Tectonic Evolution Of South China Research Articles

Integrated detrital rutile and detrital zircon ages: a new perspective on the tectonic evolution of South China

Abstract Paleogeographic reconstructions are of key importance for understanding the history of continental breakups and amalgamations during the whole history of the Earth. A special case is the history of the Asian continent, which, compared to other continents, consists of several large cratons and numerous smaller continental blocks. The history of the assembly of South China remains controversial in terms of the timing, Late Neoproterozoic or Early Paleozoic, and the participating continental blocks, e.g., Yangtze, Cathaysia, India and/or Australia. Detrital rutile U-Pb dating possesses a significant potential for deciphering tectonic settings as rutile frequently crystallizes during orogenic events associated with the processes of collision and subduction. Detrital zircon U-Pb dating is a perfect instrument for identifying provenance characteristics and age characteristics of sedimentary sources. An integration of these two methods of dating offers better opportunities for reconstructing tectonic settings. This paper presents a first attempt to reconstruct the Neoproterozoic to Early Palaeozoic tectonic history and paleogeography of the whole South China Block based on U-Pb geochronology of rutile and zircon and Hf-in-zircon isotopes from Lower Jurassic Baitianba Formation sedimentary rocks of the western margin of the Yangtze Block, a major part of South China. Our obtained integrated U-Pb rutile and zircon age data show three main age populations of 960-940 Ma, 630-610 Ma and 530-520 Ma. The new U-Pb detrital rutile and zircon ages, compared with former data from Gondwana and Australia, suggest that Yangtze amalgamated with Cathaysia to form South China during the Sibao orogeny at 960-940 Ma. The detrital rutile and zircons of the new 630-610 Ma age group could have been delivered from western Australia during Late Neoproterozoic to Cambrian Paterson-Petermann orogeny. The abundant 530-520 Ma detrital rutile and zircon ages fit well the coeval zircon age populations recorded in Gondwana-derived terranes, like India and Indochina.

The important boundary role of Lianhuashan fault zone in late Mesozoic magmatism of South China: New insights from ambient noise tomography and teleseismic data

The Lianhuashan fault zone (LHSFZ), which divides the Cathaysia Block (CB) into the coastal volcanic and Cathaysian fold belts, is an important intraplate lineament in the CB. Its fine structure is crucial to understand the Late Mesozoic tectonic evolution of South China. Herein, the fine S-velocity structure of the LHSFZ above 6.0 km and its depth extent were studied by ambient noise tomography and teleseismic relative travel-time residual analysis using a dense (∼1 km station spacing) seismic array spanning 123 km at the southern end of the LHSFZ. Our results indicate that the area within 70 km of the coast has a higher S-wave velocity, which extends to the southeast below 6 km. We propose that the high velocity anomaly is a result of magma intrusion caused by the subduction of the Paleo-Pacific plate in the Late Mesozoic, and the magma upwelling trajectory occurs from the coast to the inland. In addition, a low-velocity anomaly is found beneath the core area of the LHSFZ at a depth of 3–6 km, which is more evident in the S-wave than in the P-wave and corresponds well with the presence of hot springs and earthquakes. We hypothesize that the low-velocity anomaly represents the existing fault system of the Late Mesozoic volcanoes, which now provides channels for fluid migration and facilitates seismicity. Our model suggests that the LHSFZ plays a key role in the evolution of the coastal areas of South China.

Development of a mid-Neoproterozoic arched rift in eastern South China as a response to the Rodinia breakup

The initial time (before or after ∼ 820 Ma) and geodynamic mechanism (bottom-up rising mantle plume or top-down deep subduction) of Rodinia breakup remain unresolved. This issue has impacted our current understanding of the tectonic evolution of South China. Some scholars believe that separation of the South China Craton (SCC) from the Rodinia supercontinent and contemporary SCC rifting began at ca. 860 Ma and was induced by a subduction-related extension event. In addition, other researchers consider that the SCC rifting occurred after ca. 820 Ma. We show that renewed Rodinia breakup within or along the margin of South China occurred ca. 820–740 Ma, which is supported by early studies and our newly obtained U–Pb zircon ages of 755.4 ± 1.0 and 801.6 ± 5.2 Ma from basalts and mafic intrusive bodies in an arched (arc-shaped) belt. Major elemental variations and calculated datasets for the rift-related igneous rocks suggest a mantle plume origin for the dated rocks, which indicates that the SCC rifting was driven by a rising mantle plume and formed several rifts. This arched belt, including < 820 Ma sedimentary and igneous rocks within it, may well have been the eastern part of the original Nanhua Rift, i.e., the prototype of the Nanhua Rift should be a “T” shape. Owing to a barren magmatic area at the “T” junction, the Nanhua Rift must have split into the Nanhua Rift and arched rift. We suggest that the first stage of rifting event during 860–825 Ma may occurred in the interior Yangtze or Cathaysia Block and was associated with a subduction-related extension event.

