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Abstract: To understand the formation and the tectonic process of the Mesozoic middle–lower Yangtze metallogenic belt (YMB), the SinoProbe program deployed a quasi-linear passive source seismic array across the belt. We performed receiver function profiling and measurement of shear-wave splitting parameters with the collected data. Our results show that the Moho depth varies significantly along the profile and that a “mantle uplift” exists right beneath the YMB. We also found that the lower crust of the YMB is different from that of its adjacent areas in structure on the receiver function profile. It possesses seismic anisotropy with direction roughly parallel to the belt. Our SKS/SKKS shear-wave splitting results also show similar belt-parallel azimuthal anisotropy right beneath the YMB. We interpret the seismic anisotropy in the lower crust of the YMB as the result of mineral crystal alignment caused by melting and belt-parallel flow in the Mesozoic ore-forming process. Besides, we observed a nearly south-dipping converter extending from shallow to lower crust beneath the Hefei Basin, which most possibly resulted from the Mesozoic crustal extension. We interpret the “mantle uplift” and the crustal extensional structures to be consequences of asthenospheric upwelling during the Mesozoic ore-forming process. Our results suggest that the lower crust of the YMB was most likely one part of the multi-level metallogenic magma system in the Mesozoic magmatism and mineralization processes, and the formation of the metallogenic belt to be a result much similar to the MASH (Melting, Assimilation, Storage and Homogenization; cf. Hildreth and Moorbath, 1988; Richards, 2003) process. First, the asthenospheric upwelling resulted in a crustal extensional environment; then the melts from the upwelling asthenosphere intruded into the lower crust of the YMB, and assimilation occurred when they mixed with in situ lower crustal materials, which led to the formation of adakitic-like magma; the adakitic-like magma rose up along extensional structures, and reacted with country rocks to form mineral deposits. [Copyright &y& Elsevier]

The Cathaysia Block is located in South China, along the western margin of the Pacific plate, and well known for its widespread granitoids and rich poly-metallic mineralization. Despite the numerous studies conducted in this region, some key questions are still in debate, which revolve around the detailed crustal architecture, the boundary between the western and eastern part of Cathaysia Block, and the geodynamic evolution and metallogenic settings in the Cathaysia Block. In this study, we have conducted a dense broad-band seismic observation in the Cathaysia Block, and obtained the fine crustal structure of it by using P-wave receiver functions and analyzing other geophysical and geological studies comprehensively. Our study has following findings: (1) the crust of the Cathaysia Block is ~31.5 km thick, thinner than that of the global continent, and is interpreted to have been thinned since the Late Mesozoic; (2) the Vp/Vs ratio of the Cathaysia Block is lower than that of the global continent, which implies there is no extensive underplating beneath the Cathaysia Block, or that the magma may be confined at bottom of the crust and formed a velocity gradient belt around Moho; (3) Zhenghe-Dapu fault is marked as the structural boundary between the western and eastern Cathaysia Block; (4) the western and eastern Cathaysia Block have different intra-crustal structures, petrochronology features and mineralization settings; (5) the subduction of the paleo-Pacific plate and the following roll-back could be responsible for the geodynamic evolution of the crustal deformation, as well as the widespread magmatism and mineralization. • Fine crustal structure of Cathaysia is obtained by new seismic survey. • Zhenghe-Dapu fault is the boundary between the east and west Cathaysia. • No extensive magmatic underplating beneath the Cathaysia Block. • Two-stage paleo-Pacific subduction led to the crustal structure of Cathaysia. [ABSTRACT FROM AUTHOR]

A 3-D P-wave velocity structure down to 750 km beneath the eastern South China Block is obtained by using a large number of high-quality teleseismic data. Based on our results and those of previous studies, we suggest that late Mesozoic magmatism and lithospheric thinning in the eastern South China Block could be attributed to the subduction of the Paleo-Pacific Plate and its eastward rollback. [Display omitted] • A 3-D P-wave velocity model beneath the eastern South China Block is obtained. • The velocity structures beneath the eastern South China Block are very complicated. • The Paleo-Pacific Plate has had a profound impact on the eastern South China Block. The eastern South China Block (ESCB) is characterized by intense magmatism in the late Mesozoic. To further investigate the mechanism of late Mesozoic magmatism, we apply the tomographic method to construct a P-wave velocity model down to 750 km by using 40,989 P-wave arrival times collected from 687 teleseismic events recorded by 191 stations. Our model shows that (1) a high-Vp anomaly is observed beneath the lower Yangtze Block (YZB) and northern Cathaysia Block (CAB) in the crust and uppermost mantle, which could represent the present lithosphere; (2) two high-Vp anomalies are observed in the upper mantle beneath the YZB, which could be the detached lithosphere and the relict of the subducted SCB; (3) the break-off of the subducted Eurasian Plate has penetrated the 410 km discontinuity beneath central and northern Taiwan Island; (4) the stagnant Paleo-Pacific Plate in the MTZ is mainly beneath the lower YZB; (5) the low-Vp anomaly in the upper mantle that is immediately above the stagnant Paleo-Pacific Plate may represent the thermal asthenosphere caused by plate dehydration; and (6) the low-Vp anomaly beneath the southern CAB extends from the crust downward to the MTZ, which may represent an 'upward channel' for thermal materials. Based on our results and those of previous studies, we suggest that late Mesozoic magmatism in the ESCB could be highly associated with the subduction of the Paleo-Pacific Plate and its eastward rollback. We also suggest that thermal/chemical erosion may be responsible for lithospheric thinning in the ESCB. [ABSTRACT FROM AUTHOR]

