TY - JOUR
T1 - Cenozoic volcanism in Tibet
T2 - Evidence for a transition from oceanic to continental subduction
AU - Ding, Lin
AU - Kapp, Paul
AU - Zhong, Dalai
AU - Deng, Wanming
N1 - Funding Information:
We thank R. Xu, R. Zhang, H. Sang, J. Cao and P. Xu, Institute of Geology and Geophysics, Chinese Academy of Sciences, for assistance with major element, trace element, isotopic and electron microprobe analysis. D. M. Li at the Institute of Geology, China Seismological Bureau, assisted in K--Ar analysis. This work was supported by a grant from the Chinese National Key Project (1998040800) and Chinese Academy of Sciences grant (KZCXZ-SW-119). We thank A. Peccerillo, S. L. Chung and A. Yin for constructive comments on an early draft of this manuscript. We thank Tiffany Barry, Nick Rogers and an anonymous reviewer for their constructive reviews.
PY - 2003/10
Y1 - 2003/10
N2 - Geochronological (K-Ar or 40Ar/39Ar), major and trace element, Sr-Nd-Pb isotopic and mineral chemical data are presented for newly discovered Cenozoic volcanic rocks in the western Qiangtang and central Lhasa terranes of Tibet. Alkali basalts of 65-45 Ma occur in the western Qiangtang terrane and represent primitive mantle melts as indicated by high mg-numbers [100 × Mg/(Mg + Fe)] (54-65), Cr (204-839 ppm) and Ni (94-218 ppm) contents, and relatively low ratios of 87Sr/86Sr (0·7046-0·7061), 206Pb/204Pb (18·21-18·89), 207Pb/204Pb (15·49-15·61) and 208Pb/204Pb (38·42-38·89), and high ratios of 143Nd/144Nd (0·5124-0·5127 . In contrast, younger volcanic rocks in the western Qiangtang terrane (∼30 Ma) and the central Lhasa terrane (∼23, ∼13 and ∼8 Ma) are potassic to ultrapotassic and interpreted to have been derived from an enriched mantle source. They are characterized by very high contents of incompatible trace elements, negative Ta, Nb and Ti anomalies, and radiogenic Pb isotopic compositions (206Pb/204Pb = 18·43-19·10; 207Pb/204Pb = 15·64-15·83; 208Pb/204Pb = 39·14-39·67). 87Sr/86Sr (0·7088-0·7092) and 143Nd/144Nd (∼0·5122) ratios of the western Qiangtang terrane potassic lavas are similar to those of 45-29 Ma potassic volcanic rocks in the north-central Qiangtang terrane, whereas 87Sr/86Sr (0·7167-0·7243) and 143Nd/144Nd (∼0·5119) ratios of central Lhasa terrane lavas are similar to those of 25-16 Ma ultrapotassic volcanic rocks in the western Lhasa terrane. The 65-45 Ma alkali basalts in the western Qiangtang terrane, along with widespread calc-alkaline volcanic rocks of this age in the Lhasa terrane, may be related to roll-back of a previously shallow north-dipping slab of Tethyan oceanic lithosphere beneath Tibet. Subduction as opposed to convective thinning of continental lithosphere is favored to explain potassic volcanism in Tibet because of its occurrence in distinct, east-west-trending belts (45-29 Ma in the Qiangtang terrane; 25-17 Ma in the northern Lhasa terrane; 16-8 Ma in the southern Lhasa terrane) and temporal and spatial relationships with major thrust systems.
AB - Geochronological (K-Ar or 40Ar/39Ar), major and trace element, Sr-Nd-Pb isotopic and mineral chemical data are presented for newly discovered Cenozoic volcanic rocks in the western Qiangtang and central Lhasa terranes of Tibet. Alkali basalts of 65-45 Ma occur in the western Qiangtang terrane and represent primitive mantle melts as indicated by high mg-numbers [100 × Mg/(Mg + Fe)] (54-65), Cr (204-839 ppm) and Ni (94-218 ppm) contents, and relatively low ratios of 87Sr/86Sr (0·7046-0·7061), 206Pb/204Pb (18·21-18·89), 207Pb/204Pb (15·49-15·61) and 208Pb/204Pb (38·42-38·89), and high ratios of 143Nd/144Nd (0·5124-0·5127 . In contrast, younger volcanic rocks in the western Qiangtang terrane (∼30 Ma) and the central Lhasa terrane (∼23, ∼13 and ∼8 Ma) are potassic to ultrapotassic and interpreted to have been derived from an enriched mantle source. They are characterized by very high contents of incompatible trace elements, negative Ta, Nb and Ti anomalies, and radiogenic Pb isotopic compositions (206Pb/204Pb = 18·43-19·10; 207Pb/204Pb = 15·64-15·83; 208Pb/204Pb = 39·14-39·67). 87Sr/86Sr (0·7088-0·7092) and 143Nd/144Nd (∼0·5122) ratios of the western Qiangtang terrane potassic lavas are similar to those of 45-29 Ma potassic volcanic rocks in the north-central Qiangtang terrane, whereas 87Sr/86Sr (0·7167-0·7243) and 143Nd/144Nd (∼0·5119) ratios of central Lhasa terrane lavas are similar to those of 25-16 Ma ultrapotassic volcanic rocks in the western Lhasa terrane. The 65-45 Ma alkali basalts in the western Qiangtang terrane, along with widespread calc-alkaline volcanic rocks of this age in the Lhasa terrane, may be related to roll-back of a previously shallow north-dipping slab of Tethyan oceanic lithosphere beneath Tibet. Subduction as opposed to convective thinning of continental lithosphere is favored to explain potassic volcanism in Tibet because of its occurrence in distinct, east-west-trending belts (45-29 Ma in the Qiangtang terrane; 25-17 Ma in the northern Lhasa terrane; 16-8 Ma in the southern Lhasa terrane) and temporal and spatial relationships with major thrust systems.
KW - Continental subduction
KW - Geochemistry
KW - Indo-Asian collision
KW - Sodic and potassic volcanism
KW - Tibet
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U2 - 10.1093/petrology/egg061
DO - 10.1093/petrology/egg061
M3 - Article
AN - SCOPUS:0142057011
VL - 44
SP - 1833
EP - 1865
JO - Journal of Petrology
JF - Journal of Petrology
SN - 0022-3530
IS - 10
ER -