Delineating and characterizing the boundary of the Cathaysia Block and the Jiangnan orogenic belt in South China

• 880–850 Ma arc type rocks exposed within Jiangshan-Shaoxing fault zone at Shijiao.
• The Shijiao area display close affinity with Jiangnan belt rather than Cathaysia.
• Overall relationships constrain the location of suture between Cathaysia and Jiangnan.

The Jiangshan-Shaoxing fault zone lies along the SE margin of the Jiangnan belt, and delineates the northeastern margin of the Cathaysia Block of the South China Craton. At Shijiao in NE Zhejiang, the fault zone consists of hornblende schist intruded by migmatized quartz diorite. It constitutes a shear zone delineating the welded boundary between the Neoproterozoic Shuangxiwu Group of Jiangnan belt to the north and the Chencai Complex of Cathaysia Block to the south. The Shuangxiwu Group is composed mainly of basalt, andesite and flysch, whereas the Chencai Complex contains magmatic and sedimentary rocks that experienced amphibolite facies metamorphism. Zircons from quartz diorite and gabbro from the fault zone at Shijiao yield ages of 854 ± 6 Ma, 857 ± 5 Ma and 860 ± 5 Ma, with positive ɛHf(t) values of 7.81–11.8 and 4.57–10.39. The quartz diorite and mafic-ultramafic rock samples display minor LREE enriched pattern with obvious depletion of Nb, Ta, Rb, Ba and Ti, compared to their neighboring elements and plot in the volcanic arc field on geochemical diagrams, similar to that of volcanic rocks from Shuangxiwu Group. Overall relationships within the Jiangshan-Shaoxing fault zone at Shijiao suggest the ca. 860–850 Ma rock suites were generated in a convergent plate margin and are part of the Jiangnan belt, and not the Cathaysia Block, thus constraining the location of the suture between the two lithotectonic units in NE Zhejiang area during Neoproterozoic.

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