Late orogenic rebound and oblique Alpine convergence: New constraints from subsidence analysis of the Austrian Molasse basin   总被引：1，自引：1，他引：0  

Johann Genser  Sierd A.P.L. Cloetingh  Franz Neubauer   《Global and Planetary Change》2007,58(1-4):214

Subsidence analysis of 16 wells in the Austrian Molasse basin documents major spatial and temporal changes in tectonic subsidence as well as a late-stage surface uplift. The timing of the main phase of tectonic subsidence shifted from early Oligocene in the western part of the peripheral foreland to the early Miocene in the eastern part. These temporal and spatial changes in tectonic subsidence reflect a change from oblique dextral to sinistral convergence between the Alpine nappe stack and its foreland. The main phase of sediment accumulation was delayed to the early Miocene and led to the infill of the basin and a major second, sediment-load driven phase of basement subsidence. Sediment accumulation rates in the basin reflect the build-up of topography in the Alpine mountain chain. Since approximately 6 Ma a pronounced regional uplift of the entire Molasse basin has taken place, marking the transition from lateral extrusion to orthogonal contraction within the Alpine system and deep-seated changes in geodynamic boundary conditions, possibly due to delamination of previously thickened lithosphere. Surface uplift is contemporaneous with similar processes in extra-Alpine Central Europe, where it is interpreted to reflect intra-plate stress changes.  相似文献   

Evolution of quartz microstructures and textures during polyphase deformation within the Tauern Window (Eastern Alps)     

Walter Kurz  Wolfgang Unzog  Franz Neubauer  Johann Genser 《International Journal of Earth Sciences》2001,90(2):361-378

The interior of the Tauern Window exposes underplated Penninic continental lithosphere and the overlying obducted Penninic oceanic crust within a large antiformal dome in the internal zone of the Eastern Alps. These units have been affected by a polyphase deformation history. Generally, three deformation events are distinguished. D₁ is related to underplating of, and top-to-the-N nappe stacking within, the Penninic continental units of the Tauern Window. Deformation stage D₂ is interpreted to reflect the subsequent continent collision between the Penninic continental units and the European foreland, D₃ is related to the formation of the dome structure within the Tauern Window. During thickening of continental lithosphere and nappe stacking (D₁), and subsequent intracontinental shortening (D₂), these tectonic units have been ductilely deformed close to a plane strain geometry. Conditions for the plastic deformation of the main rock-forming mineral phases (quartz, feldspar, dolomite, calcite) have prevailed during all three phases of crustal deformation. Generally, two types of quartz microstructures that are related to D₁ are distinguished within the Tauern Window: (a) Equilibrated and annealed fabrics without crystallographic preferred orientations (CPO) have only been observed in the central part of the southeastern Tauern Window, corresponding with amphibolite-grade metamorphic conditions. (b) In the northeastern and central part of the Tauern Window microstructures are characterized by quartz grains that show equilibrated shape fabrics, but well preserved CPO with type-I cross girdle distributions, indicating a deformation geometry close to plane strain. During D₂, two types of quartz microstructures are distinguished, too: (a) Quartz grains that show equilibrated shape fabrics, but well-preserved CPO. The c-axes distributions generally are characterized by type-I cross girdles, locally by type-II cross girdles, and in places, oblique single girdle distributions. (b) A second type of quartz microstructure is characterized by highly elongated grains and fabrics typical for dislocation creep and grain-boundary migration, and strong CPO. This type is restricted to the southern sections of the western and eastern Tauern Window. The c-axis distributions show type-I cross girdles in the western part of the Tauern Window and single girdles in the southeastern part. In the western part of the Tauern Window, a continuous transition from type (b) microstructures in the south to type (a) microstructures in the north is documented. The microstructural evolution also documents that the dome formation in the southeastern and western Tauern Window has already started during D₂ and has continued subsequent to the equilibration during amphibolite to greenschist facies metamorphism. D₃ is restricted to distinct zones of localized deformation. D₃-related quartz fabrics are characterized by the formation of ribbon grains; the c-axes show small-circle distributions around the Z-axis of the finite-strain ellipsoid. During exhumation and doming (D₃), deformation occurred under continuously decreasing temperatures.  相似文献   

The Dabie UHP unit, Central China: a Cretaceous extensional allochthon superposed on a Triassic orogen   总被引：1，自引：0，他引：1  

