Geochronological and petrogenetic constraints on the regional tectonic evolution of the Guanghua Group in northeastern Jiao-Liao-Ji Belt, China

A sequence of Paleoproterozoic meta-supracrustal rocks, known as the “Guanghua Group”, is exposed to the north of Tonghua City, Jilin Province, China. The composition and ages of formation and metamorphism of the protolith, and the tectonic petrogenesis of the Guanghua Group are poorly understood. Comprehending these rocks are important in constraining the formation and evolutionary history of the northern segment of the Paleoproterozoic Jiao-Liao-Ji Belt. We have studied the petrology and geochemistry of these meta-supracrustal rocks, revealing that the protoliths can be sub-divided into two groups: metavolcanic and metasedimentary rocks. The metavolcanic rocks are mainly amphibolite, biotite-bearing plagiogneiss, and minor biotite leptynites, whose protoliths were basaltic andesite, andesite, and minor rhyolite with both calc-alkaline and tholeiite affinities. Petrogenetic studies indicate that the intermediate-basic rocks were derived from a depleted lithospheric mantle wedge that was metasomatized by slab-derived fluids or melts. The metasedimentary rocks consist of biotite-quartz schist and staurolite-bearing garnet-muscovite schist, together with minor biotite-bearing plagiogneiss and biotite leptynites, with protoliths mainly comprising mudstone with subordinate sandstone and greywacke. The structure, composition, and U-Pb ages of zircon indicate that the protoliths of the metavolcanic and metasedimentary rocks formed at ca. 2.18 Ga and 2.03 Ga, respectively, and were modified by two stages of metamorphism at ca. 1.90 and 1.85 Ga. The protoliths of the metasedimentary rocks were derived mainly from mid-Paleoproterozoic granites, with minor contributions from coeval metabasic rocks and Archean granitic rocks. Based on these findings and existing regional data, we suggest that: (i) the Paleoproterozoic supracrustal rocks of the Guanghua Group are comparable with the Laoling Group in their age of formation, composition, and petrogenesis, and were the products of the same geological event; meaning that rocks of the Guanghua Group should be considered as part of the Laoling Group; (ii) the metabasic and metasedimentary rocks formed in a back-arc basin setting; and (iii) the pre-mid-Paleoproterozoic formation and evolution of the northern segment of the Jiao-Liao-Ji Belt were related to arc-continent collision.