Early Mesozoic Granitoids Research Articles

Early Mesozoic southward subduction history of the Mongol–Okhotsk oceanic plate: Evidence from geochronology and geochemistry of Early Mesozoic intrusive rocks in the Erguna Massif, NE China

In this paper we present new zircon U–Pb ages, Hf isotope data, and whole-rock major and trace element data for Early Mesozoic intrusive rocks in the Erguna Massif of NE China, and we use these data to constrain the history of southward subduction of the Mongol–Okhotsk oceanic plate, and its influence on NE China as a whole. The zircon U–Pb dating indicates that Early Mesozoic magmatic activity in the Erguna Massif can be subdivided into four stages at ~246Ma, ~225Ma, ~205Ma, and ~185Ma. The ~246Ma intrusive rocks comprise a suite of high-K calc-alkaline diorites, quartz diorites, granodiorites, monzogranites, and syenogranites, with I-type affinities. The ~225Ma intrusive rocks consist of gabbro–diorites and granitoids, and they constitute a bimodal igneous association. The ~205Ma intrusive rocks are dominated by calc-alkaline I-type granitoids that are accompanied by subordinate intermediate–mafic rocks. The ~185Ma intrusive rocks are dominated by I-type granitoids, accompanied by minor amounts of A-types. These Early Mesozoic granitoids mainly originated by partial melting of a depleted and heterogeneous lower crust, whereas the coeval mafic rocks were probably derived from partial melting of a depleted mantle modified by subduction-related fluids. The rock associations and their geochemical features indicate that the ~246Ma, ~205Ma, and ~185Ma intrusive rocks formed in an active continental margin setting related to the southward subduction of the Mongol–Okhotsk oceanic plate. The ~225Ma bimodal igneous rock association formed within an extensional environment in a pause during the subduction process of the Mongol–Okhotsk oceanic plate. Every magmatic stage has its own corresponding set of porphyry deposits in the southeast of the Mongol–Okhotsk suture belt. Taking all this into account, we conclude the following: (1) during the Early Mesozoic, the Mongol–Okhotsk oceanic plate was subducted towards the south beneath the Erguna Massif, but with a pause in subduction at ~225Ma; and (2) the southward subduction of the Mongol–Okhotsk oceanic plate not only caused the intense magmatic activity, but was also favorable to the formation of porphyry deposits.

Petrogenesis of Indosinian Granitoids in Middle‐Segment of South Qinling Tectonic Belt: Constraints from Sr‐Nd Isotopic Systematics

Abstract:South Qinling Tectonic Belt (SQTB) is located between the Shangzhou‐Danfeng and Mianxian‐Lueyang sutures. There are a lot of early Mesozoic granitoid plutons in its middle segment, comprising the Dongjiangkou‐Zhashui granitoid plutons at the northeast, Huayang‐Wulong‐Laocheng granitoid plutons at the central part, Xiba granitoid pluton at the northwest and Guangtoushan‐Liuba granitoid plutons at the southwest. These Indonisian granitoids contain a mass of various scale mafic enclaves, which show sometimes clear boundaries and sometimes transitional boundaries with their host granitoids. These granitoids also exhibit metaluminous to peraluminous series, commonly higher Mg# and a wide range of petrochemistry from low‐K tholeiite series, through mid‐K and high‐K calc‐alkaline series to shoshonite series and predominated samples are attributed to mid‐K and high‐K calc‐alkaline series. Detailed analyses in Sr‐Nd isotopic systematics and petrochemistry reveal that there may be regionally initial granitoid magma of the Indonisian granitoid plutons, comprising Dongjiangkou‐Zhashui, Huayang‐Wulong‐Laocheng, Xiba, and Guangtoushan‐Liuba granitoid plutons, which were produced by hybrids of magmas in various degrees, and the initial magmas were derived from both the mantle and the lower continental crust (LCC) sources in the SQTB. The initial granitoid magma further did the magma hybrid with the magmas from the LCC, crystallization fractionation, and assimilation with upper crustal materials during their emplacement to produce these granitoid plutons in the SQTB. These magmatism processes are most likely to occur under continent marginal arc and syn‐collision to post‐collision tectonic backgrounds.

Late Palaeozoic–Early Mesozoic geological features of South China: Response to the Indosinian collision events in Southeast Asia

This paper provides some new evidences on stratigraphic sequence, zircon SHRIMP dating from ophiolite, granitoids, and fold-and-thrust tectonic styles in the South China Block (SCB). Stratigraphic studies suggest that the eastern and central parts of the SCB show a SW-dipping palaeoslope framework during the Late Palaeozoic–Early Mesozoic. These areas were not in a deep-sea environment, but in a shallow-sea or littoral one. Coeval volcanic rocks are missing. Deep-water deposits and submarine volcanism only took place in the western part of the SCB. The three ophiolitic mélanges of the eastern SCB formed in the Neoproterozoic, but not in the Permian or the Triassic. The sedimentary rocks associated with the Neoproterozoic oceanic relics contain abundant Proterozoic acritarchs, but no radiolarians. The Early Mesozoic granitoids (235–205 Ma) belong to the post-collision peraluminous S-type granites; they are widely exposed in the central-western SCB, and rare in the eastern SCB. The fold-and-thrust belt developed in the eastern SCB shows a top-to-the-south displacement, whereas the Xuefengshan Belt of central SCB indicates a north- or northwest-directed shearing. The geodynamic settings of the different parts of the SCB during the Triassic are discussed.

