Yun-Sheng Ren

Geochronological and geochemical constraints on the Erguna massif basement, NE China – subduction history of the Mongol–Okhotsk oceanic crust

We present new geochronological and geochemical data for granites and volcanic rocks of the Erguna massif, NE China. These data are integrated with previous findings to better constrain the nature of the massif basement and to provide new insights into the subduction history of Mongol–Okhotsk oceanic crust and its closure. U–Pb dating of zircons from 12 granites previously mapped as Palaeoproterozoic and from three granites reported as Neoproterozoic yield exclusively Phanerozoic ages. These new ages, together with recently reported isotopic dates for the metamorphic and igneous basement rocks, as well as Nd–Hf crustal-residence ages, suggest that it is unlikely that pre-Mesoproterozoic basement exists in the Erguna massif. The geochronological and geochemical results are consistent with a three-stage subduction history of Mongol–Okhotsk oceanic crust beneath the Erguna massif, as follows. (1) The Erguna massif records a transition from Late Devonian A-type magmatism to Carboniferous adakitic magmatism. This indicates that southward subduction of the Mongol–Okhotsk oceanic crust along the northern margin of the Erguna massif began in the Carboniferous. (2) Late Permian–Middle Triassic granitoids in the Erguna massif are distributed along the Mongol–Okhotsk suture zone and coeval magmatic rocks in the Xing’an terrane are scarce, suggesting that they are unlikely to have formed in association with the collision between the North China Craton and the Jiamusi–Mongolia block along the Solonker–Xra Moron–Changchun–Yanji suture zone. Instead, the apparent subduction-related signature of the granites and their proximity to the Mongol–Okhotsk suture zone suggest that they are related to southward subduction of Mongol–Okhotsk oceanic crust. (3) A conspicuous lack of magmatic activity during the Middle Jurassic marks an abrupt shift in magmatic style from Late Triassic–Early Jurassic normal and adakite-like calc-alkaline magmatism (pre-quiescent episode) to Late Jurassic–Early Cretaceous A-type felsic magmatism (post-quiescent episode). Evidently a significant change in geodynamic processes took place during the Middle Jurassic. Late Triassic–Early Jurassic subduction-related signatures and adakitic affinities confirm the existence of subduction during this time. Late Jurassic–Early Cretaceous post-collision magmatism constrains the timing of the final closure of the Mongol–Okhotsk Ocean involving collision between the Jiamusi–Mongolia block and the Siberian Craton to the Middle Jurassic.

Geochronology, petrogenesis, and tectonic setting of Mesozoic volcanic rocks, southern Manzhouli area, Inner Mongolia

We have undertaken major and trace element analyses of volcanic rocks in Northeast China, as well as U–Pb dating and Hf isotopic analysis of their zircons, in order to determine the petrogenesis and tectonic setting of the volcanics. Mesozoic volcanism in the southern Manzhouli area occurred in two stages: Middle to Late Jurassic (164–147 Ma) and Early Cretaceous (142–123 Ma). The first stage is represented by the Tamulangou, Jixiangfeng, and Qiyimuchang formations. The Jixiangfeng Formation (162–156 Ma) is a rhyolite–trachyte dominated unit that lies between two basalt units, namely the underlying Tamulangou (164–160 Ma) and overlying Qiyimuchang (151–147 Ma) formations. The second igneous stage is dominated by rhyolitic lavas and tuffs of the Shangkuli Formation and basaltic rocks of the Yiliekede Formation, and they yield zircon U–Pb ages of 142–125 and 135–123 Ma, respectively. Basaltic rocks of the Tamulangou and Yiliekede formations have a wide range of MgO contents (1.64–9.59 wt%), but are consistently depleted of Nb and Ta and enriched with incompatible trace elements such as large ion lithophile elements (LILEs) and light rare earth elements (LREEs). Trachytes and rhyolites of the Jixiangfeng and Shangkuli formations are characterized by enrichment in LILEs and LREEs relative to HFSEs and HREEs, and with negative Nb, Ta, P, and Ti anomalies and positive ϵ Hf(t) values (3.49–9.98). These data suggest that basaltic volcanic rocks in southern Manzhouli were generated by fractional crystallization of a common parental magma, which was derived by partial melting of metasomatized (enriched) lithospheric mantle, whereas the trachytic and rhyolitic magmas were produced by the melting of lower crustal mafic and felsic granulites, respectively. Geochronological data indicate that Mesozoic volcanism in southern Manzhouli was initiated in the Middle to Late Jurassic and continued into the Early Cretaceous. It was mainly induced by lithospheric extension after the closure of the Mongol–Okhotsk Ocean.

