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D. B. Guha ¹, L. N. Gupta ²

Affiliations
1 Geological Survey of India, Jaipur, IN
2 Centre of Advanced Study in Geology, Panjab University, Chandigarh, IN

Abstract

Patchy, vein, film, and crypto types of perthites, rapakivi structure, and myrmekite texture are commonly developed in the potash-feldspar augen of the granitic gneisses of the Doda area, Jammu and Kashmir State.

The scanned perthites show an interlamination of microc1ine and albite resulting in a criss-cross pattern. Islands of soda-feldspar in potash-feldspar show embayed margins. These interrelationships appear to be the result of exsolution phenomenon.

Segregated sodic-calcic components replace the host potash-feldspar releasing blebs and globules of quartz which are present in the form of myrmekite texture.

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D. B. Guha ¹, R. S. Garkhal ¹

Affiliations
1 Geological Survey of India, Jhalana Dungri, Jaipur-302 004, IN

Abstract

The Aravalli Supergroup around udaipur area, comprising volcano-sedimentary assemblage, is classified into three Groups, viz., the Delwara, the Debari and the Jharol Groups, based on two prominent horizons of conglomerate. The Lower Aravalli Delwara Group is separated from the Middle Aravalli Dcbari Group by a pronounced unconformity marked by a thick horizon of conglomerate exposed at Kabita which has heen correlated with the Debari conglomerate of the type locality. The Bari Lake volcanics are correlated with the Delwara volcanics and the quartzite-conglomerate occurring within the former are intertrappean in nature. The Ahar River Granite is identified as the post-Middle Aravalli intrusive granite, which intruded the Delwara volcanics and the Debari phyllite in comagmatic pulses of the same granitic magma.

Keywords

Proterozoic, Ahar River Granite, Rajasthan, Petrology, Udaipur Dist.

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Pratip Gupta ¹, D. B. Guha ¹, B. Chattopadhyay ²

Affiliations
1 Geological Survey of India, Jhalana Dungri, Jaipur-302 004, IN
2 Geological Survey of India, Calcutta-700 016, IN

Abstract

The Precambrian Khetri Fold Belt in northern Rajasthan, India, is bifurcated by the transverse Kantli Fault into the North Khetri Belt (NKB) and the South Khetri Belt (SKB). A new stratigraphic and structural framework has been proposed for the NKB and the SKB. The NKB and the SKB evolved independently and show different basement-cover relationships. The Proterozoic cover sequence on either side of the Kantli Fault differ significantly from each other in litho-characteristics, specially in the content of felsic-volcanics. The 1832 ± 3 Ma old synsedimentary felsic volcanism in Proterozoic sequence is considered to be coeval with the Jasrapura Granite dated at 1844 ± 7 Ma.

Geochronological data from several granite bodies suggest a plutonic event around 1500 ± 200 Ma which constrains the third phase of deformation in the basement rocks. TWo types of granites are recognised; one akin to the Hercynian-type peraluminuous, compositionally restricted ilmenite-bearing S-type granite and the other Caledonian-type, compositionally restricted I-type granite.

Both forceful ballooning and forceful permitted type processes were responsible for the plutonic activity. Significant amongst the first-type are the Udaipurwati Granite and the Chapoli Granite; the former shows stretching of the sodium-rich early consolidated intrusion as a result of inflation of the potassium-rich central part of the magma balloon.

A general readjustment of the isotopic systems within minerals occurred around 700 - 800 Ma or even later, possibly a Pan-African event, which has been correlated with widespread granitic activity in western Rajasthan.

Keywords

Stratigraphy, Proterozoic, Granite Emplacement Mechanism, Khetri Copper Belt, Rajasthan.

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D. K. Sinha ¹, A. Rai Choudhuri ², D. B. Guha ²

Affiliations
1 Plot no. 188, Laxmi Nagar, Niwaru Road, Jhothwara, Jaipur - 302 012, IN
2 Geological Survey of India, Salt Lake city, Kolkata - 700 091, IN

Abstract

No Abstract.

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A. Rai Choudhuri ¹, D. B. Guha ²

Affiliations
1 Coal Wing, Geological Survey of India, Block DK-6, Sector-II, Karunamoyee, Salt Lake, Kolkata 700091, IN
2 Western Region, Geological Survey of India, 15-16 Jhalana Institutional Area, Jaipur - 302 004, IN

Abstract

The Great Boundary Fault (GBF) in southeastern Rajasthan originated as a thrust in a brittle-ductile/Ductile regime. Since it has affected the youngest of Vindhyan formation it is post-Vindhyan in age. Both the basement and the vindhyan sediments occuring on the hanging wall side of the fault have been folded into large-scale low plunging folds trending parallel to the GBF. Increase in tightness and asymmetry of the folds near the fault suggest that these are fault related folds. Development of folds, occurrence of oriented fabric, recrystallisation in the Vicinity of the GBF and presence of undisturbed mylonite as remnant bodies along the GBF suggest that the faulting took place in a brittle-ductile/Ductile regime. Basin-ward vergence of the tight to isoclinal folds near the GBF and steep dip of the mylonite bands towards the basement indicate that the fault plane dips steeply towards the basement. Increasing tightness of the fault related folds towards the fault, moderate to steep dip of the fault towards the basement and juxtaposition of the basement rocks in the hanging wall with the younger sediments in the footwall prove that the fault originated as a thrust. Concomitant with the thrusting a conjugate set of brittle-ductile shear zone was also developed in the hanging wall side of the fault. The acute bisector of the conjugate set indicates a northwest southeasterly directed compression, which is also perpendicular to the axial planes of the fault related folds.

Subsequent to thrusting, several sets of brittle normal faults developed in the area. These faults transect the large scale fault related folds and even the GBF. One of these sets of normal faults strikes parallel to the GBF trace. Presence of such normal faults parallel to the GBF and fragments of mylonite as angular pieces within the breccia along the GBF imply that the GBF was subjected to a late brittle reactivation. Near the GBF, presence of close spaced GBF parallel joints also proves that the GBF was subjected to a late tensile stress.

Keywords

Great Boundary Fault, Re-Evaluation, Thrust, Sawai Madhopur, Rajasthan.

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Amit Sahay ¹, A. Rai Choudhuri ², D. B. Guha ²

Affiliations
1 Department of Earth Sciences, IIT Roorkee, Roorkee - 247 667, IN
2 Geological Survey of India, Kolkata - 700 009, IN

Abstract

No Abstract.

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L. N. Gupta ¹, D. B. Guha ¹

Affiliations
1 Centre of Advanced Study in Geology, Panjab University, Chandigarh, IN

Abstract

Muscovites separated from pelitic schists of the Dada area show a limited range of composition between ideal muscovite and ferrimuscovite. The paragonite content in the muscovites ranges between 14 and 21 %. The tetrahedral Al^iv increases with the increase in the grade of metamorphism though this increase is more for the muscovite of the aureole rock, i.e., in the andalusite to staurolite zone than in the kyanite-staurolite zone. Similar results are also shown by the (FeO+Fe₂O₃) and Na/(Na+K) with respect to AI₂O₃ and total Al respectively.

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D. B. Guha ¹

Affiliations
1 TC-II Division, Geological Survey of India, Western Region, Jaipur-302004, IN

Abstract

No Abstract.

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