GEOLOGY OF THE INDUS SUTURE ZONE AND HIGH HIMALAYAN CRYSTALLINE BLOCK WEST OF BESHAM SYNTAXIS AND THE STUDY OF SOME ASSOCIATED MINERALS

Syed Shahid, Hussain (2005) GEOLOGY OF THE INDUS SUTURE ZONE AND HIGH HIMALAYAN CRYSTALLINE BLOCK WEST OF BESHAM SYNTAXIS AND THE STUDY OF SOME ASSOCIATED MINERALS. Doctoral thesis, University of the Punjab, Lahore.

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Abstract

A geological map on the scale 1 :250,000 of about 5000 sq Ian of Besham, parts of Kohistan, upper Swat areas and Malakand, Bajaur and Mohmand agencies, covering the region between river Indus in the east and Afghan border to the west has been prepared from mapping carried out on 1:5000 to 1:50,000 scales after variably modifying and incorporating the already existing maps. This map was dovetailed into the existing maps further to the east across river Indus in Kaghan valley to produce the geological map of High Himalaya, Indus Suture Zone, parts of Kohistan and Lesser Himalaya from the Afghan border to the border areas of Azad Jammu and Kashmir. The entire lithostratigraphic package of the mapped areas has been described, standardized and systematized replacing a plethora of local names. The lithostratographic units east of Indus river in Kaghan were correlated with the corresponding lithostratigraphic units to the west up to Afghan border. The High Himalaya package, folded into N-S trending basins and domes, was divided into a basement upper amphibolite facies predominantly pelite-psammite rocks with anatectic migmatites in the core of the domes and granitoids (Manglaur group) overlain by a lower meta-turbidite unit with volcanic derived amphibolite towards the base (Salampur formation) and an overlying upper predominantly calc-pelite and marble (Tilgram formation), metamorphosed in upper amphibolite facies. The High Himalaya is separated from the Lesser Himalaya by a crustal scale thrust, the Main Central Thrust (MCT), south of which occur E-W trending Palaeozoic marbles of Tursak formation and calc-pelites, graphitic pelites and marbles of Girari formation, metamorphosed in greenschist facies. On the basis of geology. structure and geochemistry, the rocks occurring along the Indus Suture Zone have been divided into a Tethyan MORI fore-arc basin ophiolites in Kohistan. Besham, Alpurai and Dargai and sub-arc mantle rocks overlain by crustal gabbros across the Moho at Jijal-Dubair and Spat. Kohistan. The geology and geochemistry of volcanic rocks associated with the Indus Suture Zone has been described and discussed. These rocks were formed either within a juvenile arc setting or derived from oceanic mantle that had inherited' an anomalously depleted signature from fossil subduction. In Jijal-Dubair and Spat areas of Kohistan huge outcrops of sub arc mantle. and overlying crustal gabbros with a palaeo-Moho have been described and discussed. These rocks were described in the past as a part of the Indus Suture Zone. On the basis of geology and geochemistry, the High Himalayan granitoids have been divided into peraluminous collisional granites of Proterozoic, Pan-African and Palaeozoic periods and Himalayan alkaline granites of Carboniferous-Triassic extensional regime. On the basis of geological contact relations, mineralogical (presence of pyrochlore) and geochemical criteria (REE) calc-silicate marbles and meta-limestones, some of which were described earlier as carbonatites, have been distinguished from carbonatites. Chromite associated with sutural ultramafites show limited within group variation in their chemical composition and are either refractory (AI rich) or of chemical grade (Cr-Fe rich). Geochemical signatures suggest their formation under a spreading center. The chromite deposits associated with ultramafites, mainly dunites, of the sub-arc mantle are generally AI-poor, show quite heterogeneous compositions even across single grains due to variable reconstitution and combination of melt consuming reactions coupled with ascending fluids from the subducting lithosphere. Mg # in these chromites is lower than those of sutural chromites. Manganese mineralisation associated with metacherts and greenschists has low values of Co, Ni, Cr, Zn etc and high Mn/Fe ratios and is considered to have been formed by hydrothermal rather than hydrogenous process. Emerald mineralisation is due to the influx of Be, Al and Si bearing fluids, derived from the Himalyan beryliferous granites into Cr bearing talc-carbonates derived from mantle peridotites, of the Indus Suture Zone. Exquisite peridot occurs in veins in association with talc, antigorite and magnesite and is confined to shear zones. Late stage, post-tectonic hydrothermal fluids from the host rocks are considered responsible for peridot mineralisation in Spat. Field and geochemical studies suggest that rodingite occurring in the mafic-ultramafics of the Indus Suture Zone was formed due to metasomatic alteration of gabbros, since they contain fairly high values of Al and Ca. Field relations (association with peridotites), petrography (relict olivine and pyroxene) and geochemistry (high values of Cr, Ni etc) suggest formation of huge talc deposits from ultramafites. The gem quality epidote belongs to zoisite and epidote-clinozoisite and is crystallized in altered gabbros and metabasites, which often lack penetrative deformation, suggesting their formation under greenstone (schist) and epidote amphibolite facies hydrogenous metamorphism close to the spreading center. Green beryl is crystallized generally in calc-alkaline granitoids while blue Cs rich beryl is crystallized in alkaline granitoids. Quartz-mica-beryl veins, crystallized in greisenised zones, represent fluids derived from rest pegmatitic magma due to pressure release. Gem quality green grossular garnet discovered from the black schists calcareous black shales of High Himalayan Crysta'l1ine basement near Jambil owes its colour to high values of V and Cr in the metamorphosed black schists. Gem quality; rare and exquisite pink topaz crystallized into Lesser Himalayan reefal meta-limestone due to the influx of F, Al and Si fluids, derived from High Himalayan granitoids in combination with Cr derived from sutural rocks through a system of shears connected to the High Himalaya granitoids and Indus Suture Zone ultramafics lying to the north. Green dravite-uvite tourmaline crystallized into dolomitic marbles of the High Himalaya. The nearby granites contributed B, Si. and Al while the host dolomitic marbles provided the required Mg

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: Indus Suture Zone, High Himalayan Crystalline Block, Besham Syntaxis, lesser Himalayas, granitoids
Subjects: Q Science > QE Geology
Depositing User: Muhammad Khan Khan
Date Deposited: 21 Oct 2016 09:11
Last Modified: 21 Oct 2016 09:11
URI: http://eprints.hec.gov.pk/id/eprint/2623

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