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Khonglah, M. A.
- Polymodal Occurrence of Early Mafic Differentiate Associated with Mid-Proterozoic Calc-Alkaline Plutons of Meghalaya
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Authors
Affiliations
1 North Eastern Region, Shillong - 793 003, IN
2 Northern Region, Lucknow-226 024, IN
3 Bangalore-560 078
4 Eastern Region, Kolkata -700 091, IN
1 North Eastern Region, Shillong - 793 003, IN
2 Northern Region, Lucknow-226 024, IN
3 Bangalore-560 078
4 Eastern Region, Kolkata -700 091, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 70, No 1 (2007), Pagination: 53-58Abstract
Early mafic differentiate of quartz diorite to quartz monzodiorite composition related to Mid-ProterozoIc, late to post-tectonic calc-alkaline (diorite-granodiorite) plutons in Meghalaya occur in three different modes, viz. (l)dykes in country rock gneisses along tectonic locales, (2) endogenous inclusions in the diorite-granodionte intrusive plutons, as early differentiated product through fractional crystallization or liquid immiscibility, and (3) xenohths in Upper Proterozoic-Early Palaeozoic granite plutons (Nonpoh granite). These appear to be basic precursors of thc granitoids. The mafic inclusions were subjected to metasomatism by granitoids over an extended period starting with the formation of the granitic differentiates of calc-alkaline intrusions and ending with the placement of the later granitic plutons. Petrology and chemistry of the mafic rocks suggest a possible basic parentage.Keywords
Calc-Alkaline plutons, Mafic differentiates, Petrology, Meghalaya.- Characteristics of Mesoproterozoic Felsic Meta-Volcanics from the Shillong Group of Rocks, Meghalaya, North East India
Abstract Views :246 |
PDF Views:83
Authors
Affiliations
1 Geological Survey of India, North Eastern Region, Shillong 793 003, IN
2 Department of Applied Geology, Dibrugarh University, Dibrugarh 786 004, IN
3 Regional Training Institute, Geological Survey of India, Eastern Region, Kolkata 700 091, IN
1 Geological Survey of India, North Eastern Region, Shillong 793 003, IN
2 Department of Applied Geology, Dibrugarh University, Dibrugarh 786 004, IN
3 Regional Training Institute, Geological Survey of India, Eastern Region, Kolkata 700 091, IN
Source
Current Science, Vol 118, No 7 (2020), Pagination: 1123-1128Abstract
Shillong Group comprises a thick meta-volcano-sedimentary sequence forming a part of Shillong Plateau and Mikir Hills. The litho variants of felsic meta-volcanics are characterized in detail based on their constituent material, textural variation, depositional feature and mode of eruption. Lava flows are characterized as porphyritic, spherulitic and aphyric type whereas pyroclastic deposits are classified as tuff breccia, lapilli tuff, tuffand ignimbrite. Fractured crystal and brecciated lithic fragments in tuff; fiamme and eutaxitic texture of ignimbrite suggest for subaerial eruption. The felsic meta-volcanics are rhyolitic to dacitic in composition and interbedded with tuffaceous phyllite, phyllite and quartzite.Keywords
Felsic Volcanics, Ignimbrite, Lava Flow, Tuff, Shillong Group, Subaerial.References
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