Age and geochemistry of the Early Mesozoic granitoid massifs of the southern Bureya terrane of the Russian Far East

A massif of porhyritic microcline biotite granites located in the southern part of the Bureya (Turan) terrane has an age of 185 ± 1 Ma. The granites are characterized by (K2O + Na2O) > 8%, a K2O predominance over Na2O, and a moderately differentiated REE distribution pattern ((La/Yb)n = 14.7–28.5). The obtained age indicates that at least one stage of the Early Mesozoic granitoid magmatism in the Bureya terrane occurred in the Early Jurassic. The formation of early Mesozoic granitoids was presumably related to collision between North Asian and Sino-Korean cratons, and the intervening Amur superterrane, although a subduction origin also cannot be completely ruled out.

中部地方，飛騨帯花崗岩類の起源物質の多様性

中部地方，飛騨帯花崗岩類の起源物質の多様性

Mesozoic granitic magmatism in extensional tectonics near the Mongolian border in China and its implications for crustal growth

The Yagan area of the southernmost Sino–Mongolian border is characterized by an extensional structure where a large metamorphic core complex (Yagan–Onch Hayrhan) and voluminous granitoids are exposed. New isotopic age data indicate that the granitoids, which were previously regarded as Paleozoic in age, were emplaced in early and late Mesozoic times. The early Mesozoic granitoids have 228±7 Ma U–Pb zircon age, and consist of linear mylonitic quartz monzonites and biotite monzogranites. Their chemical compositions are similar to those of potassic granites and shoshonitic series, and show an intraplate and post-collisional environment in tectonic discrimination diagrams. Their fabrics reveal that they experienced syn-emplacement extensional deformation. All these characteristics suggest that the adjustment, thinning and extensional deformation at middle to lower crustal levels might have occurred in the early Mesozoic. The late Mesozoic granitoids have a U–Pb zircon age of 135±2 Ma, and are made up of large elliptical granitic plutons. They are high-K calc-alkaline, and were forcefully emplaced in the dome extensional setting. Both the early and late Mesozoic granitoids have εNd ( t) values of −2.3 to +5, in strong contrast with the negative εNd ( t) values (−11) of the Precambrian host rocks. This suggests that juvenile mantle-derived components were involved in the formation of the granitoids. The similar situation is omnipresent in Central Asia. This study demonstrates that tectonic extension, magmatism and crustal growth are closely related, and that post-collisional and intraplate magmatism was probably a significant process for continental growth in the Phanerozoic.

Regional geologic setting and metallogenesis of central Inner Mongolia, China: guides for exploration of mesothermal gold deposits

The central Inner Mongolia district forms one of the most important metallogenic provinces in China, because the district has been influenced by repeated distinct tectonomagmatic activity. The genetic relationships and spatial–temporal evolution of ancient tectonism and associated geologic structures and metallogeny are discussed in this paper. An integrated genetic model for gold metallogeny is proposed. During the late Archean to Paleozoic, repeated north-southward accretional tectonics between the Paleo-Mongolia Oceanic Plate and the North China Paleoplate led to the formation of not only the E–W-trending deep crustal faults but also a series of sedimentary, volcanic and metamorphic events. Numerous stratiform, Fe, Cu (Au), Pb–Zn and REE ores formed in association with sedimentation and volcanism within the platform environments at this time. During the late Paleozoic to early Mesozoic, the central Inner Mongolia district was largely influenced by northwestward subduction of the Circum-Pacific Plate beneath the Eurasia Plate. A series of NE–SW-trending faults, together with S-type granitoid intrusions, formed as a result of this subduction. Mesothermal-type gold deposits (e.g., the Saiyingwusu, Laoyanghao, Shibaqin, Wulashan and Donghuofang deposits) formed during the Permian to Jurassic (158.5 to 275.4 Ma), preferentially at or near the intersections between NE–SW-trending and E–W-trending fault systems. At these intersections, the areas of not only late Paleozoic to early Mesozoic granitoids but also late Archean to early Proterozoic metamorphic rocks (especially the gold-rich, Seertengshan, Wulashan and Bayan Obo group rocks) may be promising exploration targets for mesothermal gold deposits.

Continental crust subduction and collision along Shangdan Tectonic Belt of East Qinling, China——Evidence from Pb, Nd and Sr isotopes of granitoids

The East Qinling orogenic belt can be divided into North and South Qinling erogenic belts by the Shangdan fault. The granitoids, especially the late Paleozoic - early Mesozoic granitoids, are widely distributed in North Qinling and South Qinling orogenic belts. Pb, Nd and Sr isotopic compositions and some trace element ratios for the collision-type granitoids were measured. The data are used to evaluate the granitic magma source and to probe the chemical composition of deep crust where the granitic intrusions were emplaced. The studies indicate that the South Qinling collision-type granitoids came from the South Qinling middle-lower crust and the North Qinling collision-type granitic batholiths were also derived from the South Qinling middle-lower crust rather than from the North Qinling block itself. These results provide direct evidence for the South Qinling continental crust underplating beneath the North Qinling block in the continent-continent interaction stage of the East Qinling orogenic belt.

飛騨帯南部神岡鉱山東方の中生代前期花こう岩類の地質と構造

飛騨帯南部神岡鉱山東方の中生代前期花こう岩類の地質と構造