Wuyi-Yunkai Orogen Research Articles

Petrogenesis of early Paleozoic peraluminous A-type granites from southern China

ABSTRACT Early Paleozoic A-type granites in South China are rare, and their petrogenesis is still highly debated. This study focuses on the controversial Epo pluton in the Wuyi-Yunkai Orogen and conducts petrological and petrogeochemical research to discuss its origin. The Epo granites were emplaced at approximately 414 Ma and exhibit petrological and geochemical features of A-type granites. They contain only one ferromagnesian mineral, ferrum biotite. The granites mostly have high alkalis contents (Na2O + K2O = 6.48–8.85 wt.%), high field strength element (HFSE) contents (Zr + Nb + Ce + Y = 353–461 ppm), and high Ga/Al (104×Ga/Al = 2.50–3.72) and FeOT/(FeOT + MgO) (0.74–0.85) ratios. Besides, they formed under high-temperature (>850°C) and low-pressure (≤5 kbar) conditions. Their high A/CNK (average 1.20) and Eu/Eu* (average 0.46) values as well as Sr (average 128 ppm) and Ba (average 628 ppm) contents but relatively low Zr contents (approximately 200 ppm) further suggest a strongly peraluminous A-type affinity, a distinctive subtype of A-type granites. The Epo granites display enriched Sr-Nd-Hf isotope compositions with a whole-rock87Sr/86Sri average ratio of 0.712, whole-rock εNd(t) values ranging from − 8.9 to − 7.6, and zircon εHf(t) values clustering at − 8. Their two-stage Nd and Hf isotope model ages are 1.7 Ga to 2.0 Ga, suggesting ancient crustal sources. Furthermore, Nb/U (average 7.46), Ce/Pb (average 4.06) and other trace element ratios indicate negligible contributions from juvenile mantle materials. Our data on the Epo pluton, coupled with other contemporary A-type granites in South China, suggest that the high-temperature melting of metasedimentary basements generated strongly peraluminous A-type granites, while the involvement of metaigneous rocks or mantle-derived magmas resulted in metaluminous to weakly peraluminous A-type granites. Source diversity leads to different aluminium saturations. The heat required to produce high-temperature A-type magmas was supplied by upwelling mantle-derived magma in a postcollisional extensional setting.

The early Paleozoic Wuyi–Yunkai orogeny in South China: a collisional orogeny with a major lag in time between onset of collision and peak metamorphism in subducted continental crust

Abstract Collisional orogeny is characterized by deep subduction of continental crust and major crustal thickening, leading to high-pressure/high-temperature metamorphism and anataxis of the subducted continental crust. Since conductive heating of large slabs of cold, subducted continental crust is a slow process, heating to a temperature that is high enough to generate significant partial melting can take tens of millions of years. Where the spatial and temporal relationships are obscured due to later modification (e.g. post-collisional rifting), the peak metamorphism and magmatism may be interpreted as an orogeny that is separate from the collision, or may be interpreted as an intraplate orogeny as no contemporaneous arcs or ophiolite may be present. We propose here that this is the case for the early Paleozoic orogeny in South China. In our model, the West Cathaysia terrane of South China was part of a continent (possibly Australia) on the lower plate and collided with another continent (possibly India) in the Cambrian–Ordovician, at a late stage of Gondwana assembly, and the late Ordovician–Silurian Wuyi–Yunkai orogeny, characterized by amphibolite–granulite facies metamorphism and extensive anataxis, was a continuation of the Cambrian–Ordovician collisional orogeny. In this interpretation, the Wuyi–Yunkai orogen was part of the Kuunga orogen before Gondwana break-up.

Early Paleozoic crustal anatexis during Wuyi-Yunkai orogenesis: Insights from zircon of Fuhuling migmatites in the Yunkai region, South China

Abstract Crustal anatexis is an important process in the tectonic evolution of many orogenic systems. In the Wuyi-Yunkai orogen in the South China block, the duration of partial melting and its relationship with orogenesis are poorly constrained. In this study, we present a multifaceted approach to determine the timing of anatexis and unravel the petrogenesis of Fuhuling migmatites in the Yunkai region of the southwestern South China block. Geochemical analyses indicate that the migmatites have (meta-)sedimentary protoliths. The absence of anhydrous peritectic minerals but the presence of microstructural and outcrop-scale indicators of partial melting suggest that the Fuhuling migmatites experienced fluid-present melting. Complex zoning and variable trace element concentrations in newly formed zircons in migmatites reflect their evolutionary histories during partial melting. Anatectic melt was present at Fuhuling in the Yunkai region from ca. 449–427 Ma during early Paleozoic Wuyi-Yunkai orogenesis. The wide variety of morphologies observed in the Fuhuling migmatites implies that migmatites in the Yunkai region experienced incipient partial melting, melt segregation, and melt migration. Combining new and previous results, we argue that the Yunkai region experienced two stages of crustal anatexis during the early Paleozoic, which may have been triggered by crustal thickening followed by rapid exhumation and orogenic collapse during the intra-plate Wuyi-Yunkai orogeny in the South China block.

