Recently discovered intermediate-basic volcanic rocks in the Devonian strata at Dachang, Guangxi Zhuang Autonomous Region are dominated by basalts and andesites. Most of them belong to the calc-alkali and alkali serie...Recently discovered intermediate-basic volcanic rocks in the Devonian strata at Dachang, Guangxi Zhuang Autonomous Region are dominated by basalts and andesites. Most of them belong to the calc-alkali and alkali series. Petrology and geochemistry data indicate that the volcanic rocks may be formed in a continental rift environment. The volcanic rocks are in conformable contact with the overlying and underlying wall rocks, with such typical sedimentary structures as laminated and striped ones, and the host rocks of the volcanic rocks contain lots of marine fossils such as tentaculite. Many pieces of evidence indicate that the eruption environment of the volcanic rocks is a sea-facies one. The volcanic rocks are of the LREE-enrichment type, with high ratios of light rare-earth elements to heavy rare-earth elements. In addition, they display moderately negative δEu anomalies and moderately negative δCe anomalies with a higher degree of LREE and HREE fractionation. Through the Q-cluster analysis of the REE samples, it is indicated that the ores have a closer relation with the layered volcanic rocks, and also possess a certain inheritance-consistency relationship with the layered volcanic rocks. The source of ore-forming materials may be related with volcanism. It is proposed that the ore deposit in the study area should be genetically explained as the result of marine volcano-sedimentary exhalation of hot water and late superposition-reworking.展开更多
The basin margin slope area of Changling fault depression in Songliao Basin is dominated by intermediate-basic volcanic rocks of Huoshiling Formation,and there is still a lack of in-depth understanding of the developm...The basin margin slope area of Changling fault depression in Songliao Basin is dominated by intermediate-basic volcanic rocks of Huoshiling Formation,and there is still a lack of in-depth understanding of the development pattern and formation mechanism of high-quality reservoirs in intermediate-basic volcanic rocks in this area.Taking the intermediate volcanic rocks in Longfengshan area of Changling fault depression as an example,a comprehensive study was undertaken via core observations,thin section porosity analysis,rock physical property tests,scanning electron microscopy and X-ray diffraction analysis,combined with well log and seismic d ata.As a result,formation mechanism of a high quality reservoir was made clear based on dissolution modification effects of the volcanic rocks,and the development model of the high quality reservoir under t he dual control of lithology and fluid was established.The research shows that the volcanic rocks in this area consist of six lithologies:andesitic hydrothermal breccia,andesite,andesitic volcanic breccia,andesitic tuff,dacitic tuff and sedimentary tuff,which are controlled by structure,eruptive source,eruptive action and palaeotopography.The proximal facies of the volcanic edifice were located on the basin margin,distributed along faults mainly consisting of overflow facies intermixed with eruptive facies,and gradually transformed into thick eruptive facies(middle-source facies)and volcanic sedimentary facies(distal facies).The reservoir space of volcanic rocks was dominated by dissolution pores,which were formed by weathering and dissolution by organic acidic fluids.The thermal debris flow subphase in the middle-source facies of the volcanic edifice had a large amount of easily dissolved volcanic ash,which was close to the source rock in the centre of the basin and was a favourable area for the development of dissolution pores.This study is providing a guide for oil and gas exploration in the intermediate-basic volcanic rocks in the slope of Changling fault depression in Songliao Basin.展开更多
基金financially supported by the Applied Basic Research Projects(General Program)of Yunnan Province(2011FB015)
文摘Recently discovered intermediate-basic volcanic rocks in the Devonian strata at Dachang, Guangxi Zhuang Autonomous Region are dominated by basalts and andesites. Most of them belong to the calc-alkali and alkali series. Petrology and geochemistry data indicate that the volcanic rocks may be formed in a continental rift environment. The volcanic rocks are in conformable contact with the overlying and underlying wall rocks, with such typical sedimentary structures as laminated and striped ones, and the host rocks of the volcanic rocks contain lots of marine fossils such as tentaculite. Many pieces of evidence indicate that the eruption environment of the volcanic rocks is a sea-facies one. The volcanic rocks are of the LREE-enrichment type, with high ratios of light rare-earth elements to heavy rare-earth elements. In addition, they display moderately negative δEu anomalies and moderately negative δCe anomalies with a higher degree of LREE and HREE fractionation. Through the Q-cluster analysis of the REE samples, it is indicated that the ores have a closer relation with the layered volcanic rocks, and also possess a certain inheritance-consistency relationship with the layered volcanic rocks. The source of ore-forming materials may be related with volcanism. It is proposed that the ore deposit in the study area should be genetically explained as the result of marine volcano-sedimentary exhalation of hot water and late superposition-reworking.
基金Supported by National Natural Science Foundation of China(Nos.41972313,41790453).
文摘The basin margin slope area of Changling fault depression in Songliao Basin is dominated by intermediate-basic volcanic rocks of Huoshiling Formation,and there is still a lack of in-depth understanding of the development pattern and formation mechanism of high-quality reservoirs in intermediate-basic volcanic rocks in this area.Taking the intermediate volcanic rocks in Longfengshan area of Changling fault depression as an example,a comprehensive study was undertaken via core observations,thin section porosity analysis,rock physical property tests,scanning electron microscopy and X-ray diffraction analysis,combined with well log and seismic d ata.As a result,formation mechanism of a high quality reservoir was made clear based on dissolution modification effects of the volcanic rocks,and the development model of the high quality reservoir under t he dual control of lithology and fluid was established.The research shows that the volcanic rocks in this area consist of six lithologies:andesitic hydrothermal breccia,andesite,andesitic volcanic breccia,andesitic tuff,dacitic tuff and sedimentary tuff,which are controlled by structure,eruptive source,eruptive action and palaeotopography.The proximal facies of the volcanic edifice were located on the basin margin,distributed along faults mainly consisting of overflow facies intermixed with eruptive facies,and gradually transformed into thick eruptive facies(middle-source facies)and volcanic sedimentary facies(distal facies).The reservoir space of volcanic rocks was dominated by dissolution pores,which were formed by weathering and dissolution by organic acidic fluids.The thermal debris flow subphase in the middle-source facies of the volcanic edifice had a large amount of easily dissolved volcanic ash,which was close to the source rock in the centre of the basin and was a favourable area for the development of dissolution pores.This study is providing a guide for oil and gas exploration in the intermediate-basic volcanic rocks in the slope of Changling fault depression in Songliao Basin.
