Temporal and spatial variations of enriched source components in Linzizong volcanic succession, Tibet, and implications for the India-Asia collision
Temporal and spatial variations of enriched source components in Linzizong volcanic succession, Tibet, and implications for the India-Asia collision
复制标题
西藏林子宗火山序列富集物源成分时空变化及其对印度-亚洲碰撞的影响
DOI：
10.1093/petrology/egab103
复制
发表时间：
2022
影响因子：
3.9
通讯作者：
Xuan-Xue Mo
中科院分区：
文献类型：
--
作者：
An-Lin Liu;Qing Wang;Di-Cheng Zhu;Peter A. Cawood;Ying Xia;Shi-Min Li;Sheng-Ao Liu;Fang Huang;Li Liu;Zhi-Dan Zhao;Xuan-Xue Mo
大陆-大陆碰撞富集源组分的时空分布为研究与俯冲和碰撞相关事件相关的地幔动力学过程提供了重要的信息。然而，确定这种浓缩成分的来源仍然是一个重大挑战。我们报告了一个全面的数据集的林子宗火山序列（LVS）从四个不同的距离横向印度-雅鲁藏布江缝合线在西藏南部，这标志着印度-亚洲碰撞带的暴露表面的表达。本研究中的LVS岩石可分为两组：钙碱性第1组（69 - 55 Ma），主要包括玄武岩-安山质品种，和钾玄质第2组（52 - 50 Ma），主要由镁铁质成分较少的镁铁质岩石组成。第1组样品可能来自原始玄武质熔体的分离结晶，作为交代地幔楔部分熔融的结果。这些样品中的Nd-Hf同位素组成去耦，这表明俯冲沉积物来源的熔体纳入地幔楔。沉积物来源的熔体对地幔源区的影响从缝合带向亚洲方向增加（即，Sr、Nd、Pb、Hf同位素组成及Th/La、La/Sm比值的升高表明，自南向北，Sr、Nd、Pb、Hf同位素组成呈上升趋势。靠近缝合线的样品的高δ 26 Mg值和高Ba/Th和Sr/Th比值与俯冲的新特提斯板片的脱水相一致。第2组镁铁质岩具有亏损和耦合的ε Nd-ε Hf同位素组成，（La/Yb）N和Dy/Yb比值升高，Zr/Nb比值降低，表明岩石圈地幔来源于富集的含石榴子石地幔，并有软流圈物质的贡献。第2组硅质样品在缝合线附近和远处都富集同位素，这分别归因于特提斯喜马拉雅和拉萨中部地下基底的古下地壳熔融物的参与。结果表明，LVS是对俯冲晚期（第1组）和印度-亚洲碰撞和板片断裂初期（第2组）的岩浆响应。在地球动力学解释中，应谨慎对待~51 Ma时全岩Nd和锆石Hf同位素组成的负趋势，具体取决于样品与印度-亚洲缝合线之间的距离。
The temporal and spatial distribution of enriched source components at sites of continent–continent collision provides critical insights into mantle dynamic processes associated with subduction- and collision-related events. However, determining the origin of such enriched components remains a significant challenge. We report a comprehensive dataset of the Linzizong volcanic succession (LVS) from four locations with varying distance across-strike to the Indus–Yarlung suture in southern Tibet, which marks the exposed surface expression of the India–Asia collision zone. The LVS rocks in this study can be divided into two groups: a calc-alkaline Group 1 (69–55 Ma), mainly including basaltic–andesitic varieties, and a shoshonitic Group 2 (52–50 Ma), consisting predominantly of silicic rocks with minor mafic compositions. Group 1 samples are likely derived from the fractional crystallization of primitive basaltic melts as a result of the partial melting of a metasomatized mantle wedge. These samples are decoupled in Nd–Hf isotopic compositions, suggesting an incorporation of subducting sediment-derived melts into the mantle wedge. The influence of sediment-derived melt on the mantle source increases away from the suture zone toward Asia (i.e., from the south to the north) as indicated by the more enriched Sr, Nd, Pb, and Hf isotopic compositions, as well as elevated Th/La and La/Sm ratios. The heavy δ26Mg values, and high Ba/Th and Sr/Th ratios of samples close to the suture coincide with the dehydration of the subducting Neo-Tethyan slab. Group 2 mafic samples have depleted and coupled εNd–εHfisotopic compositions and are characterized by elevated (La/Yb)Nand Dy/Yb ratios as well as low Zr/Nb ratios, indicating an origin of enriched garnet-bearing lithospheric mantle with contributions from asthenosphere-derived materials. Group 2 silicic samples are isotopically enriched both near and far away from the suture, which can be attributed to the involvement of ancient lower crust-derived melt from Tethyan Himalaya and central Lhasa subterrane basement, respectively. Our results show that the LVS are the magmatic response to late subduction (Group 1), and to initial India–Asia collision and slab breakoff (Group 2). Negative trends in the whole-rock Nd and zircon Hf isotopic compositions at ~51 Ma should be treated with caution for geodynamic interpretations, depending on the distance between the samples and the India–Asia suture.