Geochemistry of Granitic Rocks, Swat-Malakand Area, Pakistan

Title of Thesis

Geochemistry of Granitic Rocks, Swat-Malakand Area, Pakistan

Author(s)
Abid Ahmad

Institute/University/Department Details
College of Earth and Environmental Sciences / Punjab University, Lahore

Session
2008

Subject
Geology

Number of Pages
162

Keywords (Extracted from title, table of contents and abstract of thesis)
Geochemistry, Saidu-Paroona, Granitic, Rocks, Swat, Malakand, Area, Pakistan, metaluminous

Abstract
The thesis area is located in Swat District and the Malakand Agency of NWFP. The rocks exposed in the area belong to the Swat Buner schistose group and Swat granites. The Swat granites (herein relerred as Swat-Malakand granites) are exposed at Illum-Karaker, Malakand and Kot, Saidu-Paroona, Chinglai, Chakdarra, and Besham areas. The Swat-Malakand granites are by and large metamorphosed and as a result gneissic and augen structures are developed. A few un-deformed granites are also exposed in Malakand. Chakdarra and Besham areas. Large feldspar grains in a groundmass of quartz, feldspar, muscovite, and biotite characterize the augen gneisses (Swat granite grneisses) whereas the un-deformed granites are characterized by non-foliated structure with almost the same modal composition. These granites also contain homblende, sphene and rarely gamer.
On the basis of geochemistry, the relatively fresh Swat-Malakand granites are subalkaline and peraluminous. A few granitic rocks are metaluminous and only one peralkaline. In the binary variation diagrams the Swat-Malakand granites depict fractionation of biotite, plagioclase and K-feldspar. They are enriched in LIL elements as compared to HFS elements. Using rare-elements patterns. they show enrichment in light rare-earth elements with prominent depletion in Eu, suggesting fractionation and/or early crystallization of plagioclase.
The geochronological data obtained for the Swat-Malakand granites contradict Precambrian age as reported in the past. The age of the Chakdarra granite gneisses is not well constrained: the best estimate of its age is 213 � 24 Ma. This suggests that the Chakdarra granite gneisses are Upper Triassic in age and give the initial ⁸⁷Sr/⁸⁶Sr ratio of 0.704 � 51. The Illum-Karaker granite gneisses show considerably more scatter of the data, and the best estimate of their age is 260 � 52 Ma. The Saidu-Paroona granite gneisses give best fit of data as shown by low MSWD; their age of 285 � 8 Ma (Permian) with an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.709 � 7. This is within error of the age of the Illum-Karaker granite gneisses, which show the same age, and therefore, seem to be co-magmatic.
The δ¹⁸O values in Chakdarra granite gneisses are +8.8 and +9.2. In Illum-Karaker granite gneisses, the δ¹⁸O values range up to +9.4 and +8.6 whereas in the Saidu-Paroona granite gneisses the δ¹⁸O values are +9.0 and +9.5, which are less than 10 %o and confirm that the Swat-Malakand granite gneisses including Chakdarra, Illum-Karaker and Saidu-Paroona are I-type granites. The I-type granites are sub- and metaluminous but the Chakdarra. Illum-Karaker and Saidu-Paroona granite gneisses are peraluminous, and based on the initial ⁸⁷Sr/⁸⁶Sr ratio and oxygen isotopes, these granites owe I-type characteristics and their peraluminous affinity is due to fractional crystallization, and can be grouped as W-type.
Based on the geochronological data presented herein, the Swat-Malakand granite gneisses are considered co-genetic with granites of the Ambela complex. Therefore, the Illum-Karaker and Saidu-Paroona granite gneisses belong to Permian magmatic event as envisaged for the granites of the Ambela complex. The Permian magmatic event may be correlated with the rifting of Gondwanaland when the Indian continent was separated from Australia. The petrogenetic evolution of Chakdarra granite gneisses may probably be correlated with the Permo-Triassic magmatic event spread over Indo-Pakistan-Oman-Western Australia.

 

 

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