The Northern Giudicarie and the Meran-Mauls fault (Alps,Northern Italy) in the light of new paleomagnetic and geochronological data from boudinaged Eo-/Oligocene tonalites

This study concentrates on small intrusions along two important faults of the Giudicarie fault system, the Northern Giudicarie and the Meran-Mauls fault, summarised under the term tonalitic lamellae. Magnetic fabric analyses in combination with structural field data indicate dextral strike slip deformation along the NE–SW striking northern part of the Giudicarie fault system, the Meran-Mauls fault, overprinted by younger thrusting. The regional stressfield was oriented approximately NNW–SSE during Tertiary times. The distinctive change in deformation along the Meran-Mauls fault from dextral strike slip to top-SE thrusting may be caused by a rotation or bending of the fault after the intrusion of the tonalites and the formation of their horizontal magnetic foliation. Based on the assumption of a preliminary straight Periadriatic lineament bent by the NNW-wards advancement of the Southalpine indenter, the tonalitic lamellae may be interpreted as lenses sheared off from the Adamello batholith during indentation. New U/Pb data on zircon show that some of the lamellae are of Oligocene (Rupelian), others of Late Eocene (Priabonian) age. An amphibole-gabbro lens occurring on the Meran-Mauls fault provides a Middle Eocene (Bartonian) age. Among the major Periadriatic plutons, only the southern units of the Adamello batholith also intruded in the Eocene that suggests a strong correlation between the tonalitic lamellae and the Adamello batholith. The analyses of the remanent magnetisation and the Curie point determinations argue for magnetite as the main carrier of a viscous magnetisation blocked at relatively low temperatures. This indicates slow cooling of the investigated intrusions along the Giudicarie fault system down to approximately 300°C, which is in contrast to the fast cooling determined for the Adamello intrusion units currently at the surface. The new zircon fission track data also show later cooling of the tonalites along the Giudicarie fault system when compared with the Adamello batholith in the south and the Mauls lamellae in the north, indicating that this area contains magmatic bodies exhumed from a deeper structural level than in the Adamello and the Mauls region. This may be due to important top-SE thrusting and transpressive faulting in the footwall of the Northern Giudicarie fault and the Meran-Mauls fault.     

Age,origin and geodynamic significance of a polymetamorphic felsic intrusion in the Ötztal Crystalline Basement,Tirol, Austria

Summary A multi-method approach was applied to derive the age and origin of an orthogneiss body located in the central Kaunertal, western Ötztal Crystalline Basement (ÖCB). The Tieftal orthogneiss body is an internally differentiated, polymetamorphosed epizonal intrusion, embedded in amphibolites. It comprises leucocratic hedenbergite-hornblende-, hornblende- and biotite-hornblende-gneisses, but also some melanocratic rock types. The leucocratic Tieftal gneisses are granitic, have a near eutectic melt composition and share some features of A-type granites, such as high Na₂O+K₂O(8.07 to 8.58wt%), Zr (379 to 554ppm) and Y (58 to 79ppm) contents. The REE-patterns are rather flat ((La/Yb)_N=2.4 to 3.7), with distinct negative Eu anomalies. Single zircon evaporation dating of two samples and Sm-Nd dating of relict magmatic titanite resulted in ages of 487±7, 484±3 and 487±5Ma, respectively. The weighted mean of 485±3Ma is interpreted as the primary crystallization age of the Tieftal orthogneiss body. Rb-Sr whole rock dating results in a well defined regression line, corresponding to an age of 411±9Ma. This age clearly documents at least a partial resetting of the whole rock Rb-Sr system, which is most probably due to subsequent metamorphic overprint. The leucocratic Tieftal gneisses are isotopically rather primitive with an Nd _CHUR ^{485 Ma} value of +1.7 and a calculated magmatic initial⁸⁷Sr/⁸⁶Sr ratio of 0.7047. These data suggest a major mantle contribution. Most probably, they originated through fractionation of the magmatic precursors of the accompanying tholeiitic metabasites. The more primitive isotopic composition of ÖCB metabasites and some late Archean/early Proterozoic and Cambrian inheritance in Tieftal gneiss zircons suggest some involvement of old crustal rocks, too. The amount of crustal contamination can be calculated to be in the range of 10 to 40%. The Tieftal gneisses and the accompanying metabasites are interpreted as remnants of igneous rocks related to an early Ordovician rifting and incipient formation of new oceanic crust, an event which can be traced throughout the central and western European Variscan and Alpine terranes.

