scholarly journals Thermo-mechanical modelling of subducting plate delamination in the northern Apennines

2021 ◽  
Author(s):  
Ana M. Negredo ◽  
Carlos Clemente ◽  
Eugenio Carminati ◽  
Ivone Jiménez-Munt ◽  
Jaume Vergés ◽  
...  
Keyword(s):  
Oceanic Lithosphere ◽  
High Heat ◽  
Northern Apennines ◽  
Crustal Thickening ◽  
Tyrrhenian Sea ◽  
Continental Subduction ◽  
Low Viscosity ◽  
Mechanical Modelling ◽  
Model Setup ◽  
Negative Buoyancy

<p>A number or previous studies indicate the possibility of post-collisional continental delamination in the northern Apennines. In this study we investigate by means of thermo-mechanical modelling the conditions for, and consequences of, delamination postdating continental subduction in this region. The modelled cross-section strikes approximately from Corsica to the Adriatic Sea. The initial model setup simulates the scenario at ca 20 Ma, where the oceanic lithosphere of the westward-subducting Adria plate was entirely consumed and some amount of continental subduction also occurred. The negative buoyancy of the slab remnant, together with the low viscosity of the dragged down lower continental crust, promote lithospheric mantle sinking into the mantle and asthenospheric upwelling and its lateral expansion along the lower crust. Consistent with geological data, the compressional front produced by delamination migrates about 260 km eastwards, causing a similar migrating pattern of extension from the northern Tyrrhenian Sea, to Tuscany and the seismogenically active Apennines backbone. The topographic response is computed by means of a true free-surface approach, and reflects the same eastward migrating pattern of uplift caused by asthenospheric inflow in the internal part of the system and crustal thickening; and subsidence at the front caused by the negative buoyancy of the sinking Adria slab. The conditions for the occurrence of magmatism and high heat flow beneath Tuscany are also explored. Simulations resulting in fast migration of the delamination front predict slab necking and breakoff, which could be consistent with the slab window observed beneath the central Apennines. Subcrustal seismicity beneath the Northern Apennines can be interpreted as the result to this incipient slab necking. This is a GeoCAM contribution (PGC2018-095154-B-I00)</p>

Architecture of the crust and lithosphere beneath the Semail Ophiolite from ambient noise tomography and receiver functions: insights on the tectonic evolution of eastern Arabia

2021 ◽  
Author(s):  
Christian Weidle ◽  
Lars Wiesenberg ◽  
Andreas Scharf ◽  
Philippe Agard ◽  
Amr El-Sharkawy ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Ambient Noise ◽  
Function Analysis ◽  
Oceanic Lithosphere ◽  
Receiver Functions ◽  
Crustal Thickening ◽  
Ambient Noise Tomography ◽  
First Order ◽  
Pan African ◽  
Semail Ophiolite

<p>The Semail Ophiolite is the world<span>‘</span>s largest and best exposed oceanic lithosphere on land and a primary reference site for studies of creation of oceanic lithosphere, initiation of subduction, geodynamic models of obduction, subduction and exhumation of continental rocks during obduction. Five decades of geological mapping, structural, petrological and geochronological research provide a robust understanding of the geodynamic evolution of the shallow continental crust in northern Oman and how the late Cretaceous obduction process largely shaped the present-day landscape. Yet, prior to obduction, other first-order tectonic processes have left their imprint in the lithosphere, in particular the Neoproterozoic accretion of Arabia and Permian breakup of Pangea. Due to the scarcity of deep structure imaging below the ophiolite, the presence and significance of inherited structures for the obduction process remain unclear.</p><p>We discuss a new 3-D anisotropic shear wave velocity model of the crust below northern Oman derived from ambient noise tomography and Receiver Function analysis which allows to <span>resolve</span> some key unknowns in geodynamics of eastern Arabia: (1) <span>Several NE-trending structural boundaries in the middle and lower crust are attributed to the Pan-African orogeny and align with first-order lateral changes in surface geology and topography.</span> (2) The well-known Semail Gap Fault Zone is an upper crustal feature whereas two other deep crustal faults are newly identified. (3) Permian rifting occurred on both eastern and northern margins but large-scale mafic intrusions and/or underplating occurred only in the east. (4) While obduction is inherently lithospheric by nature, its effects <span>are mostly observed at shallow crustal depths, and lateral variations in its geometry and dynamics can be explained by effects on pre-existing Pan-African and Permian structures. (5) Continental subduction and exhumation during late Cretaceous obduction may be the cause for crustal thickening below today‘s topography.</span> (6) Thinning of the continental lithosphere below northern Oman in late Eocene times – possibly related to thermal effects of the incipient Afar mantle plume - provides a plausible mechanism for the broad emergence of the Oman Mountains and in particular the Jabal Akhdar Dome. Uplift might thus be unrelated to compressional tectonics during Arabia-Eurasia convergence as previously believed.</p>

Igneous activity in central-southern Italy: Is the subduction paradigm still valid?

