Geochemical and SIMS U-Pb rutile and LA-ICP-MS U-Pb zircon geochronological evidence of the tectonic evolution of the Mudanjiang Ocean from amphibolites of the Heilongjiang Complex, NE China

摘要

This study presents new secondary-ion mass spectrometry (SIMS) rutile and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb geochronological and whole-rock geochemical data for amphibolites of the Heilongjiang Complex, located within the Yilan area of NE China, to constrain the tectonic evolution of the Mudanjiang Ocean between the Songnen-Zhangguangcai Range and Jiamusi massifs. Magmatic zircon from amphibolites collected from the Yilan Marble Quarry yields a weighted mean Pb-206/U-238 age of 274 +/- 2 Ma, which is interpreted as the protolithic age. Amphibolites from the Longlangang and Tuanshanzi areas yield rutile U-Pb ages of 177 +/- 11 Ma and 172 +/- 5 Ma, respectively, which are interpreted to reflect the cooling of these rocks below the closure temperature of Pb diffusion in ruble. Amphibolites from the Yilan Marble Quarry are enriched in light rare earth elements (LREEs) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta and P) relative to large ion lithophile elements (LILEs). Amphibolites from the Longlangang and Tuanshanzi areas have relatively flat chondrite-normalized rare earth element (REE) patterns, and remarkable negative Nb and Ta anomalies. Moreover, all of the amphibolites from the Heilongjiang Complex in the Yilan area have tholeiitic and arc-type geochemical affinities. These amphibolites formed by similar petrogenetic processes, but from distinct mantle sources. The magmas that formed these units were generated by the partial melting of mantle sources metasomatized by subducted slab fluids, and the magma that formed the amphibolites within the Yilan Marble Quarry may have also incorporated sedimentary material. Mantle peridotite from the garnet-spinel transition zone is a possible source for the protolith of amphibolites in the Yilan Marble Quarry, and spinel-peridotites may have been the magma sources for the protoliths of amphibolites in the Longlangang and Tuanshanzi areas. Combining our dat