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Alter, Genese und geologische Bedeutung einer polymetamorphen felsischen Intrusion im Ötztalkristallin, Tirol, Österreich

Zusammenfassung Ein Vielzahl von Methoden wurde angewandt, um das Alter und die Genese eines Orthogneiskörpers im mittleren Kaunertal, westliches Ötztalkristallin, abzuleiten. Der Tieftal-Orthogneiskörper ist eine in Amphiboliten eingeschaltete, intern differenzierte, polymetamorph überprägte, epizonale Intrusion. Er umfaßt sowohl leukokrate Hedenbergit-Hornblende-, Hornblende- und Biotit-Hornblende-Gneise als auch untergeordnet melanokrate Gesteine. Die leukokraten Tieftal-Gneise besitzen einen granitischen, beinahe einer eutektischen Schmelze entsprechenden Chemismus; einige Parameter wie hohe Na₂O+K₂O(8.07 bis 8.58Gew%), Zr(379 bis 554ppm) und Y(58 bis 79ppm) Gehalte weisen auf eine A-Typ Affinität hin. Die SEE-Spektren sind nur gering fraktioniert ((La/Yb)_N=2.3 bis 3.7) und weisen eine markante negative Eu-Anomalie auf. Einzelzirkon-Evaporationsdatierungen an 2 Proben und eine Sm-Nd Datierung von reliktischem magmatischem Titanit ergeben Alter von 487±7, 484±3 und 487±5Ma. Der gewichtete Mittelwert von 485±3Ma wird als das primäre magmatische Kristallisationsalter des Tieftal-Orthogneiskörpers interpretiert. Eine Rb-Sr Gesamtgesteinsdatierung ergibt eine gut definierte Regressionsgerade mit einem Alter von 411±9Ma. Dieses Alter beweist eine postmagmatische Störung des Rb-Sr Gesamtgesteinssystems, die durch die metamorphen überprägungen verursacht wurde. Die leukokraten Tieftal-Gneise besitzen eine relative primitive isotopische Zusammensetzung mit einem Nd _CHUR ^{485 Ma} a Wert von +1.7 und einem zurückgerechneten magmatischen⁸⁷Sr/⁸⁶Sr Initialverhältnis von 0.7047. Diese Daten machen eine große Beteiligung von Mantelmaterial wahrscheinlich. Am ehesten entstanden die leukokraten Tieftal-Gneise durch magmatische Fraktionierungsprozesse aus den Ausgangsgesteinen der begleitenden tholeiitischen Metabasite. Die noch primitivere isotopische Zusammensetzung der Metabasite im Ötztalkristallin und spätarchaische/frühproterozoische sowie kambrische Komponenten in den Zirkonen der leukokraten Tieftal-Gneise weisen aber auch auf die Beteiligung alten krustalen Materials hin. Der Anteil der krustalen Komponente liegt im Bereich von 10 bis 40%. Der Tieftal-Orthogneiskörper und die begleitenden Metabasite werden als Relikte magmatischer Gesteine, die während eines frühordovizischen Riftings und der beginnenden Bildung neuer ozeanischer Kruste entstanden sind, gedeutet. Zeugen dieses Vorganges sind in allen variszisch und alpidisch geprägten Gebieten Westund Mitteleuropas zu finden.

