Petrology of calc-alkaline/adakitic basement hosting A-type Neoproterozoic granites of the Malani igneous suite in Nagar Parkar,SE Sindh,Pakistan |
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| Authors: | M Qasim Jan Amanullah Laghari M Asif Khan M Hassan Agheem Tahseenullah Khan |
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| Institution: | 1.National Centre of Excellence in Geology,University of Peshawar, Peshawar, & COMSTECH,Islamabad,Pakistan;2.Centre for Pure and Applied Geology,University of Sindh,Jamshoro,Pakistan;3.National Centre of Excellence in Geology,University of Peshawar,Peshawar,Pakistan;4.Department of Earth and Environmental Sciences,Bahria University,Islamabad,Pakistan |
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| Abstract: | The Nagar Parkar area contains three distinct groups of rocks, from oldest to youngest, (1) basement rocks ranging in composition from mafic to (quartz)diorite, tonalite, granite, and younger granodiorite, (2) granite plutons similar in general features to those of the Malani Igneous Suite of Rajasthan, and (3) abundant mafic, felsic and rhyolitic dykes. The basement rocks show strong brittle and local plastic deformation, and epidote amphibolite/upper greenschist facies metamorphic overprint. The chemistry of the basement rocks contrasts the commonly agreed within plate A-type character of the Neoproterozoic granites (group 2) that are emplaced into them. The basement rock association is calc-alkaline; the granodiorite displays the compositional characteristics of adakites, whereas the tonalite has intermediate composition between typical adakite and classical island arc rocks. This paper presents detailed petrography of the basement rocks and compares their geochemistry with those of the group 2 granites as well as with rocks from other tectonic environments. It is proposed that the Nagar Parkar basement is part of a 900–840 Ma magmatic arc that was deformed before it was intruded 800–700 Ma ago by the A-type continental granitic rocks followed by mafic to felsic dykes. |
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