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Wuyishan is one of the most important terrains exposing the Precambrian basement of the Cathaysia Block, South China. Conventionally, Paleoproterozoic and Neoproterozoic sequences have been proposed in this terrain, however, the thermal histories affecting each unit within these sequences remain unclear. We report here spot analysis of 448 LA-ICPMS U-Pb zircon and >1600 EMP Th-U-Pb monazite ages for twenty samples, including schist, gneiss, migmatite and amphibolite, from different units within the basement. U-Pb zircon dating yield some concordant Neoproterozoic and/or Early Paleozoic age clusters with a wide spread of Neoarchean to Mesoproterozoic inherited ages (except amphibolite), indicating the formation of the Mayuan/Chencai core in the Early Neoproterozoic (887–827 Ma) and peripheral units in two stages of the Late Neoproterozoic (746–731 Ma and 681–660 Ma). The in-situ EMP monazite analyses give consistent Early Paleozoic ages (440–426 Ma) from inclusions in various host minerals for all but two samples from same locality that are Triassic in age (239–237 Ma). A large population of Early Paleozoic interstitial monazites shows breakdown texture and ages of secondary monazites range from 376 Ma to 358 Ma, conforming with the U-Pb zircon age of the amphibolite (370 ± 5 Ma). A few samples exhibit relict ages of ∼540 Ma from monazite cores. We conclude that the Wuyishan terrain is dominated by Early and Late Neoproterozoic basement sequences related to collisional and continental rifting orogenies, respectively, while the Badu Group in Zhejiang as a Paleoproterozoic protolith. The Neoproterozoic basement incorporating some Early Cambrian detritus, has thoroughly metamorphosed during the Silurian and further affected by the regional fluid-aided metasomatism coeval with the basic magma, now represented by amphibolites, around ∼370 Ma. The EMP monazite dating results for the Wuyishan terrain are quite different from the Yunkai massif where Triassic ages predominate, although the Wuyi-Yunkai metamorphic belt is often referred to as the same orogen in the Cathaysia Block. [ABSTRACT FROM AUTHOR]

[Display omitted] • New ages of mica schist in PDMB are obtained via monazite and zircon inclusions. • Unusual zircon ages (~1.8 Ga and ~190 Ma) need exotic source other than Cathaysia. • Monazites included in sillimanite constrain a HT/LP metamorphism at ~100 Ma. • The youngest age population of zircon inclusions supports the monazite age results. • A regional post-orogenic magmatism made up the Buchan type metamorphism of PDMB. Detailed age information of the Pingtan-Dongshan Metamorphic Belt in the coastal Cathaysia Block is important in understanding geodynamics of the Late Mesozoic South China continental margin. Geochronological determinations on monazite and zircon inclusions and zircon separates from five mica schists and two granites intruding schists are used to constrain the timing of metamorphism and sediment sources. Common ages of monazite and zircon inclusions within major constituents (quartz, muscovite, sillimanite and K-feldspar) in schists define a high temperature/low pressure metamorphic event at ~100 Ma. Along with zircon ages of granites (106 and 101 Ma), a Buchan type metamorphism is proposed regarding a heat source from the post-orogenic magmatism in the neighboring igneous province. Based on the age distribution patterns of discrete zircons, two groups of schist are distinguished by sources of sediments prior to metamorphism. One group has a simple age cluster (145–130 Ma) inferring proximal magmatic rocks in the Cathaysia Block. The other group shows a widespread age spectrum with two particular populations of ~1.8 Ga and ~190 Ma that are uncommon in the Cathaysia Block but comparable to schists in the Tailuko Metamorphic Belt of eastern Taiwan. This may suggest a general source between these two belts in which a now-concealed microcontinent would play a role. Such a new tectonic framework can account for the two provenances of sediments in schists of this belt, and its structural configuration is influenced by a high temperature regime caused by mantle upwelling as a reflection of slab rollback of the subducted Paleo-Pacific Plate during 110–90 Ma. [ABSTRACT FROM AUTHOR]

