Subduction of the Paleo-Pacific Plate plays a key role in the Early Jurassic magmatism evolution in the Yanbian area, Northeast China. In this paper, zircon U–Pb ages, whole-rock geochemical, and Sr–Nd–Hf isotopic compositions are presented. The Early Jurassic gabbros, diorite enclaves, granodiorites, and granites ages range from 183 to 189 Ma. They are characterized by enrichment in large-ion lithophile elements and depletion in high-field strength elements. The gabbros are classified as low- and medium-K tholeiitic, granodiorites and granites are high-K calc-alkaline I-type, and diorite enclaves are calc-alkaline transitional series. The gabbros have zircon εHf(t) values of 6.81–9.89, whole-rock 87 Sr/ 86 Sr (i) = 0.7043–0.7044, and εNd(t) from 2.72 to 2.80. The diorite enclaves have zircons with εHf(t) values of 8.26–12.80, whole-rock 87 Sr/ 86 Sr (i) = 0.7051, and εNd(t) from 0.96 to 1.09. The granodiorites and granites have zircon εHf(t) values of 7.59–12.87, whole-rock 87 Sr/ 86 Sr (i) = 0.7042–0.7066, and εNd(t) from 2.33 to 2.61. These data indicate that gabbroic magmas were derived from partial melting of a depleted mantle wedge metasomatized by subduction-related fluids. The basaltic magma underplated and heated the juvenile crust, whereas the granodiorites and granites might be the product of fractional crystallization of a mixture of basaltic and felsic magmas or derived from partial melting of the juvenile lower crust. Our data constrain the petrogenesis of these Early Jurassic intrusive rocks which are attributed to subduction of the Paleo-Pacific Plate beneath Eurasia continent in northeastern China.
The Biliya Ag-Pb-Zn polymetallic (SLZP) deposit (16.5 Mt, @ 52.9 g/t Ag, 2.6% Pb and 2.3% Zn) lies in the Great Xing'an Range, Northeast China. Breccia-, veinlet- and vein-type Ag-Pb-Zn ore bodies are primarily hosted in the quartz porphyry, trachyandesite and rhyolitic tuff. They are spatially and temporally related to andesitic porphyry. Three mineralization processes are identified: stage I: grey quartz - pyrite + tawny sphalerite (high Cd2+), stage II: grayish white quartz - pyrite + grey sphalerite (high Fe2+) + galena + argentite + tetrahedrite, stage III: white quartz-pyrite. The alterations consist of quartz + sericite, illite + quartz, fluorite + calcite + opal and chlorite zone. The silver-lead–zinc mineralization primarily corresponds to stage II. Five sulfide samples from stage II yielded a well-fitted isochron age of 131.3 ± 2.4 Ma (MSWD = 2.4), marking the timing of Ag-Pb-Zn polymetallic mineralization. CO2-bearing NaCl-H2O (C), gaseous CO2 (V); vapour-liquid H2O-NaCl (WL) and fluid-phase H2O-NaCl (L)-type of fluid inclusions were distinguished. Their petrographic and microthermometric features and H-O isotopic data suggest that the hydrothermal fluids were initially originated from magmatic source, with intensive mixing with meteoric water and that their temperatures and salinities are 254–130 ℃ and 7.15–1.22 wt% NaCl eqv, respectively, belonging to a reduced fluid (CO2-H2O-NaCl ± CH4) system. In-situ S and bulk Pb isotope analyses indicate that the metal materials were related to andesitic magma from the lower crust. The deposit geology, fluid inclusions, stable isotopes and chronology results suggest that the Biliya deposit belongs to a low-sulfidation (LS) epithermal SLPZ deposit. Boiling and fluid immiscibility coupled with suddenly decreasing in temperature, pressure, logfS2 of the hydrothermal fluids are likely to play important roles in Biliya SLPZ ore deposition.
Late Mesozoic intermediate–felsic volcanics and hypabyssal intrusions are common across the western slope of the Great Xing’an Range (GXAR). Spatiotemporally, these hypabyssal intrusions are closely associated with epithermal Pb–Zn polymetallic deposits. However, few studies have investigated the petrogenesis, contributions and constraints of these Pb–Zn polymetallic mineralization-related intrusions. Therefore, we examine the representative Erdaohezi deposit and show that these mineralization-related hypabyssal intrusions are composed of quartz porphyry and andesite porphyry with concordant zircon U–Pb ages of 160.3 ± 1.4 Ma and 133.9 ± 0.9 Ma, respectively. These intrusions are peraluminous and high-K calc-alkaline or shoshonitic with high Na2O + K2O contents, enrichment in large ion lithophile elements (LILEs; e.g., Rb, Th, and U), and depletion in high field strength elements (HFSEs; e.g., Nb, Ta, Zr, and Hf), similar to continental arc intrusions. The zircon εHf(t) values range from 3.1 to 8.0, and the 176Hf/177Hf values range from 0.282780 to 0.282886, with Hf-based Mesoproterozoic TDM2 ages. No differences exist in the Pb isotope ratios among the quartz porphyry, andesite porphyry and ore body sulfide minerals. Detailed elemental and isotopic data imply that the quartz porphyry originated from a mixture of lower crust and newly underplated basaltic crust, while the andesite porphyry formed from the partial melting of Mesoproterozoic lower crust with the minor input of mantle materials. Furthermore, a magmatic–hydrothermal origin is favored for the Pb–Zn polymetallic mineralization in the Erdaohezi deposit. Integrating new and published tectonic evolution data, we suggest that the polymetallic mineralization-related magmatism in the Erdaohezi deposit occurred in a back-arc extensional environment at ~133 Ma in response to the rollback of the Paleo-Pacific Plate.
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