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With 13 Figures     

Die Reaktion 2 Zoisit+1 CO2 ⇌ 3 Anorthit+1 Calcit+1 H2O

The equilibrium conditions of the following reaction 2 zoisite +1 CO₂?3 anorthite+1 calcite+1 H₂O 2 Ca₂Al₃[O/OH/SiO₄/Si₂O₇]+1 CO₂?3 CaAl₂Si₂O₈+1 CaCO₃+1 H₂O have been determined experimentally at total pressures of P _j= 2000 bars, P _f =5000 bars, and P _f =7000 bars. Owing to the vertical position of the equilibrium curves in isobaric T- \(X_{{\text{CO}}_{\text{2}} }\) diagrams, the composition of the binary H₂O-CO₂ fluid phase coexisting with zoisite is independent of temperature in the temperature interval investigated. According to our experiments, orthorhombic zoisite is only stable in equilibrium with a fluid phase at a concentration of CO₂ which is less than, respectively, ca. 2 Mol% CO₂ at P _f =2000 bars, ea. 6 Mol% at P _f =5000 bars, and ca. 10 Mol% at P _f =7000 bars. Thus, the fluid phase coexisting with zoisite is rich in H₂O. While this is independent of temperature the experimental data demonstrate that the influence of pressure cannot be neglected: With increasing pressure the concentration of CO₂ of the fluid phase coexisting with zoisite can rise a little. The position of the reaction studied, which is independent of temperature and exhibits small values of \(X_{{\text{CO}}_{\text{2}} }\) ,leads to two important petrogenetic conclusions:

1. The occurrence of zoisite is an indicator for a CO₂-poor and H₂O-rich fluid composition during metamorphism of marly calcsilicates.
2. If the concentration of CO₂ of the fluid phase coexisting with zoisite exceeds the equilibrium value of \(X_{{\text{CO}}_{\text{2}} }\) calcite+anorthite+H₂O is formed from zoisite+CO₂. Thus, a considerable increase in the anorthite-content of plagioelase is possible.

     

Listric versus planar normal fault geometry: an example from the Eisenstadt-Sopron Basin (E Austria)

In a gravel pit at the eastern margin of the Eisenstadt-Sopron Basin, a satellite of Vienna Basin (Austria), Neogene sediments are exposed in the hanging wall of a major normal fault. The anticlinal structure and associated conjugated secondary normal faults were previously interpreted as a rollover anticline above a listric normal fault. The spatial orientation and distribution of sedimentary horizons and crosscutting faults were mapped in detail on a laser scan of the outcrop wall. Subsequently, in order to assess the 3D distribution and geometry of this fault system, a series of parallel ground penetrating radar (GPR) profiles were recorded behind the outcrop wall. Both outcrop and GPR data were compiled in a 3D structural model, providing the basis for a kinematic reconstruction of the fault plane using balanced cross-section techniques. However, the kinematic reconstruction results in a geologically meaningless normal fault cutting down- and up-section. Additionally, no evidence for a weak layer serving as ductile detachment horizon (i.e. salt or clay horizon) can be identified in stratigraphic profiles. Instead, the observed deflection of stratigraphic horizons may be caused by a displacement gradient along a planar master fault, with a maximum displacement in the fault centre, decreasing towards the fault tips. Accordingly, the observed deflection of markers in the hanging wall—and in a nearby location in the footwall of the normal fault—is interpreted as large-scale fault drag along a planar fault that records a displacement gradient, instead of a rollover anticline related to a listric fault.     

Variation of colour patterns in larval Hydropsyche (Trichoptera): Implications for species identifications and the phylogeny of the genus

Larvae of the lotic caddisfly genus Hydropsyche may occur in densities of thousands to several tens of thousands of individuals/m² across continents and running water types. Therefore, stream ecologists frequently face the task of identifying larvae of this genus. Early keys to larval Hydropsyche of Asia, Europe and North America often used the relatively complicated frontoclypeal colour pattern for species discrimination, whereas equivocal views about the variation of this pattern limited its use in recent keys. Has each species of a given species group a different (although intraspecifically variable) basic pattern of lighter spots on the darker frontoclypeus, or have all species of a group the same basic colour pattern that varies more or less intraspecifically? An answer to this question has obvious implications for the identification of the species as well as for the phylogeny of the genus, so we examined the variation of this colour pattern across ∼11,000 specimens of 10 Hydropsyche species from the Loire River (France).All 10 species had the same basic colour pattern on the frontoclypeus (six contrasting light patches on a dark background) that varied intraspecifically across a certain range of colour contrasts. Comparing other sources illustrating the frontoclypeus of Hydropsyche larvae provided more support for the idea that six contrasting light patches on the frontoclypeus is the typical basic colour pattern that varies within almost all European species; males of these species have a simple phallus form. Two European and many North American species of the genus (from the Ceratopsyche group) have a different basic colour pattern of seven light patches on the frontoclypeus that varies also intraspecifically; males of these species have a complicated phallus form.If the variation of such colour patterns in co-existing populations of several species is known, the relative contrast differences among the individual patches on the frontoclypeus and the form of the individual patches can provide valuable information for rapid species identification. Analysis of this variation may also contribute to phylogenetic studies of the genus Hydropsyche and other hydropsychids.     

