Seminar

The Alxa Terrane, the Yagan and Zhusileng-Hangwula arcs (YZHAs) and the Beishan Orogenic Belt (BSOB) provide an ideal window to understand the tectonic evolution of the middle segment of the southern Central Asian Orogenic Belt (CAOB), which is closely associated with the consumption of the Paleo-Asian Ocean (PAO). Despite much work done in the past decade, many uncertainties remain, especially on the nature of the BSOB and the subduction history and closure time of the PAO. This PhD project attempts to address the above-stated uncertainties by integrating new petrologic, geochronological and geochemical results from these tectonic units. The discovery of 900-870 Ma orthogneisses in the BSOB with protoliths of subduction-related I-type granitoids suggests that the BSOB represents Neoproterozoic arcs generated in the circum-Rodinia subduction-accretion system rather than old microcontinents. New zircon U-Pb dating results reveal 460-407 Ma arc-related diorites and granitoids in the Alxa Terrane, indicating that the southward subduction of the PAO commenced in the early Paleozoic. Elemental and isotopic data demonstrate an advancing subduction at 460-440 Ma and a slab roll-back at 420-407 Ma. The final closure of the PAO in the middle segment of the CAOB probably took place in the Early-middle Permian, as evidenced by the marked shift and large variation of isotopic signatures at ca. 280-265 Ma in the Alxa Terrane as well as the notable change of sedimentary provenance between ~276 Ma and ~256 Ma in the YZHAs. By integrating preexisting investigations, a progressively eastward closure of the PAO is inferred.