Abstract

Malani Igneous Suite represents the largest felsic volcanic province in India. Despite a number of studies, the origin and the temporal extent of the Malani magmatism remain elusive. Adjacent to the Malani Igneous Suite, there exists a calcareous felsic tuff deposit at Chhoti Khatu within the younger Marwar Supergroup. It is stratigraphically separated from the Malani Igneous Suite by the Sonia Formation, the bottom-most formation of the supergroup, but falls within the temporal range of the Malani magmatism. In order to explore its genetic relationship with the Malani Igneous Suite and decipher its origin, trace element and C–O–Sr–Nd isotopic compositions of the tuff were studied. The results of the study show that the tuff differs geochemically from the MIS, and therefore, could not have been an extension of the Malani magmatism as believed by many earlier workers. On the basis of trace element patterns and Sr–Nd isotopic data, origin of the tuff is ascertained to the partial melting of Banded Gneissic Complex-II, the Archean–Paleoproterozoic basement of the region. The C and O isotopic composition of the carbonates from the tuff and a two-component mixing model reveal that the source (crustal) melt for the tuff had assimilated a significant amount of material from the rocks of the Sirohi Group. Since the timing of deposition of the tuff coincide with the emplacement of late-stage Malani dykes, it is likely that the final phase of Malani magmatism generated the heat for partial melting of the Archean–Paleoproterozoic basement.

Research Highlights

• Chhoti Khatu Tuff differs geochemically from the Malani Igneous Suite rocks.

• They were formed by partial melting of the Banded Gneissic Complex-II.

• The source melt had assimilated a significant amount of material from the Sirohi Group rocks.

中文翻译：

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拉贾斯坦邦Chhoti Khatu火山及其与Malani岩浆作用的关系：地球化学研究

摘要

Malani Igneous Suite代表印度最大的长笛火山岛。尽管进行了大量研究，但马拉尼岩浆作用的起源和时间范围仍然难以捉摸。毗邻Malani火成岩套房，年轻的Marwar Supergroup内的Chhoti Khatu有钙质的长石凝灰岩沉积物。它在地层上与马拉尼火成岩组之间是由超群最底部的索尼亚组形成的，但属于马拉尼岩浆作用的时间范围内。为了探索其与马拉尼火成岩套件的遗传关系并破译其起源，研究了凝灰岩的微量元素和C–O–Sr–Nd同位素组成。研究结果表明凝灰岩与MIS在地球化学上有所不同，因此，正如许多早期工人所相信的那样，这不可能是马拉尼岩浆作用的延伸。根据痕量元素模式和Sr–Nd同位素数据，凝灰岩的起源被确定为该地区的太古代—古古生界基底带状片麻岩复合物II的部分熔融。来自凝灰岩的碳酸盐的碳同位素同位素组成和两组分混合模型表明，凝灰岩的源（地壳）熔体吸收了来自西罗希组岩石的大量物质。由于凝灰岩的沉积时间与后期马拉尼堤防的发生相吻合，马拉尼岩浆作用的最后阶段很可能产生了太古宙古古生代基底部分熔融的热量。凝灰岩的起源被确定为该地区的太古代—古古生界基底带状片麻岩复合体—Ⅱ的部分熔融。凝灰岩中碳酸盐的碳和氧同位素组成以及两组分混合模型表明，凝灰岩的源（地壳）熔体吸收了西罗希组岩石中的大量物质。由于凝灰岩的沉积时间与后期马拉尼堤防的发生相吻合，马拉尼岩浆作用的最后阶段很可能产生了太古宙古古生代基底部分熔融的热量。凝灰岩的起源被确定为该地区的太古代—古古生界基底带状片麻岩复合体—Ⅱ的部分熔融。来自凝灰岩的碳酸盐的碳同位素同位素组成和两组分混合模型表明，凝灰岩的源（地壳）熔体吸收了来自西罗希组岩石的大量物质。由于凝灰岩的沉积时间与后期马拉尼堤防的发生相吻合，马拉尼岩浆作用的最后阶段很可能产生了太古宙古古生代基底部分熔融的热量。来自凝灰岩的碳酸盐的碳同位素同位素组成和两组分混合模型表明，凝灰岩的源（地壳）熔体吸收了来自西罗希组岩石的大量物质。由于凝灰岩的沉积时间与后期马拉尼堤防的发生相吻合，马拉尼岩浆作用的最后阶段很可能产生了太古宙古古生代基底部分熔融的热量。来自凝灰岩的碳酸盐的碳同位素同位素组成和两组分混合模型表明，凝灰岩的源（地壳）熔体吸收了来自西罗希组岩石的大量物质。由于凝灰岩的沉积时间与后期马拉尼堤防的发生相吻合，马拉尼岩浆作用的最后阶段很可能产生了太古宙古古生代基底部分熔融的热量。

研究重点

• Chhoti Khatu Tuff与Malani Igneous Suite岩石在地球化学上有所不同。

• 它们是通过部分带状片麻岩复合物II熔融而形成的。

• 源熔岩吸收了来自Sirohi Group岩石的大量物质。