Cathaysia Block in South China had accreted tremendous amounts of Mesozoic magmatic rocks. Recent zircon U Pb age results revealed existence of some Early Jurassic gneissic granites (200–190 Ma) in the Pingtan-Dongshan Metamorphic Belt (PDMB), coastal SE China which corresponds one stage of magmatic quiescence in the rest part of East Cathaysia. To better understand Mesozoic thermal evolution of the PDMB, U Pb geochronology and Hf isotope composition of zircon separates (LA-ICPMS) and inclusions (NanoSIMS, age only) are examined for two granitic rocks and one meta-sandstone in Pingtan area (northern PDMB) and three granites in Matsu Islands further north. For Pingtan rocks, ages of discrete zircons give two Early Jurassic ages (196 Ma and 173 Ma) and prossess in dominance positive ɛHf(t) values (−0.2 to 7.5). On the other hand, zircon inclusions within rock-forming minerals yield a wide age span from Permo-Triassic to Early Cretaceous in six clusters, namely 270–206 Ma, 191–170 Ma, 168–151 Ma, 146–132 Ma, 126–119 Ma and 109–100 Ma that basically coincide the major Mesozoic thermal episodes in Cathaysia except the second cluster. For Matsu granites, discrete zircons exhibit Late Jurassic (162–158 Ma) and Early Cretaceous (137 Ma) ages with ɛHf(t) values of −9.1 to −1.6 and −4.9 to −0.8, respectively. Nevertheless, zircon inclusions show ages corresponding to Pingtan samples in the last four clusters. With reference to Mesozoic magmatic rock units in the neighboring Southeast China Magmatic Belt (SCMB), our data suggest irrelevance of Pingtan samples to the Cathaysia and linkage of off-shore Matsu granites to the PDMB. Noting that there are similarities of zircon ages and ɛHf(t) values between the granite-schist associations in Tananao Metamorphic Belt (TMB) of eastern Taiwan and Pingtan island of northern PDMB, these Early Jurassic granites were probably originated from a same source. Three consistent Early Cretaceous age clusters of zircon inclusions over the studied samples match two well-known magma prevailing episodes in the coastal SE China, with one tectonic episode (128–119 Ma) in the PDMB that is often invisible from the zircon separates remains unexplainable. In response to a plausible tectonic evolution, we support the earlier proposition for a now-concealed microcontinent that had impinged on Cathaysia around 125 Ma, but further suggest that it left Pingtan Island behind as a remnant fragment when drifted away at later time. • Tectonic history of PDMB is reassessed using zircon U Pb age and Hf isotopic data. • Zircon inclusion ages can reflect more thermal episodes than discrete grains. • Characteristic εHf (t) values for Early Jurassic Pingtan granites implies an exotic source. • Northern end of PDMB may be extended further north to Matsu Islands. [ABSTRACT FROM AUTHOR]

Cooling rates for 144–134 Ma gneisses in the Chinmen area that behave similarly to ~100 Ma dioritic rocks in the Zhangzhou Igneous Complex cross the Chang-Nanao fault are explained by thermal reset in the post-orogenic stage. • Zircon double dating is conducted on plutonic rocks in two sides of a thrust fault. • Fast cooling curves constructed for Zhangzhou rocks match with shallow intrusives. • Same cooling rates obtained for deep-seated Chinmen gneisses require thermal reset. • Rapid uplift and exhumation of the PDMB were due to the collision at 130–120 Ma. • PDMB has been subjected to the post-orogenic thermal reset at 110–85 Ma. Zircon double dating technique for U-Pb and fission track (FT) ages is used to reassess the cooling conditions for the Pingtan-Dongshan Metamorphic Belt (PDMB). Three Cretaceous gneissic bodies from the Chinmen area and two dioritic plutons from the Zhangzhou Igneous Complex (ZIC) in two sides of the Changle-Nanao fault are studied. U-Pb dating results define the magma emplacement of gneisses at 144–134 Ma and dioritic rocks at 102–99 Ma, and FT dating results give ages of 96–86 Ma and ~87 Ma for corresponding samples. Combining 40Ar/39Ar mineral ages reported previously, the fast cooling curve (86 °C/Myr; 100–96 Ma) of ZIC plutons matches near-surface intrusives. However, those for deep-seated Chinmen gneisses are problematic as their resultant conditions are similar to ZIC samples. A recent concept favors the Early to Late Cretaceous tecto-magmatic evolution in the coastal SE China involving episodes of orogenic magmatism (147–130 Ma) and shallow magmatism under post-orogenic extension (110–85 Ma). As the Pingtan island in northern PDMB is considered as a remnant piece of colliding fragment, the cooling rate known for gneissic bodies in this island (35 °C/Myr; 130–120 Ma) can better represent the record of this collision. On the basis of these features, we advocate a magmatic quiescence at 130–120 Ma representing collision between PDMB and a concealed microcontinent which resulted in rapid uplift of this metamorphic belt. Cooling curves obtained for Chinmen gneisses are suggested to have further subjected to thermal reset by high temperature magmatism taking place during the post-orogenic stage. [ABSTRACT FROM AUTHOR]

