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Provenance analysis was carried out on Paleozoic siliciclastic rocks exposed in the South China Block (Lower Yangtze region, Chaohu and Nanjing areas) by sandstone petrography, U-Pb detrital-zircon geochronology, and zircon Hf isotopes. Sandstones of the Silurian Fentou Formation are feldspatho-quartzose with a few igneous and low-grade metamorphic rock fragments. Sandstones of the Devonian Wutong Formation are quartzose with a few quartz-rich metamorphic rock fragments. The Fentou and Wutong formations share similar detrital-zircon age spectra, with peaks mainly at 465−420 and 838−812 Ma. Zircons of Early Paleozoic age were with all likelihood derived from magmatic rocks associated with the Kwangsian orogeny, documented by a widespread unconformity across the South China Block. Neoproterozoic zircons were probably shed from Proterozoic basement of the Wuyi terrane in the Cathaysian block, interpreted to have been uplifted south of the Lower Yangtze region during the Kwangsian orogeny. The Permian Longtan Formation in Chaohu area and Nanjing area are litho-quartzose and feldspatho-quartzose, respectively, with dominant felsic and intermediate volcanic lithic fragments, indicating that detrital source areas did not change markedly after the Kwangsian orogeny. Zircon-age spectra from the Longtan Formation in the Chaohu area display a diagnostic peak at ~ 1866 Ma, indicating provenance from the Paleoproterozoic basement of the Wuyi terrane. Instead, detrital zircons in the Longtan Formation in the Nanjing area display peaks at ~ 445 and ~ 970 Ma, similar to those in the underlying Paleozoic sandstones. The Wuyi terrane in the Cathaysian block thus remained as a major source area for long, as supported by independent sedimentological and seismic evidence. The Longtan Formation in both Chaohu and Nanjing areas also contain detrital zircons with ages distributed continuously from 341 to 254 Ma and a major peak around 270 Ma, reflecting renewed intermediate and felsic magmatism in the source area. These zircons have e Hf( t ) ranging from −19.8 to +14.9, indicating melting of old crust and mixing with crustal magmas. Such a continuously magmatic source supplied sediments all across the South China Block from east to west. These and other lines of evidence including probability accumulation-curve analysis favor deposition in a convergent plate-tectonic setting. We suggest that source rocks were part of a continental arc developed along the southeast coast of China during the Late Paleozoic, shedding sediments to as far as north as the northern South China Block. According to previous studies, such continental arc would be related to the subduction of the paleo-Pacific plate. Magmatism generated at first by melting of old crust was mixed later on with felsic and intermediate magma newly generated during mantle upwelling and associated uplift. The continental arc remained as the main detrital source to the Lower Yangtze region and other parts of the South China Block until it was eventually denudated or buried by the Mesozoic times.

A paper titled as “Retrograde garnet amphibolite from eclogite of the Zhejiang Longyou area: New evidence of the Caledonian orogenic event in the Cathaysia block” was recently published in Chinese Science Bulletin (Chen et al., 2015). However, the petrographic features and mineral compositions that authors provided cannot demonstrate that high-pressure or ultra-high pressure metamorphism occurred in the area in Early Paleozoic. Moreover, this conclusion is inconsistent with regional geological background. Combined with our field survey and petrographic observations, it can be inferred that this garnet amphibolite did not experience eclogite-facies metamorphism, and cannot be taken as evidence for the Caledonian collisional orogeny.

In view of the recent issue proposed by some researchers that “the garnet amphibolite in Longyou county of Zhejiang was retrograded from Caledonian collision-related eclogite”. Based on detailed field geological investigation, we carried out a systematic study including petrography, mineral chemistry, zircon geochronology and bulk rock geochemistry. Our results indicate that, the relatively small amounts of plagioclase which only found in interior of garnet or clinopyroxene metacryst are anorthite, while plagioclase that largely distribute in the outer part of garnet or clinopyroxene metacryst are andesine and labradorite (with their An value within 44–66), and no sodium-rich plagioclase (albite or oligoclase) which imply omphacite decomposition structure are found. The CL images of zircon exhibit obvious core-rim structure. U-Pb dating results indicate that the weighted average age of the zircon core part is 879±11 Ma, with Th/U ratio values ranging from 0.20–1.23 which suggest their magmatic origin; while the age of the rim is 446±5 Ma, and lots of their corresponding Th/U ratio show low values ( £ 0.1), suggesting their metamorphic origin. Moreover, the bulk rock geochemistry feature of garnet amphibolite suggest that its protolith is basic (the SiO2 content within 46.8%–48.2%), and its trace element exhibit E-MORB geochemical affinity. Based on the effective bulk rock composition and EPMA analysis results, as well as the mineral association we found, the P-T pseudosection for Longyou garnet amphibolite was worked out. And this figure reveals that the Longyou garnet amphibolite at least experienced three stages of metamorphism: the prograde metamorphism stage with P-T condition of 0.67–0.75 GPa/685–719°C; the peak-metamorphism with P-T condition of 0.91–0.97 GPa/766–782°C; and the retrograde metamorphism stage with P-T condition of ~0.68 GPa/~767°C (by traditional P-T thermobarometer, we also get a P-T condition of 0.66–0.67 GPa/720–740°C for retrograde metamorphism stage). Whichever stage, its pressure is medium-pressure but not high- pressure. In combination with regional geological setting, we prefer the following genetic model for Longyou garnet amphibolite: the paleo-South China Ocean subduction under Yantze plate in Neoproterozoic→trigger back-arc extension→mantle-derived magma upwelling and forming E-MORB type basic rocks in Neoproterozoic→medium to high-grade metamorphism in Silurian.

