scholarly journals Interactions of plutons and detachments, comparison of Aegean and Tyrrhenian granitoids

2021 ◽  
Author(s):  
Laurent Jolivet ◽  
Laurent Arbaret ◽  
Laetitia Le Pourhiet ◽  
Florent Cheval-Garabedian ◽  
Vincent Roche ◽  
...  
Keyword(s):  
Root Zone ◽  
Numerical Models ◽  
Shear Zones ◽  
Normal Faults ◽  
Metamorphic Core Complexes ◽  
Kinematic Evolution ◽  
Brittle Ductile Transition ◽  
Mountain Belts ◽  
Back Arc ◽  
Metamorphic Core

Abstract. Back-arc extension superimposed on mountain belts leads to distributed normal faults and shear zones, interacting with magma emplacement in the crust. The composition of granitic magmas emplaced at this stage often involves a component of crustal melting. The Miocene Aegean granitoids were emplaced in metamorphic core complexes (MCC) below crustal-scale low-angle extensional shear zones and normal faults. Intrusion in such contexts interacts with extension and shear along detachments, from the hot magmatic flow within the pluton root zone to the colder ductile and brittle deformation along the detachment. A comparison of the Aegean plutons with the Elba Island MCC in the back-arc region of the Apennines subduction shows that these processes are characteristic of pluton-detachment interactions in general and we discuss a conceptual emplacement scenario, tested by numerical models. Mafic injections within the partially molten lower crust above the hot asthenosphere trigger the ascent within the core of the MCC of felsic magmas, controlled by the strain localization on persistent crustal scale shear zones at the top that guide the ascent until the brittle ductile transition is reached during exhumation. Once the system definitely enters the brittle regime, the detachment and the upper crust are intruded while new detachments migrate upward and in the direction of shearing. Numerical models reproduce the geometry and the kinematic evolution deduced from field observations.

scholarly journals Interactions of plutons and detachments: a comparison of Aegean and Tyrrhenian granitoids

Solid Earth ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 1357-1388
Author(s):  
Laurent Jolivet ◽  
Laurent Arbaret ◽  
Laetitia Le Pourhiet ◽  
Florent Cheval-Garabédian ◽  
Vincent Roche ◽  
...  
Keyword(s):  
Root Zone ◽  
Numerical Models ◽  
Shear Zones ◽  
Normal Faults ◽  
Metamorphic Core Complexes ◽  
Brittle Ductile Transition ◽  
Ductile Shear Zones ◽  
Mountain Belts ◽  
Back Arc ◽  
Metamorphic Core

Abstract. Back-arc extension superimposed on mountain belts leads to distributed normal faults and shear zones interacting with magma emplacement within the crust. The composition of granitic magmas emplaced at this stage often involves a large component of crustal melting. The Miocene Aegean granitoids were emplaced in metamorphic core complexes (MCCs) below crustal-scale low-angle normal faults and ductile shear zones. Intrusion processes interact with extension and shear along detachments, from the hot magmatic flow within the pluton root zone to the colder ductile and brittle deformation below and along the detachment. A comparison of the Aegean plutons with the island of Elba MCC in the back-arc region of the Apennine subduction shows that these processes are characteristic of pluton–detachment interactions in general. We discuss a conceptual emplacement model, tested by numerical models. Mafic injections within the partially molten lower crust above the hot asthenosphere trigger the ascent within the core of the MCC of felsic magmas, controlled by the strain localization on persistent crustal-scale shear zones at the top that guide the ascent until the brittle ductile transition. Once the system definitely enters the brittle regime, the detachment and the upper crust are intruded, while new detachments migrate upward and in the direction of shearing.

scholarly journals Rheological transitions in the middle crust: insights from Cordilleran metamorphic core complexes

2016 ◽  
Author(s):  
Frances J. Cooper ◽  
John P. Platt ◽  
Whitney M. Behr
Keyword(s):  
High Strain ◽  
Shear Zones ◽  
Ductile Deformation ◽  
Lower Zone ◽  
Middle Crust ◽  
Metamorphic Core Complexes ◽  
Brittle Ductile Transition ◽  
Ductile Shear ◽  
Metamorphic Core ◽  
Whipple Mountains

