Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Z. S. H. Abu-Hamatteh ¹, M. Raza ¹, T. Ahmad ²

Affiliations
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

Abstract

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.

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M. Raza ¹, S. H. Alvi ¹, Z. S. H. Abu-Hamatteh ¹

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh-202 002, IN

Abstract

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.

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Basem K. Moh'D ¹, Z. S. H. Abu-Hamatteh ¹

Affiliations
1 Natural Resources and Chemical Engineering Department, Tafila Applied University College, AI-Balqa' Applied Universliy, PO Box 26 (66241), Tafila, JO

Abstract

Siwaqa Travertine occurs about 70 km south of Amman, in the vicinity of Siwaqa Strike-Slip fault. Representative surface and subsurface samples of travertine have been analyzed by X-ray diffraction , ICP and wet chemistry to study the mineralogy and geochemistry of travertine. Data of Siwaqa traveritine is compared with travertines from other localities in Jordan. Calcite is the most dominant constituent Dolomite, quartz, kaolinite, gypsum/Bassanite, and hematite are present in minor amounts. Presence of clay minerals and Iron oxides have resulted in the departure of travertine from its creamy white colour. CaO with an average of 50 9% is mainly attributed to carbonate minerals, particularly calcite. Relatively rich trace element content in Siwaqa traverime compared to Mujeb travertine is attributed to leaching of underlying oil shale and/or marble. Higher concentrations of some of the elements probably resulted due to diagenetic processes and syngenetic mineralization.

Keywords

Travertine, Geochemistry, Mineralogy, South Amman, Jordan.

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