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K. D. Spinks - One of the best experts on this subject based on the ideXlab platform.
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Influence of the crust and crustal structure on the location and composition of high-alumina Basalts of the Taupo Volcanic Zone, New Zealand
New Zealand Journal of Geology and Geophysics, 2007Co-Authors: J. Hieß, J W Cole, K. D. SpinksAbstract:High-alumina Basalts (HABs) that occur throughout the central part of the Taupo Volcanic Zone (TVZ) are associated particularly with faulting, and many occur where faults intersect caldera margins. For convenience, the Basalts are described in terms of three geographic-tectonic segments: Okataina in the north, Kapenga in the middle, and Taupo in the south. Evidence for mixing and mingling between rising Basaltic magmas and rhyolitic rocks and magmas is common, including the frequent occurrence of xenocrysts and xenoliths, quench textures, and melting around the rims of inclusions. Chemically, the Basalts are similar in terms of major element compositions, suggesting relatively homogeneous PT conditions in the mantle source, but variation between some trace elements suggests different processes are operating in the crust with variable degrees of contamination. The model presented for HAB generation in the TVZ is for partial melting of mantle peridotite in the upper mantle, with the melt rising into the lower crust via dike swarms. In the upper crust, the distribution of HAB is strongly influenced by location and structure. In the Kapenga segment, there is little evidence for interaction between Basaltic and rhyolitic magma, other than at very shallow levels, perhaps because the rhyolitic magma chambers (or pods) were solid, allowing brittle deformation and rapid intrusion of Basalt dikes. At Okataina there is much greater mixing and mingling, suggesting there was still partially molten rhyolitic magma chambers beneath this area during Basalt intrusion. Basalt in the Taupo segment occurs outside the Taupo caldera complex and may be related to the earlier Whakamaru caldera complex. The Basalt is thought to rise through the crust as a network of unrelated melt batches into a plexus of discrete magma chambers and conduits, many of which are sited along fault zones causing fissure eruptions at the surface.
J. Hieß - One of the best experts on this subject based on the ideXlab platform.
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Influence of the crust and crustal structure on the location and composition of high-alumina Basalts of the Taupo Volcanic Zone, New Zealand
New Zealand Journal of Geology and Geophysics, 2007Co-Authors: J. Hieß, J W Cole, K. D. SpinksAbstract:High-alumina Basalts (HABs) that occur throughout the central part of the Taupo Volcanic Zone (TVZ) are associated particularly with faulting, and many occur where faults intersect caldera margins. For convenience, the Basalts are described in terms of three geographic-tectonic segments: Okataina in the north, Kapenga in the middle, and Taupo in the south. Evidence for mixing and mingling between rising Basaltic magmas and rhyolitic rocks and magmas is common, including the frequent occurrence of xenocrysts and xenoliths, quench textures, and melting around the rims of inclusions. Chemically, the Basalts are similar in terms of major element compositions, suggesting relatively homogeneous PT conditions in the mantle source, but variation between some trace elements suggests different processes are operating in the crust with variable degrees of contamination. The model presented for HAB generation in the TVZ is for partial melting of mantle peridotite in the upper mantle, with the melt rising into the lower crust via dike swarms. In the upper crust, the distribution of HAB is strongly influenced by location and structure. In the Kapenga segment, there is little evidence for interaction between Basaltic and rhyolitic magma, other than at very shallow levels, perhaps because the rhyolitic magma chambers (or pods) were solid, allowing brittle deformation and rapid intrusion of Basalt dikes. At Okataina there is much greater mixing and mingling, suggesting there was still partially molten rhyolitic magma chambers beneath this area during Basalt intrusion. Basalt in the Taupo segment occurs outside the Taupo caldera complex and may be related to the earlier Whakamaru caldera complex. The Basalt is thought to rise through the crust as a network of unrelated melt batches into a plexus of discrete magma chambers and conduits, many of which are sited along fault zones causing fissure eruptions at the surface.
Chongjin Pang - One of the best experts on this subject based on the ideXlab platform.