Geohistory of the Yunkai massif in South China Block is important in understanding the geodynamics for the build-up of this block during the Phanerozoic orogenies. To investigate this massif, we conduct EMP monazite and U-Pb zircon geochronological determinations on mineral inclusions and separate for seventeen samples in four groups, representing metamorphic rocks from core domain, the Gaozhou Complex (amphibolite facies, NE-striking) and the Yunkai Group (greenschist facies, NW-striking) of this massif and adjacent undeformed granites. Some EMP monazite ages are consistent with the NanoSIMS results. Monazite inclusions, mostly with long axis parallel to the cleavage of platy and elongated hosts, give distinguishable age results for NW- and NE-trending deformations at 244–236 Ma and 236–233 Ma, respectively. They also yield ages of 233–230 Ma for core domain gneissic granites and 232–229 Ma for undefomed granites. Combining U-Pb zircon ages of the same group, ~ 245 Ma and ~ 230 Ma are suggested to constrain the time of two phases of deformation. Aside from ubiquity of Triassic ages in studied rocks, ages of detrital monazite in the meta-sandstone match the major U-Pb zircon age clusters of the metamorphic rock that are largely concentrated at Neoproterozoic (1.0–0.9 Ga) and Early Paleozoic (444–431 Ma). Based on these geochronological data, Triassic is interpreted as representing the time for recrystallization of these host minerals on the Early Paleozoic protolith, and the also popular Neoproterozoic age is probably inherited. With this context, Yunkai massif is regarded as a strongly reactivated Triassic metamorphic terrain on an Early Paleozoic basement which had incorporated sediments with Neoproterozoic provenances. Triassic tectonic evolution of the Yunkai massif is suggested to have been controlled by converging geodynamics of the South China and Indochina Blocks as well as mafic magma emplacement related to the Emeishan large igneous province (E-LIP). [ABSTRACT FROM AUTHOR]

Abstract: Huayu, the only non-basalt islet in the Penghu Islands, consists mainly of andesite lavas intruded by some intermediate (dacite/granodiorite) and felsic (rhyolite/granite) dikes. The LA-ICPMS U–Pb zircon age determination yields 437±13Ma (n =16, MSWD=6.9) for the andesite lava and 63.3±1.5Ma (n =7; MSWD=2.9) for its potassic altered zone, and 58.7±0.8Ma (n =14; MSWD=2.5) for one rhyolite dike. The old and young groups of zircon show distinctive Hf isotope compositions: εHf(T) =−9 for ∼437Ma zircons vs. εHf(T) =+9 to +6 and +9 to −1 for ∼63Ma and ∼59Ma zircons. On the other hand, Sr and Nd isotopic compositions of the andesite lava (ISr=0.7034 and εNd(T) =+3.9 if T =437Ma) are more depleted than the alteration zone and rhyolite dike (ISr=0.7051 and εNd(T) =−1.3 to −1.9). Decoupling of zircon εHf(T) and whole-rock εNd(T) values of the andesite lava rules out the possibility of 437±13Ma to be the eruption time. Alternatively, based on the similarity between the published zircon fission track ages (65±3Ma for the andesite lava and 61±2Ma for the rhyolite dike; [Yang, H.C., Chen, W.S., Huang, J.C., Wang Lee, C.M., 2008. Volcanic lithofacies of the Huayu Island. Bulletin of Central Geological Survey 21, 143–164 (in Chinese with English Abstract)]) and our U–Pb zircon ages of the altered andesite zone and rhyolite dike, the span of 65–63Ma is suggested to be the formation time of Huayu andesites. Since Huayu is situated in a NE–SW trending high-magnetic anomaly belt which has been generally interpreted as a remnant magmatic terrain, these data, along with the geochemical results, provide insights of this belt as a split part of the Southeast Coast Magmatic Belt in which Huayu volcanics represent the younger arc volcanism comparable with those appeared in southern Fujian. [Copyright &y& Elsevier]