Early Paleozoic granodiorites and gabbros related to asthenosphere upwelling in the eastern Wuyi-Yunkai Orogen, South China

The early Paleozoic Wuyi-Yunkai Orogen (WYO) developed in the inner part of the South China Block (SCB) and underwent large scale felsic magmatism. Different tectonic models have been proposed to explain the evolution of the WYO, including intracontinental and collisional orogenesis. The debates focus on whether the asthenospheric materials were involved during evolution of the WYO. We conducted detailed petrographic and geochemical analyses on gabbros from the Qiaotou pluton and granodiorites and the hosted MMEs from the Xinsi pluton in the eastern WYO, and present the first evidence of asthenosphere upwelling that induced significant lithosphere remobilization in the SCB during early Paleozoic. Granodiorites from the Xinsi pluton (441 ± 2 Ma) contain abundant amphibole and are metaluminous, which originated from the igneous basement in the Cathaysia Block. The hosted MMEs (440 ± 2 Ma) have variable SiO2 and enriched Sr-Nd isotopic compositions with high zircon δ18O values, which were formed through hybridization of felsic melts and mafic magmas from the enriched lithosphere mantle. Gabbros from the Qiaotou pluton (448 ± 8 Ma) have low K2O with insignificant Nb-Ta-Ti anomalies and show variable Sr-Nd-O isotopic compositions. They were derived from the depleted asthenosphere and underwent crustal assimilation. The asthenosphere upwelling may be induced by slab breakoff during the collision between the western Cathaysia Block and an unknown block near northern Gondwana. The continental collision possibly transferred compressional stress and caused crustal uplifting along the weak zone in the inner SCB. The asthenosphere upwelling provided tremendous heat for the lithosphere remobilization and voluminous magmatism in the WYO.

P-T paths and U-Pb ages of pelitic and semi-pelitic granulites in the Yunkai massif and implication for the tectonic evolution of the Wuyi-Yunkai orogen, South China

Understanding the tectono-metamorphic evolution of the Wuyi-Yunkai orogen is crucial to constraining the Early Paleozoic geodynamic history of the South China Block. Here, we present petrological and geochronological characteristics of the pelitic and semi-pelitic granulites from Yunkai massif that occur as lenses or enclaves within orthogneisses and charnockites. These granulites have garnet-cordierite-spinel-sillimanite-bearing and garnet-orthopyroxene-bearing assemblages, respectively, showing typical low-pressure–high-temperature (LP-HT) granulite-facies mineral assemblages. Based on petrological characteristics, P-T calculations and phase equilibrium modelling in the NCKFMASHTO system, three-stage metamorphic evolution can be distinguished: 1) prograde stage (M1) characterized by biotite-plagioclase- or sillimanite-bearing assemblages present as inclusions in garnet or cordierite porphyroblasts, with P-T conditions of 7.0–8.0 kbar/730–780 °C; 2) peak LP-HT stage (M2) featured by garnet-orthopyroxene- or cordierite-bearing assemblages, with P-T conditions of 4.7–5.1 kbar/825–875 °C, suggesting high geothermal gradients (∼50–56 °C/km); and 3) post-peak stage (M3) represented by garnet+quartz corona or spinel-cordierite-bearing intergrowth, with P-T conditions of 4.0–4.3 kbar/650–750 °C. P-T estimates and pseudosection modelling define two consistent clockwise P-T paths involving a pre-peak prominent heating with decompression followed by a post-peak nearly isobaric cooling process. LA-ICP-MS zircon U-Pb dating results reveal that the granulite-facies metamorphism occurred at ∼445 Ma. Combined with previous studies, we proposed that the LP-HT metamorphism in the Yunkai massif might be attributed to the ridge subduction in the Early Paleozoic, which caused asthenosphere upwelling and supplied high heat flux to the lower crust when the slab window opened.

Bulk Crustal Properties and Layered Velocity Structure in Fujian, SE China: Constraints From P and S Receiver Functions

Multiple tectonic events since the Neoproterozoic era have framed the present-day lithosphere in the Fujian province affiliated with the eastern part of the South China Block. Comprehensive information of the crustal structure and bulk properties can aid to understand the geological features and tectonic processes of still much debate in this region. An attempt is made in this study to explore crustal thickness and internal velocities across Fujian using the teleseismic receiver functions (RFs). The H-V stacking of joint P and S RFs improves to simultaneously estimate crustal thickness, average Vp and Vs, and derived Vp/Vs ratio and bulk sound speed in three backazimuth sectors for each of 17 stations. Furthermore, a Neighborhood Algorithm nonlinear inversion of P RFs is employed to determine the layered structures of Vs and Vp/Vs beneath all the stations. Results indicate the crustal thickness varies from at most ∼35 km in northwest Fujian to 30–35 km in the inland mountains and 27–30 km in the southeastern coasts. The inferred Moho geometry is nonplanar or inclined across the Zhenghe-Dapu (ZD) and Changle-Zhaoan (CZ) fault zones, especially in the southern ZD fault area. The average Vp/Vs suggests that the crust is predominantly felsic in the Wuyi-Yunkai orogen and intermediate-to-mafic in the Cretaceous magmatic and metamorphic zones. A high-velocity upper crust along the coastline is revealed, which attributes to the Pingtan-Dongshan metamorphic belt. At the sites near the ZD fault zone, the intracrustal negative discontinuity occurs at a shallower depth of ∼15 km marking an abrupt Vs decrease into the low-velocity mid-to-lower crustal layer, probably linked to the closed paleo-rift basin remnants. The lower crust across the Fujian is generally characterized by relatively lower Vs and higher Vp/Vs (1.80–1.84) consistent with those of the mafic-ultramafic rocks, which do not support the proposed extensive magmatic underplating in the Late Mesozoic.

