Abstract
In this study, we performed receiver function profiling and fitted harmonic functions to the arrival time variations of Pms phases to calculate the crustal seismic anisotropy with delay time and fast polarization direction, using broadband seismic data obtained from 55 temporary stations in two linear profiles and 39 stations in the Lower Yangtze and adjacent region. Moreover, we determined the crustal thickness and Poisson’s ratio using a novel H-κ-c stacking method. Our results revealed that the Middle-Lower Yangtze Metallogenic Belt and the north east section of the Qinzhou-Hangzhou Metallogenic Belt are characterized by Moho upliftment (<32 km), a relatively high Poisson’s ratio (>0.26), local lithospheric thinning (<70 km), and a pattern of deep faults that connect the crust and asthenosphere and serve as conduits for magma upwelling. The NE-SW fast polarization direction was consistent with the SKS splitting results, and the average delay time was 0.45 s. Moreover, underplating of deep magma and upwelling along the weak zone caused local Moho uplift and ductile shear of the lower crust, resulting in the directional arrangement of amphibole and other minerals, which may be the controlling mechanism for the crustal anisotropy in the study area. The variations in crustal structure and anisotropy characteristics indicated that in the context of the northeastern Paleo-Pacific plate subduction, the existence of weak lithospheric zones and the northeastern asthenospheric flow are important conditions for metal supernormal enrichment in the Lower Yangtze region.
Highlights
The Mesozoic period is regarded as the lithospheric active period of eastern South China when multiphase structure-magma-thermal events were extensively developed and marked by massive and explosive mineralization (Li and Li, 2007; Lin et al, 2019; Wang et al, 2021)
Seismic tomography results indicated a “sandwich” structure of velocity anomalies in the upper mantle of the metallogenic area (Jiang et al, 2014, 2021), and the ambient noise tomography results suggested that the upper and lower crusts are characterized by relatively low velocities, whereas the middle crust is characterized by relatively high-velocities (Meng et al, 2021)
This paper investigated the crustal structure and anisotropy in the Lower Yangtze region and its adjacent areas by teleseismic receiver functions, combining the previous velocity structure of the crust and upper mantle
Summary
The Mesozoic period is regarded as the lithospheric active period of eastern South China when multiphase structure-magma-thermal events were extensively developed and marked by massive and explosive mineralization (Li and Li, 2007; Lin et al, 2019; Wang et al, 2021). Wide-angle reflection profiles revealed uplifting of the Moho beneath this belt and lowvelocity anomalies zone extending from the upper mantle to the crust of the metallogenic area (Xu et al, 2014; Zhang et al, 2015). The joint inversion results of receiver functions analyses and surface wave dispersions suggested that low-velocity anomalies exist in the upper mantle of the Lower Yangtze Block, several of which occur beneath the Dexing and Tongling ore deposits, and have been attributed to the ponding of relic (still cooling) mantle magma chambers (Ye et al, 2019). Existing research has predominately focused on the crust-mantle structure below the MLYMB, with few studies describing the seismic anisotropy characteristics below the belt and its adjacent areas and the correlation between the dynamic environment and mineralization
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