Search

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]

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]