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Biotite granites and muscovite-bearing granites are dominant rock types of the widespread granites in SE China. However, their petrogenesis has been enigmatic. A combined study of zircon U-Pb dating and Lu-Hf isotopes, whole-rock element geochemistry and Sr-Nd-O isotopes was performed for three late Mesozoic granitic plutons (Xinfengjie, Jiangbei and Dabu) in central Jiangxi province, SE China. All the plutons are composed of biotite granites and muscovite-bearing granites that have been poorly investigated previously. The new data not only allow us to assess their sources and magma evolution processes, but also helps us to better understand the genetic link to the large-scale polymetallic mineralization in SE China. LA-ICP-MS zircon U-Pb dating shows that three plutons were emplaced in the Late Jurassic (159-148 Ma) and that the muscovite-bearing granites are almost contemporaneous with the biotite granites. The biotite granites have SiO.sub.2 contents of 70.3-74.4 wt% and are weakly to strongly peraluminous with ASI from 1.00 to 1.26, and show a general decrease in ASI with increasing SiO.sub.2. They have relatively high zircon saturation temperatures (T.sub.Zr = 707-817 °C, most > 745 °C) and show a general decrease in T.sub.Zr with increasing SiO.sub.2. They have high initial .sup.87Sr/.sup.86Sr ratios (0.7136 to 0.7166) and high [delta].sup.18O values (9.1-12.8â°, most > 9.5â°) and clearly negative [epsilon].sub.Nd (T) (- 9.5 to - 11.8) and [epsilon].sub.Hf (T) (in situ zircon) (- 13.1 to - 13.5). The muscovite-bearing granites have high SiO.sub.2 contents (74.7-78.2 wt%). They are also weakly to strongly peraluminous with ASI of 1.04-1.18 but show a general increase in ASI with increasing SiO.sub.2. They have relatively low T.sub.Zr (671-764 °C, most < 745 °C) and also show a general decrease in T.sub.Zr with increasing SiO.sub.2. The muscovite-bearing granites have high Rb (up to 810 ppm) and high (K.sub.2O + Na.sub.2O)/CaO (up to 270), Rb/Sr (up to 42) and Rb/Ba (up to 30) as well as low K/Rb (< 150, down to 50), Zr/Hf (< 24, down to 11) and Nb/Ta (< 6, down to 2). They show similar Nd-O-Hf isotopic compositions to the biotite granites with [epsilon].sub.Nd (T) of - 8.7 to - 12.0, [delta].sup.18O of 8.7-13.0â° (most > 9.5â°) and [epsilon].sub.Hf (T) (in situ zircon) of - 11.3 to - 13.1. Geochemical data suggest the origin of the biotite granites and muscovite-bearing granites as follows: Partial melting of Precambrian metasedimentary rocks (mainly two-mica schist) in the lower crust at temperatures of ca. 820 °C generated the melts of the less felsic biotite granites. Such primary crustal melts underwent biotite-dominant fractionation crystallization, forming the felsic biotite granites. Progressive plagioclase-dominant fractionation crystallization from the evolved biotite granites produced the more felsic muscovite-bearing granites. Thus, the biotite granites belong to the S-type whereas the muscovite-bearing granites are highly fractionated S-type granites. We further suggest that during the formation of the muscovite-bearing granites the fractional crystallization was accompanied by fluid fractionation and most likely the addition of internally derived mineralizing fluids. That is why the large-scale polymetallic mineralization is closely related to the muscovite-bearing granites rather than biotite granites in SE China. This is important to further understand the source and origin of biotite granites and muscovite-bearing granites in SE China even worldwide., Author(s): Yao-Hui Jiang [sup.1], Shu-Qi Zhu [sup.1] Author Affiliations: (1) State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, 0000 0001 2314 964X, grid.41156.37, [...]

