Journal of Earth System Science ( IF 1.9 ) Pub Date : 2021-02-02 , DOI: 10.1007/s12040-020-01493-y M G Thakkar , Gaurav Chauhan , Yash Shah , Chirag Jani , Bhavyata Chavada , Abhishek Lakhote , Suraj Bhosale , C P Mistry
Abstract
An extremely small but significant exposure of possibly Precambrian or Pre-Deccan Mesozoic plutonic rocks spanning 200 × 90 m in size with 15 m elevation, remotely located amidst vast salt flats of the Great Rann of Kachchh received attention when it was first reported by Biswas in 1968; however, systematic petrological and petrographical studies remained undone. Therefore, in the present study, we addressed complete geological accounts to establish its possible origin. Our detailed geological study indicates that the complex is made up of nepheline and aegirine bearing alkali feldspar syenite with numerous fine-to-medium grained felsic dykes. It lays two viewpoints: (1) it has affinity with Trans Aravalli Belt anorogenic felsic magmatism, i.e., Precambrian and (2) it is genetically related to the pre-Deccan Mesozoic plutonic intrusives like Nir Wandh in Pachham Island and Mundwara and Sarnu–Dandali complexes in Rajasthan. The nearest felsic magmatic suite is an exposure of gray and pink granites of Nagar Parkar of Neoproterozoic age. Presence of undersaturated minerals and xenoliths of diorites within syenite parent body may suggest partial melting of lower crust probably during Rodinia supercontinent rifting. However, presence of alkali-rich minerals, alkali feldspars, kaersutite, aegirine, apatite and rutile needles and the complex being part of the Kachchh rift basin suggests its genetic resemblance with Pre-Deccan Mesozoic plutonic events. The radiometric age will confirm the age of this plutonic massif.
Research highlights
Based on the field geological and petrographical studies of Meruda Takkar syenitic complex, two viewpoints have been raised:
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1)
The alkali feldspar syenite complex of Meruda has close affinity with the anorogenic felsic igneous suites contemporaneous with Malani Igneous Suite and slightly younger than post-Delhi Erinpura granites, i.e., Neoproterozoic intraplate magmatism chronologically equivalent to the splitting of Rodinia supercontinent,
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2)
The alkali feldspar syenites of Meruda Takkar have genetic and mineralogical resemblance with the pre-Deccan trap Mesozoic plutonic activities allied to what is prevailing at alkaline complexes of Mundwara and Sarnu–Dandali and in the northern Island belt alkaline intrusives of Nir Wandh, Kuran, Kaladungar and Sadhara sills and dykes.
Radiometric age determination and geochemical analysis of the Meruda syenite are needed to establish its age and origin.
中文翻译：
卡赫（Kachchh）北部默鲁达塔卡（Meruda Takkar）山的霞石正长岩及相关岩石：新元古代马拉尼基底还是中生碱性岩浆作用？
摘要
比斯瓦斯（Biswas）首次报道，极小但显着的可能是前寒武纪或前Deccan中生代岩体的岩石，大小200×90 m，高程15 m，地处卡赫大拉恩大盐滩中。 1968年；但是，系统的岩石学和岩石学研究仍未完成。因此，在本研究中，我们处理了完整的地质记录以建立其可能的成因。我们详细的地质研究表明，该复合物是由霞石和a胺碱所组成的碱性长石正长岩，以及许多细到中粒状的长石脉。它提出了两种观点：（1）它与跨阿拉瓦利地带的成因长英质岩浆作用有亲和力，即 前寒武纪及其（2）与Deccan前中生代侵入岩如Pachham岛的Nir Wandh和拉贾斯坦邦的Mundwara及Sarnu-Dandali复合体在遗传上有关。最接近的长英质岩浆套件是新元古代的纳加尔·帕卡（Nagar Parkar）的灰色和粉红色花岗岩。榴辉岩母体内部存在不饱和矿物和闪长岩的异岩，可能表明在罗迪尼亚超大陆裂谷过程中下部地壳部分熔融。但是，存在着富含碱的矿物，碱长石，钾长石，a石，磷灰石和金红石针，并且该复合物是卡契奇裂谷盆地的一部分，这表明它的遗传与德肯前中生代岩浆事件相似。辐射年龄将确认该岩体的年龄。最接近的长英质岩浆套件是新元古代的纳加尔·帕卡（Nagar Parkar）的灰色和粉红色花岗岩。榴辉岩母体内部存在不饱和矿物和闪长岩的异岩，可能表明在罗迪尼亚超大陆裂谷过程中下部地壳部分熔融。但是，存在着富含碱的矿物，碱长石，钾长石，a石，磷灰石和金红石针，并且该复合物是卡契奇裂谷盆地的一部分，这表明它的遗传与德肯前中生代岩浆事件相似。辐射年龄将确认该岩体的年龄。最接近的长英质岩浆套件是新元古代的纳加尔·帕卡（Nagar Parkar）的灰色和粉红色花岗岩。榴辉岩母体内部存在不饱和矿物和闪长岩的异岩，可能表明在罗迪尼亚超大陆裂谷过程中下部地壳部分熔融。但是，存在着富含碱的矿物，碱长石，钾长石，a石，磷灰石和金红石针，并且该复合物是卡契奇裂谷盆地的一部分，这表明它的遗传与德肯前中生代岩浆事件相似。辐射年龄将确认该岩体的年龄。榴辉岩母体内部存在不饱和矿物和闪长岩的异岩，可能表明在罗迪尼亚超大陆裂谷过程中下部地壳部分熔融。但是，存在着富含碱的矿物，碱长石，钾长石，a石，磷灰石和金红石针，并且该复合物是卡契奇裂谷盆地的一部分，这表明它的遗传与德肯前中生代岩浆事件相似。辐射年龄将确认该岩体的年龄。榴辉岩母体内部存在不饱和矿物和闪长岩的异岩，可能表明在罗迪尼亚超大陆裂谷过程中下部地壳部分熔融。但是，存在着富含碱的矿物，碱长石，钾长石，a石，磷灰石和金红石针，并且该复合物是卡契奇裂谷盆地的一部分，这表明它的遗传与德肯前中生代岩浆事件相似。辐射年龄将确认该岩体的年龄。
研究重点
基于对梅鲁达塔卡卡尔共生体的野外地质和岩石学研究，提出了两种观点：
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1）
默鲁达的碱性长石正长岩复合物与与马拉尼火成岩时期同时形成的长成象质长成岩火成岩层具有密切的亲和力，并且比德里-埃林普拉河后的花岗岩年龄稍小，即在时间上等同于罗迪尼亚超大陆分裂的新元古代板块岩浆作用，
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Meruda Takkar的碱性长石正长岩在遗传和矿物学上与Deccan圈闭中生代的古生物活动相似，与Mundwara和Sarnu-Dandali的碱性复合物中以及北部岛带Nir Wandh，Kuran，Kaladonggar的碱性侵入物普遍存在的活动有关。萨达拉的窗台和堤坝。
梅鲁达正长岩的放射性年龄确定和地球化学分析需要确定其年龄和起源。
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