Abstract
Paleozoic rocks of southern Mongolia record an important part of the tectonic growth and amalgamation of central Asia, but have not been studied closely because of their remote location. New stratigraphic and sedimentologic data from 17 localities help constrain previous geological models and strongly suggest tectonic activity throughout much of the Paleozoic, with deposition occurring predominantly within basins associated with volcanic arcs. Ordovician and Silurian deposits are primarily marine strata containing mature siliciclastics and fossiliferous, shallow-marine carbonates. Angular unconformities developed during this time provide the main evidence for tectonic activity. Devonian and Carboniferous strata--divided into western, central, northeastern, and southern geographic regions--contain a mix of siliciclastic and carbonate marine strata, but, more significantly, also record the activity of numerous volcanic centers. The western region contains approximately 5 km of interbedded intermediate to felsic volcanic rocks and marine sedimentary rocks, interpreted to be a volcanic-arc system developed on the edge of a microcontinent or an older, inactive volcanic arc. The northeastern region is similar to the west, but contains more mafic volcanic deposits and records uplift of an older block. The rocks of this region represent deposits of volcanic arc-related basins as well as transpressional and transtensional basins. The central area is the most complex and may represent a submerged island arc with components of an accretionary complex and forearc or back-arc basins. Finally, the southern region, which contains intermediate and felsic volcanic flows, most likely formed as a mature oceanic arc or continental arc.