Wang  Neubauer  Genser  & Yang 《地学学报》1998,10(5):260-267

Petrological, geochronological and structural data show that the eastern Dabie metamorphic complex resulted from two orogenic stages. Precursor rocks of the ultrahigh-pressure (UHP) and high-pressure (HP) units in the present hanging wall tectonic position were buried, penetratively deformed and subsequently exhumed by distributed, ESE-directed shearing during Triassic time. In contrast, rocks of the Dabie orthogneiss domes, now in a footwall tectonic position, were penetratively deformed during temperature-dominated, Early Cretaceous tectonic events, that are likely related to magmatic underplating. The Dabie orthogneiss domes and the UHP/HP units were juxtaposed during Early Cretaceous exhumation of Dabie orthogneiss domes by the formation of an ESE-directed low-angle ductile normal shear zone. Consequently, the UHP/HP units now represent an extensional allochthon in the hanging wall of the younger normal shear zone. The Cretaceous extensional structures are limited by boundary strike-slip faults. Consistent with the South China regional tectonic framework, ESE-directed lateral extrusion is considered to be the driving mechanism for extension and the present-day structure of the Dabie metamorphic complex.  相似文献   

阿尔金断裂带年代学和阿尔金山隆升   总被引：36，自引：2，他引：34       下载免费PDF全文

刘永江  Franz Neubauer  葛肖虹  Johann Genser  袁四化  李伟民  巩庆林  陈元忠 《地质科学》2007,42(1):134-146,188

对阿尔金山断裂带内变形的中生代剪切带中眼球状片麻岩、糜棱岩化花岗片麻岩和新生代剪切带中强变形绿片岩系列样品中同构造新生云母矿物的⁴⁰Ar-³⁹Ar法定年,获得了164.3~178.4Ma和26.3~36.4Ma两组年龄。结合阿尔金走滑断裂水平错距的研究,认为164.3~178.4Ma的年龄代表阿尔金走滑断裂带的起始活动时间(早侏罗世末—中侏罗世),尔后分别在距今100~85Ma,40~25Ma和10~8Ma发生多次脉冲式走滑活动。新生代沉积物研究表明上干柴沟组和下干柴沟组砂岩骨架矿物成份含量明显不同,随时间变化,石英含量减少,岩屑组份和不稳定矿物含量增加,分选性逐渐变差。这表明阿尔金山在渐新世(下干柴沟组时期)开始发生明显的隆升。地震和柴达木—塔里木盆地沉积速率资料显示在晚中新世山体也发生了一次强烈的隆升。七个泉组(上新世末—早更新世初)和下伏沉积物(上新世中期)之间的角度不整合反映了最后一次强烈隆升事件发生在晚上新世。多数隆升事件和阿尔金断裂带新生代脉冲式活动的同位素年龄完全一致,表明阿尔金山的隆升和断裂带的活动具有密切的成因联系。  相似文献   

U-Pb and Ar/Ar geochronological constraints on the exhumation history of the North Qinling terrane, China     

Yunpeng Dong  Johann Genser  Franz Neubauer  Guowei Zhang  Xiaoming Liu  Zhao Yang  Bianca Heberer 《Gondwana Research》2011,19(4):881-893

The amphibolite facies grade North Qinling metamorphic unit forms the centre of the Qinling orogenic belt. Results of LA-ICP-MS U-Pb zircon, ⁴⁰Ar/³⁹Ar amphibole and biotite dating reveal its Palaeozoic tectonic history. U-Pb zircon dating of migmatitic orthogneiss and granite dykes constrains the age of two possible stages of migmatization at 517 ± 14 Ma and 445 ± 4.6 Ma. A subsequent granite intrusion occurred at 417 ± 1.6 Ma. The ⁴⁰Ar/³⁹Ar plateau ages of amphibole ranging from 397 ± 33 Ma to 432 ± 3.4 Ma constrain the cooling of the Qinling complex below ca. 540 °C and biotite ⁴⁰Ar/³⁹Ar ages at about 330–368 Ma below ca. 300 °C. The ages are used to construct a cooling history with slow/non-exhumation during 517– 445 Ma, a time-integrated cooling at a rate < 2.5 °C/Ma during the period of 445–410 Ma, an acceleration of cooling at a rate of 8 °C/Ma from 397 Ma to 368 Ma, and subsequently slow/non-cooling from 368 to 330 Ma. The data show a significant delay in exhumation after peak metamorphic conditions and a long period of tectonic quiescence after the suturing of the North China and South China blocks along the Shangdan suture. These relationships exclude classical exhumation models of formation and exhumation of metamorphic cores in orogens, which all imply rapid cooling after peak conditions of metamorphism.  相似文献   

Oligo-Miocene shearing along the Ailao Shan–Red River shear zone: Constraints from structural analysis and zircon U/Pb geochronology of magmatic rocks in the Diancang Shan massif, SE Tibet, China     

Shuyun Cao  Junlai Liu  Bernd Leiss  Franz Neubauer  Johann Genser  Chunqiang Zhao 《Gondwana Research》2011,19(4):975-993