Ca. 830 Ma alkaline mafic dykes in the southeastern Guizhou Province, South China: New constraints on the Neoproterozoic evolution of the Yangtze Block

The Neoproterozoic alkaline mafic rocks in the Yangtze Block are critical to investigate the magmatic and tectonic evolution of South China. However, these rocks are rarely exposed. We here present a detailed study of ca. 830 Ma alkaline mafic dykes newly identified from a drilled borehole at the Nage area in the southern Yangtze Block. The dykes have SIMS zircon U-Pb ages of 827 ± 8 Ma. They show coherent variations in major and trace elements, characterized by enrichment in LREE and incompatible elements and no significant Nb-Ta and Zr-Hf anomalies, suggesting that their parental magmas have experienced varying degrees of fractionation crystallization with negligible crustal contamination. Modeling calculations based on their εNd(T) values (-0.55–3.23), SiO2 contents (48.38–53.61 wt%) and elemental ratios (e.g., La/Ta and Nb/La) suggest that the Nage mafic dykes were probably generated from an asthenospheric mantle with previously input of a plume-derived enrich component occurred within the source region rather than during ascent. Rocks from the Nage dykes exhibit OIB-like trace element and REE patterns as well as trace elemental compositions, which are different from arc-related igneous rocks but similar to alkaline basalts and mafic dykes formed in mantle plume related rifting systems around the world. In combination with tectonostratigraphic evidences, the Nage dykes in this study are suggested to have been generated in an intraplate rift which was probably induced by a mantle plume beneath the Yangtze Block.

Late Tonian (ca. 785 Ma) subduction-related mafic-ultramafic cumulates in the West Cathaysia terrane, South China

The Neoproterozoic tectonic setting of the West Cathaysia terrane and its relationship with the Yangtze Block are critical to understanding the formation and tectonic evolution of South China. A detailed study of late Tonian mafic-ultramafic cumulate slivers embedded in the Shenshan tectonic mélange along the northwest margin of West Cathaysia is presented here with the aim of elucidating its Neoproterozoic tectonic history. These partly-altered mafic-ultramafic rocks include olivine-bearing cumulates (olivine pyroxene hornblendite or olivine hornblende pyroxenite), pyroxene hornblendite, and gabbroic cumulates. The early crystallization of clinopyroxene and the abundance of hornblende indicate that they formed from hydrous magmas. The rocks have similar geochemical distribution patterns and show variable initial 87Sr/86Sr ratios of 0.702679 to 0.709742 and positive εNd(t) values of +2.10 to +4.52. The mineral compositions of the clinopyroxene and hornblende and their whole-rock extended normalized trace element patterns show features (e.g., negative Nb anomalies, LILE enrichment) typical of rocks with an arc affinity. The high calculated Mg# values (58–77, average 71) of the equilibrium magmas are close to those of primary mantle-derived basalts. We conclude that these mafic and ultramafic cumulates were derived from a subduction-related, hydrous, magnesian basalt in a subduction setting. The estimated crystallization temperature and pressure, based on the composition of the amphiboles, suggest that the minerals accumulated in magma chambers at middle to lower crustal depths. LA-ICP-MS U-Pb dating of zircon from the gabbroic cumulate indicates crystallization at ca. 785 Ma. A previous interpretation for West Cathaysia at this time involved a continental rift basin (the Nanhua basin) that straddled the southeastern margin of the Yangtze Block and the northwestern margin of West Cathaysia. In contrast, our results suggest that West Cathaysia was an arc at ca. 785 Ma, which supports the interpretation that the amalgamation between Yangtze and West Cathaysia did not occur in the Tonian, but more likely in the early Paleozoic.

