GRAVITY AND MAGNETIC ANALYSIS OF THE AMU DARYA BASIN OF TURKMENISTAN AND UZBEKISTAN

The Jurassic-Tertiary Amu Darya Basin is mainly located within the Turkmenistan and Uzbekistan with a small portion being in Afghanistan and Iran. The basin is one of the largest petroleum systems in central Asia. The basin is located in the southeast corner of the Turan platform, where both the Middle Paleozoic Turkestan and Early Mesozoic Tethys oceans were closed during different orogenies. The southern boundary of the basin is along the Bande Turkestan fold belt, the Afghan-Tajik basin to the east, Paleozoic metamorphic terranes to the north and the Karakum high (Paleozoic basement rocks) to the west. Several blocks and terranes were accreted during the late Paleozoic Hercynian orogeny in the late Permian and make up the basement of the basin. The makeup is relatively unknown due to the lack of drill holes and deep geophysical studies. Tectonism occurred initially from the late Permian through to the Middle Jurassic, during this time, a complex of faults and folds were created during this orogeny. During this time the basement was broken into a series of graben that may be up to 6 km deep or deeper. Between the Jurassic to Eocene times, the region, passive margin sedimentation occurred that increased in thickness toward the south. In the Eocene, the final tectonism created the basin as known today with the collision of the Indian plate with the Asian plate and the subsequent Alpine-Himalayan orogeny. This final round of tectonism reactivated relict structures incongruently within the basin, however, not all structures were activated at the same rates, if at all. The present study uses the available magnetic and gravity data to determine and location of these structures and a model of how the basin formed. The gravity and magnetic data was analyzed via residual, derivative and isostatic anomalies, 2-D forward modeling, upward continuation, bandpass-wavelength filtering anomalies. Complete Bouguer gravity and magnetic maps reveal a large maximum in the south-central portion of the basin, near the Tajikistan-Uzbekistan border. 2-D gravity and magnetic forward modeling reveal the shape, orientation and extent of the faults, folds and other structures within the basin. Additionally, the 2-D forward modelling of the gravity and magnetic data reveals the basement and basin may be deeper than previously assumed.