Petrogenesis of Early Paleozoic I-type granitoids in the Wuyi-Yunkai Orogen, South China: Implications for the tectono-magmatic evolution of the Cathaysia Block

• The Early Paleozoic I-type granites were generated through partial melting, magma mixing and fractional crystallization . • Mantle-derived magmas provided the heat and material for the formation of the granites. • The granites formed during an intracontinental orogeny . • The granites were related to the assembly of northern East Gondwana . The tectonic setting of the Early Paleozoic granites in the South China Block (SCB) remains enigmatic, and it is uncertain as to whether they are related to intracontinental orogenic processes or oceanic subduction. Previous studies mostly focused on Early Paleozoic S–type granitoids in the SCB, and relatively little attention has been paid to Early Paleozoic I–type granitoids. Here we present whole–rock major and trace elemental data and LA–ICP–MS zircon U–Pb age and Lu–Hf isotopic data for hornblende monzogranites, monzogranites, and mylonitic granites of I–type granites affinities that comprise the Daning and Guiling plutons in the southwest part of the Wuyi–Yunkai orogen in the SCB. These rocks contain zircon with U–Pb ages of 422–418 Ma, taken as the age of emplacement. They are rich in LREEs and moderately depleted in Eu (δEu = 0.49–0.64), with negative Ba, Sr, Nb, and Ti anomalies, and positive in Rb, Th, U, and Pb anomalies. Our studies of these granites and their abundant enclaves indicate that they formed via complicated petrogenetic processes, including the partial melting of a mixed source of meta–sedimentary rocks and meta–basalts in the lower crust, magma mingling and mixing of crust–mantle materials, and fractional crystallization. Mantle–derived magma played an important role in the formation of these Early Paleozoic granites. Although an ancient and enriched mantle source might have made a significant contribution to these Early Paleozoic granites, the input of juvenile mantle–derived magma might have been insignificant. Taking into account all the other geological evidence from the Wuyi–Yunkai region, we suggest that the tectono–magmatic events of the Early Paleozoic took place during intraplate orogenesis rather than oceanic subduction and collision, and that these events were triggered by a far–field tectonic response to the assembly of northern East Gondwana.

Early Paleozoic and Late Mesozoic crustal reworking of the South China Block: Insights from Early Silurian biotite granodiorites and Late Jurassic biotite granites in the Guangzhou area of the south-east Wuyi-Yunkai orogeny

The South China Block (SCB) is considered to have undergone extensive reworking of continental crust. However, the processes and mechanisms of this reworking remain uncertain. Here, we investigated Early Silurian (442 Ma) biotite granodiorites and Late Jurassic (164–159 Ma) biotite granites in the Guangzhou area of SE Wuyi-Yunkai orogen (WYO), South China. The biotite granodiorites and biotite granites show major and trace element characteristics similar with crustal-derived melts. They have enriched whole-rock Sr–Nd ((87Sr/86Sr)i = 0.7108–0.7210; εNd(t) = − 11.7 to −7.6) and zircon Hf (εHf(t) = −17.2 to −1.7) isotopic compositions. Early Silurian biotite granodiorites have relatively homogeneous zircon δ18O values (8.6‰–9.3‰) while Late Jurassic biotite granites show a wide range of zircon δ18O values (7.4‰–10.6‰). We suggest that the Early Silurian biotite granodiorites were formed by partial melting of amphibolites and that the Late Jurassic biotite granites were formed by partial melting of a hybridized crustal source containing metasedimentary rocks with subordinate juvenile crustal rocks. Combining our results with those of previous studies in the SCB, we suggest that Early Paleozoic intracontinental reworking of the SCB can be divided into three stages: crust double-thickening, orogenic collapse, and post-orogenic lithospheric extension. During the Late Ordovician to Early Silurian, Guangzhou area of the SE WYO underwent reworking mainly of middle–lower-crustal rocks in response to crust double-thickening. In addition, during the Late Jurassic, the area underwent reworking mainly of middle–lower-crustal metasedimentary rocks, which was induced by heating from mantle-derived mafic magmas.