Seismological reference earth model in South China (SREM-SC): Upper mantle

This work is the mantle component of constructing the Seismological Reference Earth Model in South China (SREM-SC). Although there has been a wide range of research for imaging the upper mantle structures beneath South China, most of them focus on the large-scale features of the upper mantle, and the depth resolution is insufficient for existing surface wave tomography models to distinguish anomalies below 200 km. This study aims to develop a 3-D upper mantle Seismological Reference Earth Model in South China based on the prior tomography models. The shear wave velocity model comes from the analysis of several seismic surface wave tomography, supplemented by body wave tomography and the P-wave velocity model is constructed by the conversion from S-wave velocity. The radial anisotropy model is calculated from the SV-wave and SH-wave velocity. The Density model of the upper mantle is derived using the empirical relationship linking the density to the shear-wave velocity. The model is grid with 0.5° × 0.5° in latitude and longitude and 5 km interval in depth from 60 to 300 km. The mantle component of Seismological Reference Earth Model in South China is expected to provide a good representation of the upper mantle structures for further detailed studies. The mantle component of Seismological Reference Earth Model in South China provides new insights into upper mantle structures that should be meaningful to reveal the dynamic mechanism and tectonic evolution of South China.

Mineralogical, Geochronological, and Geochemical Characteristics of Early Cretaceous Granite in South China: Implications for Tectonic Evolution and REE Mineralization

One of the most important geological features of South China are the widespread Mesozoic igneous rocks that play a key role in revealing the tectonic evolution of South China. Due to the thick covering of vegetation and Quaternary sediments, the early Cretaceous magmatism in southwestern South China is still not well constrained. In this paper, we report newly identified early Cretaceous granites in Guangxi, South China. Zircon U–Pb dating results showed that representative fine-grained and coarse-grained granites in northeastern Guangxi indicate the early Cretaceous ages of 141 ± 3 Ma and 141 ± 4 Ma, respectively. Geochemically, both fine-grained and coarse-grained granites had high 10,000 × Ga/Al ratios and belonged to A-type granite. They had undergone high degrees of magma differentiation, as evidenced by extremely negative Sr, Ba, and Eu anomalies. They had high REE (rare earth elements) contents (&gt;451 ppm). The fine-grained granites were characterized by higher HREE (heavy rare earth elements) contents, lower LREE (light rare earth elements) contents, and lower LREE/HREE ratios than the coarse-grained granites. Integrated with regional geological data, the early Cretaceous granites were likely formed in a back-arc extensional environment in response to the increased subduction angle of the Paleo-Pacific plate. Different REE contents in the fine- and coarse-grained granites may be a result of fractional crystallization. Magma differentiation and hydrothermal alteration might have played an important role in REE mineralization of the early Cretaceous granites in Guangxi.

Early Cretaceous compressive structures in the Nansha block (Dangerous Grounds): Implications for the late Mesozoic tectonic regime on the southern margin of the South China Sea

The Mesozoic and Cenozoic tectonic evolution of South China is important for understanding the transition from subduction to extension related to the Paleo-Pacific plate. Here, the compressive structures of Lower Cretaceous sequences in the Liyue Bank (Reed Bank) and Nansha block (Dangerous Grounds) are presented using drilling data from Mesozoic strata and seismic data. Both south-directed and north-directed thrust nappes developed on the southern margin of the South China Sea. In addition, we observed a series of Early Cretaceous compressive structures in the Chaoshan Depression along the northern margin of the South China Sea. The compressive structures are accompanied by sedimentary environment changes from abyssal to continental deposition between 128.5 Ma and 79.5 Ma, which is perhaps associated with the collision between the South China block and Luconia block (Luconia-Dangerous Grounds-Reed Bank). The late Mesozoic thrust structures in the Chaoshan Depression and Liyue Bank (Reed Bank) and Nansha block (Dangerous Grounds) are related to the subduction of the Paleo-Pacific Ocean.

Neoproterozoic to Palaeozoic tectonic deformation history of the western Jiangnan Orogen, South China: Insights from new structural and geochronological data from northern Guangxi

