Tectonic significance of Triassic mafic rocks in the June Complex,Sanandaj–Sirjan zone,Iran     

Farzaneh Shakerardakani  Franz Neubauer  Xiaoming Liu  Manfred Bernroider  Behzad Monfaredi  Albrecht von Quadt 《Swiss Journal of Geoscience》2018,111(1-2):13-33

This study concentrates on the petrological and geochemical investigation of mafic rocks embedded within the voluminous Triassic June Complex of the central Sanandaj–Sirjan zone (Iran), which are crucial to reconstruct the geodynamics of the Neotethyan passive margin. The Triassic mafic rocks are alkaline to sub-alkaline basalts, containing 43.36–49.09 wt% SiO₂, 5.19–20.61 wt% MgO and 0.66–4.59 wt% total alkalis. Based on MgO concentrations, the mafic rocks fall into two groups: cumulates (Mg# = 51.61–58.94) and isotropic basaltic liquids (Mg# = 24.54–42.66). In all samples, the chondrite-normalized REE patterns show enrichment of light REEs with variable (La/Yb)_N ratios ranging from 2.48 to 9.00, which confirm their amalgamated OIB-like and E-MORB-like signatures. Enrichment in large-ion lithophile elements and depletion in high field strength elements (HFSE) relative to the primitive mantle further support this interpretation. No samples point to crustal contamination, all having undergone fractionation of olivine + clinopyroxene + plagioclase. Nevertheless, elemental data suggest that the substantial variations in (La/Sm)_PM and Zr/Nb ratios can be explained by variable degrees of partial melting rather than fractional crystallization from a common parental magma. The high (Nb/Yb)_PM ratio in the alkaline mafic rocks points to the mixing of magmas from enriched and depleted mantle sources. Abundant OIB alkaline basalts and rare E-MORB appear to be linked to the drifting stage on the northern passive margin of the Neotethys Ocean.  相似文献   

Alpine geodynamic evolution of passive and active continental margin sequences in the Tauern Window (eastern Alps, Austria, Italy): a review     

W. Kurz  F. Neubauer  J. Genser  E. Dachs 《International Journal of Earth Sciences》1998,87(2):225-242

The Penninic oceanic sequence of the Glockner nappe and the foot-wall Penninic continental margin sequences exposed within the Tauern Window (eastern Alps) have been investigated in detail. Field data as well as structural and petrological data have been combined with data from the literature in order to constrain the geodynamic evolution of these units. Volcanic and sedimentary sequences document the evolution from a stable continent that was formed subsequent to the Variscan orogeny, to its disintegration associated with subsidence and rifting in the Triassic and Jurassic, the formation of the Glockner oceanic basin and its consumption during the Upper Cretaceous and the Paleogene. These units are incorporated into a nappe stack that was formed during the collision between a Penninic Zentralgneis block in the north and a southern Austroalpine block. The Venediger nappe and the Storz nappe are characterized by metamorphic Jurassic shelf deposits (Hochstegen group) and Cretaceous flysch sediments (Kaserer and Murtörl groups), the Eclogite Zone and the Rote Wand–Modereck nappe comprise Permian to Triassic clastic sequences (Wustkogel quartzite) and remnants of platform carbonates (Seidlwinkl group) as well as Jurassic volcanoclastic material and rift sediments (Brennkogel facies), covered by Cretaceous flyschoid sequences. Nappe stacking was contemporaneous to and postdated subduction-related (high-pressure) eclogite and blueschist facies metamorphism. Emplacement of the eclogite-bearing units of the Eclogite zone and the Glockner nappe onto Penninic continental units (Zentralgneis block) occurred subsequent to eclogite facies metamorphism. The Eclogite zone, a former extended continental margin, was subsequently overridden by a pile of basement-cover nappes (Rote Wand–Modereck nappe) along a ductile out-of-sequence thrust. Low-angle normal faults that have developed during the Jurassic extensional phase might have been inverted during nappe emplacement.  相似文献   