Abstract. High strain mylonitic rocks in Cordilleran metamorphic core complexes reflect ductile deformation in the middle crust, but in many examples it is unclear how these mylonites relate to the brittle detachments that overlie them. Field observations, microstructural analyses, and thermobarometric data from the footwalls of three metamorphic core complexes in the Basin and Range province, USA (the Whipple Mountains, California; the northern Snake Range, Nevada; and Ruby Mountains–East Humboldt Range, Nevada) suggest the presence of two distinct rheological transitions in the middle crust. (1) The brittle-ductile transition (BDT), which depends on thermal gradient and tectonic regime, and marks the switch from discrete brittle faulting and cataclasis to continuous, but still localized, ductile shear. (2) The localized-distributed transition or LDT, a deeper, dominantly temperature-dependent transition, which marks the switch from localized ductile shear to distributed ductile flow. In this model, brittle normal faults in the upper crust persist as ductile shear zones below the BDT in the middle crust, and sole into the subhorizontal LDT at greater depths. In metamorphic core complexes, the presence of these two distinct rheological transitions results in the development of two zones of ductile deformation: a relatively narrow zone of high-stress mylonite that is spatially and genetically related to the brittle detachment, underlain by a broader zone of high-strain, relatively low-stress rock that formed in the middle crust below the LDT, and in some cases before the detachment was initiated. In some examples (e.g. the Whipple Mountains) the lower zone is spatially distinct from the detachment, although high-strain rocks from the lower zone were subsequently exhumed along the detachment. The two zones show distinct microstructural assemblages, reflecting different conditions of temperature and stress during deformation, and contain superposed sequences of microstructures reflecting progressive exhumation, cooling, and strain localization.

scholarly journals Rheological transitions in the middle crust: insights from Cordilleran metamorphic core complexes

Solid Earth ◽  
2017 ◽  
Vol 8 (1) ◽  
pp. 199-215 ◽  
Author(s):  
Frances J. Cooper ◽  
John P. Platt ◽  
Whitney M. Behr
Keyword(s):  
High Strain ◽  
High Stress ◽  
Shear Zones ◽  
Ductile Deformation ◽  
Middle Crust ◽  
Metamorphic Core Complexes ◽  
Brittle Ductile Transition ◽  
Ductile Shear ◽  
Metamorphic Core ◽  
Whipple Mountains

Abstract. High-strain mylonitic rocks in Cordilleran metamorphic core complexes reflect ductile deformation in the middle crust, but in many examples it is unclear how these mylonites relate to the brittle detachments that overlie them. Field observations, microstructural analyses, and thermobarometric data from the footwalls of three metamorphic core complexes in the Basin and Range Province, USA (the Whipple Mountains, California; the northern Snake Range, Nevada; and Ruby Mountains–East Humboldt Range, Nevada), suggest the presence of two distinct rheological transitions in the middle crust: (1) the brittle–ductile transition (BDT), which depends on thermal gradient and tectonic regime, and marks the switch from discrete brittle faulting and cataclasis to continuous, but still localized, ductile shear, and (2) the localized–distributed transition, or LDT, a deeper, dominantly temperature-dependent transition, which marks the switch from localized ductile shear to distributed ductile flow. In this model, brittle normal faults in the upper crust persist as ductile shear zones below the BDT in the middle crust, and sole into the subhorizontal LDT at greater depths.In metamorphic core complexes, the presence of these two distinct rheological transitions results in the development of two zones of ductile deformation: a relatively narrow zone of high-stress mylonite that is spatially and genetically related to the brittle detachment, underlain by a broader zone of high-strain, relatively low-stress rock that formed in the middle crust below the LDT, and in some cases before the detachment was initiated. The two zones show distinct microstructural assemblages, reflecting different conditions of temperature and stress during deformation, and contain superposed sequences of microstructures reflecting progressive exhumation, cooling, and strain localization. The LDT is not always exhumed, or it may be obscured by later deformation, but in the Whipple Mountains, it can be directly observed where high-strain mylonites captured from the middle crust depart from the brittle detachment along a mylonitic front.

