An arc terrane separated from the Yangtze Craton during Rodinia breakup: Insights from Neoproterozoic sedimentary successions of the Erguna Block, Northeast China

Abstract

The Central Asian Orogenic Belt (CAOB) is one of the largest and most complex accretionary systems and is responsible for considerable Phanerozoic juvenile crustal growth. The Erguna Block is a Precambrian microcontinent located in the eastern part of the CAOB. Controversy has long surrounded the origin and tectonic affinity of the Erguna Block, limiting reconstruction of its position in the supercontinent Rodinia. This study presents a systematic study of the petrology, whole-rock geochemistry and zircon U-Pb-Hf isotopes of metasedimentary rocks from the Ergunahe Formation, the Jiageda Formation and the Xinghuadukou Group, which are the oldest units in the Erguna Block. The samples from the Ergunahe Formation comprise phyllite and schist with detrital zircon ages of 2476–743 Ma, maximum protoliths depositional ages of 817–743 Ma and peaks at 763 Ma, 896 Ma and 1162 Ma, εHf_(t) values of −15.54 to +11.66 and T_DM2 model ages of 3464–978 Ma. The Jiageda Formation samples include metasandstone, metapelite and schist with detrital zircon ages of 2976–766 Ma, maximum protoliths depositional ages of 837–766 Ma and peaks at 776 Ma, 843 Ma, 918 Ma and 984 Ma, εHf_(t) values of −9.46 to +14.68 and T_DM2 model ages of 3207–866 Ma. From the Xinghuadukou Group, schists are studied with detrital zircon ages of 2908–785 Ma, maximum protoliths depositional ages of 839–785 Ma and peaks at 837 Ma and 907 Ma, εHf_(t) values of −14.35 to +12.68 and T_DM2 model ages of 3949–926 Ma. The protoliths of the metasedimentary rocks from the three groups have similar depositional age spans and source rocks. They are mainly siltstones and greywackes and represent a sedimentary sequence in a continental arc-related basin. The source rocks for the protoliths were mainly arc magmatic rocks in the Erguna Block, which were formed in a continental arc as oceanic lithosphere subducted during the assembly and break-up of the Rodinia supercontinent. Combined with existing data, the age spectrum and multidimensional scaling (MDS) analysis of detrital zircon indicate the Erguna Block originated from a continental arc at the margin of the Yangtze Craton. Long-term subduction at ca. 963–737 Ma accompanied by back-arc extension during ca. 904–737 Ma led to rifting of the Erguna Block off the Yangtze Craton. Neoproterozoic sedimentary rock assemblages from the Erguna Block were deposited in a large-scale long-term trench-arc-basin system that formed in front of the Yangtze Craton, along the northwest margin of Rodinia.