2022 ◽  
Author(s):  
Michele Lustrino ◽  
Claudio Chiarabba ◽  
Eugenio Carminati
Keyword(s):  
Large Scale ◽  
Oceanic Lithosphere ◽  
Tyrrhenian Sea ◽  
Calc Alkaline ◽  
Quaternary Volcanism ◽  
High K ◽  
Igneous Activity ◽  
Lateral Extent ◽  
Subduction System ◽  
Sea Area

ABSTRACT The Pliocene–Quaternary igneous record of the Tyrrhenian Sea area features a surprisingly large range of compositions from subalkaline to ultra-alkaline and from ultrabasic to acid. These rocks, emplaced within the basin and along its margins, are characterized by strongly SiO2-undersaturated and CaO-rich to strongly SiO2-oversaturated and peraluminous compositions, with sodic to ultrapotassic alkaline and tholeiitic to calc-alkaline and high-K calc-alkaline affinities. We focused on the different models proposed to explain the famous Roman Comagmatic Region, part of the Quaternary volcanism that spreads along the eastern side of the Tyrrhenian area, in the stretched part of the Apennines thrust-and-fold belt. We reviewed data and hypotheses proposed in the literature that infer active to fossil subduction up to models that exclude subduction entirely. Many field geology observations sustain the interpretation that the evolution of the Tyrrhenian-Apennine system was related to subduction of the western margin of Adria continental lithosphere after minor recycling of oceanic lithosphere. However, the lateral extent of the subducting slab in the last millions of years, when magmatism flared up, remains debatable. The igneous activity that developed in the last millions of years along the Tyrrhenian margin is here explained as originating from a subduction-modified mantle, regardless of whether the large-scale subduction system is still active.

scholarly journals Geology of the Northern Apennines nappe stack on eastern Elba (Italy): new insights on the Neogene orogenic evolution of the Northern Tyrrhenian Sea

2021 ◽  
Vol 17 (2) ◽  
pp. 519-532
Author(s):  
Samuele Papeschi ◽  
Eric Ryan ◽  
Giovanni Musumeci ◽  
Francesco Mazzarini ◽  
Paolo Stefano Garofalo ◽  
...  
Keyword(s):  
Northern Apennines ◽  
Tyrrhenian Sea

The structure and geological development of the Erickson gold mine, Cassiar District, British Columbia, with implications for the origin of mother-lode-type gold deposits

1989 ◽  
Vol 26 (12) ◽  
pp. 2645-2660 ◽  
Author(s):  
P. G. Anderson ◽  
C. Jay Hodgson
Keyword(s):  
North America ◽  
Middle Jurassic ◽  
Shear Zones ◽  
High Heat ◽  
Gold Deposits ◽  
Crustal Thickening ◽  
Orthorhombic Symmetry ◽  
Low Grade ◽  
Gold Mine ◽  
The North

The Erickson gold mine is a typical gold quartz vein deposit. The veins are hosted by a thrust-imbricated, gently dipping, synformal allochthon of low-grade metamorphic, Devonian to Upper Triassic basalts, argillites, and peridotites of oceancrustal origin belonging to the Sylvester Group, part of the Slide Mountain assemblage. The Sylvester allochthon lies concordantly on Devonian miogeoclinal sedimentary rocks of the North American continental margin and was emplaced in the Middle Jurassic as a result of the collision of the Quesnel arc with North America. The veins in the mine are hosted mainly by a moderately dipping system of shear zones with approximately orthorhombic symmetry, indicating a triaxial bulk, inhomogeneous strain pattern superimposed on the earlier formed, gently dipping thrusts. Steeply dipping extension veinlets, rotation of schistosity, and downdip slickenlines indicate the maximum shortening axis was subvertical. The veins display complex superimposed ribbon and breccia textures, indicating incremental growth. Most of the gold occurs in association with tetrahedrite, sphalerite, and chalcopyrite in steeply dipping, late, grey quartz veinlets localized within and striking perpendicular to the main veins. The vein-forming event, dated at 130 Ma, appears to have been related to extension and high heat flow associated with the rise of the Omenica geanticline, in turn the result of crustal thickening caused by the collision of the amalgamated Quesnel arc – North America plate with Stikinia in the Middle Jurassic.

