The Phanerozoic tectonic regimes of the South China Block (SCB) hold a key to understanding of its geodynamic evolution with respect to formation of numerous mineral resources. Despite long-time ...debates in the past three decades, there is still no consensus on the two key points whether the Phanerozoic tectonothermal events were due to subduction of the Pacific plate or intracontinental reworking and whether the three periods of tectonothermal events in the middle Paleozoic (Kwangsian), Triassic (Indosinian) and Jurassic–Cretaceous (Yanshanian) are mainly driven by tectonic transition in subduction of the oceanic crust from Paleotethyan in the west to Pacific in the east. This paper presents an overview of key geological observations in the SCB with respect to its Phanerozoic tectonics. Available data show that there are distinctive sedimentary, magmatic, structural and metamorphic records across the Xuefeng-Jiangnan Domain in the SCB. The geological signatures associated with the Kwangsian and Indosinian tectonothermal events are predominantly preserved in the eastern SCB, including the eastern Yangtze and Cathaysia Blocks to the east of the Xuefeng-Jiangnan Domain. They are characterized by strong thrusting/transpression, anatexic granitic magmatism, high-grade metamorphism and the poor involvement of the juvenile mantle-derived rocks. The two events were dated at ca. 400–460Ma and ca. 200–250Ma, respectively. The Yanshanian tectonothermal event is dominantly represented by the development of a wide magmatic belt of exceeding 1300km (from the coastal province to the Xuefeng-Jiangnan Domain) and a broad deformational belt of more than 2000km (from the coastal province to the Sichuan basin). The Yanshanian I-, S- and A-type granites, syenite and volcanic rocks display two arrays, which are oblique and parallel to the coastal provinces of the southeast China, respectively. They were mainly formed at the three age-spans of 152–180Ma, 120–130 and 87–107Ma with the peak of 158Ma, 125Ma and 93Ma, respectively. The stillstand time of the Yanshanian magmatism was temporally overlapped by the deformation time of the top-to-the-NW progressive transpression or sinistral strike-slip at 132–142Ma and 95–112Ma, respectively. In conjunction with the observations and controversies, a geodynamic model is proposed for the Mesozoic tectonic evolution of the SCB.
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► Introduction of the key geological observations on the Phanerozoic tectonics of the SCB hinterland. ► Description and discussion of the existing hypotheses and controversies on the Phanerozoic tectonics of the SCB. ► A geodynamic model for the Mesozoic tectonic evolution of the SCB is herein proposed.
In the eastern South China Block (SCB), the presence of middle Paleozoic volcanics and mafic rocks is poor in spite of the extensive occurrence of granites in response to the synchronous (Kwangsian) ...intracontinental orogen event. The nature of the lithosphere and its associated orogenic process are poorly known for such a major orogen. In this paper, a set of new U–Pb zircon geochronological, elemental and Sr–Nd isotopic data are presented for several gabbroic plutons, which were recently identified in the Cathaysia Block. The representative samples of the Longhugang, Xinchuan and Xinsi plutons yielded the weighted mean 206Pb/238U ages of 423±8Ma, 434±6Ma and 420±3Ma, respectively, and their gneissoid country-rocks are dated at 442–466Ma. This evidences the presence of Silurian mafic rocks in the Cathaysia Block. These gabbroic rocks can be geochemically classified into three groups. Group 1 from the western Longhugang pluton exhibits flat REE patterns represented by (La/Yb)cn=1.1–1.7, (Gd/Yb)cn=0.99–1.15, and δEu=1.29–1.51 with negative Nb–Ta and P and markedly positive Sr anomalies. It shows enrichment in LILEs and 87Sr/86Sr(t) ratios of 0.70412–0.70727 and εNd(t) values of −2.6 to −0.6. Group 2 from the Xinchuan, Zhouya and Yunlu plutons is characterized by high MgO (11.4–15.8wt.