The regional lithospheric chemical heterogeneity in-ers that the East Qinling and its adjacent cratonic re-ions , as suggested by some authors , belong to two eotectonic units,the North China subdomain including he No...The regional lithospheric chemical heterogeneity in-ers that the East Qinling and its adjacent cratonic re-ions , as suggested by some authors , belong to two eotectonic units,the North China subdomain including he North China Craton and its southern continental largin (the North Qinling Belt), and the Yangtzean ubdomain comprising the Yangtze Craton and its torthern continental margin (the South Qinh'ng Belt). In the North Qinling Belt the metamorphosed olcanic rocks and graywackes of the Early Paleozoic Oanfeng Group south of the Early Proterozoic Qinling Froup show geochemical characteristics resembling hose of the arc volcanics and arc graywackes -espectively. The Early Paleozoic granites intruding in he Qinling Group also show similar geochemical features and similar compositional polarities to the arc-type granites . The Erlangping Group north of the Qinling Group is a volcanic-sedimentary sequence produced in an Early Paleozoic back - arc basin based on geochemical evidence . It is therefore believed that the North Qinling Belt comprised the active continental margin of the North China Craton , beneath which the ancient Qinling oceanic plate underthrusted and was consumed from 480 to 380Ma ago . The South Qinling Belt is generally considered to be a passive continental margin of the Yangtze Craton on which developed the thick Sinian and Paleozoic sediments of continental shelf and continental slope fades . The source of fine -grained clastic sedimentary rocks of various geological periods has been geochemically studied.The result demonstrates that the terrigenous elastics of the South Qinling Belt came only from the Yangtze Craton prior to the Silurian , and since then began to be fed by both the Yangtze Craton and the North Qinling . The Devonian sediments display a clear two - component mixing model in their source material . The change in the source materi-al strongly suggests that the Yangtze passive continental margin approached the active continental margin of the North China Craton and finally came into contact with it during the Silurian and the Early Devonian . On both sides of the Shangdan Fault Zone , the lithospheric megasuture of the Qinh'ng orogen , are distributed the Late Paleozoic (323-262 Ma ) granites which intruded in the Danfeng Group and the Qinling Group to the north , and in the Devonian strata to the south of the suture . The older granites of that time interval are comparable in geological and geochemical characteristics to the syn - collision granites from other continent-continent collision zones . The younger calc - alkaline granites which were em placed at about 260 Ma ago have been classified as the late - collision granites by various geochemical discrimination methods . On these grounds it may be deduced that the continent - continent collision orogeny did not begin to act until the late Early Carboniferous epoch and that its main episode was the Late Paleozoic , although it might have continued to the Early Mesozoic .The collision orogeny was separated from the subduction orogeny by an interval of about 60 Ma and the subduction of the oceanic crust was accompanied by the northward shifting of the Yangtze Craton and its passive continental margin . However , the ocean basin still remained in the South Qinling Belt for a long time after the disappearance of the ocean .展开更多
文摘The regional lithospheric chemical heterogeneity in-ers that the East Qinling and its adjacent cratonic re-ions , as suggested by some authors , belong to two eotectonic units,the North China subdomain including he North China Craton and its southern continental largin (the North Qinling Belt), and the Yangtzean ubdomain comprising the Yangtze Craton and its torthern continental margin (the South Qinh'ng Belt). In the North Qinling Belt the metamorphosed olcanic rocks and graywackes of the Early Paleozoic Oanfeng Group south of the Early Proterozoic Qinling Froup show geochemical characteristics resembling hose of the arc volcanics and arc graywackes -espectively. The Early Paleozoic granites intruding in he Qinling Group also show similar geochemical features and similar compositional polarities to the arc-type granites . The Erlangping Group north of the Qinling Group is a volcanic-sedimentary sequence produced in an Early Paleozoic back - arc basin based on geochemical evidence . It is therefore believed that the North Qinling Belt comprised the active continental margin of the North China Craton , beneath which the ancient Qinling oceanic plate underthrusted and was consumed from 480 to 380Ma ago . The South Qinling Belt is generally considered to be a passive continental margin of the Yangtze Craton on which developed the thick Sinian and Paleozoic sediments of continental shelf and continental slope fades . The source of fine -grained clastic sedimentary rocks of various geological periods has been geochemically studied.The result demonstrates that the terrigenous elastics of the South Qinling Belt came only from the Yangtze Craton prior to the Silurian , and since then began to be fed by both the Yangtze Craton and the North Qinling . The Devonian sediments display a clear two - component mixing model in their source material . The change in the source materi-al strongly suggests that the Yangtze passive continental margin approached the active continental margin of the North China Craton and finally came into contact with it during the Silurian and the Early Devonian . On both sides of the Shangdan Fault Zone , the lithospheric megasuture of the Qinh'ng orogen , are distributed the Late Paleozoic (323-262 Ma ) granites which intruded in the Danfeng Group and the Qinling Group to the north , and in the Devonian strata to the south of the suture . The older granites of that time interval are comparable in geological and geochemical characteristics to the syn - collision granites from other continent-continent collision zones . The younger calc - alkaline granites which were em placed at about 260 Ma ago have been classified as the late - collision granites by various geochemical discrimination methods . On these grounds it may be deduced that the continent - continent collision orogeny did not begin to act until the late Early Carboniferous epoch and that its main episode was the Late Paleozoic , although it might have continued to the Early Mesozoic .The collision orogeny was separated from the subduction orogeny by an interval of about 60 Ma and the subduction of the oceanic crust was accompanied by the northward shifting of the Yangtze Craton and its passive continental margin . However , the ocean basin still remained in the South Qinling Belt for a long time after the disappearance of the ocean .
