中国是全球晚新生代火山发育国家之一,也是西环太平洋活动大陆边缘火山活动带重要组成部分。在我国东北地区发育着数座晚新生代喷发过的活火山(如五大连池老黑山、火烧山火山、金龙顶子火山等)或具备喷发能力的休眠火山(如云南腾冲火山...中国是全球晚新生代火山发育国家之一,也是西环太平洋活动大陆边缘火山活动带重要组成部分。在我国东北地区发育着数座晚新生代喷发过的活火山(如五大连池老黑山、火烧山火山、金龙顶子火山等)或具备喷发能力的休眠火山(如云南腾冲火山、长白山天池火山等)(Hickey,1982;Davies et al,1992;刘若新,1992)。龙岗火山群是我国东北部晚新生代仍有过喷发活动的火山群之一(隋建立等,1999).展开更多
Petrological and geochemical studies on some volcanic and sub-volcanic rocks from the Lower Benue rift indicate that they are basalts, basaltic and doleritic sills, trachybasalt and trachyte which generally belong to ...Petrological and geochemical studies on some volcanic and sub-volcanic rocks from the Lower Benue rift indicate that they are basalts, basaltic and doleritic sills, trachybasalt and trachyte which generally belong to the alkali basalt series. The alkaline affinity is clearly evident in both their normative and modal mineral compositions, as well as their chemical compositions. The generally high fractionation indices [(La/Yb)N] are 7.06 to 17.65 for the basaltic rocks and 23.59 to 135. 35 for the trachytic rocks, against low values commonly seen in subalkaline (tholeiitic) series, with strong enrichments in the incompatible elements. All this strongly supports their alkaline affinity. The basaltic rocks are generally fine-grained and porphyritic, consisting of phenocrysts of clinopyroxene and olivine in the groundmass of the same minerals together with plagioclase. The clinopyroxene is either diopside or clinoenstatite. The trachyte consists of oligoclase, orthoclase, biotite, quartz and exhibits typical trachytic, flow structure. The basaltic and doleritic sills are commonly altered, with calcite and epidote as common alteration prod-ucts. This alteration, which is reflected in the erratic behaviour of K2O, MnO and P2O5 on Harker variation diagrams, high values of LOI, strong depletions in the more mobile LILE (Rb, K, Ba and Sr) and high Th/Ta ratios, is attributed to the effects of an aqueous fluid phase and crustal contamination. On the whole, the mineralogical, as well as major-, trace-elements and REE data suggest that the rocks are co-genetic and most likely derived from differentiation of an alkali olivine-basalt magma, generating through variable low degrees of partial melting of probably an enriched lithospheric (upper) mantle following an asthenospheric uplift (mantle plume or intumescence) with HIMU signa-tures in a within-plate continental rift tectonic setting. This corroborates earlier results obtained for the intrusive rocks in the region.展开更多
Thick Neoproterozoic strata are widespread in the Dalian region, Liaodong Peninsula, Northeast China. SHRIMP zircon U-Pb dating of dolerite intruded into Neo-proterozoic strata gives its emplacement age as 211±2 ...Thick Neoproterozoic strata are widespread in the Dalian region, Liaodong Peninsula, Northeast China. SHRIMP zircon U-Pb dating of dolerite intruded into Neo-proterozoic strata gives its emplacement age as 211±2 Ma. However, abundant 0.9—1.1 Ga zircons are identified in the dolerite. The age of 1125±38 Ma corresponds with the Grenvillian collisional event. The zircons of 904±15 Ma ages have high Th/U ratios (1.31—2.25) and magmatic oscillatory zones, being possibly related to later magmatism induced during amalgamation of Rodinia.展开更多
文摘中国是全球晚新生代火山发育国家之一,也是西环太平洋活动大陆边缘火山活动带重要组成部分。在我国东北地区发育着数座晚新生代喷发过的活火山(如五大连池老黑山、火烧山火山、金龙顶子火山等)或具备喷发能力的休眠火山(如云南腾冲火山、长白山天池火山等)(Hickey,1982;Davies et al,1992;刘若新,1992)。龙岗火山群是我国东北部晚新生代仍有过喷发活动的火山群之一(隋建立等,1999).
基金Financial support for field work and thin-section preparation,which are parts of the Ph.D. thesis of the author,was provided by the Shell Professorial Chair in Geology,University of Nigeria,Nsukka under Late Umeji A.C.
文摘Petrological and geochemical studies on some volcanic and sub-volcanic rocks from the Lower Benue rift indicate that they are basalts, basaltic and doleritic sills, trachybasalt and trachyte which generally belong to the alkali basalt series. The alkaline affinity is clearly evident in both their normative and modal mineral compositions, as well as their chemical compositions. The generally high fractionation indices [(La/Yb)N] are 7.06 to 17.65 for the basaltic rocks and 23.59 to 135. 35 for the trachytic rocks, against low values commonly seen in subalkaline (tholeiitic) series, with strong enrichments in the incompatible elements. All this strongly supports their alkaline affinity. The basaltic rocks are generally fine-grained and porphyritic, consisting of phenocrysts of clinopyroxene and olivine in the groundmass of the same minerals together with plagioclase. The clinopyroxene is either diopside or clinoenstatite. The trachyte consists of oligoclase, orthoclase, biotite, quartz and exhibits typical trachytic, flow structure. The basaltic and doleritic sills are commonly altered, with calcite and epidote as common alteration prod-ucts. This alteration, which is reflected in the erratic behaviour of K2O, MnO and P2O5 on Harker variation diagrams, high values of LOI, strong depletions in the more mobile LILE (Rb, K, Ba and Sr) and high Th/Ta ratios, is attributed to the effects of an aqueous fluid phase and crustal contamination. On the whole, the mineralogical, as well as major-, trace-elements and REE data suggest that the rocks are co-genetic and most likely derived from differentiation of an alkali olivine-basalt magma, generating through variable low degrees of partial melting of probably an enriched lithospheric (upper) mantle following an asthenospheric uplift (mantle plume or intumescence) with HIMU signa-tures in a within-plate continental rift tectonic setting. This corroborates earlier results obtained for the intrusive rocks in the region.
文摘Thick Neoproterozoic strata are widespread in the Dalian region, Liaodong Peninsula, Northeast China. SHRIMP zircon U-Pb dating of dolerite intruded into Neo-proterozoic strata gives its emplacement age as 211±2 Ma. However, abundant 0.9—1.1 Ga zircons are identified in the dolerite. The age of 1125±38 Ma corresponds with the Grenvillian collisional event. The zircons of 904±15 Ma ages have high Th/U ratios (1.31—2.25) and magmatic oscillatory zones, being possibly related to later magmatism induced during amalgamation of Rodinia.
