The Rheic Ocean was one of the most important oceans of the Paleozoic Era. It lay between Laurentia and Gondwana from the Early Ordovician and closed to produce the vast Ouachita- Alleghanian-Variscan orogen during th...The Rheic Ocean was one of the most important oceans of the Paleozoic Era. It lay between Laurentia and Gondwana from the Early Ordovician and closed to produce the vast Ouachita- Alleghanian-Variscan orogen during the assembly of Pangea. Rifting began in the Cambrian as a continua- tion of Neoproterozoic orogenic activity and the ocean opened in the Early Ordovician with the separation of several Neoproterozoic arc terranes from the continental margin of northern Gondwana along the line of a former suture. The rapid rate of ocean opening suggests it was driven by slab pull in the outboard Iapetus Ocean. The ocean reached its greatest width with the closure of Iapetus and the accretion of the peri- Gondwanan arc terranes to Laurentia in the Silurian. Ocean closure began in the Devonian and continued through the Mississippian as Gondwana sutured to Laurussia to form Pangea. The ocean consequently plays a dominant role in the Appalachian-Ouachita orogeny of North America, in the basement geology of southern Europe, and in the Paleozoic sedimentary, structural and tectonothermal record from Middle America to the Middle East. Its closure brought the Paleozoic Era to an end.展开更多
A diverse suite of Archaean gneisses at Huangbaiyu village in the North China Craton, includes rare fuchsite-bearing （Cr-muscovite） siliceous rocks - known as the Caozhuang quartzite. The Caozhuang quartzite is stro...A diverse suite of Archaean gneisses at Huangbaiyu village in the North China Craton, includes rare fuchsite-bearing （Cr-muscovite） siliceous rocks - known as the Caozhuang quartzite. The Caozhuang quartzite is strongly deformed and locally mylonitic, with silica penetration and pegmatite veining common. It contains abundant 3880-3600 Ma and some Palaeoarchaean zircons. Because of its siliceous nature, the presence of fuchsite and its complex zircon age distribution, it has until now been accepted as a （mature） quartzite. However, the Caozhuang quartzite sample studied here is feldspathic. The shape and cathodoluminescence petrography of the Caozhuang quartzite zircons show they resemble those found in immature detrital sedimentary rocks of local provenance or in Eoarchaean polyphase orthog- neisses, and not those in mature quartzites. The Caozhuang quartzite intra-zircon mineral inclusions are dominated by quartz,展开更多
The Pushtashan suprasubduction zone assemblage of volcanic rocks, gabbros, norites and peridotites occurs in the Zagros suture zone, Kurdistan region, northeastern Iraq. Volcanic rocks are dominant in the assemblage a...The Pushtashan suprasubduction zone assemblage of volcanic rocks, gabbros, norites and peridotites occurs in the Zagros suture zone, Kurdistan region, northeastern Iraq. Volcanic rocks are dominant in the assemblage and consist mainly of basalt and basaltic andesite flows with interlayered red shale and limestone horizons. Earlier lavas tend to be MORB-like, whereas later lavas display island arc tholeiite to boninitic geochemical characteristics. Tholeiitic gabbros intrude the norites and display fractionation trends typical of crystallisation under low-pressure conditions, whereas the norites display calc-alkaline traits, suggesting their source included mantle metasomatised by fluids released from subducted oceanic crust. Enrichment of Rb, Ba, Sr, Th and the presence of negative Nb anomalies indicate generation in a suprasubduction zone setting. Trondhjemite and granodiorite intrusions are present in the volcanic rocks, gabbros and norites. SHRIMP U-Pb dating of magmatic zircons from a granodiorite yields a mean^(206)Pb/^(238)U age of 96.0 ±2.0 Ma(Cenomanian). The initial ε_(Hf) value for the zircons show a narrow range from +12.8 to+15.6, with a weighted mean of + 13.90±0.96. This initial value is within error of model depleted mantle at 96 Ma or slightly below that, in the field of arc rocks with minimal contamination by older continental crust. The compositional bimodality of the Pushtashan suprasubduction sequence suggests seafloor spreading during the initiation of subduction, with a lava stratigraphy from earlyerupted MORB transitioning into calc-alkaline lavas and finally by 96 Ma intrusion of granodioritic and trondhjemitic bodies with juvenile crustal isotopic signatures. The results confirm another Cretaceous arc remnant preserved as an allochthon within the Iraqi segment of the Cenozoic Zagros suture zone. Implications for the closure of Neo-Tethys are discussed.展开更多