The kinematic vorticity analysis of ductile shear zones of Ambaji Granulite, NW India and its tectonic implications

2020 ◽  
Author(s):  
Sudheer Kumar Tiwari ◽  
Anouk Beniest ◽  
Tapas Kumar Biswal
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Lateral Displacement ◽  
Pure Shear ◽  
Tectonic Setting ◽  
Shear Zones ◽  
Normal Faults ◽  
Temperature Phase ◽  
Brittle Ductile Transition ◽  
Deformation Phase

<p>The Neoproterozoic (834 – 778 Ma) Ambaji granulite witnessed four deformation phases (D<sub>1</sub>- D<sub>4</sub>), of which the D<sub>2</sub> deformation phase was most significant for the exhumation of granulites in the ductile regime. We performed a field study to investigate the tectonic evolution of the D<sub>2</sub> deformation phase and investigated the deformation evolution of the ductile extrusion of the Ambaji granulite by estimating the vorticity of flow (Wm) with the Rigid Grain Net and strain ratio/orientation techniques.</p><p>During the D<sub>2</sub> deformation phase, the S<sub>1</sub> fabric was folded by F<sub>2</sub> folds that are coaxial with the F<sub>1</sub> folds. The F<sub>2</sub> folds were produced in response to NW-SE compression. Because the large shear zones are oriented parallel to the axial plane of the F<sub>2</sub> folds, they likely formed simultaneously during the D<sub>2</sub> deformation phase. Compression during the D<sub>2</sub> deformation phase accommodated most of the exhumation of the granulite along the shear zones. D<sub>2</sub> shearing was constrained between 834 ± 7 to 778 ± 8 Ma (Monazite ages).</p><p>The shear zones evolved from a high temperature (>700 °C) thrust-slip shearing event in the lower-middle crust to a low temperature (450 °C) retrograde sinistral shearing event at the brittle-ductile-transition (BDT). The Wm estimates of 0.32–0.40 and 0.60 coincide with the high temperature event and suggests pure shear dominated deformation. The low temperature phase coincides with Wm estimates of 0.64–0.87 and ~1.0, implying two flow regimes. The shear zone was first affected by general non-coaxial deformation and gradually became dominated by simple shearing.</p><p>We interpreted that the high temperature event happened in a compressive tectonic regime, which led to horizontal shortening and vertical displacement of the granulite to the BDT. The low temperature event occurred in a transpressive tectonic setting that caused the lateral displacement of the granulite body at BDT depth. The Wm values indicate a non-steady strain during the exhumation of granulite. From the BDT to surface, the Ambaji granulite exhumed through the NW-SE directed extension for normal faults via brittle exhumation through crustal extension and thinning.</p>

Tectonic significance of synextensional ductile shear zones within the Early Miocene Alaçamdağ granites, northwestern Turkey

2009 ◽  
Vol 147 (4) ◽  
pp. 611-637 ◽  
Author(s):  
FUAT ERKÜL
Keyword(s):  
Hanging Wall ◽  
Shear Zones ◽  
Early Miocene ◽  
Aegean Region ◽  
Menderes Massif ◽  
Metamorphic Core Complexes ◽  
Ductile Shear Zones ◽  
Northwestern Turkey ◽  
Ductile Shear ◽  
Metamorphic Core

