Linking accretionary orogenesis with supercontinent assembly

Age relations for assembly of Gondwana and Pangea indicate that the timing of collisional orogenesis between amalgamating continental bodies was synchronous with subduction initiation and contractional orogenesis within accretionary orogens located along the margins of these supercontinents. Final assembly of Gondwana occurred between c.570 and 510 Ma, amalgamating the various components of East and West Gondwana. This was coeval with a switch from passive margin sedimentation to convergent margin activity along the Pacific margin of the supercontinent. Timing of subduction initiation along the Pacific margin ranges from 580 to 550 Ma as evidenced by the first appearance of arc derived detrital zircons in the upper Byrd Group sediments and the oldest supra-subduction zone plutons along the Antarctic segment of the margin. A phase of extension marked by supra-subduction zone ophiolite generation at 535–520 Ma is preserved in greenstone successions in eastern Australia and overlaps the onset of Ross–Delamerian contractional orogenesis between 520 and 490 Ma, inboard of the plate margin that coincides with the cessation of collisional orogenesis between the amalgamating blocks of Gondwana. Supra-subduction zone igneous activity was continuous throughout this period indicating that subduction was ongoing.The final stages of assembly of the Pangean supercontinent occurred between c.320 and 250 Ma. Major plate boundary reorganization during this time was accompanied by regional orogenesis along the Pacific margin. The East Gondwana margin segment experienced transpressional and transtensional activity from c.305 Ma until c.270 Ma, after which convergence along the plate margin was re-established. In eastern Australia this involved a migration of arc magmatism eastward into the old subduction complex indicating a stepping out of the plate margin. Synchronous with this phase of plate re-adjustment was the Gondwanide Orogeny (305–230 Ma) affecting the entire Pacific margin of Pangea.Temporal relations across supercontinents between interior collisional and marginal accretionary orogenies suggest a linked history between interior and exterior processes perhaps related to global plate kinematic adjustments. Orogenesis in accretionary orogens occurs in the absence of colliding bodies during ongoing subduction and plate convergence and must therefore be driven by a transitory coupling across the plate boundary. Correspondence of coupling with, or immediately following, subduction initiation and plate boundary reorganization, suggests it may reflect plate re-adjustments involving a temporary phase of increased relative convergence across the plate boundary.