Abstract
AbstractA comprehensive mineralogical, geochemical and isotopic review of six ultramafic-alkaline-carbonatite magmatic intrusions of the Shillong Plateau (Sung Valley, Jasra, Swangkre-Rongjeng, and Mawpyut) and Mikir Hills (Samchampi-Samteran and Barpung) is presented here, using the published data. These intrusions emplaced ca. 115–102 Ma ago, thus are significantly younger than the tholeiitic flood basalts erupted in Rajmahal-Sylhet province (ca. 118–115 Ma). The intrusive lithologies vary from ultramafic (dunites, clinopyroxenites, melilitolites) to mafic (ijolites, gabbros sensu lato, shonkinites), to felsic (syenites, nepheline syenites) and carbonatites (mostly calcite-rich varieties). The volcanic-subvolcanic facies (lamprophyres, phonolites) are not abundant. The range of chemical compositions of the magmatic phases in the various assemblages is notable; the intrusive rocks are thus the result of crystallization of magmas from variably evolved, independent liquid-lines-of descent, generally of alkaline/strongly alkaline lineages and sodic-to-potassic in affinity. The large variations of the Sr–Nd isotopic ratios of the silicate intrusive rocks (sensu lato) suggest a role of shallow-level crustal contamination during their formation. The carbonatites of the Sung Valley and Samchampi-Samteran have different isotope ratios than the associated silicate rocks, have some isotopic affinity with the Group I tholeiitic basalts of Rajmahal Traps and have an ultimate genesis in a carbonate-bearing lithospheric mantle.
Funder
Ministero dell’Istruzione, dell’Università e della Ricerca
Publisher
Springer Science and Business Media LLC
Subject
Geochemistry and Petrology,Geophysics
Cited by
4 articles.
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1. Petrology, mineral chemistry and geochemistry of lamprophyres from Rongjeng–Nongchram area, East Garo Hills, Shillong Plateau, Meghalaya, Northeast India;Journal of Earth System Science;2024-01-11
2. Concealed architecture, volcanism and tectonics of Deccan LIP related alkaline complexes of Rajasthan, NW India: Constrained from high resolution aero-geophysical data;Journal of Volcanology and Geothermal Research;2023-10
3. Trace element minerals from carbonatite-related fluids, The Aird, Scotland;Scottish Journal of Geology;2023-07-07
4. Magmatic-hydrothermal evolution of the Sung Valley Carbonatite, northeastern India;Journal of Earth System Science;2023-04-24