Paleontologists search the fossil record for evidence of age, ancient environments, phylogenetic reconstructions and ancient communities. Cenozoic foraminifera preserve evidence for all of these simultaneously from th...Paleontologists search the fossil record for evidence of age, ancient environments, phylogenetic reconstructions and ancient communities. Cenozoic foraminifera preserve evidence for all of these simultaneously from the water column and from at, above and below the sediment/water interface. As our understanding of foraminiferal assemblages and their place in the strata （biofacies） becomes more sophisticated, so are foraminiferal biofacies challenged to contribute to more subtle problems in Cenozoic earth and life history. Progress is described as a series of five ＂integrations＂. （Ⅰ） The quantification of foraminiferal biofacies was an advance on simple presences and absences of species meeting such questions as marine or nonmarine, or shallow or deep. （Ⅱ） Foraminiferal shells carry geochemical signals especially isotopes of oxygen （temperature, ice volume）, carbon （nutrition and the carbon cycle）, and strontium （seawater ratios through time）. （Ⅲ） From modern foraminiferal biology we have lifestyle insights leading to a model of oceans and paleo-oceans called the trophic resource continuum, a valuable way into greenhouse-icehouse comparisons and contrasts. （Ⅳ） Biofacies changes in space and time are sometimes abrupt with little evidence of diachrony, and sometimes gradual. These patterns are clarified in the context of sequence stratigraphy （which they enrich in turn）. （Ⅴ） The paleobiological counterpart of sequence stratigraphy is evolutionary paleoecology, reconstructing communities in deep time. The foraminifera are perfectly suited to investigate the possibility （or likelihood） that global environmental shifts have controlled community turnover in the pelagic, neritic and terrestrial realms.展开更多
基金an outcome of IGCP Project 497:The Rheic Ocean:its origin,evolution and correlatives.RDN acknowledges NSF grant EAR-0308105G.G-A.acknowledges Spanish Education and Science Ministry Vroject Grant CGL2009- 1367(O.D.R.E.Ⅱ)+2 种基金JDK acknowledges CONACyT(Project CB- 2005-1:24894)PAPIIT(IN 100108-3)grantsJBM acknowledges N.S.E.R.C.Discovery and Research Capacity grants for continuing support
文摘The Rheic Ocean was one of the most important oceans of the Paleozoic Era. It lay between Laurentia and Gondwana from the Early Ordovician and closed to produce the vast Ouachita- Alleghanian-Variscan orogen during the assembly of Pangea. Rifting began in the Cambrian as a continua- tion of Neoproterozoic orogenic activity and the ocean opened in the Early Ordovician with the separation of several Neoproterozoic arc terranes from the continental margin of northern Gondwana along the line of a former suture. The rapid rate of ocean opening suggests it was driven by slab pull in the outboard Iapetus Ocean. The ocean reached its greatest width with the closure of Iapetus and the accretion of the peri- Gondwanan arc terranes to Laurentia in the Silurian. Ocean closure began in the Devonian and continued through the Mississippian as Gondwana sutured to Laurussia to form Pangea. The ocean consequently plays a dominant role in the Appalachian-Ouachita orogeny of North America, in the basement geology of southern Europe, and in the Paleozoic sedimentary, structural and tectonothermal record from Middle America to the Middle East. Its closure brought the Paleozoic Era to an end.