Nature and significance of beerbachites in the Ballantrae ophiolite, SW Scotland

1980 ◽  
Vol 71 (3) ◽  
pp. 159-179 ◽  
Author(s):  
E. Jelínek ◽  
J. Souček ◽  
B. J. Bluck ◽  
D. R. Bowes ◽  
P. J. Treloar
Keyword(s):  
Crustal Contamination ◽  
Oceanic Lithosphere ◽  
High Heat ◽  
Major And Trace Elements ◽  
Ocean Floor ◽  
Spreading Ridge ◽  
Pillow Lavas ◽  
Metamorphic Development ◽  
Mineral Assemblages ◽  
Geochemical Variations

ABSTRACTMetamorphosed abyssal ocean-floor tholeiitiic rocks, little affected by crustal contamination and probably formed at a spreading ridge, occur as a dyke complex in banded gabbros with oceanic affinities and as small tectonic lenses in serpentinised peridotite. Igneous textures and mineral assemblages have been partly or completely replaced in both dykes and gabbros. Metamorphic development of clinopyroxene and very Ti-rich hornblende at 900-1000°C was followed by a low temperature actinolite-chlorite assemblage and then by pectolite-bearing veins. Geochemical variations resulting from magmatic and metasomatic processes have been distinguished and plots of major and trace elements used to establish tectonic environment. The very high temperature metamorphic mineral growth associated with beerbachite formation indicates that the dyke rocks were in a high heat-flow environment for a considerable time, presumably in the vicinity of a spreading ridge. Obduction of a very hot slab of oceanic lithosphere accounts for the superimposed mineral assemblages.Spatially associated pillow lavas have been affected by crustal contamination and are not comagmatic with the dykes. There are petrochemical characters indicating that some of the lavas are ocean-floor basalts. For other lavas, features suggesting emplacement in a continental or an island-arc environment could also be consistent with development in a marginal basin. However, there is so much variation in composition of pillows from margin to centre, from small to large and from metasomatic activity, that their compositional fields cannot be used for discrimination of basaltic type with the same confidence as for the dykes. Accordingly, it is suggested that the petrochemistry of sheeted dyke complexes, rather than of pillow lavas, be used for this purpose in the study of ophiolites.

scholarly journals Geochronology and geochemistry of the c. 80 Ma Rutog granitic pluton, northwestern Tibet: implications for the tectonic evolution of the Lhasa Terrane

2008 ◽  
Vol 145 (6) ◽  
pp. 845-857 ◽  
Author(s):  
TAI-PING ZHAO ◽  
MEI-FU ZHOU ◽  
JUN-HONG ZHAO ◽  
KAI-JUN ZHANG ◽  
WEI CHEN
Keyword(s):  
Oceanic Lithosphere ◽  
Crustal Thickening ◽  
Primitive Mantle ◽  
Magmatic Arc ◽  
Granitic Pluton ◽  
Lhasa Terrane ◽  
Arc Setting ◽  
T Values ◽  
Ree Patterns ◽  
Shrimp Zircon

AbstractThe Rutog granitic pluton lies in the Gangdese magmatic arc in the westernmost part of the Lhasa Terrane, NW Tibet, and has SHRIMP zircon U–Pb ages of c. 80 Ma. The pluton consists of granodiorite and monzogranite with SiO2 ranging from 62 to 72 wt% and Al2 O3 from 15 to 17 wt%. The rocks contain 2.33–4.93 wt% K2O and 3.42–5.52 wt% Na2O and have Na2O/K2O ratios of 0.74–2.00. Their chondrite-normalized rare earth element (REE) patterns are enriched in LREE ((La/Yb)n = 15 to 26) and do not show significant Eu anomalies (δEu = 0.68–1.15). On a primitive mantle-normalized trace element diagram, the rocks are rich in large ion lithophile elements (LILE) and poor in high field strength elements (HFSE), HREE and Y. Their Sr/Y ratios range from 15 to 78 with an average of 30. The rocks have constant initial 87Sr/86Sr ratios (0.7045 to 0.7049) and slightly positive ɛNd(t) values (+0.1 to +2.3), similar to I-type granites generated in an arc setting. The geochemistry of the Rutog pluton is best explained by partial melting of a thickened continental crust, triggered by underplating of basaltic magmas in a mantle wedge. The formation of the Rutog pluton suggests flat subduction of the Neo-Tethyan oceanic lithosphere from the south. Crustal thickening may have occurred in the Late Cretaceous prior to the India–Asia collision.

