Multiepisode subduction of a mid-oceanic ridge; insights from west Junggar, southern Central Asian orogenic belt

The subduction of major oceans may involve ridge-trench interactions at various convergence angles, but their consequences have not been well constrained. We defined orogenic components and their evolution in southern West-East Junggar of the southern Central Asian Orogenic Belt by integrating structural analysis of geological relationships, and geophysical and geochemical features, to provide insights into the changes an orogenic architecture undergoes. Late Silurian-Early Devonian adakitic rocks apparently resulted from ridge subduction. During this period, a short-lived magmatic belt in the forearc region and a long-lived Central Tianshan magmatic arc constituted double magmatic belts, which were subsequently separated by a newly generated Devonian-Carboniferous ocean. Beneath a former accretionary complex, an approximately 12-km-thick lower crustal high-velocity layer between doublet Moho zones, and positive magnetic anomalies, indicate remnants of a subducted oceanic slab. This oceanic slab resembles the architecture of the late Cenozoic California, USA and Mexico, subduction, which occurred subparallel to the trench ridge. The late Paleozoic Baogutu adakite, Miaoergou charnockite, and Karamay sanukitoid suggest another episode of ridge subduction. The zone with high total field magnetic anomalies and high Bouguer gravity anomalies is composed of mafic-ultramafic rocks, which likely are products of frozen magma upwelling of the suboceanic asthenosphere through a high angle-to-trench ridge-transform fault system. An underplated ridge-transform system possibly heated up the wallrocks and contributed to the emplacement of orthogonal Karamay sanukitoid dikes. The initiation of subparallel ridge-trench interaction triggered two episodes of ridge subduction. These results illustrate an orogenic architecture of ridge-trench interactions and provide guidance for evaluating such events during the consumption of major oceans and subsequent formation of orogenic belts worldwide.