基金the Ministry of Land and Resources of the People's Republic of China(1212010711815,1212010811033)
文摘A diverse suite of Archaean gneisses at Huangbaiyu village in the North China Craton, includes rare fuchsite-bearing （Cr-muscovite） siliceous rocks - known as the Caozhuang quartzite. The Caozhuang quartzite is strongly deformed and locally mylonitic, with silica penetration and pegmatite veining common. It contains abundant 3880-3600 Ma and some Palaeoarchaean zircons. Because of its siliceous nature, the presence of fuchsite and its complex zircon age distribution, it has until now been accepted as a （mature） quartzite. However, the Caozhuang quartzite sample studied here is feldspathic. The shape and cathodoluminescence petrography of the Caozhuang quartzite zircons show they resemble those found in immature detrital sedimentary rocks of local provenance or in Eoarchaean polyphase orthog- neisses, and not those in mature quartzites. The Caozhuang quartzite intra-zircon mineral inclusions are dominated by quartz,
基金supported by University of Kirkukpartially supported by the GeoQuEST Research Centre(University of Wollongong)
文摘The Pushtashan suprasubduction zone assemblage of volcanic rocks, gabbros, norites and peridotites occurs in the Zagros suture zone, Kurdistan region, northeastern Iraq. Volcanic rocks are dominant in the assemblage and consist mainly of basalt and basaltic andesite flows with interlayered red shale and limestone horizons. Earlier lavas tend to be MORB-like, whereas later lavas display island arc tholeiite to boninitic geochemical characteristics. Tholeiitic gabbros intrude the norites and display fractionation trends typical of crystallisation under low-pressure conditions, whereas the norites display calc-alkaline traits, suggesting their source included mantle metasomatised by fluids released from subducted oceanic crust. Enrichment of Rb, Ba, Sr, Th and the presence of negative Nb anomalies indicate generation in a suprasubduction zone setting. Trondhjemite and granodiorite intrusions are present in the volcanic rocks, gabbros and norites. SHRIMP U-Pb dating of magmatic zircons from a granodiorite yields a mean^(206)Pb/^(238)U age of 96.0 ±2.0 Ma(Cenomanian). The initial ε_(Hf) value for the zircons show a narrow range from +12.8 to+15.6, with a weighted mean of + 13.90±0.96. This initial value is within error of model depleted mantle at 96 Ma or slightly below that, in the field of arc rocks with minimal contamination by older continental crust. The compositional bimodality of the Pushtashan suprasubduction sequence suggests seafloor spreading during the initiation of subduction, with a lava stratigraphy from earlyerupted MORB transitioning into calc-alkaline lavas and finally by 96 Ma intrusion of granodioritic and trondhjemitic bodies with juvenile crustal isotopic signatures. The results confirm another Cretaceous arc remnant preserved as an allochthon within the Iraqi segment of the Cenozoic Zagros suture zone. Implications for the closure of Neo-Tethys are discussed.
文摘Paleontologists search the fossil record for evidence of age, ancient environments, phylogenetic reconstructions and ancient communities. Cenozoic foraminifera preserve evidence for all of these simultaneously from the water column and from at, above and below the sediment/water interface. As our understanding of foraminiferal assemblages and their place in the strata （biofacies） becomes more sophisticated, so are foraminiferal biofacies challenged to contribute to more subtle problems in Cenozoic earth and life history. Progress is described as a series of five ＂integrations＂. （Ⅰ） The quantification of foraminiferal biofacies was an advance on simple presences and absences of species meeting such questions as marine or nonmarine, or shallow or deep. （Ⅱ） Foraminiferal shells carry geochemical signals especially isotopes of oxygen （temperature, ice volume）, carbon （nutrition and the carbon cycle）, and strontium （seawater ratios through time）. （Ⅲ） From modern foraminiferal biology we have lifestyle insights leading to a model of oceans and paleo-oceans called the trophic resource continuum, a valuable way into greenhouse-icehouse comparisons and contrasts. （Ⅳ） Biofacies changes in space and time are sometimes abrupt with little evidence of diachrony, and sometimes gradual. These patterns are clarified in the context of sequence stratigraphy （which they enrich in turn）. （Ⅴ） The paleobiological counterpart of sequence stratigraphy is evolutionary paleoecology, reconstructing communities in deep time. The foraminifera are perfectly suited to investigate the possibility （or likelihood） that global environmental shifts have controlled community turnover in the pelagic, neritic and terrestrial realms.
