Initial Rifting of the Lhasa Terrane from Gondwana: Insights From the Permian (similar to 262Ma) Amphibole-Rich Lithospheric Mantle-Derived Yawa Basanitic Intrusions in Southern Tibet
Initial Rifting of the Lhasa Terrane from Gondwana: Insights From the Permian (similar to 262Ma) Amphibole-Rich Lithospheric Mantle-Derived Yawa Basanitic Intrusions in Southern Tibet
复制标题
拉萨地体与冈瓦纳大陆的初始裂谷：来自藏南二叠纪（类似于 262 Ma）富含角闪石岩石圈地幔的雅瓦巴桑岩侵入体的见解
DOI：
10.1029/2018jb016281
复制
发表时间：
2019
影响因子：
3.9
通讯作者：
Zhang Le
中科院分区：
文献类型：
--
作者：
Zeng Yun Chuan;Xu Ji Feng;Ducea Mihai N;Chen Jian Lin;Huang Feng;Zhang Le
西藏南部拉萨地体的二叠纪构造背景仍然存在争议（即，大陆裂谷与俯冲-碰撞），并在冈瓦纳解体期间对东特提斯的古地磁重建至关重要。在这项研究中，我们提出了新的地质年代学，地球化学和矿物学数据的二叠纪（~262马）雅瓦侵入体在拉萨地体南部。这些岩石是硅欠饱和和碱性的，具有高TiO 2和中等MgO，并表现出富集Th、轻稀土元素和Nb-Ta，而贫K。这些化学成分结合均匀的全岩（87 Sr/86 Sr）i（0.7039-0.7044）、εNd（t）（1.85-2.81）和εHf（t）（4.21-6.90）值，以及锆石εHf（t）（4.53-9.97）和δ 18 O（5.04‰-5.76‰）值，表明岩浆来自富含角闪石的岩石圈地幔的部分熔融。岩浆随后经历了单斜辉石、角闪石和铁钛氧化物的分馏。岩石圈地幔中的角闪石很可能是在初始伸展过程中由低度软流圈熔体形成的堆积物。由于富含角闪石的交代脉的熔融温度低于周围的橄榄岩，它们在地幔热扰动的早期阶段容易熔融。由于拉萨地体没有二叠纪大陆沉降的证据，我们认为雅瓦侵入体形成于岩石圈伸展的开始，与冈瓦纳大陆解体期间拉萨地体从印度板块的初始裂谷有关，这是新特提斯洋开放的前兆。
The Permian tectonic setting of the Lhasa Terrane in southern Tibet remains controversial (i.e., continental rift vs. subduction‐collision) and is crucial to palinspastic reconstructions of the eastern Tethys during the breakup of Gondwana. In this study, we present new geochronological, geochemical, and mineralogical data for the Permian (~262 Ma) Yawa intrusions in the southern Lhasa Terrane. These rocks are silica‐undersaturated and alkaline, with high TiO2and moderate MgO, and exhibit enrichments in Th, light rare earth elements, and Nb‐Ta, and depletions in K. These chemical compositions, combined with uniform whole‐rock (87Sr/86Sr)i(0.7039–0.7044), εNd(t) (1.85–2.81), and εHf(t) (4.21–6.90) values, and zircon εHf(t) (4.53–9.97) and δ18O (5.04‰–5.76‰) values, indicate the magmas were derived by partial melting of amphibole‐rich lithospheric mantle. The magmas subsequently underwent fractionation of clinopyroxene, amphibole, and Fe‐Ti oxides. The amphibole in the lithospheric mantle likely formed as cumulates from low‐degree asthenospheric melts during incipient extension. Given that the amphibole‐rich metasomatic veins have a lower melting temperature than the surrounding peridotite, they were susceptible to melting during the early stages of thermal perturbation of the mantle. Because there is no evidence of Permian continental subsidence in the Lhasa Terrane, we suggest the Yawa intrusions were formed at the onset of lithospheric extension associated with initial rifting of the Lhasa Terrane from the Indian Plate during Gondwana breakup, which was a precursor to the opening of the Neo‐Tethys Ocean.