First report of phengites in the Longyou paragneiss in the northern Early Paleozoic Wuyi-Yunkai orogen, South China: P-T conditions, zircon U-Pb ages and tectonic implications

Our recent investigations into the Longyou paragneiss (country gneiss of the Longyou garnet amphibolite) in the northern Wuyi-Yunkai orogen of South China lead to a recognition of high-pressure metamorphic phengites in the paragneiss. The paragneiss consists of phengite, muscovite, biotite, K-feldspar, plagioclase, quartz, and minor graphite and ilmenite or magnetite. Mineral compositions show that Si contents in phengites are between 3.40 and 3.25 (p.f.u., per formula unit), belonging to high-pressure metamorphic phengites. P-T estimates suggest that peak high-pressure metamorphic stage (M2) has P-T conditions of ~ 13.0 kbar and ~ 690 °C, whereas post-peak retrograde stage (M3) has lower P-T conditions of ~ 6.0 kbar and ~ 695 °C. The two-stage P-T conditions define a clockwise P-T path of post-peak isothermal decompression, reflecting a typical collisional orogenic process. SIMS zircon U-Pb age data show a weighted mean 206Pb/238U age of 445 ± 3 Ma, consistent with the metamorphic age of the Longyou garnet amphibolite, suggesting that the peak high-pressure metamorphic event occurred in the Early Palaeozoic orogeny in the Cathaysia block in South China. Thus, we consider that both the Longyou paragneiss and enclosed garnet amphibolite together experienced a phase of high-pressure metamorphism during the Early Palaeozoic continent–continent collisional orogeny likely along the Zhenghe-Dapu fault between the South China block and an unknown block on the northern margin of eastern Gondwana continent.

High-Mg andesitic rocks formed through crustal magmatic differentiation

High-Mg andesitic rocks are enriched in both compatible (Mg, Cr and Ni) and incompatible elements (Si, Ba and Sr), which indicates the complexity of their petrogenesis. Models involving hybridization of the mantle sources and input of adakitic melts have been invoked, but struggle to explain the low Mg# values (<0.65) of some low Sr/Y (<40) high-Mg andesitic rocks, because these rocks cannot represent primary melts (Mg# ≥ 0.72) produced by the partial melting of mantle peridotite. This study presents a petrological and geochemical analysis of the Xinsi diorite (443 ± 3 Ma) and Tiechang gabbro (440 ± 3 Ma) from the Early Paleozoic Wuyi-Yunkai Orogen in South China, and demonstrates the role of magmatic differentiation in the petrogenesis of high-Mg andesitic rocks. These rocks contain high SiO2, MgO, Ba and Sr concentrations with low Mg# values (≤0.69) and Sr/Y ratios (≤16.7), resembling typical low Sr/Y high-Mg andesitic rocks. Amphiboles and clinopyroxenes in the Xinsi diorite contain variable contents of Ba and Sr, both of which negatively correlate with Mg#. This indicates that their parental melts had low Ba and Sr and underwent significant enrichment of Ba and Sr through the fractionation of Mg-rich minerals within upper crust (3.1–4.4 kbar). Clinopyroxene, plagioclase and biotite in the Tiechang gabbro all contain lower Ba and Sr than those in the Xinsi diorite, suggesting that their parental melts were also initially low in Sr and Ba and experienced enrichment of these elements during magma evolution at middle crustal levels (5.7–6.3 kbar). The low Ba and Sr concentrations and Sr/Y ratios for parental melts of the Xinsi diorite and Tiechang gabbro suggest their derivation from the partial melting of mantle sources with input from slab melts at shallow depths without involvement of abundant garnet in petrogenesis. This study demonstrates the importance of fractional crystallization in the genesis of low Sr/Y high-Mg andesitic rocks and is conflict with past views that their geochemical features were related to the involvement of adakitic melts in their mantle sources. Therefore, this study presents an alternative model for the production of low Sr/Y and high Sr/Y high-Mg andesitic rocks, particularly in the Late Archean, which reflects the intense melting of subducted slab at different depths in the hotter mantle regime at that time.

Neoproterozoic and middle Paleozoic geological events in the eastern Wolhyeonri complex of the southwestern Gyeonggi Massif, South Korea, and their tectonic correlations in northeastern Asia

The eastern Wolhyeonri complex in the southwestern Gyeonggi Massif, South Korea, which has a close affinity with the northern margin of the South China Craton, primarily consists of Neoproterozoic igneous and sedimentary rocks that were metamorphosed by the middle Paleozoic thermal event. In this study, we present the results from thermobarometry, whole-rock chemistry, and zircon geochronology of rocks in the eastern Wolhyeonri complex near Gwangcheon. The main rock type, such as the migmatitic biotite gneisses, was deposited after ca. 722–680 Ma, and the associated foliated amphibolites exhibit a rift-related Neoproterozoic origin. The ca. 845–820 Ma arc-related metadolerite and mafic layer in the metavolcanic-sedimentary unit are also exposed. Two Neoproterozoic magmatic events support the idea that the southwestern Gyeonggi Massif developed along the northern margin of the South China Craton. These Neoproterozoic rocks experienced upper amphibolite-facies (7–10.5 kbar and 710–735 °C) to low-pressure granulite-facies metamorphism (10.5–12.0 kbar and 810–830 °C) during 424–412 Ma, were associated with ca. 418 Ma leucogranite formation, and then underwent retrograde amphibolite-facies metamorphism. Combined with the results from previous studies, the early-middle Paleozoic orogeny in the southern Gyeonggi Massif is characterized by 470–456 Ma subduction associated with a high P/T metamorphism, and the initiation of intermediate P/T metamorphism from ca. 445 Ma followed by low-pressure granulite-facies metamorphism at 432–403 Ma, and high-pressure granulite-facies metamorphism at 392–381 Ma, indicating that the tectonic setting transitioned from a continental collision to a post-collisional setting between 432 Ma and 392 Ma. These events and the absence of Paleozoic ultrahigh-pressure metamorphism strongly correlated with the Wuyi-Yunkai orogen in the South China Craton, rather than the Qinling belt in the North China Craton. Therefore, the early-middle Paleozoic orogeny in the southern Gyeonggi Massif was caused by the subduction and subsequent collision within the South China Craton.

