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PETROLOGY OF THE NAGAR PARKAR GRANITES AND ASSOCIATED BASIC ROCKS, THAR DISTRICT, SINDH, PAKSITAN

Laghari, Amanullah (2004) PETROLOGY OF THE NAGAR PARKAR GRANITES AND ASSOCIATED BASIC ROCKS, THAR DISTRICT, SINDH, PAKSITAN. PhD thesis, University of Peshawar, Peshawar.

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Abstract

Covering 480 km, the Nagar Parkar area in southeastern Sindh is a part of the Thar Desert adjacent to the Runn of Kutch. Detailed petrology of the area, based on mapping, petrography, and major, trace, and rare-earth element geochemistry, has been studied during the course of this investigation. The area is occupied by a variety of magmatic rocks referred to as the Nagar Parkar igneous Complex. At least six phases are recognizable: 1) basement rocks (oldest), 2) riebeckite-aegirine grey granite, 3) biotite pink granite, 4) acid dykes, some of which contain riebeckite and aegirine, 5) devitrified rhyolite “plugs” , and 6) basic dykes (youngest). Of these, the last three are insignificant in volume. Radiometric dates are lacking, but the grey and pink granites are petrographically comparable to the Siwana and Jalalore plutons, respectively, emplaced in the Malani volcanic series that covers large areas in western Rajasthan. Based on these similarities and proximity, it is thus suggested that the phase 2 to 6 bodies in Nagar Parkar may belong to the late Proterozoic (720-745 Ma) Malani magmastism. The basement (age unknown) comprises deformed and epidote-amphibolite facies metamorphosed rocks ranging from mafic to granodioritic composition. They appear to be the products of crystallization differentiation of a calc-alkaline magma of island are affinity. The phase 2 to 5 rocks, forming stock-size plutons to minor dykes and plugs, range from peralkaline (Most common) to peraluminous grabutes nucroigrabutes, rhyolite and trachyte. The display very similar trace element characteristics and classiy as typical within plate. A type “granitiod”. Their trace element patterns are akin to those of Mull (Scotland), Skaergaard (Greenland) and Sabaloka (Sudan) Granites, which are emplaced in attenuatedto normal continental crust. The mafic dykes are divisible into hornblende-bearing (dioritic / lamprophric) and pyroxene+olivine-bearing (doleritic) types. Both are alkaline and show some chmical resemblance to continental alkaline basalts. Significantly, the mantle-normalized diagrams of the basic dykes are similar to those of the main granites except for relatively lower concentrations of trace and rare earth elements. This similarity provides a strong argument in favour of derivation of the parent magmas of phase 2 to 6 rocks from the upper mantle. However, during ascent, the magmas that produced the granitic rocks were contaminated with crustal material. In trems of tectonic evolution, the Nagar parkar region appears to be a composite terrance that developed initially as an island arc. It was accreted to other terrances to constitute a Precambrian continental crust. During the collision it may have experienced deformation and metamorphism in epidote-amphibolite facies. During the late Proterozoic, the terrance played host to continental magmatism related to epeirogenic uplift ((doming) and extension.

Item Type:Thesis (PhD)
Uncontrolled Keywords:nagar parkar granites, thar, dykes, granites, basement rocks, riebeckite-aegirine grey granite, biotite pink granite, acid dykes, riebeckite, aegirine, devitrified rhyolite, basic dykes
Subjects:Physical Sciences (f) > Earth Sciences(f4) > Geology, (f4.1)
ID Code:650
Deposited By:Mr. Muhammad Asif
Deposited On:14 Sep 2006
Last Modified:04 Oct 2007 21:02

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