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Abu-Hamatteh, Z. S. H.
- Geochemistry of Early Proterozoic Mafic and Ultramafic Rocks of Jharol Group, Rajasthan, Northwestern India
Authors
1 Deptt. of Geology, Aligarh Muslim University, Aligarh-202002, IN
2 Wadia Insitute of Himalayan Geology, 33, Gen. Mahadeo Singh Road, Dehra Dun-248001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 44, No 2 (1994), Pagination: 141-156Abstract
The deep water Jharol sediments of Aravalli Supergroup host sporadic bodies of mafic-ultramafic. rocks. Field evidence suggests that at least some of these rocks are extrusive in nature. Low to medium grade metamorphism and intense deformation has obliterated the original mineralogy and texture of these rocks. The ultramafic rocks are relatively more altered (serpentinized) with highly disturbed geochemical composition which cannot be used for petrogenetic interpretations. On the other hand, the mafic rocks are relatively less altered with some relict plagioclase feldpars. Geochemically, these mafic volcanics are Mgand Fe- rich tholeiites.
These tholeiites have nearly flat to slightly enriched REE patterns (about 30 to 40x % chondrite La and 20 to 25x % Chondrite Yb), with (LalYb)N ratio ranging between 1.29 and 1.54 and (GdIYb)N ratio ranging between 0.97 and 1.07. All samples show slight to strong positive Eu anomaly. Immobile incompatible-element geochemical patterns and other binary plots suggest that these tholeiites have enriched chemistry and that grobably they have been derived from enriched source(s) and resemble closely with within plate and initial rift tholeiites.
Trace elements, including REE based petrogenetic modelling indicate that (a) the source had about 3x% chondoritic REE abundances with nearly flat to slightly depleted pattern and (b) that these rocks were generated by about 8 to 12% partial melting of the modelled source followed by some olivine and clinopyroxene fractionation. Field as well as trace element characteristics indicate rift related (lithospheric extension) generation of these basalts with some influence of asthenosphere (deep mantle) on the lithospheric source(s) as indicated by positive Nb and Sr anomalies.
Keywords
Geochemistry, Jharol Mafics, Aravalli Supergroup, Proterozoic Volcanism, Rajasthan.- Geochemistry and Tectonic Significance of Ongarbira Volcanics, Singhbhum Craton, Eastern India
Authors
1 Department of Geology, Aligarh Muslim University, Aligarh-202 002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 45, No 6 (1995), Pagination: 643-652Abstract
The Ongarbira volcanics of middle Proterozoic age occur with the Sahedba sedimentaries in the south of Singhbhum shear zone. The volcanics are of tholeiitic composition with high content of MgO (> 8%) and high MgO/Al2O3, ratio (> 0.6). In terms of REE data these rocks show LREE depleted patterns which resemble those of basaltic rocks from Dalma volcanic belt and basaltic komatiite of Kolar schist belt. MORB- normalized incompatible element patterns of these rocks display distinct enrichment of LILE including Th and depletion of HFSE and marked trough at Nb and Ta. These features suggest a subduction zone component in the source of Ongarbira volcanics. Nb-normalized ratio spidergrams and incompatible element ratio plots Ce/Yb- Ta/Yb-, Th/Yb- Ta/Yb and Th- Hf- Ta are consistent with their eruption in a subduction related environment. REE modelling spggests that they were generated through 14 to 18 percent partial melting of a LREE depleted source. The source was probably selectively enriched in LILE by materials derived from the subducting slab.
Geochemical-Geological evidences indicate that Ongarbira volcanics were probably erupted on a thin continental crust or even on oceanic crust as a result of a southward plate convergence below the Singhbhum craton.
Keywords
Geochemistry, Tectonics, Proterozoic Voicanics, Singhbhurn Craton.- Mineralogy and Geochemistry of Siwaqa Travertine, South Amman, Jordan
Authors
1 Natural Resources and Chemical Engineering Department, Tafila Applied University College, AI-Balqa' Applied Universliy, PO Box 26 (66241), Tafila, JO