A compromise aspect-adaptive cylindrical projection for world maps

There are two problems with current cylindrical projections for world maps. First, existing cylindrical map projections have a static height-to-width aspect ratio and do not automatically adjust their aspect ratio in order to optimally use available canvas space. Second, many of the commonly used cylindrical compromise projections show areas and shapes at higher latitudes with considerable distortion. This article introduces a new compromise cylindrical map projection that adjusts the distribution of parallels to the aspect ratio of a canvas. The goal of designing this projection was to show land masses at central latitudes with a visually balanced appearance similar to how they appear on a globe. The projection was constructed using a visual design procedure where a series of graphically optimized projections was defined for a select number of aspect ratios. The visually designed projections were approximated by polynomial expressions that define a cylindrical projection for any height-to-width ratio between 0.3:1 and 1:1. The resulting equations for converting spherical to Cartesian coordinates require a small number of coefficients and are fast to execute. The presented aspect-adaptive cylindrical projection is well suited for digital maps embedded in web pages with responsive web design, as well as GIS applications where the size of the map canvas is unknown a priori. We highlight the projection with a height-to-width ratio of 0.6:1, which we call the Compact Miller projection because it is inspired by the Miller Cylindrical projection. Unlike the Miller Cylindrical projection, the Compact Miller projection has a smaller height-to-width ratio and shows the world with less areal distortion at higher latitudes. A user study with 448 participants verified that the Compact Miller – together with the Plate Carrée projection – is the most preferred cylindrical compromise projection.     

Late‐stage deformation in a collisional orogen (Western Alps): nappe refolding,back‐thrusting or normal faulting?

ABSTRACT Nappe refolding, back-thrusting and normal faulting frequently cause severe late-stage overprinting of the architecture of an orogen. A combined investigation of nappe stack polarity, kinematics of shearing and metamorphic gradients in the Western Alps develops criteria for distinguishing between these three modes of late-stage deformation. This distinction is a prerequisite for any retro-deformation necessary for understanding the main tectonic and metamorphic evolution of collisional orogens. In the case of the Western Alps overprint was by mega-scale nappe refolding in the Oligocene. This implies exhumation of the HP-rocks prior to postnappe folding, i.e. during nappe stacking and by foreland-directed ascent within a subduction channel.     

Impact of an 0.2 km3 Rock Avalanche on Lake Eibsee (Bavarian Alps,Germany) – Part I: Reconstruction of the paleolake and Effects of the Impact

Rock avalanches destroy and reshape landscapes in only a few minutes and are among the most hazardous processes on Earth. The surface morphology of rock avalanche deposits and the interaction with the underlying material are crucial for runout properties and reach. Water within the travel path is displaced, producing large impact waves and reducing friction, leading to long runouts. We hypothesize that the 0.2 km³ Holocene Eibsee rock avalanche from Mount Zugspitze in the Bavarian Alps overran and destroyed Paleolake Eibsee and left a unique sedimentological legacy of processes active during the landslide. We captured 9.5 km of electrical resistivity tomography (ERT) profiles across the rock avalanche deposits, with up to 120 m penetration depth and more than 34 000 datum points. The ERT profiles reveal up to ~50 m thick landslide debris, locally covering up to ~30 m of rock debris with entrained fine-grained sediments on top of isolated remnants of decametre-wide paleolake sediments. The ERT profiles allow us to infer processes involved in the interaction of the rock avalanche with bedrock, lake sediments, and morainal sediments, including shearing, bulging, and bulldozing. Complementary data from drilling, a gravel pit exposure, laboratory tests, and geomorphic features were used for ERT calibration. Sediments overrun by the rock avalanche show water-escape structures. Based on all of these datasets, we reconstructed both position and size of the paleolake prior to the catastrophic event. Our reconstruction of the event contributes to process an understanding of the rock avalanche and future modelling and hazard assessment. Here we show how integrated geomorphic, geophysical, and sedimentological approaches can provide detailed insights into the impact of a rock avalanche on a lake. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd