Fault reactivation in the Junggar region, northwest China: the role of basement structure during Mesozoic-Cenozoic compression

Basement structures exposed at the margins of the Junggar Basin were created during the Altaid orogeny in the Late Palaeozoic. The most prominent structures are backstops to subduction-accretion complexes (North Tien Shan Fault), or major thrusts within these complexes (Dalabute and Kelameili faults). Both types of basement structure are far more common in accretionary, Turkic-type, orogens such as the Altaids than true sutures. Probably the only suture sensu stricto in the Junggar area is cryptic, and lies under the Junggar Basin’s thick Mesozoic-Cenozoic cover. The exposed Palaeozoic fault zones have been reactivated by Mesozoic-Cenozoic compressional events, which are the long-distance expression of orogenies at the southern margin of Asia. Latest Palaeozoic and Mesozoic events reactivated a larger number of fault zones than have been affected by the Cenozoic India-Asia collision, possibly because of an increase in the strength of the Junggar basement over time, following Late Permian rifting. Cenozoic strain is partitioned between strike-slip motion on basement structures within the Palaeozoic orogenic belts around the Junggar Basin, and numerous thrusts and transpressive faults in regions marginal to and within the basin itself. Most major strike-slip faults are reactivated structures, and occupy narrower zones than their Palaeozoic precursors. Thrust zones follow the Palaeozoic basement grain, but active faults have propagated into the Mesozoic-Cenozoic cover.