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origin of arc like continental Basalts implications for deep earth fluid cycling and tectonic discrimination
Lithos, 2016Co-Authors: Xuance Wang, Simon A Wilde, Bei Xu, Chongjin PangAbstract:Abstract Continental Basalts generally display enrichment of fluid-mobile elements and depletion of high-field-strength elements, similar to those that evolved in the subduction environment, but different from oceanic Basalts. Based on the continental flood Basalt database for six large igneous provinces, together with rift-related Basalt data from the Basin and Range Province, this study aimed to test the validity of geochemical tectonic discrimination diagrams in distinguishing arc-like intra-continental Basalts from arc Basalts and to further investigate the role of deep-Earth water cycling in producing arc-like signatures in large-scale intra-continental Basalts. Our evaluation shows that arc-like intra-continental Basalts can be distinguished from arc Basalts by integrating the following factors: (1) the FeO, MgO, and Al 2 O 3 concentrations of the primary melt; (2) Ti V, Zr Zr/Y, Zr Ti, and Ti/V Zr/Sm Sr/Nd discrimination diagrams; (3) the coexistence of arc-like and OIB-like subtype Basalts within the same province; (4) primitive mantle-normalized trace element distribution patterns. The similarity of enrichment in fluid-mobile elements (Ba, Rb, Sr, U, and K) between arc-like and true arc Basalts suggests the importance of water flux melting in producing arc-like signatures in continental Basalts. Experimentally determined liquid lines of descent (LLD) imply high magma water concentrations for continental flood Basalts (CFBs) and the Basin and Range Basalts. Furthermore, estimates based on the Al 2 O 3 –LLD method indicates 4.0–5.0 wt% pre-eruptive magma H 2 O concentration for CFBs and the Basin and Range Basalts. The tight relationships between H 2 O/Ce and Ba/La, Ba/Nb and Rb/Nb based on global arc Basalt data were further used to estimate the primary H 2 O concentrations. With the exception of the Emeishan CFBs (mainly containing 4.0–5.6 wt% H 2 O), all other CFBs investigated have similar estimated primary H 2 O contents, with values ranging from 1.0 to 2.0 wt%. The estimated primary H 2 O content of the Basin and Range Basalts is extremely high and up to 10.0 wt%. Thus, this study demonstrates that water flux melting played an important role in the generation of many intra-continental igneous provinces. This new finding was further employed to investigate the tectonic setting of 320–270 Ma Basalts in Inner Mongolia, North China. Most Basalts from three key rock units (i.e. Amushan, Benbatu, and Dashizhai formations) from the Central Asian Orogenic belt are classified as non-arc types. The estimated magma H 2 O concentrations suggest a strong link between H 2 O content and arc-like geochemical signatures. Together with established geological evidence, we proposed that these 320–270 Ma Basaltic rocks were most likely produced in a post-orogenic extensional environment facilitated by subducted slab-driven deep-Earth fluid cycling. We propose a mantle transition zone water-filtering model that links deep-Earth fluid cycling, large-scale intra-continental Basaltic magmatism, and supercontinent cycles into a self-organized system.
Yigang Xu - One of the best experts on this subject based on the ideXlab platform.
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late cenozoic Basaltic lavas from the changbaishan baoqing volcanic belt ne china products of lithosphere asthenosphere interaction induced by subduction of the pacific plate
Journal of Asian Earth Sciences, 2018Co-Authors: Songyue Yu, Yigang Xu, Shenghua Zhou, Liemeng Chen, Nengping Shen, Jianxin Zhao, Yuexing FengAbstract:Cenozoic intraplate Basalts are low in volume but widespread in eastern China. They are predominantly alkaline and have oceanic island Basalt (OIB)-like trace element compositions. Despite numerous studies, the origin of Cenozoic Basalts in eastern China remains elusive. Possible roles of lithosphere thickness, subduction of Pacific plate and lithosphere-asthenosphere interaction in triggering spatial geochemical variations have not yet been clarified. Here, we have carried out mineral chemistry, major and trace element and Sr–Nd–Hf isotope analyses of the late Cenozoic (<20 Ma) Basaltic rocks from the Changbaishan-Baoqing Volcanic Belt (CVB), NE China, which revealed clear spatial compositional variations. The North CVB is dominated by basanites and alkali Basalts with OIB-like trace element patterns and depleted Sr–Nd–Hf isotopic compositions (Sr/Sr = 0.7039–0.7047, e = 3–5.6; e = 6.7–12), which may have been derived from low degree partial melting of a depleted source from asthenospheric mantle beneath a thick lithosphere. On the other hand, the South CVB consists of both alkali and sub-alkali lavas (alkali Basalts, tholeiites and Basaltic andesites) that display generally higher SiO, Sm/Nd, Ba/Nb, Th/U, and lower Nb/Th, La/Sm and more enriched Sr–Nd–Hf isotopic compositions (Sr/Sr = 0.7038–0.7056, e = −2.4 – +3.2; e = 3–8.2). These rocks may have been produced by larger degrees of partial melting of asthenospheric mantle beneath a relatively thin lithosphere. Ancient metasomatized lithospheric mantle might also have contributed to their genesis. In addition, the similar ranges of Mn, Ni and Fe/Mn for olivine phenocrysts from both the North and the South CVB suggest that they may have been derived from hybrid mantle sources containing similar proportions of peridotite and pyroxenite/eclogite components. We propose that decompression melting of upwelling asthenosphere and mechanical-chemical erosion of basal lithosphere related to lithosphere-asthenosphere interaction responsible for the genesis of the CVB magmas were likely associated with upper mantle convection and back-arc extension induced by deep subduction of the Pacific plate and its stagnancy in the transition zone.