AbstractSynextensional granitoids may have significant structural features leading to the understanding of the evolution of extended orogenic belts. One of the highly extended regions, the Aegean region, includes a number of metamorphic core complexes and synextensional granitoids that developed following the Alpine collisional events. The Alaçamdağ area in northwestern Turkey is one of the key areas where Miocene granites crop out along the boundary of various tectonic units. Structural data from the Early Miocene Alaçamdağ granites demonstrated two different deformation patterns that may provide insights into the development of granitic intrusions and metamorphic core complexes. (1) Steeply dipping ductile shear zones caused emplacement of syn-tectonic granite stocks; they include kinematic indicators of a sinistral top-to-the-SW displacement. This zone has also juxtaposed the İzmir–Ankara Zone and the Menderes Massif in the west and east, respectively. (2) Gently dipping ductile shear zones have developed within the granitic stocks that intruded the schists of the Menderes Massif on the structurally lower parts. Kinematic data from the foliated granites indicate a top-to-the-NE displacement, which can be correlated with the direction of the hanging-wall movement documented from the Simav and Kazdağ metamorphic core complexes. The gently dipping shear zones indicate the presence of a detachment fault between the Menderes Massif and the structurally overlying İzmir–Ankara Zone. Mesoscopic- to map-scale folds in the shallow-dipping shear zones of the Alaçamdağ area were interpreted to have been caused by coupling between NE–SW stretching and the accompanying NW–SE shortening of ductilely deformed crust during Early Miocene times. One of the NE-trending shear zones fed by granitic magmas was interpreted to form the northeastern part of a sinistral wrench corridor which caused differential stretching between the Cycladic and the Menderes massifs. This crustal-scale wrench corridor, the İzmir–Balıkesir transfer zone, may have controlled the asymmetrical and symmetrical extensions in the orogenic domains. The combination of the retreat of the Aegean subduction zone and the lateral slab segmentation leading to the sinistral oblique-slip tearing within the Eurasian upper plate appears to be a plausible mechanism for the development of such extensive NE-trending shear zones in the Aegean region.

Migration of deformation, subsidence, and basin formation in the SW Pannonian Basin (central Europe) and the change to contractional deformation

2021 ◽  
Author(s):  
László Fodor ◽  
Attila Balázs ◽  
Gábor Csillag ◽  
István Dunkl ◽  
Gábor Héja ◽  
...  
Keyword(s):  
Pannonian Basin ◽  
Numerical Models ◽  
Hanging Wall ◽  
Shear Zones ◽  
Normal Faults ◽  
Rift System ◽  
Distal Margin ◽  
Late Middle Miocene ◽  
Basin Scale ◽  
Basin Formation

<p>The Pannonian Basin is a continental extensional basin system with various depocentres within the Alpine–Carpathian–Dinaridic orogenic belt. Along the western basin margin, exhumation along the Rechnitz, Pohorje, Kozjak, and Baján detachments resulted in cooling of diverse crustal segments of the Alpine nappe stack (Koralpe-Wölz and Penninic nappes); the process is constrained by variable thermochronological data between ~25–23 to ~15 Ma. Rapid subsidence in supradetachment sub-basins indicates the onset of sedimentation in the late Early Miocene (Ottnangian? or Karpatian, from ~19 or 17.2 Ma). In addition to extensional structures, strike-slip faults mostly accommodated differential extension between domains marked by large low-angle normal faults. Branches of the Mid-Hungarian Shear Zone (MHZ) also played the role of transfer faults, although shear-zones perpendicular to extension also occurred locally.</p><p>During this period, the distal margin of the large tilted block in the hanging wall of the detachment system, the pre-Miocene rocks of the Transdanubian Range (TR) experienced surface exposure, karstification, and terrestrial sedimentation. The situation changed after ~15–14.5 Ma when faulting, subsidence, and basin formation shifted north-eastward. Migration of normal faulting resulted in fault-controlled basin subsidence within the TR which lasted until ~8 Ma.</p><p>3D thermo-mechanical lithospheric and basin-scale numerical models predict similar spatial migration of the depocenters from the orogenic margin towards the basin center. The reason for this migration is found in the interaction of deep Earth and surface processes. A lithospheric and smaller crustal-scale weak zones inherited from a preceding orogenic structure localize initial deformation, while their redistribution controls asymmetric extension accompanied by the upraising of the asthenopshere and flexure of the lithosphere. Models suggest ~4–5 Myr delay of the onset of sedimentation after the onset of crustal extension and ~150–200 km of shift in depocenters during ~12 Myr. These modeling results agree well with our robust structural and chronological data on basin migration.</p><p>Simultaneously with or shortly after depocenter migration, the southern part of the former rift system, mostly near the MHZ, underwent ~N–S shortening; the basin fill was folded and the boundary normal faults were inverted. The style of deformation changed from pure contraction to transpression. The Baján detachment could be slightly folded, although its synformal shape could also be considered a detachment corrugation. Deformation was dated to ~15–14 Ma (middle Badenian) in certain sub-basins while in other sub-basins deformation seems to be continuous throughout the late Middle Miocene from ~15 Ma to ~11.6 Ma.</p><p>Another contractional pulse occurred in the earliest Late Miocene, between ~11.6 and ~9.7 Ma while the western part of the TR was still affected by extensional faulting and subsidence. All these contractional deformations can be linked to the much larger fold-and-thrust belt that extends from the Southern and Julian Alps through the Sava folds region in Slovenia. Contraction is still active, as indicated by recent earthquakes in Croatia.</p><p>Mol Ltd. largely supported the research. The research is supported by the scientific grant NKFI OTKA 134873 and the Slovenian Research Agency (research core funding No. P1-0195).</p>

