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Granitoids are the predominant geological constituents of South China and important for the understanding of the formation and evolution of continental crust. We describe field structural features of four small-scale granitic plutons and their country rocks in southern Jiangxi Province and present new zircon U-Pb and mica 40Ar/39Ar ages that are used to discuss the tectonic-magmatic evolution and thermal overprint events, that is, the tectonic rejuvenation of continental crust of the Cathaysia Block. The muscovite-bearing granite of Mashuang pluton shows sub-north-south mylonitic foliation and stretching/mineral lineation that shallowly plunges to the northeast, generally consistent with fabrics in the host rocks that are composed of widely migmatized metasediments. Zircons and muscovites yielded U-Pb and 40Ar/39Ar ages at 457±4 and 199±1 Ma, which are considered to represent the ages of emplacement and postmylonitic thermal overprint, respectively. The undeformed granites of Tianjiu and Junmenling plutons display massive structure, porphyritic texture bearing huge phenocrysts of feldspar, and a sharp contact with the host rocks that consist of greenschist- to amphibolite-facies metamorphic rocks and/or early Paleozoic granite. New dating results suggest that these granites formed during 235 ± 2 to 231 ± 2 Ma and cooled down at 224 ± 3 Ma. The biotite K-feldspar granite of Jitan pluton has an apparent compositional foliation in northeast-southwest direction defined by grain shape-preferred orientation of euhedral feldspar, biotite, and hornblende; such foliation is indicative of a syntectonic crystallization dominated by a southeast-northwest compressional stress field. The age of emplacement of this biotite K-feldspar granite is constrained at 158 ± 3 Ma, and the granite was reheated at 98 ± 1 Ma. On the basis of our observations and chronological data combined with previously published results, it is suggested that the continental crust of the Cathaysia Block was subjected to multistage rejuvenation during the Phanerozoic, including (1) reworking of crustal rocks induced by partial melting mainly in early Paleozoic and also in the Triassic to the Cretaceous by mixing of crustal melts with increasing involvement of juvenile materials and (2) tectonic and thermal overprints during early Paleozoic and Triassic intracontinental deformation events and Jurassic to Cretaceous magmatism. [ABSTRACT FROM AUTHOR]

This paper reports the systematic study on petrology, geochemistry, LA ICPMS zircons U-Pb dating, and in situ Hf isotope geology of the four plutons in the central-southern Jiangxi Province, an important part of the South China Block. In the outcrops, rocks are gradually changed from wall rock (slate or schist) to pluton (gneissic granite); some residual blocks of sandy rock occur in the margin of pluton, and the foliations of residual blocks are parallel to those of both wall rock and gneissic granite. The thin-section observations show that the four plutons contain peraluminous minerals such as muscovite and sillimanite. The flattened and elongated feldspar and quartz grains are often visible in the gneissic granite, parallel to direction of lineation, suggesting that the granitic rock were subjected to a strong ductile shearing. Geochemically, the A/CNK values from 13 granitic samples are between 1.03 and 1.37 with an average of 1.16, indicating that the granites are of strongly peraluminous plutons. The REE compositions of the 13 samples are similar, showing higher ΣREE contents, with enrichment in LREEs, depletion in Eu and REE patterns with relative LREE-enrichment and negligible Eu anomalies. They show enrichment in Rb, Th, U and depletion in Ba, Sr, Nb, Ti, belonging to a low Ba-Sr type of granite. Thus, the four bodies should be derived from the same magmatic source. Zircons used as U-Pb dating mostly exhibit euhedral shape and high Th/U values from 0.52 to 1.54 with an average of 1.08, suggesting that most zircons are of magmatic genesis. The zircons from four plutons yielded rather similar Pb/U vs. Pb/U concordia ages: 436.1±5.7 Ma for the Tangwan granite, 440.6±4 Ma for the Jiekou gneissic granite, 435.9±6.2 Ma for the Dongbao gneissic granite, and 441.9±3.1 Ma for the Jinxi K-granite, respectively, corresponding to Silurian Llandovery. Several xenocrysts yielded U-Pb ages around 700 Ma, implying that a breakup event took place during Neoproterozoic in the South China Block. In situ Lu-Hf isotopic analysis shows that all ɛ( t) values of zircons are negative and have two-stage Hf model ages (TDM2) from 1.4 to 3.6 Ga, indicating that the Silurian granitic magma came from the recycle of Meso-Paleoproterozoic basement and even partly Archean rocks, and had not been effected by mantle magma. Researches on regional geology suggest that an intracontinental tectono-magmatic event took place during the early Paleozoic in the study areas, which is characterized by folding and thrusting, leading to crustal shortening and thickening, up to 20 km thickness. The high geothermal temperature from thickening crust and accumulation of producing high-heat radioactive elements gradually softened crustal rocks and caused a partial melting, forming peraluminous granitic magma. Under the post-orogenic extensional and de-pressure condition, these granitic magma rose and was emplaced in the upper crust, leading to development of S-type plutons [ABSTRACT FROM AUTHOR]

Reports the finding that the trace elements of small ion radius, big specific gravity and high potential form the accumulative series in fault rocks, instead of divergence series. Systematic sampling test and mass equilibrium analysis of intrusive, tectonic and metamorphic complexes penetrating the core complex (MCC) in the Xingzu area of north Jiangxi, China.

This paper presents geochemical analyses of a lamprophyre intruding the Caledonian Doushui granite body in Shangyou County, southern Jiangxi Province. U-Pb dating and Hf-isotope analyses are especially carried out for zircons from it. Petrological and geochemical features show that the lamprophyre belongs to a high-K, weakly alkaline pyroxene-biotite lamprophyre. It is characterized by high Mg# (0.74), Ni (253 μg/g) and Cr (893 μg/g) contents, and also enriched in incompatible elements, such as REE, Rb, Sr, Ba and K. It is suggested that its primitive melt probably derived from enriched mantle metasomatized by non-crust-derived agent. Morphology and LAM-ICPMS dating results of zircons in the lamprophyre indicate that they are xenocrysts captured from deep crustal rocks. Most xenocrystic zircons formed at -.1.86 Ga, and a few in different Phanerozoic periods. The Paleoproterozoic zircons are of magmatic origin and have similar 176Hf/177Hf and 176Lu/177Hf ratios, indicating that they probably are from the same igneous basement rock. The ages and Hf-isotope compositions of zircons from this basement rock are similar to those of Paleoproterozoic Danzhu granite in the southern Zhejiang Province, but extremely distinguished from the Nanhing basement, suggesting that the study area probably is a westward extension part of Paleoproterozoic Wuyishan terrane in the eastern Cathaysia Block. These Paleoproterozoic zircons have low Hf-isotope compositions, characteristic of crustal source. Hf model ages of these zircons and the presence of older inherited cores within them, coupled with available other data reported by previous studies, suggest that the source of Paleoproterozoic magma is Neoarchaean crust, implying the existence of older basement in the Wuyishan terrane. U-Pb ages and Hf isotopes of five Phanerozoic zircons indicate that Paleoproterozoic basement underwent multi-reworking occurring in Caledonian, Indosinian and early Yanshanian, respectively. The Caledonian magmatism also involves reworking of juvenile crust. [ABSTRACT FROM AUTHOR]