A mafic granulite has been found in southern Yiyang county in northeastern Jiangxi Province. This granulite has a mineral assemblage of garnet+plagioclase+hypersthene+biotite+magnetite. Based on the composition variation of minerals and relationships among them, pre-peak metamorphism (M1) and peak metamorphism (M2) are recognized. A petrogenetic grid and geothermobarometry measurements yield pre-peak metamorphic conditions of 830-870℃ and ~1.0 GPa, and peak metamorphic conditions of 850-900℃ and 0.7-0.8 GPa, suggesting a near isothermal decompression clockwise PTt path. LA ICPMS zircon U-Pb dating indicates that granulite facies metamorphism occurred about 436 Ma, and its protolith was possibly formed in the early Neoproterozoic. Coupled with available data, we suggest that early Paleozoic (Caledonian) high-grade metamorphism in the Cathaysia Block is related to collisional orogeny, which probably results from the collision-compression between the Yangtze Block and Eastern Gondwana.

The petrochemical as well as zircon U-Pb and Lu-Hf isotopic studies of granulite facies metamorphic rock from the Taoxi Group in eastern Nanling Range, Central Cathaysia indicate that its protolith is the sedimentary rock with low maturation index. The clastic materials are mostly from middle Neoproterozoic (~736 Ma) granitoid rocks with minor Neoarchaean and Paleoproterozoic rocks. The timing of this Neoproterozoic magmatism is in agreement with the second period of magmatism widespread surrounding the Yangtze Block. Hf isotopic data indicate that the Neoproterozoic granitoids resulted from the recycled Paleoproterozoic mantle-derived crustal materials. The sedimentary rock was deposited in Late Neoproterozoic Era, and carried into low crust in Early Paleozoic. The partial melting of the meta-sedimentary rock took place at about 480 Ma and subsequently granulite facies metamorphism occurred at ca. 443 Ma. The zircons forming during this time interval (Early Paleozoic) show large Hf isotope variations, and their eHf(t) values increase from -13.2 to +2.36 with decreasing age, suggesting the injection of mantle-derived materials during partial melting and metamorphism processes in the Early Paleozoic. Calculation results show that this metamorphic rock, if evolved to Mesozoic, has similar isotopic composition to the nearby Mesozoic high Si peraluminous granites, implying that this kind of granulite facies metamorphic rock is probably the source material of some Mesozoic peraluminous granitoids in eastern Nanling Range.

A systematic Sm-Nd isotopic study was carried out for sediments and metasediments of different ages from Mesoproterozoic to early Mesozoic era in southwestern Fujian, Eastern Nanling Range. The results show that Nd model age (t DM) and eNd(t) value of most sediments are closely similar to those of Paleoproterozoic Mayuan Group, indicating that they may mainly be the recycling product of Paleoproterozoic crustal materials. However, the Nd model age significantly decreases with a corresponding increase in the eNd(t) value at Neoproterozoic (ca. 0.8-0.7 Ga) and Late Paleozoic (ca. 0.25 Ga), respectively. This is manifested by prominent vales and apexes on the diagrams of t DM vs. t Str. (stratum age) and eNd(t) vs. t Str.. The decrease in t DM and the increase in eNd(t) are explained as a result of the significant incorporation of juvenile crustal materials that originated from depleted mantle due to strong lithospheric extension during both periods. It appears that tectonic magmatism in the Neoproterozoic and the Late Paleozoic is of prominent importance in affecting the geochemical nature of sediments in South China.