Petrogenesis of Middle–Late Triassic volcanic rocks from the Gangdese belt, southern Lhasa terrane: Implications for early subduction of Neo-Tethyan oceanic lithosphere
Petrogenesis of Middle–Late Triassic volcanic rocks from the Gangdese belt, southern Lhasa terrane: Implications for early subduction of Neo-Tethyan oceanic lithosphere
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DOI：
10.1016/j.lithos.2016.07.021
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发表时间：
2016-10
期刊：
影响因子：
3.5
通讯作者：
Chao Wang;L. Ding;Liyun Zhang;P. Kapp;A. Pullen;Yahui Yue
中科院分区：
文献类型：
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作者：
Chao Wang;L. Ding;Liyun Zhang;P. Kapp;A. Pullen;Yahui Yue
冈底斯带主要由岩浆岩组成，形成于新特提斯洋岩石圈向北俯冲到拉萨造山带之下的过程中，对认识藏南碰撞前的演化具有重要作用。本文介绍了拉萨火山岩最南端昌果地区新近发现的火山岩的年代学和地球化学（全岩常量、微量元素和Sr-Nd、锆石Hf同位素）数据。6个样品的锆石U-Pb定年结果表明，冈底斯带最南端的岩浆侵位时代为237.1 ± 1.1 ~ 211.7 ± 1.5 Ma，反映了冈底斯带中晚三叠世岩浆活动的特征。长果火山岩主要由玄武质和安山质岩石组成，表现为LILE富集和HFSE亏损。它们的Nd-Hf同位素组成也比较均匀（εNd（t）= + 5.20 ~+ 7.74，εHf（t）锆石= + 10.2 ~+ 15.9）。玄武质岩浆可能来源于弧下地幔楔的部分熔融，不仅被俯冲蚀变洋壳的含水流体交代，也被俯冲海底沉积物的含水熔体交代，随后在上升过程中经历了分离结晶和幼年地壳混染。安山质岩浆是由镁铁质-超镁铁质交代体在板幔界面通过熔体/流体-橄榄岩反应部分熔融而成。结合早中生代岩浆岩的时空分布和区域碎屑锆石资料，进一步提出新特提斯洋岩石圈向北俯冲至拉萨盆地之下始于中三叠世。
The Gangdese belt is dominantly composed of igneous rocks that formed during the northward subduction of Neo-Tethyan oceanic lithosphere beneath the Lhasa terrane and has played a crucial role in understanding the pre-collisional evolution of southern Tibet. This paper presents new geochronological and geochemical (whole-rock major and trace element and Sr–Nd and zircon Hf isotope) data for recently identified volcanic rocks exposed in Changguo area, southernmost part of the Lhasa terrane. Zircon U–Pb dating from six samples yields consistent ages of 237.1 ± 1.1 Ma to 211.7 ± 1.5 Ma for magma emplacement through volcanic eruption, showing the Middle–Late Triassic magmatic activity in the southernmost Gangdese Belt. The Changguo volcanic rocks are mainly composed of basaltic and andesitic rocks and exhibit LILE enrichment and HFSE depletion. They also exhibit relatively uniform Nd–Hf isotopic compositions (εNd(t) = + 5.20 to + 7.74 and εHf(t)zircon= + 10.2 to + 15.9). The basaltic magmas were likely sourced from partial melting of sub-arc mantle wedge that was metasomatized by not only the aqueous fluid derived from subducting altered oceanic crust but also hydrous melt derived from subducting seafloor sediments, and subsequently experienced fractional crystallization and juvenile crustal contamination during ascent. The andesitic magmas were generated by partial melting of mafic–ultramafic metasomes through melt/fluid–peridotite reaction at slab–mantle interface. Taking into account the temporal and spatial distribution of the Early Mesozoic magmatic rocks and regional detrital zircon data, we further propose that the northward subduction of Neo-Tethyan oceanic lithosphere beneath the Lhasa terrane commenced by Middle Triassic.