Recognition of deformation events documented in Neoproterozoic sedimentary sequences of the Jiangnan Orogen is critical in understanding the tectonic evolution of South China. In this contribution, we present new field based structural observations, microstructural analysis, and geochronological data for the Sibao and Danzhou groups in the southwestern Jiangnan Orogen of northern Guangxi, South China. Integrating the new information with previously published structural and geochronological data, we have identified three major deformation events. The earliest event generated E–W‐trending high‐angle tight linear and overturned isoclinal folds in the Sibao Group with their fold axial planes dipping to the south. This shortening event occurred in the mid‐Neoproterozoic time (840–800 Ma) and was associated with the orogenic collision between the Yangtze and Cathaysian blocks in South China. The angular unconformity between Sibao and Danzhou groups provides strong evidence for the collision. The second deformation event produced the large‐scale NNE–SSW‐striking ductile shear zones in the region. It also overprinted the pre‐existing E–W‐trending folds, refolded the Sibao Group, and generated the large‐scale NNE–SSW‐trending open folds in the overlying Danzhou Group and the west‐dipping cleavage within both groups. The second event occurred during the early Palaeozoic time (460–410 Ma) as a result of a WNW–ESE‐oriented intracontinental shortening process. The latest deformation event generated slight crenulation cleavage in the Sibao Group, some folds in the marble units of the Danzhou Group, and normal‐sense shearing along the pre‐existing NNE–SSW‐striking shear zones, all of which are the result of a NW–SE‐directed crustal extension during the late Palaeozoic (410–350 Ma) Kwangsian (Caledonian) orogenic collapse.

Origin and age of the Shenshan tectonic mélange in the Jiangshan-Shaoxing-Pingxiang Fault and late Early Paleozoic juxtaposition of the Yangtze Block and the West Cathaysia terrane, South China

AbstractWhen and how the Yangtze Block (Yangtze) and the West Cathaysia terrane (West Cathaysia) in South China were amalgamated are critical to a better understanding of the Neoproterozoic to early Paleozoic tectonic evolution of South China and remain highly debatable. A key to this debate is the tectonic significance of the Jiangshan-Shaoxing-Pingxiang (JSP) Fault, the boundary between Yangtze and West Cathaysia. The Shenshan mélange along the JSP Fault has the typical block-in-matrix structure and is composed of numerous shear zone-bounded slivers/lenses of rocks of different types and ages that formed in different tectonic environments, including middle to late Tonian volcanic and volcanogenic sedimentary rocks (turbidite) of arc/back-arc affinity, a series of middle Tonian ultramafic to mafic plutonic rocks of oceanic island basalt affinity, a carbonaceous shale that was deposited in a deep marine environment, and a red mudstone. U-Pb zircon ages and acritarch assemblages (Leiosphaeridia-Brocholaminaria association) found in the turbidite confirm its Tonian age, and fossils from the carbonaceous shale (Asteridium-Comasphaeridium and Skiagia-Celtiberium-Leiofusa) constrains its age to the Early to Middle Cambrian. Field relationships and available age data leave no doubt that the ultramafic-mafic rocks are exotic blocks (rather than intrusions) in the younger metasedimentary rocks. We conclude that the Shenshan mélange is not an ophiolitic mélange, but rather a tectonic mélange that formed as a result of movement along the JSP Fault in the early Paleozoic. We suggest that Yangtze and West Cathaysia were two separate microcontinents, were accreted to two different parts of the northern margin of Gondwana in the early Early Paleozoic, and juxtaposed in the late Early Paleozoic through strike-slip movement along the JSP Fault. We further suggest that the ca. 820 Ma collision in the Jiangnan Orogen took place between Yangtze and a (micro)continent that is now partly preserved as the Huaiyu terrane and was not related to West Cathaysia. We compare our model for South China with the accretion of terranes in the North American Cordillera and propose a similar model for the relationship between the Avalon and Meguma terranes in the Canadian Appalachians, i.e., the two terranes were accreted to two different parts of the Laurentian margin and were later juxtaposed through margin-parallel strike slip faulting.

The Mojiawan I-type granite of the Kangding Complex in the western Yangtze Block: new constraint on the Neoproterozoic magmatism and tectonic evolution of South China

ABSTRACT Studies of Neoproterozoic granites near the western margin of the Yangtze Block provide new evidence on the mechanism leading to the Neoproterozoic break-up of the Rodinia Supercontinent. This contribution focusses on the structural geology, geochemistry, zircon U-Pb geochronology, and Hf-O isotope systematics of the poorly documented Mojiawan Monzogranite in the Kangding Complex, which gives us better constraints on the break-up of the supercontinent. Zircon U-Pb data show that two samples of the Mojiawan Monzogranite were emplaced during 797 ± 13 Ma and 785 ± 11 Ma (ca. 791 Ma). The granitic samples are Na-rich, calc-alkaline, peraluminous with A/CNK values of 1.13 and 1.25, and their zircons have positive εHf(t) values between +4.28 and +9.79 with crustal model ages TDM2 of 1424 to 1079 Ma, indicative of a juvenile source. The granitic samples also have low Rb/Sr and Rb/Ba ratios and high δ18O values of 5.42‰–8.97‰, consistent with derivation from the partial melting of the lower to middle crust. Combined with the geochemistry of other granitic plutons along the western margin of the Yangtze Block, we propose that the region records rifting at ca. 800 Ma due to the action of a mantle super-plume leading to the break-up of the Rodinia Supercontinent.

