The effects of a Meso-Alpine collision event on the tectono-metamorphic evolution of the Peloritani mountain belt (eastern Sicily, southern Italy)

AbstractThe Peloritani Mountains, in the southern part of the Calabrian Terranes, southern Italy, have been classically interpreted as the product of the Paleogene brittle deformation of the European continental back-stop of the Neotethyan subduction complex. This reconstruction conflicts with the occurrence of an Alpine metamorphic overprint that affected portions of both the Variscan metamorphic units and part of the Mesozoic sedimentary covers of the mountain belt. New field data, integrated with petrographic, micro- and meso-structural analyses and stratigraphic investigation of the syn-tectonic terrigenous covers, well constrain a Paleogene collision event along the Africa–Nubia convergent margin that caused the exhumation of the Alpine metamorphic units of the Peloritani Mountains. The syn-collisional exhumation was associated with shearing along two major Africa-verging crustal thrusts arising from the positive tectonic inversion of the former European palaeomargin. Early tectonic motions occurred within the mountain belts and produced the exhumation of the external portions of the edifice. Later tectonic motions occurred along the sole-thrust of the entire edifice and caused the definitive exhumation of the entire mountain belt. The whole crustal thrusting lasted for a period ofc. 10 Ma, during the entire Oligocene. The definitive southwestward emplacement of the Peloritani Mountain Belt onto the Neotethyan accretionary wedge was followed by two Late Oligocene – Early Miocene NW–SE-oriented right lateral shear zones, replacing the previous crustal thrust. These two strike-slip belts are interpreted as the surface expression of the deep-seated suture zone between the colliding Africa and Europe continental crusts.

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The Pg-Pn method of determining depth of focus with applications to Nevada earthquakes

Bulletin of the Seismological Society of America ◽

10.1785/bssa0550020391 ◽

1965 ◽

Vol 55 (2) ◽

pp. 391-403

Author(s):

Roger W. Greensfelder

Keyword(s):

Error Analysis ◽

Shear Zone ◽

Surface Expression ◽

Crustal Thickness ◽

Depth Of Focus ◽

Lateral Shear ◽

Walker Lake ◽

Walker Lane ◽

Crustal Model

Abstract The Pg-Pn method is theoretically developed, including a complete error analysis, and then applied to some Nevada earthquakes. It is found that, as expected, the method is very sensitive to the crustal model used, and the appearance of large errors in depths of focus calculated for some earthquakes leads to the conclusion of a major discontinuity in crustal thickness (ca. 10 km) north and east of Walker Lake, Nevada. This discontinuity may have its surface expression in the Walker Lane, a major right-lateral shear zone which has been defined on both physiographic and geologic grounds.

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Timing of Paleozoic Exhumation and Deformation of the High-Pressure Vestgӧtabreen Complex at the Motalafjella Nunatak, Svalbard

Minerals ◽

10.3390/min10020125 ◽

2020 ◽

Vol 10 (2) ◽

pp. 125 ◽

Cited By ~ 3

Author(s):

Christopher J. Barnes ◽

Katarzyna Walczak ◽

Emilie Janots ◽

David Schneider ◽

Jarosław Majka

Keyword(s):

High Pressure ◽

Tectonic Evolution ◽

Shear Zones ◽

White Mica ◽

Strike Slip ◽

Structural Studies ◽

Metamorphic Overprint ◽

Subaerial Exposure ◽

Facies Metamorphism

The Vestgӧtabreen Complex exposed in the Southwestern Caledonian Basement Province of Svalbard comprises two Caledonian high-pressure units. In situ white mica 40Ar/39Ar and monazite Th-U-total Pb geochronology has resolved the timing of the tectonic evolution of the complex. Cooling of the Upper Unit during exhumation occurred at 476 ± 2 Ma, shortly after eclogite-facies metamorphism. The two units were juxtaposed at 454 ± 6 Ma. This was followed by subaerial exposure and deposition of Bullbreen Group sediments. A 430–400 Ma late Caledonian phase of thrusting associated with major sinistral shearing throughout Svalbard deformed both the complex and the overlying sediments. This phase of thrusting is prominently recorded in the Lower Unit, and is associated with a pervasive greenschist-facies metamorphic overprint of high-pressure lithologies. A c. 365–344 Ma geochronological record may represent an Ellesmerian tectonothermal overprint. Altogether, the geochronological evolution of the Vestgӧtabreen Complex, with previous petrological and structural studies, suggests that it may be a correlative to the high-pressure Tsäkkok Lens in the Scandinavian Caledonides. It is suggested that the Vestgӧtabreen Complex escaped to the periphery of the orogen along the sinistral strike-slip shear zones prior to, or during the initial stages of continental collision between Baltica and Laurentia.