The left-lateral strike-slip shearing along the Ailao Shan–Red River (ASRR) shear zone in the Southeastern Tibet, China, has been widely advocated to be a result of the Indian–Eurasian plate collision and post-collisional processes. The Diancang Shan (DCS) massif, which occurs at the northwestern extension of the Ailao Shan massif, is a typical high-grade metamorphic complex aligned along the ASRR tectonic belt. Structural and microstructural analysis of the plutonic intrusions in the DCS revealed different types of granitic intrusions spatially confined to the shear zone and temporally related to the left-lateral shearing along the ASRR shear zone in the DCS massif. The combined structural and geochronological results of SHRIMP-II and LA-ICP-MS zircon U/Pb isotopic dating have revealed successive magmatic intrusions and crystallization related to the Oligo-Miocene shearing in the DCS massif. The pre-, early- and syn-kinematic emplacements are linked to regional high-temperature deformation (lower amphibolite facies) at relatively deep crustal levels. The zircon U/Pb geochronological results suggest that the left-lateral ductile shearing along the ASRR shear zone was initiated at ca. 31 Ma, culminated between ca. 27 and 21 Ma resulting in high-temperature metamorphic conditions and slowed down at ca. 20 Ma at relatively low-temperatures.  相似文献   

Über die Entstehung und die Natur radioaktiver Quellen     

Carl Genser 《International Journal of Earth Sciences》1932,23(3-4):188-237

Zusammenfassung Es wird gezeigt, da\ radioaktive Quellen, insbesondere solche von bedeutender Aktivität, stets an saure Eruptivgesteine und an ausgeprägte Spalten- und Kluftsysteme gebunden sind. Dies gilt sowohl für radiumemanationshaltige wie auch für radiumsalzhaltige Quellen.Die Genesis radioaktiver Quellen ist durchaus nicht einheitlich. Die Entstehung der Quellen von Brambach i. Vogtl. wird auf die Vereinigung von auf Gasspalten zirkulierender emanationshaltiger Kohlensäure mit wasserführenden Spalten zurückgeführt, wobei als emanationslieferndes Gestein der normale Brambacher Granit in Frage kommt. Die Wässer von Oberschlema verdanken ihre hohe Aktivität einem, unter der Wirkung gering sulfathaltiger Wässer zustandekommenden, hochaktiven Belag der Spalten- und Kluftwände. Beim Durchflie\en des Wassers durch die Spalten nimmt das Wasser die von dem hochaktiven Belag abgegebene Emanation in Lösung. Genetisch sehr nahe stehen den Oberschlemaer Wässern die Quellen im Bereiche des Eibenstocker Granitmassivs. Der aktive emanationsspendende Spaltenbelag wird hier durch sekundäre Uranmineralien, insbesondere Uranglimmer, gebildet. Für den Radiumsalzgehalt der Heidelberger Therme wird angenommen, da\ das radiumsalzhaltige Wasser auf Spalten aus dem tiefliegenden Granit hochsteigt und sich dann erst mit der thermalen Sole vereinigt. Für die dem Heidelberger Thermalwasser sehr nahe stehenden Wässer von Kreuznach kommt eine ähnliche Entstehung in Frage. Das saure Gestein ist hier die Ergu\form des granitischen Magmas, ein Quarzporphyr. Beim Aufstieg in den Spalten nimmt das radiumsalzhaltige Wasser aber weiterhin die von den Spaltenwänden abgegebenen wesentlichen Emanationsmengen in Lösung.Auf geologisch-chemischer und radiologischer Grundlage wird schlie\lich noch eine übersicht und natürliche Einteilung der radioaktiven Wässer gegeben.  相似文献   

Origin of deformed halite hopper crystals, pseudomorphic anhydrite cubes and polyhalite in Alpine evaporites (Austria, Germany)     

C. Leitner  F. Neubauer  R. Marschallinger  J. Genser  M. Bernroider 《International Journal of Earth Sciences》2013,102(3):813-829

The Alpine Haselgebirge Formation represents an Upper Permian to Lower Triassic evaporitic rift succession of the Northern Calcareous Alps (Eastern Alps). Although the rocksalt body deposits are highly tectonised, consisting mainly of protocataclasites and mylonites of halite and mudrock, the early diagenetic history can be established from non-tectonised mudrock bodies: Cm-sized euhedral halite hopper crystals formed as displacive cubes within mud just during shallow burial. The crystals were deformed by subsequent compaction. Later, migrating fluids led to the replacement of halite by anhydrite retaining the shapes of deformed halite cubes. Polyhalite formed from subsequent enhanced fluid migration. Mudrock provided water by dewatering, while potassium and magnesium were dissolved from primary salt minerals. When these fluids interacted with sulphates, polyhalite precipitated. ⁴⁰Ar/³⁹Ar analyses date the polyhalite from within the retaining shapes of deformed halite hopper-shaped cubes from two localities to ca. 235–232 Ma (Middle Triassic). At this time, ca. 20–25 Ma after sedimentation, polyhalite crystallised at shallow levels.  相似文献