Petrogenesis Research of Basic Rock in the Hongliugou Area of the Altun Orogen Based on Baddeleyite Chronology and Whole-Rock Geochemical Analyses

Previous studies suggest that the Alton Block may have participated in the breakup of the Rodinia supercontinent, however, there have been no prior reports of intraplate basic-ultrabasic rock bodies in the region. A suite of basic-ultrabasic rock bodies has been exposed in the Hongliugou area of the Alton Orogen. An integrated analytical approach utilizing LA-ICP-MS, XRF, ICP-MS, and MC-ICP-MS was employed to systematically investigate the mafic components, including baddeleyite U-Pb geochronology, whole-rock major and trace elements (including rare earth elements), and Sr-Nd isotopic compositions. The results indicate a crystallization age of 748±87Ma for the basic rocks, with geochemical characteristics consistent with the tholeiitic basalt. The Zr/Sm ratio ranges from 26 to 33, and the Zr/Y ratio from 3.2 to 5.5, reflecting the elemental characteristics typical of intraplate basalt. The presence of La, Ba, Nb, Zr, and Th suggests that the magma source region may have experienced alteration by subduction-related fluids. Whole-rock major and trace element analyses, along with Sr and Nd isotopic data, indicate that the basic magma originated from low-degree (<5%) partial melting of the aesthenosphere mantle, with a source region characterized by low garnet content (<1%). These geochemical features imply that the basic-ultrabasic rock bodies discovered in the Alton region formed in a continental rift environment. The Hongliugou mafic rocks exhibit robust temporal and geochemical parallels with Neoproterozoic mafic magmatism documented in the South China and Tarim blocks, both of which have been genetically linked to the Rodinia supercontinent breakup. The temporal congruence (~750Ma) and diagnostic intraplate basalt affinities (tholeiitic series with subduction-modified mantle signatures) observed in these rocks strongly support their classification as petrogenetic products of Rodinia’s rifting episodes.