Two suites of granitoids, the Late Jurassic (158 [+ or -] Ma) Linglong suite and the Early Cretaceous (130-126 Ma) Guojialing suite, crop out in the northwestern Jiaodong Peninsula, eastern China. The Linglong suite is a monzogranite, comprising alkali feldspar, plagioclase, quartz and Ferich biotite. The Guojialing suite includes at least five plutonic bodies of both granodiorite and monzogranite. The rocks are composed of plagioclase, alkali feldspar, quartz, Mg-rich amphibole and Mg-rich biotite. Both the Linglong and Guojialing suites have adakitic affinity. They are enriched in LREE with high La/Yb ratios and show positive Eu anomalies. The rocks are also enriched in LILE and depleted in HFSE with high Sr/Y ratios. The Linglong granite shows very uniform Sr-Nd isotopic compositions with initial [sup.87]Sr/[sup.86]Sr ratios of 0.7119-0.7126 and [[epsilon].sub Nd]end (T) values of -21.3 to -21.6, which are similar to those of the local Neoarchaean basement. The Guojialing suite has variable initial [sup.87]Sr/[sup.86]Sr ratios (0.7108-0.7120) and [[epsilon].sub.Nd] (T) values (-10.8 to -17.2), which are distinct both from those of the Neoarchaean basement and from those of the local enriched lithospheric mantle inferred from the coeval mafic dykes in the studied area. Detailed petrological and geochemical data indicate that the Linglong suite was derived by partial melting of Neoarchaean metamorphic lower-crustal rocks at depth of > 50 km with a eclogite residue, whereas the Guojialing suite was formed by the reaction of delaminated eclogitic crust-derived melt with the upwelling asthenospheric mantle. The petrogenesis of these two contrasting adakitic granitoids suggests intensive lower-crustal delamination during Early Cretaceous times, following a crustal thickening process from the late stage of the Early Jurassic to early stage of the Late Jurassic with crustal thickness of < 32 km to > 50 km, respectively. Keywords: granitoid, adakite, crustal thickening, delamination, Jiaodong Peninsula.

A late Mesozoic belt of volcanic-intrusive complexes occurs in Southeast China. The Qianlishan granites are distributed in the northwest of the belt. The pluton is composed of porphyritic biotite granite (153 Ma) and equigranular biotite granite (151 Ma) and was intruded by graniteporphyry dykes (144 Ma) and mafic dykes such as lamprophyre and diabase (142 Ma). The granitic rocks, consisting mainly of K-feldspar, plagioclase, quartz and Fe-rich biotite, have Si[O.sub.2] contents of 72.9-76.9%, and are enriched in alkalis, rare earth elements (REE), high field strength elements (HFSE) and Ga with high Ga/Al ratios, but depleted in Ba, Sr and transition metals. Trace-element geochemistry and Sr-Nd isotope systematics further imply that the Qianlishan granitic magmas were most probably derived by partial melting of Palaeo- to Mesoproterozoic metamorphic lower-crustal rocks that had been granulitized during an earlier thermal event. These features suggest an A-type affinity. The Qianlishan lamprophyre and neighbouring coeval mafic dykes (Si[O.sub.2] = 47.9-53.8 wt %) have high MgO and compatible element contents. These rocks also have high [K.sub.2]O contents and are enriched in alkalis, light REE, large ion lithophile elements, and depleted in HFSE. They have low initial end values and relatively high initial [sup.87]8r/[sup.86]Sr ratios. We suggest a subduction-modified refractory lithospheric mantle (phlogopite-bearing harzburgite or lherzolite) for these high-Mg potassic magmas. The Qianlishan diabases (Si[O.sub.2] = 48.4-48.7 wt %) are alkaline and have high Ti[O.sub.2] and total [Fe.sub.2][O.sub.3] contents, together with the positive initial [[epsilon].sub.Nd] value, suggesting derivation from fertile asthenopheric mantle (phlogopite-bearing lherzolite). A back-arc extensional setting, related to subduction of the Palaeo-Pacific plate, is favoured to explain the petrogenesis of the Qianlishan granites and associated mafic dykes. Between 180 and 160 Ma, Southeast China was a continental arc, forming the 180-160 Ma plutons of the late Mesozoic volcanic-intrusive complex belt, and the lower-crust was granulitized. Since 160 Ma the northwestern belt has been in a back-arc extensional setting as a consequence of slab roll-back, resulting in the lithosphere thinning and an influx of asthenophere. The upwelling asthenosphere, on the one hand, induced the local lithospheric mantle to melt partially, forming high-Mg potassic magmas, and on the other hand it underwent decompression melting itself to form alkaline diabase magma. Pulsatory injection of such high-temperature magmas into the granulitized crustal source region induced them to partially melt and generate the A-type magmas of the Qianlishan granitic rocks. Keywords: A-type granite, mafic dykes, back-arc extension setting, Qianlishan, SE China.