Abstract
The Central Asian Orogenic Belt is sandwiched between the Siberian, East European (Baltica), Tarim, and North China cratons, which contain several Precambrian micro-continental blocks, such as the Kazakhstan-Yili-Central Tianshan blocks, the Junggar Block and the Amuria Block. The tectonic nature and positions of these micro continental blocks are unclear and disputed in many supercontinent reconstructions. In particular, the position of the Amuria Block in the eastern Central Asian Orogenic Belt, which is important for the reconstructions of the Precambrian Rodinia supercontinent, remains unknown because of the lack of late Palaeoproterozoic to Neoproterozoic geological and geochronological data. The Erguna Block, a part of the Amuria Block in NE China, has been considered as a constituent block of the Rodinia supercontinent. However, the late Palaeoproterozoic to Neoproterozoic tectonic evolution of the Erguna Block with respect to the assembly and break-up of Rodinia remains poorly understood. Here we present zircon U-Pb-Hf-O isotopic data and whole-rock elemental data of the newly discovered late Palaeoproterozoic and Neoproterozoic records in the northern Erguna Block. The gneissic granites have protolith and metamorphic ages of 1839 & PLUSMN; 24 and 497 & PLUSMN; 6 Ma, respectively, and relatively uniform two-stage Hf model ages (TDM1) of 2.67-1.26 Ga, indicating that the Erguna Block has a Palaeoproterozoic crystalline basement. The zircon U-Pb ages for the Neoproterozoic intrusive rocks define two stages of magmatism in early Neoproterozoic (Stage 1; i.e., ca. 946 Ma) and middle Neoproterozoic (Stage 2; i.e., 833-737 Ma), respectively, implying that the Erguna Block had switched to an intra-continental extensional setting (833-737 Ma) after the early Neoproterozoic (ca. 946 Ma) convergence-accretion. A comparison of data from the Erguna Block and its adjacent units reveals that the Erguna and Central Mongolia blocks were likely in a single crustal entity with the Tarim Craton associated with the Rodinia assembly at ca. 900 Ma. This composite block then detached from the Tarim Craton at ca. 800 Ma following the break-up of Rodinia, and drifted southwards to the vicinity of the Siberia Craton during the Cambrian.
NSTL
Elsevier