地质通报2025，Vol.44Issue(2)：441-458,18.DOI:10.12097/gbc.2024.01.010
拉萨地块扎扛地区晚寒武世—早奥陶世流纹岩锆石U-Pb定年、岩石成因及其对原特提斯洋俯冲的启示
Zircon U-Pb age,petrogenesis and the revelation to the Proto-Tethyan ocean of the Late Cambrian-Early Ordovician rhyolite from Zhakang area in the Lhasa terrane
摘要
Abstract
[Objective]The Early Paleozoic magmatisms in the southern Qinghai-Tibet Plateau are important for researching the nature of the continental margin of the northern margin of the Gondwana continent and the subduction process of the Proto-Tethys Ocean.Based on the reaserch of the Late Cambrian-Early Ordovician rhyolite found in the Zhakang area in the northern part of Xainza County,Lhasa block,this paper discusses the petrogenesis and geological significance of the rhyolite,so as to further constrain the time limit of the Zhakang unconformity in the Xainza area,and provide a basis for understanding the geological evolution process of the northern margin of the Gondwana continent in the Early Paleozoic.[Methods]In this study,we report the zircon U-Pb age,rock geochemistry and zircon Hf isotope analysis of rhyolites in Zhakang area,northern Xainza County,Lhasa Block,Qinghai-Tibet Plateau.[Results]The results show that the weighted average age of zircon 206Pb/238U of rhyolite is 485±5 Ma.The rock geochemistry shows high silicon,rich alkali,rich aluminum,low phosphorus and low magnesium.The content of SiO2 is 75.10%～77.39%,the content of Al2O3 is 10.74%～12.90%,the content of K2O+Na2O is 6.65%～7.99%,the content of P2O5 is 0.03%～0.11%,the content of MgO is 0.27%～0.35%and the A/CNK is 1.20～1.61,which is greater than 1.1.It belongs to a set of strongly peraluminous shoshonite series.The character in rare earth elements of the rhyolite is enrichment of light rare earth elements and relatively flat right-inclined curve of heavy rare earth elements.The fractionation of light and heavy rare earth elements is obvious,accompanied by obvious negative Eu anomalies(δEu=0.44～0.48).The Zhakang rhyolite has high Rb(368.43×10-6～489.42×10-6)content,low Zr/Hf(31.97～37.35)and Nb/Ta(12.17～15.32)values,indicating that strong crystallization differentiation occurred during its formation.In the SiO2-Zr diagram and ACF diagram,the samples fell into the S-type granite area,showing the characteristics of highly differentiated S-type granite.The εHf(t)value of zircon varies from-2.0 to-5.5,with an average of-3.7,which is negative,indicating the rhyolite might be the product of partial melting of the crust.The two-stage model age of Hf isotope is 1581～1752 Ma,indicating that the source area may be Mesoproterozoic crustal material.[Conclusions]This study believes that the Late Cambrian-Early Ordovician rhyolite in the Zhakang area may be formed under the tectonic background of the subduction of the proto-Tethys oceanic crust to the northern margin of the Gondwana continent.关键词
青藏高原/扎扛地区/流纹岩/地球化学/锆石U-Pb年龄Key words
Qinghai-Tibet Plateau/Zhakang area/rhyolites/geochemisitry/zircon U-Pb age分类
地质学引用本文复制引用
陈红灿,解超明,张家俊,白希泰,段梦龙..拉萨地块扎扛地区晚寒武世—早奥陶世流纹岩锆石U-Pb定年、岩石成因及其对原特提斯洋俯冲的启示[J].地质通报,2025,44(2):441-458,18.基金项目
国家自然科学基金项目《唐加-松多蛇绿岩及对青藏高原古特提斯洋演化制约》(批准号:42172226) （批准号:42172226）
