A Paleoproterozoic nappe on Meso‑Archean gneisses exhumed by a Cretaceous metamorphic core complex in northeastern North China Craton

摘要

The Paleoproterozoic Jiao-Liao-Ji Orogenic Belt provides key evidence of evolution from an early rift-basin (or back-arc basin) to final collision of the Longgang block (Eo-Meso Archean granitic gneiss) and the Nangrim block in the Liaodong peninsula, northeastern North China Craton. A structural investigation of schists and phyllites in the Langzishan Formation of the North Liaohe Group reveals two new major structures: (1) a sub-horizontal nappe on Meso-Archean granitic gneiss belonging to a similar to 1.95-1.9 Ga Paleoproterozoic D1-2 fold-thrust system produced by terminal collision; From the south basin to the north basement, the metamorphic gradient transferred from greenschist facies metamorphism into amphibolite facies produced by crustal thickening in the Paleoproterozoic orogenesis; the intensity of deformation was also increasing from south to north, the pure shearing style changed into simple shearing. (2) A metamorphic core complex (The Gongchangling metamorphic core complex) formed during Cretaceous extension and doming enabled delamination and diapiric rise and exhumation in the core complex. This extensional-delamination event affected a wide area of the orogenic belt, as part of the delamination of the northeastern half of the North China Craton. This is the first example of the Paleoproterozoic thrust-nappe tectonics exhumed and preserved by Cretaceous diapirism in northeast China.