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Flow of Rutford Ice Stream and Comparison with Carlson Inlet, Antarctica

Annals of Glaciology ◽

10.1017/s0260305500006959 ◽

1989 ◽

Vol 12 ◽

pp. 51-56 ◽

Cited By ~ 18

Author(s):

R.M. Frolich ◽

D.G. Vaughan ◽

C.S.M. Doake

Keyword(s):

Surface Expression ◽

Ice Thickness ◽

Shear Stresses ◽

Lateral Shear ◽

Ice Stream ◽

Grounding Line ◽

Subglacial Topography ◽

Characteristic Features ◽

Basal Shear ◽

Thickness Measurements

Results from movement surveys on Rutford Ice Stream are presented with complementary surface-elevation and ice-thickness measurements. Surface velocities of 300 m a−1 occur at least 130 km up-stream of the grounding line and contrast strongly with the neighbouring Carlson Inlet, where a velocity of 7 m a−1 has been measured. This contrast in velocity is not topographically controlled but appears to be due instead to differences in basal conditions, with Carlson Inlet probably being frozen to its bed. Concentration of lateral shear close to the margins and surface expression of subglacial topography both support a view of significant basal shear stresses in the central part of Rutford Ice Stream. The pattern of principal strain-rate trajectories shows a small number of characteristic features which can be compared with results from future modelling of the glacier's flow.

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How steady are steady-state mountain belts? A reexamination of the Olympic Mountains (Washington state, USA)

Earth Surface Dynamics ◽

10.5194/esurf-7-275-2019 ◽

2019 ◽

Vol 7 (1) ◽

pp. 275-299 ◽

Cited By ~ 2

Author(s):

Lorenz Michel ◽

Christoph Glotzbach ◽

Sarah Falkowski ◽

Byron A. Adams ◽

Todd A. Ehlers

Keyword(s):

Steady State ◽

Washington State ◽

Cascadia Subduction Zone ◽

Mountain Range ◽

Accretionary Wedge ◽

Pleistocene Glaciation ◽

Kinematic Modeling ◽

Olympic Mountains ◽

Mountain Belts ◽

Exhumation Rates

Abstract. The Olympic Mountains of Washington state (USA) represent the aerially exposed accretionary wedge of the Cascadia Subduction Zone and are thought to be in flux steady state, whereby the mass outflux (denudation) and influx (tectonic accretion) into the mountain range are balanced. We use a multi-method approach to investigate how temporal variations in the influx and outflux could affect previous interpretations of flux steady state. This includes the analysis of published and new thermochronometric ages for (U–Th) ∕ He dating of apatite and zircon (AHe and ZHe, respectively), fission-track dating of apatite and zircon (AFT and ZFT, respectively), 1-D thermo-kinematic modeling of thermochronometric data, and independent estimates of outflux and influx. In total, we present 61 new AHe, ZHe, AFT, and ZFT thermochronometric ages from 21 new samples. AHe ages are generally young (< 4 Ma), and, in some samples, AFT ages (5–8 Ma) overlap ZHe ages (7–9 Ma) within uncertainties. Thermo-kinematic modeling shows that exhumation rates are temporally variable, with rates decreasing from > 2 to < 0.3 km Myr−1 around 5–7 Ma. With the onset of Plio–Pleistocene glaciation, exhumation rates increased to values > 1 km Myr−1. This demonstrates that the material outflux varies through time, requiring a commensurate variation in influx to maintain flux steady state. Evaluation of the offshore and onshore sediment record shows that the material influx is also variable through time and that the amount of accreted sediment in the wedge is spatially variable. This qualitatively suggests that significant perturbations of steady state occur on shorter timescales (105–106 years), like those created by Plio–Pleistocene glaciation. Our quantitative assessment of influx and outflux indicates that the Olympic Mountains could be in flux steady state on long timescales (107 years).

