The Linzizong Volcanic Successions, Southern Tibet: Ages, Geochemical Characteristics and Geodynamic Significance
Date Issued
2007
Date
2007
Author(s)
Lee, Hao-Yang
DOI
en-US
Abstract
The Linzizong volcanic successions that crop out in the Lhasa terrane, southern Tibet have been widely regarded as the products of northward subduction of the Neo-Tethyan oceanic slab that resulted in an Andean-type convergent margin along South Asia before its collision with India. In this study, 2 zircon U-Pb ages and 26 whole-rock Ar-Ar ages along with geochemical analysis of 129 volcanic rocks collected from the Lhasa terrane were carried out to better constrain the temporal-spatial distribution and petrogenesis of the Linzizong volcanism. The age results delineate two discrete episodes of volcanic activity. These are (1) a widespread Cretaceous episode (ca. 112~71 Ma), and (2) an intense, but geographically confined, Paleogene episode (ca. 63~43 Ma) that occurred only in the southern part of the Lhasa terrane. The second episode is here re-defined as the “real” Linzizong volcanic successions that comprise, from bottom to top, Dianzhong, Nianbo and Pana Formations. The age results furthermore indicate a southward migration and intensification of volcanism, which culminated at ca. 50 Ma (“flare-up” period).
The Linzizong volcanic successions consist dominantly of calc-alkaline rocks that range from basalt to rhyolite compositions (SiO2=45~80 wt.%) and show typical arc-lava geochemical features marked with LILE enrichment and HFSE depletion in the spidergram. Those formed during the flare-up period, i.e., the Pana Formation, however, show significant geochemical variations from low-K tholeiitic through calc-alkaline to shoshonitic compositions coupled with increasing enrichment in LREEs. Therefore, the volcanic successions are divided into four suites, namely, calc-alkaline suite, low-K suite, high-REE suite and shoshonitic suite.
Most Linzizong calc-alkaline rocks (ca. 63 to 50 Ma) show Sr and Nd isotope compositions [
Subjects
林子宗火山岩
西藏
年代
地球化學
新特提斯洋隱沒
板塊脫離
Linzizong volcanic successions
Tibet
age
geochemistry
Neo-Tethyan subduction
slab breakoff
Type
thesis
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