%), mg-number (66–74) and Cr and Ni contents. It is marked by significantly negative Nb–Ta, Zr–Hf and P–Ti anomalies with high 87Sr/86Sr(t) (0.70920–0.71072) and low εNd(t) values (−3.9 to −7.9). Group 3 from the Xinsi and eastern Longhugang plutons has εNd(t) values from −2.8 to −5.7 and shows high Nb content of 7.05–9.89ppm with pronounced enrichment in LILE and weak depletion in HFSE, resembling Nb-enriched arc basalt in HFSE composition. A synthesis of these geochemical data points to the following petrogenesis: Groups 1 and 2 derived from a spinel-bearing, plagioclase-rich source and a garnet-bearing, orthopyroxene-rich source, respectively, proportionally modified by slab- and sediment-derived melts plus fluid fluxing from the earliest Neoproterozoic subduction. The HFSE composition for Group 3 inherited from a metasomatized mantle wedge column with the input of large-proportional slab melts and the absence of residual rutile during partial melting. In conjunction with other available observations, it is proposed that there preserved a paleosubduction-modified wedge column beneath the Cathaysia Block, which might be undisturbed until the Kwangsian intracontinental orogen. During the Silurian post-orogenic collapse of the event, the elevated lithosphere thermal boundary facilitated the partial melting of the column to generate these Silurian gabbroic rocks.
► Three gabbro plutons from Yunkai–Nanling are dated at 420–434Ma, confirming the presence of Silurian mafic rocks in SCB. ► These mafic rocks originated from the wedge column previously modified by subduction-derived components. ► The post-collisional collapse of the Kwangsian intracontinental orogen is proposed as the petrogenetic model of the gabbro. ► The earliest Neoproterozoic subduction-related metasomatism might occur along the southern Cathaysia Block.
► Two metabasites from the northern Yunkai gave the weighted mean ages of 978–997Ma. ► Group 1 is similar geochemically to Saunders island-arc and Group 2 to Nb-enriched basalt. ► Both groups ...originated from MORB source newly modified by subduction-derived fluid/melt. ► A Grenvillian arc–back-arc basin was developed along the southern Cathaysia Block.
The tectonic nature of the Cathaysia Block during earliest Neoproterozoic period has been long disputed and attracted considerable attentions. One reason for this problem is rare exposure and few data for the igneous rocks of Grenvillian age in this Block. In this paper, a set of new U–Pb zircon geochronological, elemental and Nd isotopic data are presented for the metabasites in the Yunkai Group which shows WNW-trending extension with a length of more than 100km along the northern Yunkai Domain of the Cathaysia Block. The plagioclase amphibolite and metabasite from Shiwo (Beiliu) and Tantu (Xinyi) from the northern Yunkai Domain, representative of Groups 1 and 2, yielded the 206Pb/238U weighted mean ages of 997±21Ma and 978±19Ma, respectively, evidencing the presence of the Grenvillian mafic rocks within the Cathaysia Block. Based on the Nb, Nb/La and Nb/U, these samples can be geochemically subdivided into two groups (Groups 1 and 2). Group 1 has Nb/La=0.33–0.54 and Nb=1.71–2.85ppm, and exhibits similar geochemical signatures to those of Saunders island-arc. Group 2 gives Nb/La of 0.57–0.86 and Nb of 7.58–12.70ppm, resembling to those of Phanerozoic Nb-enriched basalts, and shows the geochemical affinity to the Okinawa back-arc basin basalt. Both groups have positive ɛNd(t) values, ranging from +3.84 to +5.36 and +3.93 to +6.55, respectively. These geochemical and isotopic characteristics suggest that Group 1 might have been originated from a MORB-like source modified by subduction-derived fluids. The source of Group 2 Nb-enriched basalt might be metasomatized by melt released from a newly subducted slab. In conjunction with other geological observations, it is identified for the Grenville-aged (ca. 1.0Ga) arc and back-arc basin along the northern Yunkai Domain of the Cathaysia Block, analog to the modern West Pacific. The South China Block probably located at the margin of Rodinia supercontinent between west Australia and east India.