Geochemical and Hf isotopic compositions of Late Triassic–Early Jurassic intrusions of the Erguna Block, Northeast China: petrogenesis and tectonic implications

ABSTRACT Late Triassic–Early Jurassic intrusions of the Erguna Block, Northeast China, are located along the southern margin of the Mongol–Okhotsk orogenic belt. They comprise granodiorite, monzogranite, syenogranite, and lesser gabbro–diorite, of adakitic and calcalkaline affinity. The adakite-like and calcalkaline granites share similar light rare earth elements (LREE) characteristics; however, their heavy rare earth elements (HREE) trends differ from one another. The relative abundances of HREE in the calcalkaline granites are relatively consistent and are similar to those of intrusive rocks formed from dehydration melting of garnet-free amphibolitic source rocks at relatively low pressures. In contrast, the adakite-like granites show more prominent HREE fractionation trends, indicating that they crystallized at higher pressures, where garnet in the source rocks was stable. At least two isotopically distinct sources were involved in the petrogenesis of the granites, but the extent to which they contributed varies between plutons. Most intrusions have incorporated an isotopically primitive component, possibly juvenile mafic crust. The other sources include a small proportion of old continental crustal material and isotopically evolved wall rocks. The gabbro–diorites have high MgO contents (>7 wt.%), a high Mg# (>0.6), and show moderate LREE and HREE fractionation, indicating they formed from the melting of subducted metasomatized lithospheric mantle. All of the intrusions in the study area are characterized by a relative enrichment in large ion lithophile elements (LILE) and depletion in high field strength elements (HFSE), indicating they were emplaced in an Andean-type active continental margin setting related to southward subduction of the Mongol–Okhotsk oceanic plate.

Re–Os Isotopic Dating of the Molybdenite from the Tongshan Porphyry Cu–Mo Deposit in Heilongjiang Province, NE China

Strata outcropped in Tongshan area is mainly composed of the Middle Ordovician Tongshan Fm. and Duobaoshan Fm. The Ordovician granodiorite intrusions spread widely. The NW–trending reversed S–shaped structures control the occurrence of alteration and mineralization. Four ore bodies have been identified in the deposit. No. III ore body, also in the footwall of the Tongshan fault, is the largest and the major ore body in the area, with 1140 m in length, more than 800 m along the dip. Metallic minerals account for 3–7% of the minerals in the ore, primarily pyrite and chalcopyrite, with some molybdenite, bornite, galena, sphalerite, etc.. Wall–rock alteration is well developed in the Tongshan deposit, and from southwest to northeast are successively potassium–silicification zone, sericite–silicification zone and propylitization zone. The data mentioned in this paper and previous studies (Zhao et al., 1997, 2011; Wu et al., 2009) demonstrate that the Tongshan is a porphyry Cu–Mo deposit. 2 Molybdenite Re–Os Isotopic Analysis

Detrital provenance, depositional environment, and palaeogeographic implications of Lower Triassic marine sediments in central Tibet

ABSTRACT We present our new investigation into the depositional environment and provenance of the Yingshuiquan Formation in the central Qiangtang region of northern Tibet, in order to further our understanding of the environment of the Longmu Co–Shuanghu Palaeo–Tethys during the Early Triassic. The Yingshuiquan Formation is composed of oolitic limestone, calcareous sandstone, calcarenite, thin-bedded ribbon limestone, bioclastic limestone, and coarse oolite limestone that were deposited in a shallow-marine basin and contain abundant Lower Triassic conodont fossils (e.g. Hadrodontina anceps, Pachycladina sp., gen. et sp, Pachyclaina oblique, Hibbardelloides sp). We selected detrital zircons from four calcareous sandstone samples for U–Pb dating, yielding minimum age peaks of 263, 269, 275, and 280 Ma, respectively, and a minimum age of 249 Ma, based on several zircons around the same age. Analysis of the conodont biofacies and zircon LA-ICP-MS dating of calcareous sandstone indicates that the data is consistent with deposition in the Early Triassic. The Yingshuiquan Formation records Early Triassic shallow-water sediment in the Longmu Co–Shuanghu Palaeo–Tethys, and has a Southern Qiangtang and Northern Qiangtang terranes provenance. During the Early Triassic, the carbonate sediments of the Yingshuiquan Formation were deposited in an active environment around the Longmu Co–Shuanghu Palaeo–Tethys, which has became a residual sea basin.

Sulfur and Lead Isotope Characteristics of Naozhi Gold Deposit in Yanbian Area (NE China) and Their Metallogenetic Implications

metallogenic provinces in the Northeast China. It is located in the Circum-Pacific Metallogenic Belt and developed many deposits including porphyry, skarn and epithermal ore deposit types. Although the Naozhi gold deposit, one of the representative deposits, was discovered earlier, its source of ore-forming materials and ore genesis remain in debate. This paper discusses sulfur and lead isotopic characteristics of sulphides from the ore in Naozhi gold deposit, comparison with those data in several other deposits in Yanbian area, which is helpful for determining the metallogenetic material source and ore genesis of the Naozhi deposit.