Nappe structure in a crustal scale duplex in Swat, Pakistan

Conference · Tue Jan 01 00:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6454519

Lawrence, R D; Snee, L W; Rosenberg, P S

In the internal zone of thrust belts of continental collision orogens like the Himalaya metamorphic rocks of deep origin record penetrative ductile deformation. In Swat, Pakistan, this zone between the Indus suture and the sedimentary fold-and-thrust belt is narrower and tectonically simpler than elsewhere along the Himalayan orogenic belt. Here the authors have recognized large overturned, orthogneiss cored nappes of 15 km half wavelength. These are defined by para-amphibolite marker beds found in upright stratigraphic section above and in overturned section below the gneissic cores. They distinguish premetamorphic granite porphyry and tourmaline granite intruded into quartzose metasediments as gneissic cores of the nappes and a surrounding sequence of quartzites, amphibolites, and carbonates that were either deposited unconformably above the cores or premetamorphically thrust over them. Metamorphic isogrades cut across the nappe and /sup 40/Ar//sup 39/Ar hornblende dates indicate that metamorphic culmination occurred around 37-40 Ma at about 550/sup 0/C and at depths of about 20 km. These structures thus appear to predate the recognized age of metamorphism and thrusting of crystalline rocks on the MCT in the central Himalaya. They represent an early deep burial of the leading edge of the Indian shield by ophiolite slabs of oceanic lithosphere and/or the Kohistan island arc. By 30 Ma metamorphic temperatures (/sup 40/Ar//sup 39/Ar muscovite) had dropped to 320/sup 0/C, and the nappes were rising through the crust on underlying thrusts. The entire structure is very similar to that of the internal zone of the Alps, but such features have not previously been described in the Himalaya.

• Research Organization: Oregon State Univ., Corvallis (USA)
• OSTI ID: 6454519
• Report Number(s): CONF-8510489-
• Journal Information: Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
METAMORPHIC ROCKS
AGE ESTIMATION
PETROLOGY
PAKISTAN
PLATE TECTONICS
DRILL CORES
GEOLOGIC FAULTS
GEOLOGIC HISTORY
GEOTHERMOMETRY
HIMALAYAS
METAMORPHISM
OCEANIC CRUST
OROGENESIS
PETROGENESIS
STRATIGRAPHY
SUBDUCTION ZONES
ASIA
DEVELOPING COUNTRIES
EARTH CRUST
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOLOGY
MOUNTAINS
ROCKS
TECTONICS
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)
580201 - Geophysics- Seismology & Tectonics- (1980-1989)