Late Mesozoic tectonic evolution and thermal history in the northeast Xing'an Block, NE China: Implications for gold mineralization and preservation

Abstract

Late Triassic–Jurassic orogenic and Early Cretaceous epithermal Au deposits are significant producers of Au, Ag, and potentially critical elements (e.g., Te, Se and Sb) in the North Heilongjiang Belt in the Xing'an Block, NE China. However, the preservation mechanism of these Au deposits associated with tectonic evolution is unclear. Here, we conducted zircon U–Pb, sericite Ar–Ar, zircon and apatite (U–Th)/He dating as well as whole‐rock geochemistry in the Xing'an Block. Zircon U–Pb dating shows the ages of 174.1 ± 2.4 Ma for the granodiorite, 169.9 ± 1.6 Ma for the tonalite, 154.0 ± 2.0 Ma for the monzogranite and ca.122 Ma for the diorite. Sericite Ar–Ar dating presents plateau and isochron ages of 163.2 ± 1.8 Ma and 163.4 ± 2.8 Ma. The average apatite (U–Th)/He (AHe) and zircon (U–Th)/He (ZHe) ages from the Jurassic rocks have the ranges of ca. 146–89 Ma and ca. 150–116 Ma and from the Cretaceous are ca. 109–76 Ma and ca. 117–111 Ma, respectively. The Early‐Middle Jurassic intrusions are featured by the tonalite‐trondhjemite‐granodiorite (TTG) rock type. Late Jurassic monzogranite has the geochemical signature of adakitic rocks. The Early Cretaceous granitoids are classified as volcanic arc granites with a part of the Early Cretaceous granodiorite featured by adakitic. These new results reveal five group ages associated with tectonic evolution, Au mineralization and the preservation of the Au deposits. (i) Magmatic events were related to the subduction of the Mongolia‐Okhotsk Ocean during the Early Jurassic (ca. 177–170 Ma) and then the compressional settings with regional deformation (ca. 167–163 Ma). (ii) Thickening crust and orogenic Au mineralization were related to the closure of the Mongolia‐Okhotsk Ocean (ca. 154–145 Ma). (iii) The transformation was from compressional to extensional settings followed by exhumation during the Early Cretaceous (ca. 145–120 Ma), which is the factor of the exhumation of the orogenic Au deposits formed from the Late Triassic to Late Jurassic. (iv) Epithermal Au–Ag mineralization was associated with an extension related to the subduction of the Palaeo‐Pacific Plate (ca. 120–100 Ma). (v) Thermal history shows one thermal event during the Late Cretaceous (ca. 89–76 Ma). The Au deposits have been preserved since the Late Cretaceous.