Matched‐Filter Analysis of Aeromagnetic Anomaly in Mid‐Western Tibetan Plateau and Its Tectonic Implications

Abstract

AbstractAeromagnetic anomaly data of ΔT reduced to the pole in the mid‐western Tibetan plateau are reprocessed, using matched‐filter method, to extract local and regional anomaly fields from total field. The best depth of filter‐windows is about 19 km. Based on other geophysical evidence, this depth of 19 km is considered an important boundary in the crust, which separates the upper crust from middle crust. The extracted regional anomaly field shows that there is an NNE trending strip of negative aeromagnetic anomaly in central Tibet. The evidence from teleseismic P‐wave tomography shows that the location of negative anomaly strip coincides with the deformed lithospheric mantle of Indian plate, which became a scoop‐like shape. A large quantity of thermal anomaly from deep athenosphere, trapped by the scoop‐like Indian lithospheric mantle, caused thermal demagnetization in the original lithosphere, giving rise to the negative anomaly strip under the central Tibetan plateau. Moreover, an anomaly indicative of a blind fault exists in both the local and regional anomaly fields. The fault is located between the north margin of Lhasa terrane and the south side of Banggonghu‐Nujiang Suture, about along the north of Gê'gyai to south of Gêrzê to north of Coqên to north of Xainza, from west to east. Combined with a lot of data from surface geology, focal mechanisms, distribution of hypocenters, the latest regional geological survey and Bouguer gravity anomaly, the fault is considered the western part of the right‐lateral strike‐slip Jiali Fault.