Paleoproterozoic deep processes and tectono-thermal evolution in the Jiao-Liao Massif

Abstract

New data obtained over the past few years indicate that the North China Craton consisted of the eastern and western blocks that collided along Trans-North China Orogen at 1.85 Ga. Before the collision, the western margin of the eastern block was active continental margin that has been studied in detail. However, the Paleoproterozoic Jiao-Liao-Ji orogenic belt in the eastern margin of the eastern block has received little attention. New multi-disciplinary study indicates that the tectono-thermal evolution and deep processes in the Jiao-Liao-Ji orogenic belt are summarized as following. The early mantle-plume-related underplating at a range from 2.53 to 2.36 Ga led to the 2.47 ∼ 2.33 Ga intrusion of alkaline granite and malfic dyke swarm, the rifting of the Jiao-Liao-Ji rift and the bi-modal volcanism. The early underplating also resulted in not only sedimentary environments in the rift but also the differentiation of the initial thermal architecture in the crust that controlled different metamorphism types and P-T-t paths in he different part of the rift. The later underplating resulted in the formations of the A-type Liaoji Granites of about 2.17 Ga in the lower crust and the pegmatite of 2.2 Ga and 2.0 Ga, and bedding-parallel deformation. However, the main orogenic deformations occurred at a range from 1.911 to 1.883 Ga accompanying with the high-pressure metamorphism in the southern part of the orogen, the closing of the rift and the compressional deformations. Then, from 1.875 to 1.66 Ga, a little lithospheric blocks were delaminated, anorogenic plutons such as rapakivii granite and syenite intruded, the pegmatite veins and mafic dyke swarm developed and crosscut all the structural traces, the Yishulazi Group deposited. Meanwhile, the Dabie-Sulu orogen in the south of the eastern block was an intensive active continental margin at a range from 1.7 to 1.6 Ga. After 1.6 Ga, the Dabie-Sulu orogen underwent a series of crust reworking, evidently differentiating from the major eastern block. In summary, the tectono-thermal evolution in the crust is dominated by the underplating style, collisional processes and delamination types in the deep lithosphere.