The South China block (SCB) is located at the southeastern margin of the Eurasian plate, where intense Mesozoic magmatism and metallogenic belts occurred. The mechanism of mineralization is still unclear and debated. To clarify this issue, we determine a robust 3-D model of P-wave tomography of the upper mantle beneath the SCB by using 77,969 high-quality travel-time data of 934 teleseismic events recorded at 315 permanent and 72 portable stations in the SCB. Our results show that high-velocity (high-V) zones exist in the upper mantle under the Yangtze block and in the mantle transition zone under the eastern segment of the Jiangnan orogen. The former reflects thicker cratonic lithosphere, whereas the latter may reflect the deeply subducted paleo-Pacific plate. Low-velocity (low-V) anomalies are revealed in the upper mantle beneath the Cathaysia block, which are located above the high-V anomaly in the mantle transition zone. These low-V anomalies may reflect hot upwelling flows in the upper mantle, which might be related to the large-scale magmatic activities in the late Mesozoic. Our results suggest that the low-V hot mantle materials beneath the Cathaysia block have risen to the shallow lithosphere along magmatic channels such as fault zones, which eroded the nearby cratonic root of the Yangtze block and the overlying lithosphere and destroyed the lithosphere beneath the eastern SCB. The hot upwelling materials mineralized in the shallow part and so formed many metallogenic belts in the SCB. • The 3-D upper-mantle structure under the South China block (SCB) is studied using teleseismic tomography. • The Yangtze and Cathaysia blocks exhibit higher and lower P-wave velocities, respectively. • Hot mantle upwelling under the Cathaysia block caused lithospheric thinning and rich metallogenic belts in the eastern SCB. [ABSTRACT FROM AUTHOR]

• Tomography with a dense seismic array reveals the upper-mantle structure in SE China. • A low-velocity zone with high Poisson's ratio exists under the western Cathaysia block. • The low-velocity zone reflects thermal flow causing the late Mesozoic mineralization. Our study region is located in the Cathaysia block (CB), Southeast China. The most significant feature of the CB is the widespread Mesozoic magmatism and poly-metallic mineralization. However, there is still no consensus on their genesis and related tectonic processes. In this study, we determine high-resolution (0.3° in the horizontal direction) tomographic images of Vp and Vs and Vp/Vs ratio in the crust and upper mantle using 6773 P-wave and 4526 S-wave travel-time data of teleseismic events recorded by a broadband linear seismic array. The array was deployed by our team in the middle part of the CB, consisting of 81 portable stations with an interval of 5–8 km. Our tomographic results reveal two obvious low-velocity (low-V) zones with high Vp/Vs ratio (high-σ) beneath the Nanling ore belt and the Wuyishan terrane, which may reflect magmatic channels formed by partial melting that may provide heat for metal mineralization. Two high-V anomalies with low-σ are located beneath the western Wuyishan terrane and the eastern CB, which may represent refractory lithosphere or remnants of delaminated lithospheric material caused by underplating of the magma due to the subduction of the paleo-Pacific plate and its following rollback. There exists an anomaly with low-Vp, high-Vs and low-σ at depths of 150–300 km beneath the western Wuyishan terrane, which may be related to the reserved trace of magmatic conduits. On the basis of the tomographic results, we propose a geodynamic model to explain the deep mechanism of mineralization beneath the CB. [ABSTRACT FROM AUTHOR]

Geophysical methods identify lithospheric structures and potential fluid conduits. Tectonicblock boundaries acted as fluid conduits for ore development. The Late Mesozoic Fe–Cu (Au) mineral system of LYMB was formed by multi-level sources, processes, and conduits communicating each other within an exceptional lithospheric architecture. [Display omitted] • An extensive ore system occurred in the Lower Yangtze Metallogenic Belt. • Geophysical methods identify lithospheric structures and potential fluid conduits. • Tectonic block boundaries acted as fluid conduits for ore development. Diverse seismic (active and passive) and magnetotelluric (MT) surveys have been conducted in the past decade over the Lower Yangtze Metallogenic Belt (LYMB) and adjacent areas, in eastern China. We present an integrated interpretation of these data describing the lithospheric architecture of an extensive Fe–Cu system in the LYMB. A combination of anomalous geophysical features has been observed in the sub-continental lithospheric mantle (SCLM) and asthenospheric mantle, which include: anomalously thin lithosphere (thickness ~70 km), low S- and P-wave seismic velocity in the upper mantle (70–150 km), and a dipping high-conductivity body extending from the lower crust to the asthenosphere (~150 km). We interpret these features to be the result of lithospheric delamination and asthenospheric upwelling during Late Mesozoic orogenesis. Melts and metal-rich (e.g., Cu, and Au) fluids produced by the asthenosphere would have metasomatized the lithospheric conduits (faults) and the lower part of the SCLM. Therefore, we suggest that these areas acted as the primary source regions for the Fe–Cu (Au) mineral system in the LYMB. Seismic reflection profiles across different parts of the LYMB reveal various large-scale structures, including crustal wedges, Moho stacks, mega-thrusts, and even lower crust underthrusting at block boundaries; these features are consistent with collisional orogeny. The spatial coincidence of major block boundaries with the distribution of deposits is evidence that deep-penetrating boundary faults acted as conduits for migrating magmas/fluids from lower crust to the upper crust. Conductive zones in the crust beneath the LYMB are interpreted as the result of alteration by fluids within the conduits. We conclude that the Late Mesozoic Fe–Cu (Au) mineral system of LYMB was formed by during an intra-continental orogeny with multi-level sources, processes, and conduits communicating each other within an exceptional lithospheric architecture. [ABSTRACT FROM AUTHOR]