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" Petrology and stable isotope geochemistry of the Nanga Parbat-Haramosh Massif, northern Pakistan "
M. U. K. Khattak
J. W. Shervais
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Latin Dissertation
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English
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| Record Number
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1113173
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TLpq304249738
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| Main Entry
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J. W. Shervais
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M. U. K. Khattak
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| Title & Author
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Petrology and stable isotope geochemistry of the Nanga Parbat-Haramosh Massif, northern Pakistan\ M. U. K. KhattakJ. W. Shervais
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| College
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University of South Carolina
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| Date
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1995
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| student score
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1995
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| Degree
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Ph.D.
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| Page No
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158
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| Abstract
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The Nanga Parbat-Haramosh Massif in northern Pakistan records the Tertiary metamorphism and dynamics of the Himalayan collision and subsequent overthrusting of the Asian plate onto the Indo-Pakistan plate. The massif consists of an intercalated sequence of para- and orthogneisses, of minor metabasics and calc-silicate rocks, and of post-metamorphic pegmatite dikes. These gneisses are metamorphosed under high pressure upper amphibolite facies conditions. The P-T estimates and the P-T-t paths of the pelitic samples from the massif and the adjacent areas of the Kohistan and Ladakh arcs along two cross-strike transects (Indus and Astore Rivers) through the massif show that the massif followed a compressional (counterclockwise) and the Kohistan-Ladakh arc a decompressional (clockwise) P-T-t path. Geothermobarometry on zoned garnets from core to rim indicates that the massif rocks started their metamorphic history with 5.5 kb and 650C. During collision, the pressure and temperature rose to >10 kb and about 750C. The Ladakh garnets started to grow at >10 kb, 750C with subsequent decrease in metamorphic pressure to 8.5 kb. After the collision, the massif and the Kohistan-Ladakh rocks equilibrated at similar conditions of usd O thermometry results are consistent with the phase equilibrium studies of the massif and the Kohistan-Ladakh arc. Temperatures were calculated from O fractionations among quartz, garnet, feldspar, biotite, muscovite and amphibole. Among the analyzed samples, the whole rock usd\rm\delta\spO\sb{SMOW}usd isotopic values range from 7 to 15.3usd\perthoususd, quartz 7.4 to 16.4usd\perthoususd, feldspar 7 to 16.1usd\perthoususd, garnet 5.3 to 13.7usd\perthoususd, biotite 3.9 to 12.6usd\perthoususd, muscovite 6.7 to 12.7usd\perthoususd, and hornblendic amphibole from 4.4 to 7.2usd\perthoususd. Calculation of the O composition of fluids that were in equilibrium with different minerals in the temperature range of 500-700C reveals that there is one pre-metamorphic and one post-metamorphic fluid activity affecting the isotopic composition of the rocks of the massif. The pre-metamorphic fluids probably originated from an igneous parent, depleting the rocks in 2usd\perthoususd, especially along the major faults. The post-metamorphic fluids probably originated from prograde metamorphic reactions and were heavy enough to enrich the feldspars up to 18usd\perthoususd.
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Earth sciences
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Geochemistry
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Geology
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Mineralogy
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oxygen-18
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