Crustal structure at Nanga Parbat, northern Pakistan, from magnetotelluric soundings

Abstract

A magnetotelluric survey in northern Pakistan contains effects from both 2-D and 3-D structure. Identification of the effects of the sediments along the Indus River valley using 3-D modeling permitted the selection of modes that could be accurately inverted with 2-D inversions. The resulting 2-D model reveals generally resistive (> 500 ohmm) upper crust (0-8 km), a more conductive (30-50 ohm-m) middle to lower crust (8-40 kin), and a resistive (> 300 ohm-m) upper mantle. Shallow crustal (< 10 km) conductors correlate with a hydrothermally altered fault zone and/or carbonaceous metamorphic rocks near the Raikot fault. A prominent midcrustal conductor located beneath Nanga Parbat is required to fit the data, but its depth, dimensions, and conductivity are poorly constrained by existing data.