Differences in isotopic signature of Neoproterozoic crust of NW India - evidence for a lithospheric boundary?

印度西北部新元古代地壳同位素特征的差异——岩石圈边界的证据？

• 批准号: 445235288
• 负责人: Professorin Dr. Helga de Wall
• 金额: --
• 依托单位: Arbeitsgruppe Strukturgeologie und Tektonik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/445235288?language=en
• 关键词: Differences; isotopic; signature; Neoproterozoic; crust

The Neoproterozoic crust of NW India is mostly composed of two felsic magmatic suites, the Erinpura granites and the Malani Igneous Suite (MIS). Timing of the two events fall into the time period of worldwide rifting, related to Rodinia break-up, whereby India was situated at the periphery of the supercontinent. Different tectono-magmatic models have been proposed (arc, back-arc setting, plume activity) in order to explain the Neoproterozoic evolution of the NW Indian terrane and its relationship to neighboring terranes in South China (Yangtze and Cataysia blocks). However, these models are not consistent with the results from our previous project. Our results in combination with literature data show a spatial discrimination of the NW Indian into regions with positive and negative eNd values and suggest that the inferred lineament separate two different lithospheric blocks. There is indication that this lithospheric boundary formed already during the earlier magmatic episode (Erinpura granites, ca. 890 to 820 Ma) and we suspect pre-Malani crustal extension and rifting along a continental margin as a more appropriate scenario We anticipate that the isotopic ratios of the Malani type rocks just mimic a preexisting crustal configuration which would have important implications for interpretation of the tectonic setting for this younger (770 to 750 Ma) magmatic activity. In order to verify this hypothesis we would like to analyse Sr and Nd isotopes of samples from transects from the craton to the rifted margin, to get better constrains on the transition from negative to positive eNd values. Moreover, we would like to measure Sr, Nd and Pb isotopes from Malani mafic dykes that appear in the same region and which can give insights into the underlying mantle.

印度西北部新元古代地壳主要由两个长英质岩浆岩套组成，Erinpura花岗岩和Malani火成岩套（MIS）。这两个事件发生的时间属于全球裂谷时期，与Rodinia分裂有关，印度位于超大陆的边缘。不同的构造-岩浆模型（弧，弧后设置，羽活动），以解释新元古代的演化西北印度板块及其与邻近的中国南方（扬子和Cataysia块体）的关系。然而，这些模型与我们以前项目的结果不一致。我们的研究结果与文献数据相结合，显示了空间歧视的西北印度地区的积极和消极的eNd值，并建议推断的线性构造分开两个不同的岩石圈块。有迹象表明，这个岩石圈边界已经形成在早期的岩浆幕（Erinpura花岗岩，约。890至820 Ma），我们怀疑前Malani地壳伸展和裂谷沿着大陆边缘作为一个更合适的方案。我们预计，Malani型岩石的同位素比值只是模仿一个预先存在的地壳配置，这将有重要意义的解释构造环境的年轻（770至750 Ma）岩浆活动。为了验证这一假设，我们想分析样品的Sr和Nd同位素从克拉通到裂陷边缘的断面，得到更好的约束从负到正的eNd值的过渡。此外，我们想测量Sr，Nd和Pb同位素从马拉尼基性岩墙出现在同一地区，这可以给洞察下伏地幔。