Academic literature on the topic 'Polyphase exhumation history'

Abstract. Mylonitic rocks involved within a polyphase crustal-scale shear zone, cropping out in the Aspromonte Massif (Calabria, Italy), has been investigated to reveal the meso- and micro-structural evolution (from ductile- to brittle-type deformation) occurred during exhumation trajectory. A relatively small area (about 4 km2) has been selected in the central-eastern part of the massif to constrain the sequence of the structural features from the earliest ones (Hercynian in age), almost totally obliterated by a pervasive mylonitic foliation (plastic regime), up to recent ones, consisting of various sets of veins typical of semibrittle to brittle regime. The former ductile evolution was followed by a compressive thin-skinned thrusting stage developed during the Apennine phase of the Alpine Orogeny, interested by a second brittle stage, consistent with the switching from compressive to extensional tectonics. This last stage accompanied the final exhumation process causing the activation of regional scale normal faults, which partly disarticulated previous mylonitic microstructures. A suite of oriented specimens were collected and analyzed to complete the deformational history already recognized in the field. Quartz c axis orientation patterns confirm the greenschist facies conditions of the former ductile exhumation stage with a dominant top-to-NE sense of shear. Microstructural investigations highlighted the progressive development from plastic- to brittle-type structures, allowing to constrain each step of the multistage exhumation history, and to establish the relative timing of the stress field variation causing thrusting and subsequent normal faulting. Obtained results support a continue compressional exhumation of this sector since the opening of Tyrrhenian basin (10 Ma).

Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.

Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.

Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.

Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.

Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.

Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.

Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.

Rock recycling within the forearcs of subduction zones involves subduction of sediments and hydrated lithosphere into the upper mantle, exhumation of rocks to the surface, and erosion to form new sediment. The compositions of, and inclusions within detrital minerals revealed by electron microprobe analysis and Raman spectroscopy preserve petrogenetic clues that can be related to transit through the rock cycle. We report the discovery of the ultrahigh-pressure (UHP) indicator mineral coesite as inclusions in detrital garnet from a modern placer deposit in the actively exhuming Late Miocene–Recent high- and ultrahigh-pressure ((U)HP) metamorphic terrane of eastern Papua New Guinea. Garnet compositions indicate the coesite-bearing detrital garnets are sourced from felsic protoliths. Carbonate, graphite, and CO2 inclusions also provide observational constraints for geochemical cycling of carbon and volatiles during subduction. Additional discoveries include polyphase inclusions of metastable polymorphs of SiO2 (cristobalite) and K-feldspar (kokchetavite) that we interpret as rapidly cooled former melt inclusions. Application of elastic thermobarometry on coexisting quartz and zircon inclusions in six detrital garnets indicates elastic equilibration during exhumation at granulite and amphibolite facies conditions. The garnet placer deposit preserves a record of the complete rock cycle, operative on <10-My geologic timescales, including subduction of sedimentary protoliths to UHP conditions, rapid exhumation, surface uplift, and erosion. Detrital garnet geochemistry and inclusion suites from both modern sediments and stratigraphic sections can be used to decipher the petrologic evolution of plate boundary zones and reveal recycling processes throughout Earth’s history.

