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The stratigraphy and dating of lacustrine sediments and loess derivatives from Rodderberg, a crater of the East Eifel Volcanic Field in Germany, is based on luminescence dating and incorporates radiocarbon ages, fingerprinting of key tephra layers of the East Eifel Volcanic Field (Rieden Tephra, Hüttenberg Tephra, Laacher See Tephra), pollen stratigraphy, varve counting data, and a correlative age–depth model. These methods yield a robust age–depth model for the last 258 ka. Beyond this, luminescence ages differ from tephra‐derived ages. In light of the apparent presence of the Rieden Tephra, the lowermost interglacial is assigned to Marine Isotope Stage (MIS) 11 or 420 ka. This provides a high‐resolution record of environmental conditions representing an analogue for the Holocene, characterized by a warming planet. However, new luminescence ages may indicate a younger age for basal sediments, with the lowermost interglacial representing MIS 9. Both age–depth models constrain regional environmental changes during the Middle Pleistocene controlled by global climate variations. For the hydrologically closed nature of the Rodderberg crater, with limited pathways for sediment inflow and erosional export, these results shed new light on the continuity of long Middle Pleistocene records. [ABSTRACT FROM AUTHOR]

The Alpine nappe stack in the Penninic-Austroalpine boundary zone in the Rätikon (Austria) contains a 4×1 km tectonic sliver of meta-diorite, known as the Schwarzhorn Amphibolite. It was deformed and metamorphosed in the amphibolite facies and is unconformably overlain by unmetamorphic Lower Triassic sandstone, indicating pre-Triassic metamorphism. Cataclastic deformation and brecciation of the amphibolite is related to normal faulting and block tilting during Jurassic rifting. Zircon dating of the Schwarzhorn Amphibolite using LA-ICP-MS gave a U-Pb age of 529+9/-8 Ma, interpreted as the crystallization age of the protolith. Geochemical characteristics indicate formation of the magmatic protolith in a supra-subduction zone setting. The Cambrian protolith age identifies the Schwarzhorn Amphibolite as a pre-Variscan element within the Austroalpine basement. Similar calc-alkaline igneous rocks of Late Neoproterozoic to Early Cambrian age are found in the Upper Austroalpine Silvretta Nappe nearby and in several other Variscan basement units of the Alps, interpreted to have formed in a peri-Gondwanan active-margin or island-arc setting.

A well‐preserved remnant of the middle crust of the former Adriatic passive margin is exposed in the Southern Alps (Italy). The Dervio–Olgiasca Zone is located south of the Insubric Line along the northern part of Como Lake and, because of the lack of Alpine overprint, provides favourable conditions to investigate the pre‐Alpine (rift‐related) history. We reconstruct the P–T–t–d evolution of the Adria middle crust through petrological (petrography, mineral chemistry, thermobarometry and thermodynamic modelling) and geochronological (Lu/Hf in garnet and U–Pb in monazite) data from pegmatites and host micaschists. These data allow reconstruction of a complex tectono‐thermal evolution of the future proximal Adriatic margin at the onset of Alpine rifting. The amphibolite‐facies Carboniferous metamorphic basement (7.6–10 kbar and 610–660°C at 318–312 Ma) was affected by pervasive extensional deformation (5.1–7.6 kbar and 580–660°C) in the Middle‐ to Late‐Permian (257.5 ± 3.8 Ma). Pegmatite intruded at 249.8 ± 1.1 Ma in an extensional phase that re‐equilibrated rocks of the basement at 3.5–4.5 kbar and 560–600°C. During the Middle‐ to Late‐Triassic (241–235 Ma), the basement experienced static thermal recrystallization (T = 689 ± 41°C and ~5.0 kbar). This Late‐Anisian to Early‐Carnian thermal event was simultaneous with the emersion of carbonate platforms, volcanism and ore deposition in the future proximal Adriatic margin. The subsequent cooling of the middle crust was synchronous with large‐scale extensional detachments developed in the upper crust (e.g., the Lugano‐Val Grande Fault), which controlled the formation of the Monte Generoso Basin. This study reveals that the local post‐Carboniferous thinning and heating events recorded in the Adriatic middle crust were interconnected to other processes occurring at different crustal levels that were, in turn, induced by crustal stretching in the early stages of the Alpine rifting. [ABSTRACT FROM AUTHOR]