Amalgamation between the Yangtze and Cathaysia blocks in South China: Evidence from the ophiolite geochemistry

Neoproterozoic ophiolites in the southeastern margin of the Yangtze Block record tectonic evolution of South China. The ∼1.0 Ga Xiwan ophiolite and the ca. 830 Ma Fuchuan ophiolite indicate a long-term assembly of the Yangtze and Cathaysia blocks during the Neoproterozoic time. Peridotites from the Xiwan ophiolite show high Al2O3 (1.24–2.67 wt%) and low MgO contents (39.61–44.26 wt%), similar to the abyssal and back-arc peridotites that experienced low degrees of partial melting. Their U-shaped REE patterns and HFSE enrichment indicate weak melt metasomatism. Whole rock 187Re/188Os (0.09–0.29) and 187Os/188Os ratios (0.11526–0.12193) yield a melt-extraction age of 1.8–2.1 Ga. However, peridotites from the Fuchuan ophiolite are more refractory and have low Al2O3 (0.51–0.95 wt%) and high MgO contents (43.99–48.24 wt%), similar to the forearc peridotites that underwent high degrees of melt extraction. Their 187Re/188Os (0.01–1.08) and 187Os/188Os (0.11852–0.12867) variations may have resulted from fluxed melting induced by the subduction-related fluids. The peridotites, in combination with the overlying mafic oceanic crustal rocks, suggest that the Xiwan and Fuchuan ophiolites are SSZ-type ophiolites which were formed in back-arc and forearc settings, respectively, followed by the collision between the Yangtze and Cathaysia blocks at ca. 830 Ma.

Geographic proximity of Yangtze and Cathaysia blocks during the late Neoproterozoic demonstrated by detrital zircon evidence

The late Neoproterozoic (~720–541 Ma) tectonic evolution of South China may have included the development of a paleo-ocean basin (the South China Ocean Basin, SCOB) between the Yangtze and Cathaysia blocks. The Niuhe section in the Yongfu area of northern Guangxi Zhuang Autonomous Region, owing to its location on the southeastern margin of the Yangtze Block and its preservation of an alternating succession typical of both Yangtze- and Cathaysia-type deposits, provides an important window to test if this oceanic basin existed during the late Neoproterozoic. Cryogenian-Ediacaran siliciclastics in the northern Guangxi region were deposited in the intracontinental Xiang-Gui Basin. Detrital zircon assemblages from the Cryogenian Lijiapo Formation at Niuhe yield a prominent UPb age peak of ~774 Ma, with a minor peak of ~891 Ma, indicative of provenance from the Yangtze Block to the northwest. In contrast, zircon samples from the Cryogenian Zhengyuanling Formation of the Laoshan area (Guangxi Zhuang Autonomous Region), which is located closer to the Cathaysia Block than Niuhe, yield a prominent age peak of 959–1112 Ma, consistent with a Cathaysian provenance. Furthermore, three samples of Ediacaran sandstones from Niuhe yield an age peak of ~900–1100 Ma, also demonstrating provenance from the southeast (i.e., Cathaysia). The Cathaysian provenance of Ediacaran sandstones on the southeastern margin of the Yangtze Block does not support the scenario of a broad SCOB between the Yangtze and Cathaysia blocks during the Ediacaran, and the Xiang-Gui Basin is best regarded as an immature intracontinental rift (aulacogen). Uplift of the Cathaysian Block through slab retreat on its external (southeastern) margin (i.e., the ‘top-down’ model of Rodinian breakup) may have been responsible for generation of a massive influx of siliciclastics into the Xiang-Gui Basin during the Ediacaran.

Sedimentary Facies, Provenance and Geochronology of the Heshangzhen Group: Implications for the Tectonic Evolution of the Eastern Jiangnan Orogen, South China

AbstractThe Neoproterozoic Jiangnan orogen plays an important role in the study of the Precambrian tectonic evolution of South China. The tectonic nature of the Neoproterozoic sedimentary basins is still controversial, due to poor understanding of the sedimentary sequences and the lack of geochronological data. Here, we present sedimentological, provenance and geochronological data from the Heshangzhen Group in the eastern Jiangnan orogen. Sedimentological analysis shows that the Luojiamen Formation was deposited in a submarine fan, and the overlying Hongchicun Formation was deposited in front of a fan delta. The youngest detrital zircons constrain the lower Luojiamen and Hongchicun formations with ages of 827.3 ± 8.4 Ma and 825 ± 12 Ma, respectively. The sandstones of the Luojiamen Formation are characterized by a large number of intermediate to felsic volcanic grains, suggesting a volcanic arc source. In contrast, quartz and sedimentary lithic grains increase in the Hongchicun Formation, showing a new input from a collisional orogenic source. Detrital zircon from six sandstone samples in the Luojiamen and Hongchicun formations yield similar age spectra of 930–820 Ma with a peak at ca. 845–860 Ma, with one main cluster at 930–820 Ma. Detrital zircons of 930–845 Ma show a positive value of ∊Hf (t) (+2.4 to +11, mean +7.6), which is similar to the volcanic arc of the nearby Shuangxiwu Group. There are a minor group of zircons with U‐Pb ages ranging from 820 Ma to 845 Ma from the middle part of the Luojiamen Formation and Hongchicun Formation, with ∊Hf (t) values between –20 to +2.4, which are consistent with the characteristics of the Shuangqiaoshan Group. within light of the bidirectional paleocurrents in the Luojiamen Formation, it is speculated that the zircons of 820–845 Ma were recycled from the Shuangqiaoshan Group, which is derived from a continental arc to the northwest. Our data suggests that the Luojiamen Formation was formed in an inter‐arc basin, while the Hongchicun Formation was formed in an accretionary wedge‐top basin. When juxtaposed with the conglomeratic characteristics at the bottom of the Luojiamen Formation, it is believed that the unconformity represented by the ‘Shen Gong Movement’ reflects the rapid erosion and accumulation process of island arc volcanic material. The disconformity between the Luojiamen and Hongchicun formations is the imprint of transition from inter‐arc basin to accretionary wedge‐top basin, which represents the collision between the Shuangxiwu arc and the Yangtze Plate.

Cenozoic tectonic evolution of South China: A brief review, and new insights from the Huangshadong‐Shiba area, south‐east China

The Cenozoic tectonic dynamic process controlled by the Pacific subduction and Tethyan subduction/collision in South China are still controversial and lacks geological evidence of intracontinental deformation to define. Here, we focused on the Huangshadong‐Shiba area (HSA) in the south‐eastern coastal area of China. This study aims to obtain multi‐stage geological events by an integrated multidisciplinary investigation to decipher the multiple tectonic deformation in Cenozoic South China. We found that the Jurassic and Cretaceous granite not only dominates in surface magmatic rocks but also integrates into a whole with buried depth more than 2 km. This plate‐like granite (it means the occurrence of granite is like a tremendous plate) with thickness more than 3 km is sliced by Heyuan Fault, Renzishi Fault, and Zijin‐Boluo Fault. The basalts in the Shiba Basin have an Ocean Island Basalt‐like property, and the Heyuan Fault controlled the distribution of basalt. Our results, merged with a review of the Cenozoic tectonic evolution in South China, emphasise the decisive role of the India–Eurasia collision on the tectonics of South China in the Palaeogene and suggest the continuous northward drift of the Philippine Sea Plate and Australian Plate had a substantial effect on South China in the Neogene. This study also proposes a two‐stage tectonic activity model to visualise the Cenozoic tectonic activity acting on the HSA or South China.

Three-stage Mesozoic intracontinental tectonic evolution of South China recorded in an overprinted basin: evidence from stratigraphy and detrital zircon U–Pb dating

AbstractThe NE–NNE-trending Yuan-Ma Basin in central South China, an overprinted basin, is important for understanding the transition in Mesozoic intracontinental deformation in South China from compressional to extensional settings. A detailed sedimentary and structural cross-section across the basin reveals the Upper Triassic – Lower Jurassic black coal-bearing shale, greyish-green sandstone and brick-red claystone, and the Middle Jurassic brick-red sandstone, pebbly sandstone and conglomerate in the eastern segment of the basin. The Lower Cretaceous brick-red coarse sandstone, pebbly sandstone and siltstone occurred in the western and central segments, as well as fault breccia and Lower Cretaceous sandstone at the western margin of the basin. Detrital zircon U–Pb dating by laser ablation inductively coupled plasma mass spectrometry shows that the magmatic and metamorphic zircons yield significant age clusters at 900–700, 500–350 and 300–150 Ma, as well a minor age cluster at 120–100 Ma. Synthesizing the stratigraphic sequences, structures, isotopic dating results and palaeocurrent data, we infer that the Yuan-Ma Basin experienced three evolutionary stages and tectonic settings: (1) during Late Triassic – Early Jurassic time, the Yuan-Ma Basin was related to the diachronous progressive intracontinental deformation as a result of the early Mesozoic Xuefeng intracontinental orogeny in South China; (2) during Middle–Late Jurassic time, the Yuan-Ma Basin was related to intracontinental compression in South China; and (3) during late Early Cretaceous time, the Yuan-Ma Basin was constrained by the intracontinental extension that occurred in eastern China. These three stages, a result of various tectonic regimes, caused the intracontinental deformation that was controlled by the evolution of the continents and their margins.

Geochronology and geochemistry of tuffaceous rocks from the Banxi Group: Implications for Neoproterozoic tectonic evolution of the southeastern Yangtze Block, South China

The Neoproterozoic tectonic evolution of South China is important for understanding the tectonic assembly of modern East Asia. As a key sedimentary-volcanic sequence, the Banxi Group in South China contains a wealth of information on the genesis of the Nanhua rift basin, which is linked to the assembly and breakup of the Rodinia supercontinent. However, the geochronological and tectonic signatures of the Banxi Group in the Jiangnan orogenic belt are still controversial. In this study, the tuffaceous rocks in the Banxi area were analyzed with regard to their whole-rock major- and trace-element concentrations, and zircons in the tuffaceous rocks were analyzed for LA-(MC)-ICPMS U–Pb ages, trace elements and Hf isotopic compositions. These rocks are well preserved and show high concentrations of SiO2 (61.7–72.3%), K2O (1.7–4.5%), Al2O3 (8.4–18.9%), Rb (55–195 ppm) and Th (4.3–12.4 ppm), low concentrations of TiO2 (0.24–0.95%), Sr (54–128 ppm), Nb (5.6–12.1 ppm) and Ta (0.4–0.9 ppm), LREE enrichment (LaN/YbN = 6.6–14.7), and negative Eu anomalies (Eu/Eu* = 0.45–0.85). They have chemical affinities with high-K calc-alkaline S-type granites and exhibit continental volcanic-arc characteristics. The zircons are magmatic in origin and yield a U-Pb age distribution with three peaks: (1) Neoproterozoic (597–949 Ma, mostly 761–788 Ma), (2) Mesoproterozoic (1122–1387 Ma), and (3) Paleoproterozoic (1952–2605 Ma). The Neoproterozoic zircons yield slightly different, but overlapping, mean ages as a function of lithology: 770.2 ± 3.7 Ma for tuffaceous siltstones, 768.2 ± 6.7 Ma for tuffs, and 766.4 ± 5.2 Ma for tuffaceous slates. All zircons in the study units exhibit high U/Yb ratios (0.1–0.6) and low Hf (7106–12554 ppm) and Y (305–6617 ppm) contents, suggesting continental crustal derivation. Some of the zircons have larger LREE contents and smaller Ce anomalies relative to typical magmatic zircons, suggesting later fluid modification. The Neoproterozoic zircons have εHf(t) values ranging from −16.5 to 16.7 (mostly −8 to 10), corresponding to crustal model ages (TDMC) of 0.97–2.73 Ga. These ages imply a mixture of juvenile (i.e., Neoproterozoic) arc-derived material and Paleoproterozoic heterogeneous crust as magmatic sources for the tuffaceous sequences. Based on our integrated dataset, we infer that the Banxi tuffaceous rocks were extrusive equivalents of S-type granitoids that show volcanic-arc affinities but that were nonetheless deposited in a post-collisional and subsequent rifting-related extensional setting within the newly amalgamated South China Block. We account for this apparent contradiction by proposing that, following collision of the Yangtze and Cathaysia blocks, a rapid breakup of the continental arc caused by deep mantle upwelling led to initiation of post-collisional extension and rifting in the Nanhua Basin.

