Geochemical and Sr-Nd-Pb-Os isotopic compositions of Miocene ultrapotassic rocks in southern Tibet: petrogenesis and implications for the regional tectonic history.
Geochemical and Sr-Nd-Pb-Os isotopic compositions of Miocene ultrapotassic rocks in southern Tibet: petrogenesis and implications for the regional tectonic history.
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藏南中新世超钾岩的地球化学和Sr-Nd-Pb-Os同位素组成：岩石成因及其对区域构造历史的意义。
DOI：
10.1016/j.lithos.2014.09.008
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发表时间：
2014-11
期刊：
影响因子：
3.5
通讯作者：
Wang LiQuan
中科院分区：
文献类型：
--
作者：
Wang BaoDi;Chen JianLin;Xu JiFeng;Wang LiQuan
超钾质熔岩在西藏南部广泛分布，一般认为是由早期俯冲事件期间被交代的富集地幔源部分熔融产生的岩浆形成的。本文报道了西藏拉萨西部赛力堡地区中新世超钾质岩石的地球化学和Sr-Nd-Pb-Os同位素数据。赛里堡超钾质岩石相对于高场强元素富集大离子亲石元素，具有极强的放射成因Sr（87Sr/86Sr（i）= 0.714480-0.727323），Pb（206 Pb/204 Pb = 18.414- 18.787，207 Pb/204 Pb = 15.693- 15.749，208 Pb/204 Pb = 39.439-39.765），以及Os同位素特征（187 Os/188 Os（i）= 0.1095-0.37454）和非放射成因Nd（εNd（t）= − 11.5-− 15.2）同位素组成。这些地球化学和同位素特征，加上高K2 O（> 5重量%）和MgO（5.20-13.70重量%）Sailipu超钾质岩石的Mg#值为68-76，Rb/Sr比值高（0.13-0.95），Ba/Rb比值低（3.33-12.3），Os含量和放射成因Os同位素组成相对较低，不支持有明显的地壳混染。相反，我们认为这些岩石是类似的新生代超钾质岩石从意大利和巴尔干半岛，这表明它们是由来自金云母丰富的单斜辉石脉和周围的橄榄岩地幔物质之间的相互作用产生的Sailipu超钾质岩石可以分为1型和2型套房的基础上的差异，在主要和微量元素的浓度，同位素组成。第一类超钾质岩石相对富集重稀土元素，可能是富金云母单斜辉石脉的熔体与周围含尖晶石橄榄岩物质相互作用的结果，而第二类岩石富集稀土元素，具有高的（Gd/Yb）N值（8.3-12.2），这两个都是来自金云母丰富的单斜辉石脉和周围的石榴石橄榄岩材料，也含有碳酸盐的熔体之间的相互作用的指示。虽然现有的对流迁移模型和斜向俯冲模型都可以解释与青藏高原形成相关的一些地质观测结果，但我们认为前者更准确地解释了该地区超钾质岩石和其他新生代熔岩的时空分布以及藏南记录的相关地形隆起。
Ultrapotassic lavas are widespread throughout southern Tibet and are generally thought to have formed from magmas generated by partial melting of an enriched mantle source that was metasomatized during earlier subduction events. Here, we report new geochemical and Sr–Nd–Pb–Os isotope data for Miocene ultrapotassic rocks within the Sailipu area of the western Lhasa terrane, southern Tibet. The Sailipu ultrapotassic rocks are enriched in the large ion lithophile elements relative to the high field strength elements, and have extremely radiogenic Sr (87Sr/86Sr(i)= 0.714480–0.727323), Pb (206Pb/204Pb = 18.414–18.787,207Pb/204Pb = 15.693–15.749,208Pb/204Pb = 39.439–39.765), and Os isotopic signatures (187Os/188Os(i)= 0.1095–0.37454), and unradiogenic Nd (εNd(t)= − 11.5 to − 15.2) isotopic compositions. These geochemical and isotopic characteristics, coupled with high K2O (> 5 wt.%) and MgO (5.20–13.70 wt.%) concentrations, Mg# values of 68–76, high Rb/Sr (0.13–0.95) and low Ba/Rb (3.33–12.3) ratios, and the relatively low Os contents and radiogenic Os isotopic compositions of the Sailipu ultrapotassic rocks, do not support any significant crustal contamination. Instead, we consider these rocks to be analogous to the Cenozoic ultrapotassic rocks from Italy and the Balkans, suggesting that they were produced by interaction between melts derived from phlogopite-rich clinopyroxene veins and surrounding peridotitic mantle material.The Sailipu ultrapotassic rocks can be divided into type-1 and type-2 suites based on differences in major and trace element concentrations, and isotopic compositions. Type-1 ultrapotassic rocks are relatively enriched in the heavy rare earth elements, most likely as a result of interaction between melts derived from phlogopite-rich clinopyroxene veins and the surrounding spinel-bearing peridotite material, whereas the type-2 rocks are enriched in rare earth elements and have high (Gd/Yb)Nvalues (8.3–12.2), both of which are indicative of interaction between melts derived from phlogopite-rich clinopyroxene veins and surrounding garnet-bearing peridotite material that also contained carbonates. Although both the existing convective removal and oblique subduction models can explain some of the geological observations associated with the formation of the Tibetan Plateau, we suggest that the former more accurately explains the spatial and temporal distributions of ultrapotassic rocks and other Cenozoic lavas in this area and the associated topographic uplift recorded in southern Tibet.
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影响因子：
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作者：
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通讯作者：
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