Partial Melting and Counterclockwise P T Path of Subducted Oceanic Crust (Sierra del Convento Melange, Cuba)   总被引：1，自引：0，他引：1  

Garcia-Casco  Antonio; Lazaro  Concepcion; Rojas-Agramonte  Yamirka; Kroner  Alfred; Torres-Roldan  Rafael Luis; Nunez  Kenya; Neubauer  Franz; Millan  Guillermo; Blanco-Quintero  Idael 《Journal of Petrology》2008,49(1):129-161

Partial melting of subducted oceanic crust has been identifiedin the Sierra del Convento mélange (Cuba). This serpentinite-matrixmélange contains blocks of mid-ocean ridge basalt (MORB)-derivedplagioclase-lacking epidote ± garnet amphibolite intimatelyassociated with peraluminous trondhjemitic–tonalitic rocks.Field relations, major element bulk-rock compositions, mineralassemblages, peak metamorphic conditions (c. 750°C, 14–16kbar), experimental evidence, and theoretical phase relationssupport formation of the trondhjemitic–tonalitic rocksby wet melting of subducted amphibolites. Phase relations andmass-balance calculations indicate eutectic- and peritectic-likemelting reactions characterized by large stoichiometric coefficientsof reactant plagioclase and suggest that this phase was completelyconsumed upon melting. The magmatic assemblages of the trondhjemitic–tonaliticmelts, consisting of plagioclase, quartz, epidote, ±paragonite, ± pargasite, and ± kyanite, crystallizedat depth (14–15 kbar). The peraluminous composition ofthe melts is consistent with experimental evidence, explainsthe presence of magmatic paragonite and (relict) kyanite, andplaces important constraints on the interpretation of slab-derivedmagmatic rocks. Calculated P–T conditions indicate counterclockwiseP–T paths during exhumation, when retrograde blueschist-faciesoverprints, composed of combinations of omphacite, glaucophane,actinolite, tremolite, paragonite, lawsonite, albite, (clino)zoisite,chlorite, pumpellyite and phengite, were formed in the amphibolitesand trondhjemites. Partial melting of subducted oceanic crustin eastern Cuba is unique in the Caribbean realm and has importantconsequences for the plate-tectonic interpretation of the region,as it supports a scenario of onset of subduction of a youngoceanic lithosphere during the early Cretaceous (c. 120 Ma).The counterclockwise P–T paths were caused by ensuingexhumation during continued subduction. KEY WORDS: amphibolite; Cuba; exhumation; partial melting; trondhjemite; subduction  相似文献   

高效液相色谱-等离子体质谱技术在溴元素形态分析中的应用     

珀金埃尔默公司分析科学部 《岩矿测试》2008,27(6):483-484

溴是一种在自然水体中都含有的元素,通常以B r-的形式存在。目前最常用的水净化方式就是向水中通入臭氧以杀灭细菌;而臭氧分解的副产物即为B r-转换成的B rO3-,这是一种公认的致癌物质。本实验室曾使用阴离子交换高效液相色谱(HPLC)与等离子体质谱(ICP-MS)联用分析B rO3-和B r-,方法虽能有效地将这两种溴形态分离,但分析每个样品需8 m in。本文试图建立新的方法缩短分析时间,并验证该方法应用于实际水样分析时测定其他含溴化合物的能力。1实验部分1.1高效液相色谱分析条件表1列出了等度淋洗和梯度淋洗两种模式下HPLC的分析条件,完成形态的分离。等度淋洗和梯度淋洗在分析中显示出不同  相似文献   

Uniform Permian 40Ar/39Ar detrital mica ages in the eastern Qaidam Basin (NW China): where is the source?     