Petrogenesis of Silurian ultramafic–mafic plutons in southern Jiangxi: implications for the Wuyi–Yunkai orogen, South China

AbstractThe South China Block is one of the largest continental blocks located on the East Asian continent. The early Palaeozoic Wuyi–Yunkai orogen of the South China Block (known as the Caledonian orogen in Europe) is a major orogenic belt in East Asia and represents the first episode of extensive crustal reworking since Neoproterozoic time. Although this orogen is key to deciphering the formation and evolution of the South China Block, details about the orogen remain poorly defined. The Songshutang and Wushitou ultramafic–mafic units in southern Jiangxi Province, South China, have206Pb–238U ages ofc. 437 Ma, suggesting a Silurian formation age. All the Songshutang and Wushitou ultramafic–mafic rocks show relatively flat chondrite-normalized rare earth element patterns, depletions in Nb, Ta, Zr, Hf and Ti, and low ϵNd(t) values from −9.12 to −5.49 with negative zircon ϵHf(t) values from −10.84 to −2.58, resembling a typical arc magma affinity. Geochemical and isotopic data indicate that the newly identified ultramafic–mafic rocks, along with the reported Silurian mafic rocks in South China, possibly originated from the similar partial melting of an ancient subducted slab, fluid/sediment and metasomatized lithospheric mantle with varying degrees of fractional crystallization. In conjunction with other records of magmatism and metamorphism in South China, a late-orogenic extensional event led to the melting of the sub-continental lithospheric mantle in Silurian time and generated ultramafic–mafic rocks with a limited distribution along the Wuyi–Yunkai orogen and widespread late-orogenic granitic plutons in the South China Block.

Early Paleozoic tectonic evolution of the South China Block: Constraints from geochemistry and geochronology of granitoids in Hunan Province

The Early Paleozoic Wuyi–Yunkai orogeny in the South China Block (SCB) remains enigmatic. A geochemical and geochronological investigation was carried out for the four poorly-studied granitoid intrusions (i.e., Hongxiaqiao, Xuehuading, Baimashan and Wanyangshan granitoids) in Hunan Province, and within the SCB, to determine their petrogenesis and give enlightening insights into the tectonic evolution of the Wuyi–Yunkai Orogen. The Hongxiaqiao, Xuehuading and Baimashan granitoids have lower SiO2 contents, and total alkali (Na2O + K2O) and A/CNK values, but higher Fe2O3T, MgO and TiO2 contents, compared with those of the Wanyangshan granitoid. All the studied granitoids are strongly depleted in Ba, Nb, Zr, Ti, and HREEs, but are enriched in Rb, Th, U, K, and LREEs, with significant negative Eu anomalies, particularly in the Wanyangshan granitoid. Bulk-rock geochemical compositions indicate that the Hongxiaqiao, Xuehuading and Baimashan granitoids are metaluminous–weakly peraluminous I-type granitoids, whereas the Wanyangshan granitoid is peraluminous and moderately fractionated S-type granitoid. Zircon LA-ICP-MS U–Pb dating results indicate that the Hongxiaqiao, Xuehuading, Baimashan and Wanyangshan granitoids were intruded at 451 ± 1 Ma (MSWD = 1.8), 412 ± 1 Ma (MSWD = 2.4), 415 ± 1 Ma (MSWD = 3.0) and 445 ± 1 Ma (MSWD = 3.9), respectively. The I-type granitoids have variable initial 87Sr/86Sr values of 0.71160–0.72362, high εNd(t) values (−6.5 to −8.1), and young T2DM ages of 1717–1894 Ma. In contrast, the S-type granitoid has consistent initial 87Sr/86Sr values of 0.71448–0.71887, slightly lower εNd(t) values (−9.8 to −10.3), and older T2DM ages (1977–2015 Ma), which suggests that they were derived from partial melting of different Paleoproterozoic basement rocks, without significant crustal contamination. The older Hongxiaqiao and Wanyangshan granitoids were formed in a compressional setting, whereas the younger Xuehuading and Baimashan granitoids were generated in a post-orogenic extensional setting. Integrated with geological evidence, we proposed that the Early Paleozoic Wuyi–Yunkai orogeny in the SCB resulted from intraplate orogenesis triggered by far-field tectonic response to the assembly of the northern East Gondwana, rather than from oceanic subduction–collision.

