Cambrian bimodal volcanism in the Lhasa Terrane, southern Tibet: Record of an early Paleozoic Andean-type magmatic arc in the Australian proto-Tethyan margin
Cambrian bimodal volcanism in the Lhasa Terrane, southern Tibet: Record of an early Paleozoic Andean-type magmatic arc in the Australian proto-Tethyan margin
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DOI：
10.1016/j.chemgeo.2011.12.024
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发表时间：
2012-10
期刊：
影响因子：
3.9
通讯作者：
Di‐Cheng Zhu;Zhidan Zhao;Y. Niu;Y. Dilek;Qing Wang;Wenhua Ji;G. Dong;Qing-lin Sui;Yongsheng L
中科院分区：
文献类型：
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作者：
Di‐Cheng Zhu;Zhidan Zhao;Y. Niu;Y. Dilek;Qing Wang;Wenhua Ji;G. Dong;Qing-lin Sui;Yongsheng L
本文报道了藏南拉萨次地体中部寒武纪变质火山岩的锆石LA-ICPMS U-Pb年龄和Hf同位素、全岩主量元素和微量元素、锶-钕同位素数据。这些岩石形成了一个双峰式火山岩套，主要由硅质变火山岩和次要的变质玄武岩组成。5个硅质变质火山岩样品的年龄约为492 Ma，1个变质玄武岩样品的206Pb/238U年龄为492±4 Ma，表明镁铁质和硅质火山喷发是同时代的。变质玄武岩以高钾钙碱性为主，富Th、U和轻稀土元素(LREE)，亏损Nb、Ta、Ti、Zr和Hf，与安第斯弧玄武岩的地球化学特征相似。硅质变火山岩为高钾钙碱性、低Nb、低Zr的岩石。变质玄武岩具有负的全岩εND(T)值(−4.7~−3.5)和变化的锆石εHf(T)值(−0.7~+7.5)，这与硅质变火山岩的全岩εND(T)值为负的−8.4~−7.2和变化的锆石εHf(T)值(−13.9~−4.6)明显不同。变质玄武岩被解释为被俯冲相关成分交代的富集岩石圈地幔源区部分熔融的结果，而硅质变火山岩则来自具有继承性地幔熔体特征的古拉萨基底的玄武岩熔融深熔作用。西羌塘-安多-特提斯喜马拉雅位于印度原特提斯边缘和拉萨以及其他可能的微大陆或地体(如贡山、保山、腾冲、缅甸和锡布拉苏)中，代表着面向原特提斯洋的早古生代安第斯型岩浆弧。拉萨次地体中部双峰式火山岩的侵位和寒武纪-奥陶纪角度不整合的发育，可归因于原特提斯大洋岩石圈在岩浆弧外侧(可能是东羌塘和南中国)碰撞吸积后的板片剥离。
This paper reports new zircon LA-ICP-MS U–Pb age and Hf-isotope, whole-rock major and trace element, and Sr–Nd isotope data from Cambrian metavolcanic rocks in the central Lhasa subterrane of southern Tibet. These rocks form a bimodal volcanic suite consisting mainly of silicic metavolcanic rocks with subordinate metabasalts. Five silicic metavolcanic samples dated at ca. 492Ma and one metabasalt sample yielding a near-concordant206Pb/238U age of 492±4Ma indicate that mafic and silicic eruptions were contemporaneous. The metabasalts are mostly high-K calc-alkaline, enriched in Th, U, and light rare earth elements (LREEs), and depleted in Nb, Ta, Ti, Zr, and Hf, geochemically resembling the Andean arc basalts. The silicic metavolcanic rocks are high-K calc-alkaline and low in Nb and Zr. The metabasaltic rocks have negative whole-rock εNd(t) values (−4.7 to −3.5) and varying zircon εHf(t) values (−0.7 to +7.5), differing significantly from those of the silicic metavolcanic rocks, which yield negative whole-rock εNd(t) values of −8.4 to −7.2 and varying zircon εHf(t) values (−13.9 to −4.6). The metabasaltic rocks are interpreted as resulting from partial melting of an enriched lithospheric mantle source that was metasomatized by subduction-related components, whereas the silicic metavolcanic rocks were derived from basaltic melt-induced anatexis of the ancient Lhasa basement with inherited mantle melt signatures. The Western Qiangtang–Amdo–Tethyan Himalaya situated in the Indian proto-Tethyan margin and the Lhasa and other possible microcontinents or terranes (e.g., Gongshan, Baoshan, Tengchong, Burma, and Sibumasu) paleographically located in the Australian proto-Tethyan margin represent an early Paleozoic Andean-type magmatic arc facing the proto-Tethyan Ocean. The emplacement of the bimodal volcanic rocks and the development of the Cambro–Ordovician angular unconformity in the central Lhasa subterrane can be attributed to slab break-off of the proto-Tethyan Ocean lithosphere following the collisional accretion of microcontinents or terranes located outboard of the magmatic arc (possibly Eastern Qiangtang and South China).