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Pre-Caledonian granulite and gabbro enclaves in the Western Gneiss Region, Norway: indications of incomplete transition at high pressure

Geological Magazine ◽

10.1017/s0016756800004015 ◽

2000 ◽

Vol 137 (3) ◽

pp. 235-255 ◽

Cited By ~ 53

Author(s):

M. KRABBENDAM ◽

A. WAIN ◽

T. B. ANDERSEN

Keyword(s):

High Pressure ◽

Shear Zones ◽

Granulite Facies ◽

Amphibolite Facies ◽

Ultrahigh Pressure ◽

Western Gneiss Region ◽

Ultrahigh Pressure Metamorphism ◽

Mountain Belts ◽

Orogenic Cycle ◽

Highly Strained

The Western Gneiss Region of Norway is a continental terrane that experienced Caledonian high-pressure and ultrahigh-pressure metamorphism. Most rocks in this terrane show either peak-Caledonian eclogite-facies assemblages or are highly strained and equilibrated under late-Caledonian amphibolite-facies conditions. However, three kilometre-size rock bodies (Flatraket, Ulvesund and Kråkenes) in Outer Nordfjord preserve Pre-Caledonian igneous and granulite-facies assemblages and structures. Where these assemblages are preserved, the rocks are consistently unaffected by Caledonian deformation. The three bodies experienced high-pressure conditions (20–23 kbar) but show only very localized (about 5%) eclogitization in felsic and mafic rocks, commonly related to shear zones. The preservation of Pre-Caledonian felsic and mafic igneous and granulite-facies assemblages in these bodies, therefore, indicates widespread (∼ 95%) metastability at pressures higher than other metastable domains in Norway. Late-Caledonian amphibolite-facies retrogression was limited. The degree of reaction is related to the protolith composition and the interaction of fluid and deformation during the orogenic cycle, whereby metastability is associated with a lack of deformation and lack of fluids, either as a catalyst or as a component in hydration reactions. The three bodies appear to have been far less reactive than the external gneisses in this region, even though they followed a similar pressure–temperature evolution. The extent of metastable behaviour has implications for the protolith of the Western Gneiss Region, for the density evolution of high-pressure terranes and hence for the geodynamic evolution of mountain belts.

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Topographic evolution of mountain belts controlled by rheology and surface process efficiency

10.5194/egusphere-egu2020-4317 ◽

2020 ◽

Author(s):

Sebastian G. Wolf ◽

Ritske S. Huismans ◽

Jean Braun ◽

Xiaoping Yuan

Keyword(s):

Steady State ◽

Process Efficiency ◽

Surface Process ◽

Tight Coupling ◽

Active Growth ◽

Term Survival ◽

Erosion Rates ◽

Mountain Belt ◽

Tectonically Active ◽

Mountain Belts

<p>It has been a long-standing problem how mountain belts gain and loose topography during their tectonically active growth and inactive decay phase. It is widely recognized that mountain belt topography is generated by crustal shortening, and lowered by river bedrock erosion, linking climate to tectonics. However, it remains enigmatic how to reconcile high erosion rates in active orogens as observed in Taiwan or New Zealand, with long term survival of topography for 100s of Myrs as observed for example in the Uralides and Appalachians. Here we use for the first time a tight coupling between a landscape evolution model (FastScape) with an upper mantle scale tectonic (thermo-mechanical) model to investigate the different stages of mountain belt growth and decay. Using two end-member models, we demonstrate that growing orogens with high erosive power remain small (<200 km), reach steady state between tectonic in- and erosional material eff-flux, and are characterized by transverse valleys. Contrarily, mountain belts with medium to low erosive power will not reach growth steady state, grow wide, and are characterized by longitudinal rivers deflected by active thrusting. However, during growth both types of orogens reach the same height, controlled by rheology and independent of surface process efficiency. Erosional efficiency controls orogenic decay, which is counteracted by regional isostatic rebound. Rheological control of mountain height implies that there is a natural upper limit for the steepness index of rivers on Earth. To compare model results to various natural examples, we quantify the degree of longitudinal flow of modeled rivers with river &#8220;longitudinality&#8221; in several active or recently active orogens on Earth. Application of the river &#8220;longitudinality index&#8221; gives information whether (parts of) an orogen is or was at steady state during orogenic growth.</p>

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The Liguride Complex of Southern Italy —a Cretaceous to Paleogene accretionary wedge

Tectonophysics ◽

10.1016/0040-1951(87)90124-7 ◽

1987 ◽

Vol 142 (2-4) ◽

pp. 217-226 ◽

Cited By ~ 84

Author(s):

Steven D. Knott

Keyword(s):