scholarly journals From orogeny to rifting: insights from the Norwegian ‘reactivation phase’

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Gwenn Peron-Pinvidic ◽  
Per Terje Osmundsen
Keyword(s):  
Continental Crust ◽  
Shear Zones ◽  
Detachment Faults ◽  
Metamorphic Core Complexes ◽  
Crustal Thinning ◽  
Collapse Mode ◽  
Collapse Structures ◽  
Normal Thickness ◽  
Further Development ◽  
Metamorphic Core

Abstract Based on observations from the Mid-Norwegian extensional system, we describe how, when and where the post-Caledonian continental crust evolved from a context of orogenic disintegration to one of continental rifting. We highlight the importance of a deformation stage that occurred between the collapse mode and the high-angle faulting mode often associated with early rifting of continental crust. This transitional stage, which we interpret to represent the earliest stage of rifting, includes unexpected large magnitudes of crustal thinning facilitated through the reactivation and further development of inherited collapse structures, including detachment faults, shear zones and metamorphic core complexes. The reduction of the already re-equilibrated post-orogenic crust to only ~ 50% of normal thickness over large areas, and considerably less locally, during this stage shows that the common assumption of very moderate extension in the proximal margin domain may not conform to margins that developed on collapsed orogens.

scholarly journals Structural and thermal evolution of the eastern Aar Massif: insights from structural field work and Raman thermometry

2021 ◽  
Vol 114 (1) ◽  
Author(s):  
Lukas Nibourel ◽  
Alfons Berger ◽  
Daniel Egli ◽  
Stefan Heuberger ◽  
Marco Herwegh
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Shear Zones ◽  
Swiss Alps ◽  
Normal Faults ◽  
En Bloc ◽  
Temperature Conditions ◽  
Kinematic Evolution ◽  
Structural Style ◽  
Aar Massif

AbstractThe thermo-kinematic evolution of the eastern Aar Massif, Swiss Alps, was investigated using peak temperature data estimated from Raman spectroscopy of carbonaceous material and detailed field analyses. New and compiled temperature-time constraints along the deformed and exhumed basement-cover contact allow us to (i) establish the timing of metamorphism and deformation, (ii) track long-term horizontal and vertical orogenic movements and (iii) assess the influence of temperature and structural inheritance on the kinematic evolution. We present a new shear zone map, structural cross sections and a step-wise retrodeformation. From $$\text{ca.\;26\,Ma}$$ ca.\;26\,Ma onwards, basement-involved deformation started with the formation of relatively discrete NNW-directed thrusts. Peak metamorphic isograds are weakly deformed by these thrusts, suggesting that they initiated before or during the metamorphic peak under ongoing burial in the footwall to the basal Helvetic roof thrust. Subsequent peak- to post-metamorphic deformation was dominated by steep, mostly NNW-vergent reverse faults ($$\text{ca.}$$ ca.  22–14 Ma). Field investigations demonstrate that these shear zones were steeper than $$50^{\circ}$$ 50 ∘ already at inception. This produced the massif-internal structural relief and was associated with large vertical displacements (7 km shortening vs. up to 11 km exhumation). From 14 Ma onwards, the eastern Aar massif exhumed “en bloc” (i.e., without significant differential massif-internal exhumation) in the hanging wall of frontal thrusts, which is consistent with the transition to strike-slip dominated deformation observed within the massif. Our results indicate 13 km shortening and 9 km exhumation between 14 Ma and present. Inherited normal faults were not significantly reactivated. Instead, new thrusts/reverse faults developed in the basement below syn-rift basins, and can be traced into overturned fold limbs in the overlying sediment, producing tight synclines and broad anticlines along the basement-cover contact. The sediments were not detached from their crystalline substratum and formed disharmonic folds. Our results highlight decreasing rheological contrasts between (i) relatively strong basement and (ii) relatively weak cover units and inherited faults at higher temperature conditions. Both the timing of basement-involved deformation and the structural style (shear zone dip) appear to be controlled by evolving temperature conditions.