Early Paleozoic intracontinental granites in the Guangzhou region of South China: Partial melting of a metasediment-dominated crustal source

Whether the formation of early Paleozoic granites in the South China Block was related to intracontinental orogenic processes or oceanic subduction continues to be debated. Here, we present whole-rock major element, trace element, and SrNd isotopic data, as well as secondary ion mass spectrometry and laser ablation–inductively coupled plasma–mass spectrometry zircon UPb geochronological and HfO isotopic data, from biotite, two-mica, and muscovite granites in the Baiyunshan and Maofengshan areas of Guangzhou City, South China. Zircon UPb ages reveal that these rocks were formed during the early Paleozoic (446–438 Ma). These muscovite- and biotite-bearing granites have high SiO2 (69.0–80.4 wt%) and K2O (3.19–5.32 wt%) contents, and low MgO (0.46–1.17 wt%) contents. The granites are enriched in Rb, Th, U, and Pb, and depleted in Ba, Sr, Nb, and Ti. The Baiyunshan muscovite granites and Maofengshan biotite granites are slightly to moderately enriched in light rare-earth elements [LREEs; (La/Yb)CN = 2.27–15.1] with slight to pronounced negative Eu anomalies (Eu/Eu* = 0.27–0.72), whereas the Baiyunshan two-mica granites are significantly enriched in LREEs [(La/Yb)CN = 19.6–32.1] with moderate negative Eu anomalies (Eu/Eu* = 0.42–0.58). These muscovite- and biotite-bearing granites have enriched whole-rock Nd and zircon Hf isotopic compositions (εNd(t) = −12.1 to −7.6; εHf(t) = −11.4 to −0.8), and high zircon δ18O values (8.5‰–10.0‰). We suggest that the Baiyunshan granites were formed by partial melting of metasedimentary rocks, as they contain primary muscovite and have high zircon δ18O values. The Maofengshan granites were formed by partial melting of a hybridized crustal source containing metasedimentary rocks with subordinate amphibolites, as they have high zircon δ18O values, variable whole-rock SiO2 contents, and biotite compositions similar to those crystallized in I- and S-type magmas. These granites, along with the widespread early Paleozoic S-type granites in the Wuyi–Yunkai orogen, are distributed across a broad area rather than in a narrow belt. In addition, early Paleozoic S-type granites in the South China Block generally do not show younging trends from east to west or south to north. Moreover, the Baiyunshan–Maofengshan granites show geochemical characteristics similar to syn- or post-collisional granites and different from volcanic arc granites. We therefore propose that these muscovite- and biotite-bearing granites were formed in an intracontinental orogenic setting.

Provenance and tectonic setting of the Ordovician sedimentary succession at the southeastern margin of the Yangtze Block, South China: Implications for paleotopographic evolution of northestern Gondwana

Abstract Ordovician sedimentary strata at the southeastern margin of the Yangtze Block consist of, from bottom to top, fine-grained siliciclastic rocks, cherts with interlayers of siliceous/carbonaceous slate, and coarse-grained siliciclastic rocks, which are important for understanding the tectono-sedimentary evolution in South China. A combined analysis of petrography, whole-rock geochemistry, and zircon U–Pb dating was carried out on these strata. The cherts with radiolarian fossils have high Al/(Al + Fe + Mn) values (0.38–0.94) and no obvious Ce anomalies (1.09 ± 0.05), suggesting a biogenic origin on a continental margin. The geochemical features of the siliciclastic rocks, including ratios of elements, discriminant functions, and ternary diagram positions, suggest a passive margin setting that received detritus mostly derived from intermediate to felsic igneous rocks and recycled quartzose sedimentary rocks. The source areas of the Ordovician siliciclastic rocks existed in semiarid–arid paleoclimate and moderate weathering conditions. The sandstone modal grain compositions and detrital zircon cumulative curves indicate a collisional setting of the source areas. Zircon age populations have been time-varying during the Early Paleozoic. Based on the above-mentioned evidences, the following basin filling and paleotopographic evolution process has been proposed in research area. In the Cambrian, a bilateral filling pattern reflected a flat and broad basin. In the Early Ordovician, longer transportation of SE-sourced sediments reflected the uplift of Gondwana. In the Late Ordovician, uplift of the Wuyi–Yunkai Orogen blocked some Gondwanan detritus (500–700 Ma) and released recycled (900–1100 Ma) and syn-orogenic detritus. Meanwhile, synchronous uplift of the Jiangnan Orogen led to a steeper and narrower basin, and sediments could reach farther distances in a shorter time. In the Silurian, a unidirectional filling pattern with overwhelming SE-sourced detritus indicated intense uplift of Gondwana and the Wuyi–Yunkai Orogen.

Major lithologies of the high-grade Zhoutan terrane within the Cathaysia Block and their tectonic implications for the Neoproterozoic - Paleozoic South China