Southern Italy ◽

Accretionary Wedge

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Accretion, Soft and Hard Collision: Similarities, Differences and an Application from the Newfoundland Appalachian Orogen

Geoscience Canada ◽

10.12789/geocanj.2020.47.161 ◽

2020 ◽

Vol 47 (3) ◽

pp. 103-118

Author(s):

Cees Van Staal ◽

Alexandre Zagorevski

Keyword(s):

Volcanic Rocks ◽

Leading Edge ◽

Qualitative Assessment ◽

Fault System ◽

Accretionary Wedge ◽

The North ◽

Show Evidence ◽

Accreted Terranes ◽

Mountain Belts ◽

Laurentian Margin

We argue there is no distinction between accretion and collision as a process, except when accretion is used in the sense of incorporating small bodies of sedimentary and/or volcanic rocks into an accretionary wedge by off-scraping or underplating. There is also a distinction when these terms are used in classifying mountain belts into accretionary and collisional orogens, although such classifications are commonly based on a qualitative assessment of the scale and nature of the accreted terranes and continents involved in formation of mountain belts. Soft collisions occur when contractional deformation and associated metamorphism are principally concentrated in rocks of the leading edge of the partially pulled-down buoyant plate and the upper plate forearc terrane. Several young arc-continent collisions show evidence for partial or wholesale subduction of the forearc such that the arc is structurally juxtaposed directly against lower plate rocks. This process may explain the poor preservation of forearcs in the geological record. Soft collisions generally change into hard collisions over time, except if the collision is rapidly followed by formation of a new subduction zone due to step-back or polarity reversal. Thickening and metamorphism of the arc's suprastructure and retro-arc part of upper plate due to contractional deformation and burial are the characteristics of a hard collision or an advancing Andean-type margin. Strong rheological coupling of the converging plates and lower and upper crust in the down-going continental margin promotes a hard collision. Application of the soft–hard terminology supports a structural juxtaposition of the Taconic soft collision recorded in the Humber margin of western Newfoundland with a hard collision recorded in the adjacent Dashwoods block. It is postulated that Dashwoods was translated dextrally along the Cabot-Baie Verte fault system from a position to the north of Newfoundland where the Notre Dame arc collided ca. 10 m.y. earlier with a wide promontory in a hyperextended segment of the Laurentian margin.

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Chapter 14 Regional context and lithotectonic framework of the 1.1–0.9 Ga Sveconorwegian orogen, southwestern Sweden

Geological Society London Memoirs ◽

10.1144/m50-2018-17 ◽

2020 ◽

Vol 50 (1) ◽

pp. 337-349 ◽

Cited By ~ 7

Author(s):

Michael B. Stephens ◽

Ulf Bergström ◽

Carl-Henric Wahlgren

Keyword(s):

High Pressure ◽

Tectonic Evolution ◽

Shear Zones ◽

Crustal Extension ◽

Frontal Part ◽

Eastern Segment ◽

Mountain Belts ◽

Sveconorwegian Orogen ◽

Scale Shear ◽

Early Neoproterozoic

AbstractThe 1.1–0.9 Ga Sveconorwegian orogen in southwestern Scandinavia belongs to the global system of mountain belts established during the assembly of the supercontinent Rodinia. An overall north–south structural trend and five lithotectonic units bounded by crustal-scale shear zones characterize this orogen. In Sweden, the Eastern Segment abuts the orogen's cratonic foreland eastwards and is separated from the Idefjorden terrane westwards by a ductile shear zone, up to 5 km thick, displaying a sinistral transpressive component. These two lithotectonic units differ on the basis of their pre-Sveconorwegian accretionary tectonic evolution, and the timing of Sveconorwegian high-pressure metamorphism, anatexis and polyphase deformation. High-pressure granulites and migmatites formed at c. 1.05–1.02 Ga in the Idefjorden terrane; eclogites, high-pressure granulites and migmatites at c. 0.99–0.95 Ga in the Eastern Segment. Magmatic activity and crustal extension progressed westwards at c. 0.98–0.92 Ga. Prior to or at 0.93–0.91 Ga, greenschist facies shear deformation with top-to-the-foreland movement affected the frontal part of the orogen. Geodynamic uncertainties concern the affinity of the Idefjorden terrane relative to Fennoscandia (Baltica), the character of the Sveconorwegian orogenesis, and the contiguous or non-contiguous nature of the erosional fronts of the late Mesoproterozoic–early Neoproterozoic orogens in Sweden and Canada.

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