Paper No. 15
Presentation Time: 9:00 AM-6:00 PM
AFGHANISTAN, A DANGEROUS, MYSTERIOUS LAND WHOSE GEOLOGY IS POORLY KNOWN - NEW GEOLOGIC-MAPPING PHILOSOPHIES SHED LIGHT ON HOW THIS COMPLEX TERRANE WAS ASSEMBLED
The most recent geologic map of Afghanistan was published in 1977, and all the ideology embodied in it predates plate tectonics. Located on the edge of the great Indian-plate indention, this region is crucial to our tectonic understanding of how major continental collision zones evolve, but given the paucity of modern maps, it represents a bit of a hole in our global dataset. War- and insurgent-related dangers make Afghanistan a tough place for a modern boots-on-the-ground geologist, but its landscape is well suited for remote sensing analysis. Two new 1:100,000-scale geologic maps are presented here of the region around and east of Kabul. Most of the new information on these maps was derived remotely using Shuttle-Radar, Landsat, Digital-Globe, Ikonos, AVNIR, HyMap, ASTER, and air-photograph data. The remote data are integrated with the limited pre-existing geologic maps, limited ground-truth, and new geochronologic data. This mapping approach represents a significant departure from tradition where field studies provide the primary data input. These are the first of what is hoped will be a series of such maps of Afghanistan. Several important tectonic conclusions can be reached based on the new maps. 1) Paleoproterozoic crystalline basement and superjacent platform carbonate strata around Kabul form a thin tectonic flake above Mesozoic and Paleogene mélange. 2) Widespread sheets of serpentinized ultramafic rocks, also flakes above mélange, were probably spalled off the lithospheric mantle at the base of the overriding plate in a subduction zone. 3) Supposed Proterozoic rocks that collided with Asia during the Mesozoic in Nuristan and Konar may not be! Instead they are likely metamorphosed Mesozoic and early Tertiary sediments of the pre-collision Asian margin. 4) The Kabul block, bounded by left-slip on the west and right-slip on the east, probably protruded north into the Asian margin not unlike the larger Indian indenter.