Pre-Devonian crystalline basement of the Cathaysia Block was united through the Wuyi-Yunkai orogeny. The uplifted orogenic core is dominantly composed of Paleozoic high-grade terranes occurring in a northeast-southwest trending belt. The Zhoutan terrane in the middle part of this belt is one of the key terranes to reveal the tectonic architecture of the South China Block. However, how to correlate it with other high-grade terranes, what kind of rock records are preserved in this terrane and their tectonic implications for the Wuyi-Yunkai orogen are still unresolved. This paper carries out an integrated study on the petrology, zircon U--Pb geochronology, geochemistry and zircon Lu--Hf isotopic compositions of the main rock types in the Zhoutan terrane, with a purpose of better understanding the Wuyi-Yunkai orogeny. Mafic granulite (noritic) of high-T and low-P conditions occurs as lenses within the Zhoutan Formation. The zircon U--Pb geochronological data give magmatic and metamorphic ages of 460–450 Ma and ~ 430 Ma, respectively. Neoproterozoic and Paleoproterozoic (1.89 Ga) xenocrysts also occur. Meta-pelites of the Zhoutan Formation experienced high T/P amphibolite facies metamorphism, and ages of their detrital zircons are dominantly Neoproterozoic (810–820 Ma) with some subordinate Paleo- to Mesoproterozoic and Archean signatures. Amphibole gneiss layers of this formation give a Paleozoic metamorphic age of ~450 Ma, consistent with the high-P amphibolite facies metamorphism of the neighboring Longyou terrane. Fine-grained garnet mica-schist of the Wanyuan Formation consists of greenschist to amphibolite facies mineral assemblage and detrital zircons of these meta-sediments display both Neoproterozoic and early Precambrian ages at ~770 Ma, ~820 Ma, ~850 Ma, ~1.84 Ga and 2.48 Ga. Metamorphosed calc-silicates of the Wanyuan Formation show similar detrital zircon age peaks of 624 Ma, 780–790 Ma, ~810 Ma, 840–850 Ma, 1.8–1.98 Ga and ~ 2.48 Ga, and a Paleozoic metamorphic age of ~447 Ma. The Cizhu pluton is a composite granitoid body intruding the Zhoutan and Wanyuan formations, with emplacement ages ranging at least from 485 Ma to 446 Ma. εHf(t) values of zircons from the mafic granulite range from −10.9 to +8.5, indicating its protolith derived from enriched mantle sources with or without crustal contaminations. The Cizhu magmatic event is a crustal reworking event as indicated by the coherently negative zircon εHf(t) values and ancient Hf crustal model ages of 1530–1830 Ma. Zircon εHf(t) values of the metamorphosed calc-silicates show large variations, ranging from −21.2 to +11, consistent with its complex provenances. The deposition of the sedimentary rocks of the Zhoutan and Wanyuan formations is consistent with the development of the Neoproterozoic-Paleozoic Nanhua Rift. The development of continental margin sequences like the Zhoutan and Wanyuan formations, the evolution of the Paleozoic metamorphism from early higher P/T metamorphic stage to later lower P/T stage, as well as the generation of the Paleozoic mafic-ultramafic rocks and the intermediate Cizhu pluton, are best explained by collision to post-collision settings. We, therefore, conclude that the Zhuotan terrane (as well as other high-grade terranes) witnessed a whole geological cycle, from early rifting to the closure of a rifted basin (Nanhua Basin), and the final lithospheric delamination following the rejoining of continental blocks flanking the rift.

Origin of the Heping granodiorite pluton: Implications for syn-convergent extension and asthenosphere upwelling accompanying the early Paleozoic orogeny in South China

We present geochemical and geochronological data of host granodiorites and mafic microgranular enclaves (MMEs) from the Heping pluton, which is situated in the central part of the Wuyi-Yunkai Orogen (WYO) in the South China Block (SCB), and reveal syn-convergent extension and asthenosphere upwelling during the early Paleozoic intracontinental orogeny. Two host and two MME samples from the Heping pluton yield LA-ICP-MS zircon UPb ages of ca. 445 Ma, coincident with the peak magmatism-metamorphism of the WYO. The host granodioritic samples are metaluminous (A/CNK = 0.68–0.91) and have abundant amphibole and low-moderate SiO2 (59.1 to 67.3 wt%), belonging to high-K calc-alkaline I-type granite, whereas the MMEs are more basic with SiO2 of 56.3 to 59.6 wt%. Both the host and MME samples display weakly negative Eu anomalies and distinctly relative depletions of Ta, Nb, and Ti, and most of them share similar initial 87Sr/86Sr ratios of 0.7089–0.7112 and εNd(t) values of −6.52 to −7.12, except one MME sample with a lower initial 87Sr/86Sr of 0.70758 and a higher εNd(t) of −4.33. The zircon εHf(t) values exhibit a wide range from −13.68 to −0.87. Petrological, geochemical, and chronological data suggest that the Heping pluton were generated by mingling of mafic and felsic magmas. The mafic endmember magma was originated mainly from the enriched subcontinental lithosphere mantle at the spinel–garnet transitional zone (~70 km), subsequently underplated/intraplated into the lower-middle crust resulting in the melting of the intermediate rock at pressure < 8 kbar to produce the felsic endmember magma. We proposed a new tectonic model “syn-convergent extension and asthenosphere upwelling during the intracontinental orogeny”. The syn-convergent extension zones, which include a series of NW-trending transverse faults and the NE-trending reactivated pre-exsiting suture and rift zone (i.e. Shaoxing-Jiangshan -Pingxiang- Chenzhou fault) within the WYO, are in favor of asthenosphere upwelling leading to intensive crust-mantle interaction.