AbstractThe Alaska Range suture zone exposes Cretaceous to Quaternary marine and nonmarine sedimentary and volcanic rocks sandwiched between oceanic rocks of the accreted Wrangellia composite terrane to the south and older continental terranes to the north. New U-Pb zircon ages, 40Ar/39Ar, ZHe, and AFT cooling ages, geochemical compositions, and geological field observations from these rocks provide improved constraints on the timing of Cretaceous to Miocene magmatism, sedimentation, and deformation within the collisional suture zone. Our results bear on the unclear displacement history of the seismically active Denali fault, which bisects the suture zone. Newly identified tuffs north of the Denali fault in sedimentary strata of the Cantwell Formation yield ca. 72 to ca. 68 Ma U-Pb zircon ages. Lavas sampled south of the Denali fault yield ca. 69 Ma 40Ar/39Ar ages and geochemical compositions typical of arc assemblages, ranging from basalt-andesite-trachyte, relatively high-K, and high concentrations of incompatible elements attributed to slab contribution (e.g., high Cs, Ba, and Th). The Late Cretaceous lavas and bentonites, together with regionally extensive coeval calc-alkaline plutons, record arc magmatism during contractional deformation and metamorphism within the suture zone. Latest Cretaceous volcanic and sedimentary strata are locally overlain by Eocene Teklanika Formation volcanic rocks with geochemical compositions transitional between arc and intraplate affinity. New detrital-zircon data from the modern Teklanika River indicate peak Teklanika volcanism at ca. 57 Ma, which is also reflected in zircon Pb loss in Cantwell Formation bentonites. Teklanika Formation volcanism may reflect hypothesized slab break-off and a Paleocene–Eocene period of a transform margin configuration. Mafic dike swarms were emplaced along the Denali fault from ca. 38 to ca. 25 Ma based on new 40Ar/39Ar ages. Diking along the Denali fault may have been localized by strike-slip extension following a change in direction of the subducting oceanic plate beneath southern Alaska from N-NE to NW at ca. 46–40 Ma. Diking represents the last recorded episode of significant magmatism in the central and eastern Alaska Range, including along the Denali fault. Two tectonic models may explain emplacement of more primitive and less extensive Eocene–Oligocene magmas: delamination of the Late Cretaceous–Paleocene arc root and/or thickened suture zone lithosphere, or a slab window created during possible Paleocene slab break-off. Fluvial strata exposed just south of the Denali fault in the central Alaska Range record synorogenic sedimentation coeval with diking and inferred strike-slip displacement. Deposition occurred ca. 29 Ma based on palynomorphs and the youngest detrital zircons. U-Pb detrital-zircon geochronology and clast compositional data indicate the fluvial strata were derived from sedimentary and igneous bedrock presently exposed within the Alaska Range, including Cretaceous sources presently exposed on the opposite (north) side of the fault. The provenance data may indicate ∼150 km or more of dextral offset of the ca. 29 Ma strata from inferred sediment sources, but different amounts of slip are feasible.Together, the dike swarms and fluvial strata are interpreted to record Oligocene strike-slip movement along the Denali fault system, coeval with strike-slip basin development along other segments of the fault. Diking and sedimentation occurred just prior to the onset of rapid and persistent exhumation ca. 25 Ma across the Alaska Range. This phase of reactivation of the suture zone is interpreted to reflect the translation along and convergence of southern Alaska across the Denali fault driven by highly coupled flat-slab subduction of the Yakutat microplate, which continues to accrete to the southern margin of Alaska. Furthermore, a change in Pacific plate direction and velocity at ca. 25 Ma created a more convergent regime along the apex of the Denali fault curve, likely contributing to the shutting off of near-fault extension-facilitated arc magmatism along this section of the fault system and increased exhumation rates.

The Lower Units of Alpine Corsica (France) include a stack of tectonic units detached from the European plate margin. These units, that crop out in the central Corsica along a narrow strip at the boundary between the Hercynian Corsica (to the west) and the Alpine Corsica (to the east), are directly thrust on the Hercynian Corsica (i.e. the European plate not involved in the Alpine Orogeny) and topped by the Schistes Lustrés Complex (i.e. the oceanic and continental units buried at the deepest level during the Alpine Orogeny). Slices of the Schistes Lustrés Complex are also found within the Lower Units. In this thesis, the Lower Units cropping out in six selected areas, from Asco and Fium’Orbo valleys, have been studied, in order to provide stratigraphic, structural and metamorphic data needed to constrain their tectonic history. The Hercynian Corsica and the Schistes Lustrés Complex strictly associated to the Lower Units have been also characterized in terms of stratigraphy, structural and metamorphic features. Moreover, some geochronological data related to the Lower Units have been provided, in order to constrain the events that affected these units. The collected data indicate that the stratigraphic log of the Lower Units consists of a Paleozoic basement intruded by Permo-Carboniferous metagranitoids associated to a Permian to Middle - Late Eocene metasedimentary covers. All the formations of this succession are affected by a polyphase deformation history (D1-D3 phase) and the associated multi-step metamorphism as highlighted by the 3 generations of phyllosilicates grown along the S1 and S2 foliations. The study of the metamorphism associated the mesoand micro-structures has indicated that the Lower Units underwent to HP/LT metamorphic conditions (early D1 phase) followed by a polyphase retrograde metamorphism (late D1-D2-D3). The deformation and metamorphic history of the Lower Units is coherent with their subduction and rapid exhumation in the continental collision setting during the Late Eocene–Oligocene time span. The tectono-metamorphic study of several of these units pointed out a clear linkage between their positions in the tectonic stack and the P-T conditions reached during their subduction/exhumation paths. Although the deformation history shows common features in all the Lower Units, several differences in their metamorphism have been observed, in particular concerning the P-T values related to the geobaric and geothermic peaks. The comparison between several areas indicates that these variations can be found systematically in the Alpine Corsica, even if the maximum depth reached by the Lower Units never exceed ~50 km. Investigating the last stages of the exhumation of the Lower Units emerges that the switching from convergence to extension that affected the Western Mediterranean Sea during the Oligocene played an important role in terms of mechanics, leading to the collapse of the orogenic wedge (i.e. the last ductile event) and the activation of a strike-slip fault system (i.e. the Central Corsica Shear Zone). Extending the tectono-metamorphic study to the rim of the Hercynian Corsica at the boundary with the Alpine Corsica and to the slices of the Schistes Lustrés Complex sandwiched between the Lower Units, it made possible to describe the main tectono-metamorphic events that affected the Lower Units as (1) the subduction at depth of the continental crust, (2) its exhumation in a still convergent setting and 3) its further exhumation in an extensional setting.