Search

Numerous scholars have used traditional thermal anomaly extraction methods and time series prediction models to study seismic anomalies based on longwave infrared radiation data. This paper selected bidirectional long short-term memory (BILSTM) as the research algorithm after analyzing and comparing the prediction performance of five time series prediction models. Based on the outgoing longwave radiation (OLR) data, the time series prediction model was used to predict the infrared longwave radiation values in the spatial area of 5° × 5° at the epicenter for 30 days before the earthquake. The confidence interval was used as the evaluation criterion to extract anomalies. The examples of earthquakes selected for study were the Yangbi Ms6.4-magnitude earthquake in Yunnan on 21 May 2021 and the Luding Ms6.8-magnitude earthquake in Sichuan on 5 September 2022. The results showed that the observed values of the Yangbi earthquake 15 to 16 days before the earthquake (5 May to 6 May) exceeded the prediction confidence interval over a wide area and to a large extent. This indicates a strong and concentrated OLR anomaly before the Yangbi earthquake. The observations at 27 days (9 August), 18 days (18 August), and 8 days (28 August) before the Luding earthquake exceeded the prediction confidence interval in a local area and by a large extent, indicating a strong and scattered OLR anomaly before the Luding earthquake. Overall, the method used in this paper extracts anomalies in both spatial and temporal dimensions and is an effective method for extracting infrared longwave radiation anomalies. [ABSTRACT FROM AUTHOR]

The Gejiu ore district (~ 3.2 Mt Sn) is located in eastern Yunnan Province, southwest China, and is one of the largest Sn polymetallic ore districts in the world. Athough it has been widely studied, the petrogenesis of ore-related granites is still unclear. In this paper, we present petrological, geochemical, and geochronological data on the granites associated with the Kafang Cu–Sn deposit in the Gejiu ore district (65 Mt Cu ore at a grade of 1.2% and 32 Mt Sn ore at a grade of 0.6%). We use these data to constrain the source, evolution, oxygen fugacity, and tectonic setting of the granitic magmatism. Zircon U–Pb dating yielded an age of 82.8 ± 0.6 Ma for the Kafang granite. The high zircon δ18O values (7.45–9.74‰; mean = 8.80‰) and narrow range of εNd(t) values (–9.0 to –7.7) of the Kafang granite indicate a highly evolved S-type granite derived by partial melting of metamorphic basement rocks of the Jiangnan orogenic belt. Rayleigh fractional crystallization modeling, along with the increase in Hf and Sn contents and decrease in Eu/Eu* values of zircons, record extensive fractional crystallization, and Sn enrichment during magmatic evolution. The Kafang granite was relatively reduced, as evidenced by low zircon Ce/Ce* (10.0–366; mean = 171), (Ce/Nd)N (0.76–8.32; mean = 4.41), △FMQ (–2.5 to 1.2) values, and Fe3+-depleted biotite compositions (Fe3+/(Fe3+ + Fe2+) = 0–0.10), which were favorable for Sn mineralization but not for Cu mineralization. Copper in the Kafang deposit may not have been derived from the granite. Our results suggest that biotite and zircon geochemical compositions, particularly biotite Mg# and A/CNK values and zircon Hf contents, Eu anomalies, and Ce/Ce* and (Ce/Nd)N ratios, are robust tracers of different types of magmatic-hydrothermal ore deposits (i.e., Cu, Mo, W, and Sn). Late Cretaceous magmatism in the Gejiu region and other areas along the southern margin of South China formed an E–W-trending igneous belt that was likely related to northward subduction of the Neo-Tethyan plate rather than northwestward subduction of the Paleo-Pacific plate. [ABSTRACT FROM AUTHOR]