Partial Melting and Crustal Deformation during the Early Paleozoic Wuyi–Yunkai Orogeny: Insights from Zircon U-Pb Geochronology and Structural Analysis of the Fuhuling Migmatites in the Yunkai Region, South China

：Migmatites record crucial information about the rheology and tectonothermal evolutionof the deep crust during orogenesis. In the Wuyi–Yunkai orogen in South China, migmatites at Fuhuling record Early Paleozoic high temperatures and associated partial melting. However, the absolute timing and implications for the rheology of the deep crust during orogenesis are poorly constrained. In this contribution, we used spatial analysis of migmatitic leucosomes, structural analysis, and U-Pb geochronology of zircon to elucidate the absolute timing of crustal partial melting, the degree of partial melting, and the role of partial melting on the rheology of the crust during the Wuyi–Yunkai orogeny. Partial melting of the Fuhuling migmatites occurred at c. 440 Ma during Early Paleozoic Wuyi–Yunkai orogenesis. Subsequent lower temperature metamorphism associated with Indosinian movement that caused minor zircon recrystallization was temporally associated with the crystallization of nearby biotite monzogranites, but it did not influence the morphology of the Fuhuling migmatites. The migmatites preserve a morphological transition from metatexite to diatexite with an increasing proportion of leucosome. This transition preserves different structural characteristics that represent the response of the solid framework and melt network to variable melt fractions during partial melting. The large proportion of in situ or in source leucosome in the Fuhuling migmatites suggests that it was a melt-rich crustal horizon during orogenesis, and that a substantial proportion of anatectic melt was retained in the deep crust. The rheological transition documented in the Fuhuling migmatites was caused by changes in the melt fraction, and it is an analogue for the rheological transition characteristics of melt-rich crustal horizons in the Yunkai region during Early Paleozoic Wuyi–Yunkai orogenesis and subsequent orogenic collapse.

Early Paleozoic granitoids from South China: implications for understanding the Wuyi-Yunkai orogen

ABSTRACTThe early Paleozoic Wuyi-Yunkai orogeny involves voluminous magmatism and represents the first major tectonothermal event in the South China block since the Neoproterozoic break-up of the Rodinia supercontinent. Here we investigate three representative granitic plutons in Guangxi province of southwest China with a view to understand the magmatic response of the Wuyi-Yunkai orogeny. We present the results of major and trace elements, Sr-Nd isotopes, zircon U-Pb ages and Hf isotope. LA-ICPMS zircon U-Pb geochronology reveals that these plutons emplaced during the early Silurian (441–432 Ma), overlapping with the reported ages of the early Paleozoic magmatism in this orogen. Among the three plutons investigated in this study, the Qinjia pluton is characterized by weakly to strongly peraluminous (A/CNK = 1.0–1.2) nature with SiO2 content varing from 70.6 to 72.3 wt.%. Combined with the relatively high εNd(t) values (−4.9 to −4.2) and εHf(t) values (−2.9 to +6.1), the Qinjia pluton is thought to derive from partial melting of metasedimentary and metabasic rocks and there may exsit juvenile components in magma source. The Damingshan porphyritic granites (SiO2 = 74.8–76.5 wt.%) and Yingqiao granites (SiO2 = 76.5–76.6 wt.%) are strongly peraluminous (A/CNK = 1.1–1.6) and they have negative zircon εHf(t) values (−6.8 to −4.2, −12.8 to −6.1, respectively) and whole-rock εNd(t) values (−6.3 to −6.2, −8.4, respectively). These signatures indicate that the Damingshan and Yingqiao plutons were derived from partial melting of ancient metasedimentary rocks. Combining our data with those from previous studies on the magmatic, sedimentary and metamorphic records of this area, we suggest that the early Paleozoic magmatism is likely associated with lithospheric delamination and the Wuyi-Yunkai orogen is an intracontinental orogen linked to the far-field response to the assembly of the South China block with the Gondwana in the early Paleozoic.

Melt evolution of crustal anatexis recorded by the Early Paleozoic Baiyunshan migmatite-granite suite in South China

The Early Paleozoic orogeny in the South China Block was accompanied by crustal anatexis, as indicated by the voluminous granites and migmatites. Here we report on the migmatite-granite suite within the Neoproterozoic biotite gneiss of the Baiyunshan Domain, which has directly recorded the process of anatectic melt formation, segregation and extraction. The crystallization of leucosome in migmatite was dated at ca. 438 Ma by U–Pb analysis of zircon, and the granitic vein that intruded the migmatite was dated at ca. 433 Ma. Petrological and geochemical data suggest that anatexis resulted from fluid-present melting of the biotite gneiss at low temperature and pressure conditions (~650–700 °C and ~4–6 kbar). The leucosome mainly consists of plagioclase + K-feldspar + quartz and has positive Eu anomaly (Eu/Eu* = 1.70–2.89), which is attributed to feldspar accumulation. This means that some melt has been extracted from the migmatite, and the granitic veins are likely to represent these extracted melts since they have similar trace element compositions and zircon LuHf isotopes to the leucosomes. The degree of partial melting and chemical differentiation to generate the migmatite and the granitic veins are revealed by mass balance calculations. Calculations suggest that the primary melt could be a result of ~40 wt% melting of the Baiyunshan biotite gneiss, and fractionated melt (~24–26 wt%) was extracted from the deeper sections to form the intrusive veins. Combined with regional dating results, it is suggested that the crustal anatexis in the Wuyi-Yunkai orogen started no later than 465 Ma with a duration of >55 Myr. Generation of the granitoids and migmatites are a result of water-fluxed melting and linked to extra heat from mantle magmas provided to the middle-lower crust.