are in the range of +8.1 to -1.9. Within the framework of the Tibetan-Himalayan orogenesis we attribute these rocks to represent partial melting and mixing products of two end-member components of the lower Tibetan crust: the roots of the relatively juvenile Gangdese arc crust and newly-underplated high-potassium mafic magmas. Adakitic magmatism initiated at 30-26Ma near the eastern Himalayan syntaxis and systematically decreases in age to the west to 18-9Ma near Shigatse. We attribute this temporal-spatial distribution of adakitic magmatism within the Gangdese arc, along with the regional Oligo-Miocene geology, to the progressive tearing of the Indian plate. Based on the decrease in age of adakitic magmatism from east to west we hypothesize that the tear initiated beneath the eastern Himalayan syntaxis and propagated westward.
AB - Oligocene-Miocene granitoids exposed within the 1500-km-long Gangdese arc of southern Tibet exhibit adakitic compositions. Five plutonic samples from the southeastern Lhasa terrane near Namche Barwa area were analyzed to determine their geochemical characteristics and to better understand the geodynamic evolution of the eastern Himalayan syntaxis orogen. The samples, yielded U-Pb zircon ages in the range of 30-26Ma, are intermediate to silicic in composition and have elevated K2O (1.5-8.9), Th/La ratios (0.14-1.10), low MgO (<2%) and Mg# (<50), as well as high initial 87Sr/86Sri (0.7062-0.7103) and low εNd(t) (-10.9 to -1.0) isotopic compositions. In addition, these granitic and granodioritic rocks have high Sr/Y (66-306) and La/Yb (25-312) ratios, a characteristic of adakitic rocks. In-situ zircon εHf(t) isotopic compositions are in the range of +8.1 to -1.9. Within the framework of the Tibetan-Himalayan orogenesis we attribute these rocks to represent partial melting and mixing products of two end-member components of the lower Tibetan crust: the roots of the relatively juvenile Gangdese arc crust and newly-underplated high-potassium mafic magmas. Adakitic magmatism initiated at 30-26Ma near the eastern Himalayan syntaxis and systematically decreases in age to the west to 18-9Ma near Shigatse. We attribute this temporal-spatial distribution of adakitic magmatism within the Gangdese arc, along with the regional Oligo-Miocene geology, to the progressive tearing of the Indian plate. Based on the decrease in age of adakitic magmatism from east to west we hypothesize that the tear initiated beneath the eastern Himalayan syntaxis and propagated westward.
KW - Adakitic granitoids
KW - Eastern Himalayan syntaxis
KW - Postcollisional
KW - SE Tibet
KW - Slab tearing
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U2 - 10.1016/j.lithos.2014.09.029
DO - 10.1016/j.lithos.2014.09.029
M3 - Article
AN - SCOPUS:84909959085
SN - 0024-4937
VL - 210-211
SP - 209
EP - 223
JO - Lithos
JF - Lithos
ER -