A Paleoproterozoic complex in the Hong' an orogenic belt, central China: New evidence for a Paleoproterozoic collisional orogenic belt in the Yangtze Block.

The relationship between the Yangtze Block (YTB) and the supercontinent Columbia remains unclear. Our new identification of Jinpen Complex in the southern Hong' an orogenic belt provides new constraints on the Palaeoproterozoic tectonic evolution of the YTB. Emplacement ages of the gneissic monzogranite, trondhjemite and mafic dyke are 2478 +/- 5 Ma, 2049 +/- 16Ma, and 1999 8Ma, respectively. Trondhjemites are rich in SiO2 (71. 62% similar to 76. 92%) and Na2O (4. 58% similar to 6. 47%), depleted in K-2 O (0. 50% similar to 1. 06%), FeOT + MgO (0. 81% similar to 3. 86%), Y (5. 34 X 10(-6) similar to 14. 7 X 10(-6)) and Yb (0. 55 X 10(-6) - 1. 07 x 10(-6)), with variable Sr/Y (10. 9 - 28. 5) and (La/Yb) N (4. 7 - 21. 6) ratios and enriched zircon Hf isotope values (e, (t) = - 13. 1 3. 4). These features suggest that the trondhjemites were derived from partial melting of a basaltic source at the base of a thickened magmatic arc, with garnet and amphibole in residuals. The mafic dykes have high Nb contents (11. 4 x 10 -6 - 14. 8 x 10 -6) with high Nb/U (19. 2 similar to 23. 6), Nb/La (0. 53 similar to 0. 65) and Nb/Th (3. 71 similar to 4. 67) ratios. Their primitive mantle -normalized trace element patterns are characterized by enrichment of light rare-earth element and large -ion lithophile elements, but depletion of HREE and HFSE. Zircons from the mafic dyke display negative epsilon(Hf) (t) values (- 11 similar to 5. 6), and whole -rock samples show negative epsilon(Nd)(t) values (- 3. 47 similar to - 2. 47). Geochemical signatures suggest that mafic dyke in this study were derived from an enriched subarc mantle and underwent some degrees of crustal contamination. On the basis of our new data and the data from Paleoproterozoic rocks in the YTB, we propose a 2. 15 - 1. 95Ga subduction-collision zone along Huangling-Zhongxiang. The western YTB finally collided with the eastern YTB along this zone during 2. 0 similar to 1. 95 Ga to form the united YTB, favoring tight linkage between YTB and the proposed Columbia.