scholarly journals Detailed tectonic reconstructions of the Western Mediterranean region for the last 35 Ma, insights on driving mechanisms

2020 ◽  
Vol 191 ◽  
pp. 37
Author(s):  
Adrien Romagny ◽  
Laurent Jolivet ◽  
Armel Menant ◽  
Eloïse Bessière ◽  
Agnès Maillard ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Large Scale ◽  
Complex Dynamics ◽  
Numerical Models ◽  
Western Mediterranean ◽  
Northern Margin ◽  
Driving Mechanisms ◽  
Tectonic Reconstructions ◽  
Mountain Belts ◽  
Back Arc

Slab retreat, slab tearing and interactions of slabs are first-order drivers of the deformation of the overriding lithosphere. An independent description of the tectonic evolution of the back-arc and peripheral regions is a pre-requisite to test the proposed conceptual, analogue and numerical models of these complex dynamics in 3-D. We propose here a new series of detailed kinematics and tectonic reconstructions from 35 Ma to the Present shedding light on the driving mechanisms of back-arc rifting in the Mediterranean where several back-arc basins all started to form in the Oligocene. The step-by-step backward reconstructions lead to an initial situation 35 Ma ago with two subduction zones with opposite direction, below the AlKaPeCa block (i.e. belonging to the Alboran, Kabylies, Peloritani, Calabrian internal zones). Extension directions are quite variable and extension rates in these basins are high compared to the Africa-Eurasia convergence velocity. The highest rates are found in the Western Mediterranean, the Liguro-Provençal, Alboran and Tyrrhenian basins. These reconstructions are based on shortening rates in the peripheral mountain belts, extension rates in the basins, paleomagnetic rotations, pressure-temperature-time paths of metamorphic complexes within the internal zones of orogens, and kinematics of the large bounding plates. Results allow visualizing the interactions between the Alps, Apennines, Pyrenean-Cantabrian belt, Betic Cordillera and Rif, as well as back-arc basins. These back-arc basins formed at the emplacement of mountain belts with superimposed volcanic arcs, thus with thick, hot and weak crusts explaining the formation of metamorphic core complexes and the exhumation of large portions of lower crustal domains during rifting. They emphasize the role of transfer faults zones accommodating differential rates of retreat above slab tears and their relations with magmatism. Several transfer zones are identified, separating four different kinematic domains, the largest one being the Catalan-Balearic-Sicily Transfer Zone. Their integration in the wider Mediterranean realm and a comparison of motion paths calculated in several kinematic frameworks with mantle fabric shows that fast slab retreat was the main driver of back-arc extension in this region and that large-scale convection was a subsidiary driver for the pre-8 Ma period, though it became dominant afterward. Slab retreat and back-arc extension was mostly NW-SE until ∼ 20 Ma and the docking of the AlKaPeCa continental blocks along the northern margin of Africa induced a slab detachment that propagated eastward and westward, thus inducing a change in the direction of extension from NW-SE to E-W. Fast slab retreat between 32 and 8 Ma and induced asthenospheric flow have prevented the transmission of the horizontal compression due to Africa-Eurasia convergence from Africa to Eurasia and favored instead upper-plate extension driven by slab retreat. Once slab retreat had slowed down in the Late Miocene, this N-S compression was felt and recorded again from the High Atlas to the Paris Basin.

Sign in / Sign up

Export Citation Format

Share Document