The Seve Nappe Complex of the Scandinavian Caledonides is thought to be derived from the distal passive margin of Baltica which collided with Laurentia in the Scandian Phase of the Caledonian Orogeny at 430-400 Ma. Parts of the Seve Nappe Complex were affected by pre-Scandian high- and ultrahigh-pressure metamorphism, in a tectonic framework that is still unclear, partly due to uncertainties about the exact timing. Previous age determinations yielded between ~ 505 and ~ 446 Ma, with a general trend of older ages in the North (Norrbotten) than in the South (Jämtland). New age determinations were performed on eclogite and garnet-phengite gneiss at Tjeliken in northern Jämtland. Thermodynamic modelling yielded peak metamorphic conditions of 25-27 kbar/680-760 °C for the garnet-phengite gneiss, similar to published peak metamorphic conditions of the eclogite (25-26 kbar/650-700 °C). Metamorphic rims of zircons from the garnet-phengite gneiss were dated using secondary ion mass spectrometry and yielded a concordia age of 458.9 ± 2.5 Ma. Lu-Hf garnet-whole rock dating yielded 458 ± 1.0 Ma for the eclogite. Garnet in the eclogite shows prograde major-element zoning and concentration of Lu in the cores, indicating that this age is related to garnet growth during pressure increase, i.e. subduction. The identical ages from both rock types, coinciding with published Sm-Nd ages from the eclogite, confirm subduction of the Seve Nappe Complex in Northern Jämtland during the Middle Ordovician in a fast subduction-exhumation cycle., Author(s): Kathrin Fassmer [sup.1] , Iwona Klonowska [sup.2] , Katarzyna Walczak [sup.3] , Barbro Andersson [sup.2] , Nikolaus Froitzheim [sup.1] , Jaroslaw Majka [sup.2] [sup.3] , Raúl O. C. Fonseca [...]

Previous work suggested a double collision suture, including ophiolites from two oceanic basins (Valais and Piemont-Liguria), on the southern side of Monte Rosa (Penninic Alps, northern Italy). This area was studied using field mapping, microstructural analysis, and neutron texture goniometry. After its formation and eclogite-facies metamorphism of continental and oceanic units, the suture was deformed by four successive folding and shearing events under greenschist-facies conditions, all of them taking place between 40 and 28 Ma. After fold retrodeformation, the following tectonostratigraphy results, from base to top: Monte Rosa gneiss (European margin), Balma serpentinite/eclogite unit (Cretaceous crust of Valais ocean), Stolemberg gneiss (Iberia-Brianconnais continent), Zermatt-Saas and Tsate ophiolites (Jurassic crust of Piemont-Ligurian ocean), Sesia nappe (continental fragment off the Adria margin). The preservation of this lithological sequence suggests that deep-seated deformation during multiple continent collision produces heterogeneous strain and extreme thinning of nappes but their original stacking order can still be reconstructed using kinematic analysis and overprinting criteria. This is due to the ductile nature of the collisional deformation which retains the continuity of tectonic contacts. doi: 0.1029/2004TC001737.

[1] The first evidence for ultrahigh-pressure (UHP) metamorphism in the Eastern Alps is reported from kyanite eclogites of the Pohorje Mountains in Slovenia. Polycrystalline quartz inclusions surrounded by radial fractures in garnet, omphacite, and kyanite are interpreted to be pseudomorphs after coesite. Abundant quartz rods and needles in omphacite indicate an exsolution from a preexisting supersilicic clinopyroxene that contained a CaEskola component. Geothermobarometry on the mineral assemblage garnet + omphacite + kyanite + phengite + quartz/or coesite yields peak pressure and temperature conditions of 3.0-3.1 GPa and 760[degrees]-825[degrees]C, well within the stability field of coesite, thus supporting the microtextural evidence for UHP metamorphism. This records the highest-pressure conditions of Eo-Alpine metamorphism during the Cretaceous orogeny in the Alps, implying a very deep subduction of the continental crust to at least 90-100 km depths. The new data are evidence for a regional southeastward increase of peak pressures in the Lower Central Austroalpine, indicating a south- to eastward dip of the subduction zone. Subduction was intracontinental; northwestern parts of the Austroalpine (Lower Central Austroalpine) were subducted under southeastern parts (Upper Central Austroalpine). The subduction zone formed in the Early Cretaceous in the northwestern foreland of the Meliata suture after Late Jurassic closure of the Meliata Ocean and the resulting collision, by a forward subduction shift to a Permian rift. INDEX TERMS: 5475 Planetology: Solid Surface Planets: Tectonics (8149); 3660 Mineralogy and Petrology: Metamorphic petrology; 8102 Tectonophysics: Continental contractional orogenic belts; 9335 Information Related to Geographic Region: Europe; 9609 Information Related to Geologic Time: Mesozoic; KEYWORDS: ultrahigh-pressure metamorphism, eclogite, Alps, Pohorje. Citation: Janak, M.. N. Froitzheim, B. Luptak, M. Vrabec, and E. J. K. Ravna (2004), First evidence for ultrahigh-pressure metamorphism of eclogites in Pohorje, Slovenia: Tracing deep continental subduction in the Eastern Alps.