The Mesozoic geology of southeastern (SE) China was characterized by emplacement of voluminous felsic magmas. We present zircon U–Pb–Hf isotopic compositions and whole-rock major and trace elemental ...compositions of a series of felsic volcanic rocks from the eastern Guangdong and Fujian provinces. The volcanic rocks have been divided into three formations (the Douling, Nanyuan and Shimaoshan Fms.). Zircon U–Pb dating defines three eruption cycles: 168–145Ma for the Douling Fm., 143–130Ma for the Nanyuan Fm., and 104–95Ma for the Shimaoshan Fm. In situ Hf isotope analyses on dated zircon yield an εHf(t) range of −13.8 to +6.9 and a TDM(Hf) range from 1400 to 486Ma with a peak at ca. 930Ma. The majority of the Mesozoic felsic lavas have more radiogenic Hf than that of metamorphic basement rocks and related igneous rocks, requiring the involvement of a juvenile component in their origin. The Mesozoic felsic magmas are predominantly dacites and rhyolites – with only minor basalt and andesite – and show relatively homogeneous Hf isotopic compositions of zircon in single sample. Combined these data indicated that neither differentiation of a mantle-derived magma, nor mixing of magmas from different sources, was a dominant petrogenetic process. Both the εHf(t) of zircon and the magma temperature increase from the Douling and Nanyuan Fms. to the Shimaoshan Fm. All these facts imply an increasing contribution of contemporaneous underplated hot and dry mantle-derived magmas, as both a heat source inducing crustal melting and as a source of material (melt) that variably mixed with the local crustal melts. The felsic crustal melt component was generated at amphibolite-facies conditions with a residual assemblage of plagioclase+/−hornblende+/−garnet+/−zircon. Our results suggest a progressive role of crust–mantle interaction in generating the episodic felsic volcanic eruption during the Mesozoic.
► Three stages (168–145Ma, 143–130Ma and 104–94Ma) of volcanic eruption are identified in SE China. ► The Mesozoic felsic lavas were derived from medium- to high-K protoliths. ► The residual assemblage of the felsic melts was plagioclase+/−hornblende+/−garnet+/−zircon. ► The felsic magmas were formed through crust–mantle interaction under lithospheric extension.
Subduction of the Paleo-Pacific Oceanic Plate is widely considered to have caused extensive Mesozoic magmatism, lithospheric deformation and mineralization in East Asia. However, it is still unclear ...when this subduction began. Here we report an Early Jurassic (~187Ma) mafic intrusive complex (including olivine norite, gabbro, and diorite) from the Tumen area in NE China. The olivine norite contains a mineral assemblage of olivine, pyroxene, Ca-plagioclase, and hornblende that crystallized in a water-saturated parental magma. The rocks in the complex show variable degrees of plagioclase and ferromagnesian mineral accumulation as reflected by positive Sr and Eu anomalies in primitive mantle-normalized incompatible element patterns. Mass-balance calculations indicate that the parental magma was calc-alkaline with arc-type trace element features (i.e., large ion incompatible and light rare earth element enrichment and Nb–Ta depletion). It also had Sr–Nd–Hf isotopic compositions (87Sr/86Sr(i)=0.7042 to 0.7044, εNd(t)=+2.5 to +3.5 and εHf(t)=+8.4 to +10.5) similar to those of modern arc basalts. The parental magma was likely derived from 5 to 20% melting of a mantle wedge metasomatized by an addition of 3–4% hydrous sediment melt from the subducting Paleo-Pacific Oceanic slab. The Tumen mafic intrusive complex, together with other contemporaneous mafic intrusions, I-type granitoids, and felsic lavas, constitutes an Early Jurassic N–S-trending arc magmatic belt that was formed by westward subduction of the Paleo-Pacific Ocean.
•The Early Jurassic Tumen mafic intrusion crystallized in a water-saturated magma.•The parental magma was calc-alkaline with arc-type elemental and isotopic features.•The N–S-trending magmatic belt in NE China was formed by the westward subduction of the Paleo-Pacific Ocean.
•The metabasic rocks in Cathaysia yield U–Pb ages of 969–984Ma and TDM(Hf) of 0.92–1.44Ga.•They originated from a subduction-modified MORB-like source linked to an arc–back-arc setting.•The South ...China Block was created by episodic amalgamation of a series of arc fragments between ∼970 and 820Ma.•The South China Block is an exterior accretionary orogen along the periphery of Rodinia rather than in the interior.
U–Pb geochronology along with elemental and Nd–Hf–Os isotopic data from the earliest Neoproterozoic metabasic rocks within the Cathaysia Block of the South China Block (SCB) constrain the tectonic setting and paleogeography of the block within the Rodinia supercontinent. The metabasic rocks give zircon U–Pb ages of 969–984Ma, ɛHf(t) values of +1.8 to +15.3 and Hf model ages of 0.92–1.44Ga. They are subalkaline basalts that can be geochemically classified into four groups. Group 1 has low Nb contents (1.24–4.33ppm), highly positive ɛNd(t) values (+4.3 to +5.2), and REE and multi-elemental patterns similar to fore-arc MORB-type basalt. Group 2 has Nb contents ranging from 3.13ppm to 6.48ppm, ɛNd(t) of +3.1 to +6.2, low Re and Os contents and high initial Os isotopic ratios, and displays an E-MORB geochemical signature. Group 3 has Nb=7.18–29.87ppm, Nb/La=0.60–1.40, Nb/U=5.0–37, Ce/Pb=1.1–6.6, ɛNd(t)=+2.9 to +7.0, 187Re/188Os=5.87–8.87 and γOs (t)=178–772, geochemically resembling to the Pickle Nb-enriched basalt. Group 4 has strong LREE/HREE and HREE fractionation and high ɛNd(t) values (+2.3 to +5.6), and is characterized by similar element patterns to arc volcanic rocks. Serpentinites coeval to Group 4 show 187Os/188Os of 0.1143–0.1442 and γOs (t) of −7.8 to +0.1. Groups 1 and 2 are interpreted to originate from the N-MORB and E-MORB-like sources with the addition of an arc-like component, genetically linked to fore- and back-arc settings, respectively. Groups 3 and 4 show inputs of newly subduction-derived melt and fluid in the wedge source. These geochronological and geochemical signatures fingerprint the development of an earliest Neoproterozoic (∼970Ma) arc–back-arc system along the Wuyi-Yunkai domain of the Cathaysia Block. Regional relationships indicate that the Wuyi-Yunkai arc–back-arc system was one of a series of separate convergent margin settings, which included the Shuangxiwu (∼970–880Ma) and Jiangnan (∼870–820Ma) systems that developed in the SCB. The formation and closure of these arc–back-arc systems resulted in the northwestwardly episodic amalgamation of various pieces of the Yangtze and Cathaysia to finally form the SCB. These signatures require the SCB to occupy an exterior accretionary orogen along the periphery of Rodinia during 990–820Ma, rather than to have formed through Mesoproterozoic Sibao orogenesis within the interior of Rodinia.
