{"title":"纳米比亚Vioolsdrif地区岩浆岩的地球化学演化","authors":"R. Minnitt, K. Esbensen","doi":"10.25131/sajg.126.0001","DOIUrl":null,"url":null,"abstract":"\n Geological, lithological, petrographical, geochemical, and geochronological data in the Palaeoproterozoic Richtersveld Subprovince/Magmatic Arc (RMA) of Precambrian basement rocks of the Vioolsdrif Domain in southern Namibia, strongly support linkages in the history of formation between the volcanic rock types of the Orange River Group (ORG) and the plutonic rocks of the Vioolsdrif Suite (VS). Previous age dating indicates volcanics of the ORG are more-or-less synchronous with granitic phases of the VS. Geochemical, mineralogical, and comprehensive field and petrological characteristics of the volcanic and granitic rocks suggest genetically linked, parallel igneous-effusive rock suites through processes of fractional crystallisation. Intermittent tapping of evolving residual magmas produced an extrusive carapace of volcanic rocks covering the granitic rocks in a classic magmatic differentiation context of parallel geochemical and lithological evolution. As the magma chamber fractionated plutonic phases of the VS at depth, it extruded residual liquids as volcanic flows and ejecta at surface to form the ORG. A first principal model, based on Ba, Rb and Sr trace element and SiO2, MgO, Al2O3, TiO2 major element behaviour, is supported by multivariate modelling of 28 major and trace elements in 129 rock analyses using Principal Component Analysis (PCA). PCA indicates the first four components account for more than 80% of the total compositional variance in all rock types lending comprehensive support for a linked geochemical differentiation model for both the igneous and the volcanic suites. Strong evidence for the magmatic co-evolution of the plutonic and effusive series includes the Cu-mineralisation event, which manifests itself as a resolvable, orthogonal fifth principal component, geochemically overprinting the intermediate ‘porphyry monzogranite’ differentiation stages, but not related to the terminal leuco-granites. The full spectrum of geochemical relationships is consistent with current models of a direct genetic relationship between evolving high Sr/Y magmas and hydrothermal porphyry Cu deposits, in overall agreement with the full context of field, rock, mineralogical, geochemical, and economic geology interpretations presented here.","PeriodicalId":49494,"journal":{"name":"South African Journal of Geology","volume":" ","pages":""},"PeriodicalIF":1.2000,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Geochemical evolution of magmatic rocks in the Vioolsdrif Domain, Namibia\",\"authors\":\"R. Minnitt, K. Esbensen\",\"doi\":\"10.25131/sajg.126.0001\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"\\n Geological, lithological, petrographical, geochemical, and geochronological data in the Palaeoproterozoic Richtersveld Subprovince/Magmatic Arc (RMA) of Precambrian basement rocks of the Vioolsdrif Domain in southern Namibia, strongly support linkages in the history of formation between the volcanic rock types of the Orange River Group (ORG) and the plutonic rocks of the Vioolsdrif Suite (VS). Previous age dating indicates volcanics of the ORG are more-or-less synchronous with granitic phases of the VS. Geochemical, mineralogical, and comprehensive field and petrological characteristics of the volcanic and granitic rocks suggest genetically linked, parallel igneous-effusive rock suites through processes of fractional crystallisation. Intermittent tapping of evolving residual magmas produced an extrusive carapace of volcanic rocks covering the granitic rocks in a classic magmatic differentiation context of parallel geochemical and lithological evolution. As the magma chamber fractionated plutonic phases of the VS at depth, it extruded residual liquids as volcanic flows and ejecta at surface to form the ORG. A first principal model, based on Ba, Rb and Sr trace element and SiO2, MgO, Al2O3, TiO2 major element behaviour, is supported by multivariate modelling of 28 major and trace elements in 129 rock analyses using Principal Component Analysis (PCA). PCA indicates the first four components account for more than 80% of the total compositional variance in all rock types lending comprehensive support for a linked geochemical differentiation model for both the igneous and the volcanic suites. Strong evidence for the magmatic co-evolution of the plutonic and effusive series includes the Cu-mineralisation event, which manifests itself as a resolvable, orthogonal fifth principal component, geochemically overprinting the intermediate ‘porphyry monzogranite’ differentiation stages, but not related to the terminal leuco-granites. The full spectrum of geochemical relationships is consistent with current models of a direct genetic relationship between evolving high Sr/Y magmas and hydrothermal porphyry Cu deposits, in overall agreement with the full context of field, rock, mineralogical, geochemical, and economic geology interpretations presented here.\",\"PeriodicalId\":49494,\"journal\":{\"name\":\"South African Journal of Geology\",\"volume\":\" \",\"pages\":\"\"},\"PeriodicalIF\":1.2000,\"publicationDate\":\"2023-03-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"South African Journal of Geology\",\"FirstCategoryId\":\"93\",\"ListUrlMain\":\"https://doi.org/10.25131/sajg.126.0001\",\"RegionNum\":4,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"GEOLOGY\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"South African Journal of Geology","FirstCategoryId":"93","ListUrlMain":"https://doi.org/10.25131/sajg.126.0001","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOLOGY","Score":null,"Total":0}
Geochemical evolution of magmatic rocks in the Vioolsdrif Domain, Namibia
Geological, lithological, petrographical, geochemical, and geochronological data in the Palaeoproterozoic Richtersveld Subprovince/Magmatic Arc (RMA) of Precambrian basement rocks of the Vioolsdrif Domain in southern Namibia, strongly support linkages in the history of formation between the volcanic rock types of the Orange River Group (ORG) and the plutonic rocks of the Vioolsdrif Suite (VS). Previous age dating indicates volcanics of the ORG are more-or-less synchronous with granitic phases of the VS. Geochemical, mineralogical, and comprehensive field and petrological characteristics of the volcanic and granitic rocks suggest genetically linked, parallel igneous-effusive rock suites through processes of fractional crystallisation. Intermittent tapping of evolving residual magmas produced an extrusive carapace of volcanic rocks covering the granitic rocks in a classic magmatic differentiation context of parallel geochemical and lithological evolution. As the magma chamber fractionated plutonic phases of the VS at depth, it extruded residual liquids as volcanic flows and ejecta at surface to form the ORG. A first principal model, based on Ba, Rb and Sr trace element and SiO2, MgO, Al2O3, TiO2 major element behaviour, is supported by multivariate modelling of 28 major and trace elements in 129 rock analyses using Principal Component Analysis (PCA). PCA indicates the first four components account for more than 80% of the total compositional variance in all rock types lending comprehensive support for a linked geochemical differentiation model for both the igneous and the volcanic suites. Strong evidence for the magmatic co-evolution of the plutonic and effusive series includes the Cu-mineralisation event, which manifests itself as a resolvable, orthogonal fifth principal component, geochemically overprinting the intermediate ‘porphyry monzogranite’ differentiation stages, but not related to the terminal leuco-granites. The full spectrum of geochemical relationships is consistent with current models of a direct genetic relationship between evolving high Sr/Y magmas and hydrothermal porphyry Cu deposits, in overall agreement with the full context of field, rock, mineralogical, geochemical, and economic geology interpretations presented here.
期刊介绍:
The South African Journal of Geology publishes scientific papers, notes, stratigraphic descriptions and discussions in the broadly defined fields of geoscience that are related directly or indirectly to the geology of Africa. Contributions relevant to former supercontinental entities such as Gondwana and Rodinia are also welcome as are topical studies on any geoscience-related discipline. Review papers are welcome as long as they represent original, new syntheses. Special issues are also encouraged but terms for these must be negotiated with the Editors.