Neoproterozoic A -type granites in northern Beishan Orogenic Belt: Early response of the Rodinia supercontinent break-up

The Beishan Orogenic Belt is located in the southern margin of the Central Asian orogenic belt ( CAOB) and there are several Precambrian microcontinents in the belt. A correct understanding of these Precambrian microcontinents is the key to the study of structural framework division and tectonic evolution process of the orogenic belt. In this paper, the Xiaoguliang gneissic syenogranite from the Mingshui block in the northern belt of Beishan is selected for petrology, zircon U-Pb chronology, element geochemistry and Hf isotope analysis. The results show that the LA-ICP-MS zircon U-Pb age of the Xiaoguliang gneissic syenogranite is 784 +/- 2. 7Ma, revealing the existence of Neoproterozoic basement rocks in the northern belt of Beishan. The whole rock samples are high in SiO2 ( 72.22% similar to 74. 06%), ALK (7.50% similar to 8. 33%), Zr + Y + Nb + Ce (567.6 x 10(-6) similar to 644.7 x 10(-6)) and 10000 x Ga/A1 ( 2. 71 similar to 2. 81), low in Al2O3, (12. 39% similar to 12. 95%), MgO (0.40% similar to 0. 54%) and CaO (0. 91% similar to 1. 38%). The trace elements are rich in Rb, K, Th and U and poor in Sr, Nb, Ta, P and Ti. All samples are enriched in LREE and depleted in HREE with obvious negative Eu anomaly. Calculated by zirconium saturation temperature, the crystallization temperature of Xiaoguliang gneissic syenogranite is 824 -859 degrees C. Combined with the geochemical characteristics above, the Xiaoguliang gneissic syenogranites should be defined as A -type granite. The zircon epsilon(Hf) (t) values ranges from - 19. 55 to - 13. 81, which are all negative values. t, model ages from 1.56 to 1. 33Ga and t(DM2) model ages from 2. 02 to 1. 65 Ga, indicating that there magma source may be originated from Paleoproterozoic crust partial melting. Al -type granites showed in the diagrams of tectonic setting discrimination imply that the Xiaoguliang gneissic syenogranites were most likely the products of continental rifting magmatism. Combined with regional geological data and previous research results, the Xiaoguliang gneissic syenogranite may be the earliest granitic record in response to the break-up of the Rodinia supercontinent in the Beishan Orogenic Belt.

Automated summary

The study reveals the presence of Neoproterozoic basement rocks in the Beishan Orogenic Belt, specifically in the Xiaoguliang gneissic syenogranites in the northern belt. These syenogranites exhibit characteristics of A-type granite and are likely products of continental rifting magmatism. The findings suggest that the Xiaoguliang gneissic syenogranites may be the earliest granitic record in response to the break-up of the Rodinia supercontinent in the Beishan Orogenic Belt.