This paper presents a set of new SHRIMP zircon U–Pb geochronological, elemental and Sr–Nd–Pb isotopic data for the Wusu and Yaxuanqiao basaltic rocks (the Mojiang area) along the Ailaoshan tectonic ...zone. The Wusu basaltic sequence is dominated by SiO
2-poor, MgO- and TiO
2-rich basalts with a major mineral assemblage of plagioclase
+
clinopyroxene. These rocks gave a SHRIMP zircon U–Pb age of 287
±
5
Ma (MSWD
=
0.58). In contrast, the Yaxuanqiao basaltic sequence is predominantly composed of high-Al basaltic andesite, which gave a SHRIMP zircon U–Pb age of 265
±
7
Ma (MSWD
=
0.34). The analyzed samples for both sequences exhibit significant enrichment in LILEs and depletion in HFSEs with (Nb/La)n of 0.38–0.81, similar to arc-like volcanics. They have positive εNd(t) values (+
3.52 to +
5.54). In comparison with MORB-derived magmatic rocks, the Wusu basalts are more enriched in LILEs and REEs, and the Yaxuanqiao samples are more enriched in LILEs but variably depleted in Ti, Y and HREE. The Wusu samples show high Pb isotopic ratios, similar to the Tethyan basalts, whereas the Yaxuanqiao samples plot in the field of the global pelagic sediments. The geochemical and Sr–Nd–Pb isotopic characteristics suggest that the Wusu basalts originated from a MORB-like source metasomatised by slab-derived fluids, while the Yaxuanqiao rocks have a fluid-modified MORB source with the input of subducted sediments. The geochemical affinity to both MORB- and arc-like sources, together with other geological observations, appears to support the development of a Permian arc–back-arc basin along the Ailaoshan–Song Ma tectonic zone in response to the northward subduction of the Paleotethys main Ocean. The final closure of the arc–back-arc basin took place in the uppermost Triassic due to the diachronous amalgamation between the Yangtze and Simao–Indochina Blocks.
► The Wusu and Yaxuanqiao basaltic sequences gave the zircon U-Pb ages of 287 and 265 Ma, respectively. ► Both sequences exhibit the geochemical affinity to both MORB- and arc-like sources. ► They originated from a fluid-modified or with the input of subducted sediments. ► A Permian arc-back-arc basin along the Ailaoshan-Song Ma tectonic zone.
This paper presents petrology, mineralogy, zircon U–Pb ages, and whole-rock major, trace element and Sr–Nd–Hf isotopic compositions of four Permian (273–253Ma) subduction-related mafic intrusions ...(including the Qinggoushan and Qianshan gabbros, and the Wangqing and Shuguang diorites) from the Yanbian region, NE China, with aims to understand the role of subducted sediment flux in generation of arc mafic cumulates. These intrusions have mineral assemblages crystallized in water-saturated parental magmas and show variable degrees of crystal accumulation as observed in mafic cumulates in subduction zones. Mass-balance consideration indicates that their parental magmas were calc-alkaline with arc-type trace element features (enrichments in large ion lithophile elements (LILE) and light rare earth elements (LREE) and depletions in Nb–Ta). They also have Sr–Nd–Hf isotopic compositions, i.e., 87Sr/86Sr(i)=0.7029–0.7047, εNd(t)=+0.9~+6.8, εHf(t)=+5.6~+14.6, similar to modern arc basalts. The parental magmas were likely derived from a mantle wedge variably metasomatized by sediment melt and fluid from the subducting paleo-Asian Oceanic slab. Combined trace elemental and isotopic modeling results suggest that the parental magma of Qinggoushan gabbro was formed through 5–20% melting of the mantle wedge with 1% and 1.5% additions of sediment fluid and sediment melt, respectively; 5–10% melting of the mantle wedge through inputs of 1% sediment fluid and 2% sediment melt produced the Qianshan gabbro; 10–20% melting of the mantle wedge with additions of 1% sediment fluid and 3% sediment melt formed the Wangqing diorite; whereas 5–20% melting of the mantle wedge through an input of 1.5% sediment melt produced the Shuguang diorite.
The Hf–Nd isotopic array of the Yanbian Permian mafic intrusions reflected the existence of an Indian Ocean-type mantle, which was isotopically distinct from the Pacific-type mantle during early Paleozoic in the Central Asian Orogenic Belt. Such a transformation from the Pacific-type to the Indian Ocean-type mantle was primarily attributed to addition of the recycled components, which contained more radiogenic Hf than Nd isotopic compositions, from the subducting paleo-Asian Oceanic slab.
•Four Permian subduction-related mafic intrusions were identified in NE China.•Variable subducted sediment fluxes were introduced in the mantle wedge.•The paleo-Asian Ocean transformed from a Pacific- to an Indian-type mantle.•A new method is build to calculate parental magma composition of diorite.
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