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oceanic crust components in continental Basalts from shuangliao northeast china derived from the mantle transition zone
Chemical Geology, 2012Co-Authors: Yigang Xu, Huihuang Zhang, Wenchun Ge, Fuyuan WuAbstract:Abstract Basaltic rocks from Shuangliao, northeast China include basanite, alkali olivine Basalt, transitional Basalt and sub-alkaline diabase. Ar–Ar dating shows that the basanites and alkali olivine Basalts formed earlier (48.5–51 Ma) than the transitional Basalts and diabases (43–41.6 Ma). These rocks have the highest Fe 2 O 3 contents (13.4–14.6 wt.%) and lowest ( 87 Sr/ 86 Sr) i ratios ( 206 Pb/ 204 Pb = 18.13–18.34) do not show the high time-integrated 238 U/ 204 Pb mantle component expected for a HIMU Basalt. On a 206 Pb/ 204 Pb versus 207 Pb/ 204 Pb diagram, most samples straddle the Northern Hemisphere Reference Line (NHRL), in salient contrast to the majority of Chinese Cenozoic Basalts, which plot above the NHRL. These data, as well as a comparison with high-pressure experimental melts, are consistent with the presence of young subducted oceanic crust (SOC) in the source of Shuangliao Basalts. Varying ( 87 Sr/ 86 Sr) i , La/Nb and Eu/Eu* with rock-type suggests that the upper oceanic crust (with variable amount of lower oceanic crust) was preferentially sampled by earlier (51–48 Ma), highly alkaline rocks, whereas the lower oceanic crust was predominantly sampled in later (41–43 Ma) transitional Basalts and diabases. This temporal trend is attributed to the differential melting of a heterogeneous source in association with lithospheric thinning, during which fusible upper oceanic crust melted earlier than lower oceanic crust and peridotites. We postulate that the SOC components may have been derived from the seismically detected stagnant Pacific slab within the mantle transition zone. This hypothesis is supported by the same Indian MORB-like isotopic composition being found in the Shuangliao Basalts and in the extinct Izanaghi–Pacific plate of NW Pacific. The latter has been subducting underneath the eastern Asian continent since the early Cretaceous.
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os pb and nd isotope geochemistry of the permian emeishan continental flood Basalts insights into the source of a large igneous province
Geochimica et Cosmochimica Acta, 2007Co-Authors: Jifeng Xu, Yigang Xu, Katsuhiko Suzuki, Jie LiAbstract:Abstract The nature of the source of continental flood Basalts (CFB) is a highly debated topic. Proposed mantle sources for CFBs, including both high- and low-Ti Basalts, include subcontinental lithospheric mantle (SCLM), asthenospheric mantle, and deep, plume-related mantle. Re–Os isotope systematics can offer important constraints on the sources of both ocean island Basalts (OIB) and CFB, and may be applied to distinguish different possible melt sources. This paper reports the first Re–Os isotope data for the Late Permian Emeishan large igneous province (LIP) in Southwest China. Twenty one CFB samples including both low- and high-Ti Basalts from five representative sites within the Emeishan LIP have been analyzed for Os, Nd, and Pb isotopic compositions. The obtained Os data demonstrate that crustal assimilation affected Os isotopic compositions of some Emeishan Basalt samples with low Os concentrations but not all of the samples, and the Emeishan Basalts with high Os contents likely experienced the least crustal contamination. The low and high-Ti Basalts yield distinct Os signatures in terms of 187Os/188Os and Os content. The low-Ti Basalt with the highest Os concentration (400 ppt) has a radiogenic Os isotopic composition (γOs(t), +6.5), similar to that of plume-derived OIB. Because the Os isotopic composition of Basalts with relatively high Os concentrations (typically >50 ppt) likely represents that of their mantle source, this result implies a plume-derived origin for the low-Ti Basalts. On the other hand, the high-Ti Basalts with high Os concentration (over 50 ppt) have unradiogenic Os isotopic signatures (γOs(t) values range from −0.8 to −1.4), suggesting that a subcontinental lithosphere mantle (SCLM) component most likely contributed to the generation of these magmas. Combining Pb and Nd isotopic tracers with the Os data, we demonstrate that the low-Ti Basaltic magmas in the Emeishan CFB were mainly sourced from a mantle plume reservoir, whereas the high-Ti Basaltic magmas were most likely derived from a SCLM reservoir or were contaminated by a significant amount of lithospheric mantle material during plume-related magma ascent through the SCLM.
