REGIONAL GRAVITY AND MAGNETIC ANALYSIS OF THE CRUSTAL STRUCTURE OF MONGOLIA

Mongolia is composed of numerous tectonic terranes ranging from Precambrian to Cenozoic in age. While the exact tectonic environment of each of these terranes is still open to debate, there is a general consensus that the continental crust was formed by a number of accretionary collisions. The Central Asian Orogenic Belt of Precambrian and Paleozoic age is composed of mainly oceanic types of tectonic features including ocean basins, backarc basins, island arcs and interarc basins. Also within these oceanic features, numerous slices of continental microcontinents are found. In more recent times, Mongolia has been the site of Mesozoic and Cenozoic volcanism, and possible hot spot activity, and Cenozoic crustal shortening resulting in the formation of large-scale strike-slip faults caused by the collision of India into Asia. All these features create a complex geologic environment that has been difficult to unravel and the lack of deep crustal information makes the determination of the crustal features even more difficult. In order to aid in the interpretation of the regional geological environment, we present a preliminary interpretation of regional gravity anomaly and aeromagnetic maps. At a first-order interpretation, the Bouguer gravity anomaly and magnetic anomaly maps indicate anomalies that follow the trends of the Precambrian and Paleozoic accretionary terranes. However, low-pass filtered gravity anomaly maps that emphasize long-wavelength anomalies show a high-amplitude minimum over the Kobdin Trough,which is the site of more than 2 km of early Paleozoic sediments, may have a more deeper source than the exposed sediments. To the northeast of the Kobdin Trough, a large amplitude gravity maximum occurs over uplifted Paleozoic sediments and volcanic units some of which have been metamorphosed. The source of the anomaly is unknown but maybe due to Cenozoic crustal thinning.