New insights into Phanerozoic tectonics of South China: Early Paleozoic sinistral and Triassic dextral transpression in the east Wuyishan and Chencai domains, NE Cathaysia

AbstractThe northeast Cathaysia area is characterized by an archetypical, transpressional system with widespread strike‐slip shear zones whose geometries, kinematics, and ages are critical for deciphering the Phanerozoic tectonic evolution of South China. We present new structural, geochronological and thermochronological data from the shear zones in the east Wuyishan and Chencai domains, which record two phases of deformation. The first phase corresponds to sinistral oblique shearing along arrays of NNE oriented, steep‐dipping zones under amphibolite facies conditions. The sinistral oblique shearing commenced at ~451 Ma, concurrently with regional NW/SE directed thrust shearing and folding; the coexistence of sinistral and thrust structures indicates NW‐SE transpressive shortening deformation. Dating by40Ar/39Ar shows that such deformation terminated before 400 Ma and was followed by cooling through ~450–350°C at ~400–370 Ma. Our results, merged with published data, aid in tracing an Early Paleozoic orogen that extends through the Jiangnan domain into the northeast Cathaysia, with the southeast Yangtze acting as a foreland belt. The synorogenic shortening was interpreted as resulting from underthrusting of the Cathaysia beneath the east Yangtze. The second phase involved dextral oblique shearing associated with NNE‐SSW transpression under greenschist to amphibolite facies conditions at 245–228 Ma, which was followed by postkinematic magmatism and cooling at ~221–200 Ma. In the Cathaysia, similar Middle Triassic dextral shear zones were widespread and operated with approximately east striking thrusts as mutually complementary structures; their kinematic coupling can be explained by a contractional termination model. Geodynamically, we attributed Middle Triassic dextral transpression to the collisions of South China with North China and Indochina.

Gold mineralization in the Jiangnan Orogenic Belt of South China: Geological, geochemical and geochronological characteristics, ore deposit-type and geodynamic setting

Located in the southeastern margin of the Yangtze Block and generally interpreted as the Neoproterozoic collisional product of the Yangtze with the Cathaysia Blocks of South China, the Jiangnan Orogenic Belt (JOB) contains a number of gold (Au) (-polymetallic) ore deposits and mineral showings, mostly hosted by Neoproterozoic low-grade metamorphic volcaniclastic and sedimentary rocks. The mineralization styles mainly include auriferous quartz veins and disseminated mineralization in altered mylonite and cataclasite that are developed along shear zones, fracture zones and inter- or intra-formational fault zones closely related to regional folding and shearing deformation. Three gold mineralizing epochs are recognized in the JOB. The ca. 423–397Ma mineralization was associated with the early Paleozoic tectonothermal event(s), which induced widespread emplacement of Silurian S-type granites, low-grade metamorphism and enrichment of gold in the Neoproterozoic rocks (i.e., forming Au source beds). The second Au mineralization epoch, occurring at ca. 176–170Ma (Jurassic), was related to the subduction of the Paleo-Pacific plate beneath the South China continental margin. The third and most important Au mineralization epoch took place at ca. 144–130Ma (early Cretaceous), when a Basin-and-Range tectonic pattern was developed, characterized by NE–NNE-trending strike-slip faults, granitic domes and metamorphic core complexes (MCC), and basins filled with red bed lithologies. C, H, O, He-Ar, S and Pb isotopic and fluid-inclusion data suggest that the ore fluids were predominantly metamorphic and/or magmatic, with variable input of mantle-derived fluids and the progressive involvement of meteoric waters in the later stages of mineralization. Ore materials were mostly contributed by the Neoproterozoic source beds, plus a possible contribution from mantle- or magma-derived components. The Au (-polymetallic) deposits in the JOB, particularly those formed in the early Cretaceous, share many geological and geochemical features with the orogenic-type and Carlin-type deposits. In the context of tectonic evolution of South China, the gold mineralization in the JOB may be considered an “intracontinental reactivation type”, characterized by synchronous development of Au–polymetallic mineralization, reactivation of stuctures developed in Neoproterozoic metamorphic rocks, and widespread granite emplacement in the late Mesozoic.

Magma source feature and eruption age of volcanic rocks in the Tram Tau district, Tu Le Basin

Magma source feature and eruption age of volcanic rocks in the Tram Tau district, Tu Le Basin