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Geochronologic and petrochemical evidence for the genetic link between the Maomaogou nepheline syenites and the Emeishan large igneous province
Chinese Science Bulletin, 2007Co-Authors: Yigang Xu, Bin He, Xiao-long HuangAbstract:The Maomaogou nepheline syenite is located at the inner zone of the Emeishan large igneous province and exhibits intrusive contact with the Emeishan Basalts. SHRIMP U-Pb dating on zircons from this syenite yields an age of 261.6±4.4 Ma, in agreement with the age of the Panzhihua layered intrusion and the eruption age of the Emeishan Basalts as constrained by stratigraphic data. Geochemical data further suggest that the Maomaogou syenite has a source analogue to the Emeishan Basalt, and may have been formed by partial melting of gabbroic cumulates underplated in the lower crust. As s result, temporal and spatial relationships and petrogenetic constraints provide evidence for the genetic link between Basalts, mafic/ultramafic and intermediate/acidic intrusives in the Panxi area.
James S. Scoates - One of the best experts on this subject based on the ideXlab platform.
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The architecture of oceanic plateaus revealed by the volcanic stratigraphy of the accreted Wrangellia oceanic plateau
Geosphere, 2010Co-Authors: A. R. Greene, E. C. Katvala, James S. Scoates, Shoshana Israel, D. Weis, G. T. NixonAbstract:The accreted Wrangellia flood Basalts and associated sedimentary rocks that compose the prevolcanic and postvolcanic stratigraphy provide an unparalleled view of the architecture, eruptive environment, and accumulation and subsidence history of an oceanic plateau. This Triassic large igneous province extends for similar to 2300 km in the Pacific Northwest of North America, from central Alaska and western Yukon (Nikolai Formation) to Vancouver Island (Karmutsen Formation), and contains exposures of submarine and subaerial volcanic rocks representing composite stratigraphic thicknesses of 3.5-6 km. Here we provide a model for the construction of the Wrangellia oceanic plateau using the following information and visualization tools: (1) stratigraphic summaries for different areas of Wrangellia; (2) new 40Ar/39Ar geochronology results; (3) compilation and assessment of geochronology and biostratigraphy for Wrangellia; (4) compiled digital geologic maps; (5) an online photographic archive of field relationships; and (6) a Google Earth file showing the mapped extent of Wrangellia flood Basalts and linked field photographs. Based on combined radiometric (U-Pb, 40Ar/39Ar, K-Ar), paleontological, and magnetostratigraphic age constraints, the Wrangellia flood Basalts were emplaced during a single phase of tholeiitic volcanism ca. 230-225 Ma, and possibly within as few as 2 Myr, onto preexisting submerged arc crust. There are distinct differences in volcanic stratigraphy and basement composition between Northern and Southern Wrangellia. On Vancouver Island, similar to 6 km of high-Ti Basalts, with minor amounts of picrites, record an emergent sequence of pillow Basalt, pillow breccia and hyaloclastite, and subaerial flows that overlie Devonian-Mississippian (ca. 380-355 Ma) island arc rocks and Mississippian-Permian marine sedimentary strata. In contrast, Alaska and Yukon contain 1-3.5-km-thick sequences of mostly subaerial high-Ti Basalt flows, with low-Ti Basalt and submarine pillow Basalts in the lowest parts of the stratigraphy, that overlie Pennsylvanian-Permian (312-280 Ma) volcanic and sedimentary rocks. Subsidence of the entire plateau occurred during and after volcanism, based on late-stage interflow sedimentary lenses in the upper stratigraphic levels and the presence of hundreds of meters to >1000 m of overlying marine sedimentary rocks, predominantly limestone. The main factors that controlled the resulting volcanic architecture of the Wrangellia oceanic plateau include high effusion rates and the formation of extensive compound flow fields from low-viscosity, high-temperature tholeiitic Basalts, sill-dominated feeder systems, limited repose time between flows (absence of weathering, erosion, sedimentation), submarine versus subaerial emplacement, and relative water depth (e. g., pillow Basalt-volcaniclastic transition).