Andrea B. Rieser  Yongjiang Liu  Johann Genser  Franz Neubauer  Robert Handler  Xiao‐Hong Ge 《地学学报》2006,18(1):79-87

New single‐grain ⁴⁰Ar/³⁹Ar detrital white‐mica ages from the Lulehe section at the eastern Qaidam Basin yield uniform Permian ages between 250 ± 3 and 279 ± 3 Ma throughout the whole Cenozoic sequence. This is inconsistent with the present hinterland, which is composed of early Palaeozoic metamorphic units with subordinate early Palaeozoic and few Permian granites. The new data indicate that Permian tectonic units are likely more widespread at the north‐eastern margin of the Tibetan plateau as known at present, particularly within the Qilian Mountains. The preferred explanation is that the Qaidam block represents a rigid indenter, which indented during late Tertiary times into early Palaeozoic orogenic units. This is consistent with recent findings of a NW‐trending sinistral Permian ductile shear zone and a dextral, NW‐trending Tertiary fault system close to the north‐eastern margin of the Qaidam Basin.  相似文献   

Ecosystem Responses of a Tidal Freshwater Marsh Experiencing Saltwater Intrusion and Altered Hydrology   总被引：5，自引：0，他引：5  

Scott C. Neubauer 《Estuaries and Coasts》2013,36(3):491-507

Tidal freshwater marshes exist in a dynamic environment where plant productivity, subsurface biogeochemical processes, and soil elevation respond to hydrological fluctuations over tidal to multi-decadal time scales. The objective of this study was to determine ecosystem responses to elevated salinity and increased water inputs, which are likely as sea level rise accelerates and saltwater intrudes into freshwater habitats. Since June 2008, in situ manipulations in a Zizaniopsis miliacea (giant cutgrass)-dominated tidal freshwater marsh in South Carolina have raised porewater salinities from freshwater to oligohaline levels and/or subtly increased the amount of water flowing through the system. Ecosystem-level fluxes of CO₂ and CH₄ have been measured to quantify rates of production and respiration. During the first 20 months of the experiment, the major impact of elevated salinity was a depression of plant productivity, whereas increasing freshwater inputs had a greater effect on rates of ecosystem CO₂ emissions, primarily due to changes in soil processes. Net ecosystem production, the balance between gross ecosystem production and ecosystem respiration, decreased by 55% due to elevated salinity, increased by 75% when freshwater inputs were increased, and did not change when salinity and hydrology were both manipulated. These changes in net ecosystem production may impact the ability of marshes to keep up with rising sea levels since the accumulation of organic matter is critical in allowing tidal freshwater marshes to build soil volume. Thus, it is necessary to have regional-scale predictions of saltwater intrusion and water level changes relative to the marsh surface in order to accurately forecast the long-term sustainability of tidal freshwater marshes to future environmental change.  相似文献   

Provenance of Palaeozoic sandstones from the Carnic Alps (Austria): petrographic and geochemical indicators   总被引：1，自引：0，他引：1  

Dieter?MaderEmail author  Franz?Neubauer 《International Journal of Earth Sciences》2004,93(2):262-281

An integrated approach of petrographic analysis, whole rock geochemistry and microprobe analysis has been applied to obtain information on the geodynamic development and the provenance for Ordovician to Permian siliciclastic successions exposed within the Carnic Alps (Austria). Sandstone detrital mode and geochemical results refine previous geodynamic interpretations. Late Ordovician samples indicate a stable craton and recycled orogenic and, possible, extensional setting. The Early Carboniferous is interpreted to represent a compressional environment, followed by a Late Carboniferous molasse-type foreland basin, and a Permian extensional geodynamic setting. Contrasting geochemical patterns of post-Variscan and Permian sequences suggest a rift setting. Electron microprobe data of detrital white mica also indicate changes in the provenance. Compositional data reflect a shift from low- to medium-grade metamorphic (Ordovician) to high-grade metamorphic (Carboniferous) to low- to medium-grade metamorphic and plutonic source rocks (Permian). Additionally, our data show that various chemical discrimination diagrams do not include all possible ranges of sandstones, and that high contents of detrital mica and ultra-stable heavy minerals may cause misclassification. Consequently, we propose the use of multi-method approach for provenance studies, including the control of geochemical data by modal analysis and heavy mineral investigations.  相似文献   

TRANSALP—deep crustal Vibroseis and explosive seismic profiling in the Eastern Alps     

