Gravity, Crustal Tectonics and Mantle Structure in the Central Asian Syntaxis
Abstract
An attempt is made to interpret the gravity field in the zone of the Tien Shan-Hindu Kush-Kun Lun-Karakorum-Kashmir Himalaya Syntaxis, considering the local features of the field generated by density anomalies in the Lithosphere separately from the regional geoidal features generated by anomalous density distributions in the Mantle as obtained by satellite geodetic methods. The local isostatic anomalies show a marked dlchotomy astride of a line representing the prolongation of the Chaman Fault lineament. Remarkably, the nest of intermediate Hindu Kush earthquakes is to be found at the intersection between the same line with the Herat Fault lineament. Strong negative anomalies unrelated to either the topography or the geology prevail NW of such line, whereas SE of the line the field is characterized by stripes of alternating negative and positive anomalies all having the Himalayan trend.
Bath the Himalayan and the Chaman Fault trends are to be recognized in the geoidal features of GEM 10. The Himalayan trend is here related to the upheaval of the geoid that accompanies all along the Alpine-Himalayan geosyncline, and the Chaman Fault trend to the geoidal downwarping that follows the northern continuation of the tensional zone of the Arabian Sea crossing the syntaxial zone and continuing in the Balkash-Baykal Rift Zone in Central Asia. A tentative hypothesis is made to interpret the relationship between mantle structure and the crustal tectonics by the mechanism of gravity sliding.
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