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首页> 外文期刊>Journal of Asian earth sciences >Petrology and geochemistry of high-titanium and low-titanium mafic dykes from the Damodar valley, Chhotanagpur Gneissic Terrain, eastern India and their relation to Cretaceous mantle plume(s)
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Petrology and geochemistry of high-titanium and low-titanium mafic dykes from the Damodar valley, Chhotanagpur Gneissic Terrain, eastern India and their relation to Cretaceous mantle plume(s)

机译：印度东部乔达纳格普尔片麻岩地形的达莫达河谷高钛和低钛铁镁质岩的岩石学，地球化学及其与白垩纪地幔柱的关系

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摘要

The Damodar valley within the Chhotanagpur Gneissic terrain at the northern-most margin of the Sing-hbhum craton, eastern India, is perhaps the only geological domain in the entire Indian shield which hosts the early Cretaceous Rajmahal as well as the late Cretaceous Deccan igneous activities. A number of Cretaceous mafic dykes intrude the Gondwana sedimentary formations and are focus of the present study. One set of these dykes strike NNE to ENE, are very fresh and mainly exposed within the Jharia, Bokaro and Karanpura basins; whereas the other set of dykes (including the well-known Salma mega dyke) trend NW to NNW, intrude mainly the Raniganj basin and show meagre hydrothermal alteration. Majority of the samples from both these dyke groups display ophitic or sub-ophitic textures and are essentially composed of augite/titan augite and plagioclase. On the basis of petrographic and geochemical characteristics the NNE to ENE dykes are identified as high-Ti dolerite (HTD) dykes and the NW to NNW dykes are referred to as low-Ti dolerite (LTD) dykes. Apart from the first-order distinction on their titanium contents, both these groups also show conspicuous geochemical differences. The HTD dykes contain relatively high values of iron, and high-field strength elements than those from the LTD dykes with an overlapping MgO contents. Although available field, paleomagnetic and limited geochronological data for most of the studied dykes suggests their emplacement during early Cretaceous period (110-115 Ma), the Salma dyke, dated to be of Deccan-age at ～65 Ma, is an exception. Geochemically all the studied samples show an undoubted plume-derived character but their unequivocal affinity to either the early Cretaceous Kergue-len (Rajmahal) or the late-Cretaceous Reunion (Deccan) plume is not straightforward since they share bulk-rock characteristics of rocks derived from both these plumes. Even though, the spatial and temporal association of the mafic dykes of present study with the Rajmahal Traps are suggestive of their linkage to the Kerguelen plume activity, robust geochronological and paleomagnetic constraints are clearly required to understand the relative contributions of the two Cretaceous mantle plumes in the genesis of the mafic igneous activity in this interesting domain.
机译：位于印度东部Sing-hbhum克拉通最北端的Chhotanagpur片麻岩地带内的Damodar谷可能是整个印度盾构中唯一拥有早白垩世拉贾马哈尔和晚白垩纪Deccan火成岩活动的地质领域。许多白垩纪铁镁质岩侵入冈瓦纳的沉积地层，是本研究的重点。这些堤防中有一组是从NNE到ENE的，非常新鲜，主要暴露在Jharia，Bokaro和Karanpura盆地内。而另一组堤防（包括著名的萨尔玛巨型堤防）则从西北向西北偏向，主要侵入Raniganj盆地并显示出微不足道的热液蚀变。来自这两个堤坝组的大多数样品均显示出卵石质或亚蛇纹质，并且基本上由辉石/钛辉石和斜长石组成。根据岩相学和地球化学特征，将NNE到ENE堤称为高钛白云石（HTD）堤，将NW到NNW堤称为低Ti钙铝石（LTD）堤。除了钛含量的一阶区分外，这两个族群还显示出明显的地球化学差异。与具有重叠MgO含量的LTD堤坝相比，HTD堤坝包含较高的铁含量和高场强元素。尽管有可用的磁场，但大多数研究的堤坝的古地磁和有限的年代学数据表明，它们的位置在白垩纪早期（110-115 Ma），而萨尔玛堤坝（年代为〜65 Ma的德干时代）是一个例外。从地球化学角度来看，所有研究样品均显示出毫无疑问的羽状特征，但它们与早白垩世克格伦（Rajmahal）或晚白垩世留尼汪（Deccan）羽的明确亲和力并不直接，因为它们具有衍生出的岩石的块岩特征从这两个羽流。尽管本研究中的铁质岩脉与拉杰马哈尔陷阱的时空联系表明它们与Kerguelen羽流活动有关，但显然需要鲁棒的年代学和古地磁约束才能了解这两个白垩纪地幔羽流的相对贡献。镁铁质火成岩活动的起源。

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