Ewald Lüschen  Daniela Borrini  Helmut Gebrande  Bernd Lammerer  Karl Millahn  Franz Neubauer  Rinaldo Nicolich  TRANSALP Working Group   《Tectonophysics》2006,414(1-4):9

The TRANSALP consortium, comprising institutions from Italy, Austria and Germany, carried out deep seismic reflection measurements in the Eastern Alps between Munich and Venice in 1998, 1999 and 2001. In order to complement each other in resolution and depth range, the Vibroseis technique was combined with simultaneous explosive source measurements. Additionally, passive cross-line recording provided three-dimensional control and alternative north–south sections. Profits were obtained by the combination of the three methods in sectors or depths where one method alone was less successful.The TRANSALP sections clearly image a thin-skinned wedge of tectonic nappes at the northern Alpine front zone, unexpected graben or half-graben structures within the European basement, and, thick-skinned back-thrusting in the southern frontal zone beneath the Dolomite Mountains. A bi-vergent structure at crustal scale is directed from the Alpine axis to the external parts. The Tauern Window obviously forms the hanging wall ramp anticline above a southward dipping, deep reaching reflection pattern interpreted as a tectonic ramp along which the Penninic units of the Tauern Window have been up-thrusted.The upper crystalline crust appears generally transparent. The lower crust in the European domain is characterized by a 6–7 km thick laminated structure. On the Adriatic side the lower crust displays a much thicker or twofold reflective pattern. The crustal root at about 55 km depth is shifted around 50 km to the south with respect to the main Alpine crest.  相似文献   

GEOCHRONOLOGY OF ~(Ar)/~(39)Ar DATING IN THE BASEMENT ROCKS IN EASTERN KUNLUN MOUNTAINS AND ITS TECTONIC IMPLICATIONS     

Liu Yongjiang    Genser Jenser  Neubauer Franz  Jin Wei  Ge Xiaohong  Handler Robert 《地学前缘》2000,(Z1)

GEOCHRONOLOGY OF ~(Ar)/~(39)Ar DATING IN THE BASEMENT ROCKS IN EASTERN KUNLUN MOUNTAINS AND ITS TECTONIC IMPLICATIONS  相似文献   

Seismic image of the deep crust at the eastern margin of the Alps (Austria): indications for crustal extension in a convergent orogen     

H. Graßl  F. Neubauer  K. Millahn  F. Weber 《Tectonophysics》2004,380(1-2):105-122

A 39-km-long deep seismic reflection profile recorded during two field campaigns in 1996 and 2002 provides a first detailed image of the deep crust at the eastern margin of the Eastern Alps (Austria). The ESE–WNW-trending, low-fold seismic line crosses Austroalpine basement units and extends approximately from 20 km west of the Penninic window group of Rechnitz to 60 km SSE of the Alpine thrust front.The explosive-source seismic data reveals a transparent shallow crust down to 5 km depth, a complexly reflective upper crust and a highly reflective lowermost crust. The upper crust is dominated by three prominent west-dipping packages of high-amplitude subparallel reflections. The upper two of these prominent packages commence at the eastern end of the profile at about 5 and 10 km depth and are interpreted as low-angle normal shear zones related to the Miocene exhumation of the Rechnitz metamorphic core complex. In the western portion of the upper crust, east-dipping and less significant reflections prevail. The lowermost package of these reflections is suggested to represent the overall top of the European crystalline basement.Along the western portion of the line, the lower crust is characterised by a 6–8-km-thick band of high-amplitude reflection lamellae, typically observed in extensional provinces. The Moho can be clearly defined at the base of this band, at approximately 32.5 km depth. Due to insufficient signal penetration, outstanding reflections are missing in the central and eastern portion of the lower crust. We speculate that the result of accompanying gravity measurements and lower crustal sporadic reflections can be interpreted as an indication for a shallower Moho in the east, preferable at about 30.5 km depth.The high reflectivity of the lowermost part of the lower crust and prominent reflection packages in the upper crust, the latter interpreted to represent broad extensional mylonite zones, emphasises the latest extensional processes in accordance with eastward extrusion.  相似文献