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Differentiation and crystallization conditions of Basalts from the Kerguelen large igneous province: an experimental study
Contributions to Mineralogy and Petrology, 2009Co-Authors: Marcus Freise, James S. Scoates, Francois Holtz, Marcus Nowak, Holger StraussAbstract:Phase relations of Basalts from the Kerguelen large igneous province have been investigated experimentally to understand the effect of temperature, f O_2, and fugacity of volatiles (e.g., H_2O and CO_2) on the differentiation path of LIP Basalts. The starting rock samples were a tholeiitic Basalt from the Northern Kerguelen Plateau (ODP Leg 183 Site 1140) and mildly alkalic Basalt evolved from the Kerguelen Archipelago (Mt. Crozier on the Courbet Peninsula), representing different differentiation stages of Basalts related to the Kerguelen mantle plume. The influence of temperature, water and oxygen fugacity on phase stability and composition was investigated at 500 MPa and all experiments were fluid-saturated. Crystallization experiments were performed at temperatures between 900 and 1,160°C under oxidizing (log f O_2 ~ ΔQFM + 4) and reducing conditions (log f O_2 ~ QFM) in an internally heated gas-pressure vessel equipped with a rapid quench device and a Pt-Membrane for monitoring the f H_2. In all experiments, a significant influence of the f O_2 on the composition and stability of the Mg/Fe-bearing mineral phases could be observed. Under reducing conditions, the residual melts follow a tholeiitic differentiation trend. In contrast, melts have high Mg# [Mg^2+/(Mg^2+ + Fe^2+)] and follow a calk-alkalic differentiation trend at oxidizing conditions. The comparison of the natural phenocryst assemblages with the experimental products allows us to constrain the differentiation and pre-eruptive conditions of these magmas. The pre-eruptive temperature of the alkalic Basalt was about 950–1,050°C. The water content of the melt was below 2.5 wt% H_2O and strongly oxidizing conditions (log f O_2 ~ ΔQFM + 2) were prevailing in the magma chamber prior to eruption. The temperature of the tholeiitic melt was above 1,060°C, with a water content below 2 wt% H_2O and a log f O_2 ~ ΔQFM + 1. Early fractionation of clinopyroxene is a crucial step resulting in the generation of silica-poor and alkali-rich residual melts (e.g., alkali Basalt). The enrichment of alkalis in residual melts is enhanced at high f O_2 and low a H_2O.
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Wrangellia flood Basalts in Alaska: A record of plume-lithosphere interaction in a Late Triassic accreted oceanic plateau
Geochemistry Geophysics Geosystems, 2008Co-Authors: Andrew R. Greene, James S. Scoates, D. WeisAbstract:The Wrangellia flood Basalts are part of one of the best exposed accreted oceanic plateaus on Earth. They provide important constraints on the construction of these vast submarine edifices and the source and temporal evolution of magmas for a plume head impinging beneath oceanic lithosphere. Wrangellia flood Basalts (∼231–225 Ma) extend ∼450 km across southern Alaska (Wrangell Mountains and Alaska Range) where ∼3.5 km of mostly subaerial flows are bounded by late Paleozoic arc volcanics and Late Triassic limestone. The vast majority of the flood Basalts are light rare earth element (LREE) -enriched high-Ti Basalt (1.6–2.4 wt % TiO2) with uniform ocean island Basalt (OIB) -type Pacific mantle isotopic compositions ($\varepsilon$ Hf(t) = +9.7 to +10.7; $\varepsilon$ Nd(t) = +6.0 to +8.1; t = 230 Ma). However, the lowest ∼400 m of stratigraphy in the Alaska Range is LREE-depleted low-Ti Basalt (0.4–1.2 wt % TiO2) with pronounced negative high field strength element (HFSE) anomalies and Hf isotopic compositions ($\varepsilon$ Hf(t) = +13.7 to +18.4) that are decoupled from Nd ($\varepsilon$ Nd(t) = +4.6 to +5.4) and displaced well above the OIB mantle array (Δ$\varepsilon$ Hf = +4 to +8). The radiogenic Hf of the low-Ti Basalts indicates involvement of a component that evolved with high Lu/Hf over time but not with a correspondingly high Sm/Nd. The radiogenic Hf and HFSE-depleted signature of the low-Ti Basalts suggest pre-existing arc lithosphere was involved in the formation of flood Basalts that erupted early in construction of part of the Wrangellia plateau in Alaska. Thermal and mechanical erosion of the base of the lithosphere by the impinging plume head may have led to melting of arc lithosphere or interaction of plume-derived melts and subduction-modified mantle. The high-Ti lavas dominate the main phase of construction of the plateau and were derived from a depleted mantle source distinct from the source of MORB and with compositional similarities to that of ocean islands (e.g., Hawaii) and plateaus (e.g., Ontong Java) in the Pacific Ocean.
