Mid-Neoproterozoic intraplate magmatism in the northern margin of the Southern Granulite Terrane, India: Constraints from geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes

作者：Deeju, T. R.; Santosh, M.; Yang, Qiong-Yan; Pradeepkumar, A. P.^*; Shaji, E.

来源：Journal of Asian Earth Sciences, 2016, 130: 88-115.

DOI：10.1016/j.jseaes.2016.06.016

• Intraplate magmatism
• Geochemistry
• Zircon U-Pb geochronology and Lu-Hf isotopes
• Mid neoproterozoic
• Southern Granulite Terrane, India

The northern margin of the Southern Granulite Terrane in India hosts a number of mafic, felsic and alkaline magmatic suites proximal to major shear/paleo-suture zones and mostly represents magmatism in rift-settings. Here we investigate a suite of gabbros and granite together with intermediate (dioritic) units generated through mixing and mingling of a bimodal magmatic suite. The massive gabbro exposures represent the cumulate fraction of a basic magma whereas the granitoids represent the product of crystallization in felsic magma chambers generated through crustal melting. Diorites and dioritic gabbros mostly occur as enclaves and lenses within host granitoids resembling mafic magmatic enclaves. Geochemistry of the felsic units shows volcanic arc granite and syn-collisional granite affinity. The gabbro samples show mixed E-MORB signature and the magma might have been generated in a rift setting. The trace and REE features of the rocks show variable features of subduction zone enrichment, crustal contamination and within plate enrichment, typical of intraplate magmatism involving the melting of source components derived from both depleted mantle sources and crustal components derived from older subduction events.
The zircons in all the rock types show magmatic crystallization features and high Th/U values. Their U-Pb data are concordant with no major Pb loss. The gabbroic suite yields (206)pb/U-238 weighted mean ages in the range of 715 +/- 4-832.5 +/- 5 Ma marking a major phase of mid Neoproterozoic magmatism. The diorites crystallized during (206)pb/U-238 weighted mean age of 724 +/- 6-830 +/- 2 Ma. Zircons in the granite yield (206)pb/-U-238 weighted mean age of 823 +/- 4 Ma. The age data show broadly similar age ranges for the mafic, intermediate and felsic rocks and indicate a major phase of bi-modal magmatism during mid Neoproterozoic. The zircons studied show both positive and negative epsilon Hf(t) values for the gabbros (-6.4 to 12.4), and negative values for the diorites (-7.8 to -16.7) and granite (-16.6 to -6.7). Together with the Hf depleted model ages and crustal model ages, we infer that the magma sources involved both juvenile depleted mantle and reworked Mesoproterozoic, Paleoproterozoic and Neoarchean components. The mid Neoproterozoic intraplate magmatism is considered to be a response to mantle upwelling in an aborted rift setting.

• 出版日期2016-11-15
• 单位中国地质大学（北京）