scholarly journals Extrusion of subducted crust explains the emplacement of far-travelled ophiolites

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kristóf Porkoláb ◽  
Thibault Duretz ◽  
Philippe Yamato ◽  
Antoine Auzemery ◽  
Ernst Willingshofer
Keyword(s):  
High Pressure ◽  
Continental Crust ◽  
Plate Tectonics ◽  
Oceanic Lithosphere ◽  
Causal Link ◽  
Combine Data ◽  
Continental Subduction ◽  
Ophiolite Emplacement ◽  
Oceanic Plates ◽  
Tectonic Windows

AbstractContinental subduction below oceanic plates and associated emplacement of ophiolite sheets remain enigmatic chapters in global plate tectonics. Numerous ophiolite belts on Earth exhibit a far-travelled ophiolite sheet that is separated from its oceanic root by tectonic windows exposing continental crust, which experienced subduction-related high pressure-low temperature metamorphism during obduction. However, the link between continental subduction-exhumation dynamics and far-travelled ophiolite emplacement remains poorly understood. Here we combine data collected from ophiolite belts worldwide with thermo-mechanical simulations of continental subduction dynamics to show the causal link between the extrusion of subducted continental crust and the emplacement of far-travelled ophiolites. Our results reveal that buoyancy-driven extrusion of subducted crust triggers necking and breaking of the overriding oceanic upper plate. The broken-off piece of oceanic lithosphere is then transported on top of the continent along a flat thrust segment and becomes a far-travelled ophiolite sheet separated from its root by the extruded continental crust. Our results indicate that the extrusion of the subducted continental crust and the emplacement of far-travelled ophiolite sheets are inseparable processes.

Late evolution of the inner Northern Apennines from the structure of the Monti del Chianti-Monte Cetona Ridge (Tuscany, Italy)

2021 ◽  
Author(s):  
Andrea Brogi
Keyword(s):  
Middle Miocene ◽  
Sedimentary Basins ◽  
Northern Apennines ◽  
Normal Faults ◽  
Tyrrhenian Sea ◽  
Scientific Debate ◽  
Marine Deposits ◽  
Accommodation Space ◽  
Tectonic Events ◽  
Late Evolution

<p>The Neogene and Quaternary tectonic evolution of the inner Northern Apennines (i.e southern Tuscany and northern Tyrrhenian Sea), as well as its crustal features (i.e. low crustal thickness, Neogene-Quaternary magmatism, widespread geothermal anomalies, lateral segmentation of the stacked tectonic units, extensive deep sedimentary basins), are framed in different geodynamic scenarios: compressional, extensional or both, pulsing. Consequently, the basin and range structure that characterises the northern Tyrrhenian Sea and southern Tuscany is considered as a consequence of (i) out-of-sequence thrusts and related thrust-top-basins, (ii) polyphased normal faulting that formed horst and graben structures or (iii) a combination of both. This paper provides a new dataset from a sector of the eastern inner Northern Apennines (i.e. Monti del Chianti - Monte Cetona ridge) contributing to this scientific debate. New fieldwork and structural analysis carried out in selected areas along the ridge allowed to define the chronology of the main tectonic events on the basis of their influence on the marine and continental sedimentation. The dataset supports for early Miocene - (?) Serravallian in-sequence and out-of-sequence thrusting. Thrusting produced complex staking patterns of Tuscan and Ligurian Units. Extensional detachments developed since later middle Miocene and controlled the Neogene sedimentation in bowl-shaped structural depressions, later dissected by normal faults enhancing the accommodation space for Pliocene marine deposits in broad NNW-trending basins (Siena-Radicofani and Valdichiana Basins). In this perspective, no data supports for active, continuous or pulsing, compressional tectonics after late Serravalian. As a result, in the whole inland inner Northern Apennines the extensional tectonics was continuously active at least since middle Miocene and controlled the basins development, magmatism and structure of the crust and lithosphere.</p>

The structure and evolution of the Northern Tyrrhenian Sea

1996 ◽  
Vol 133 (1) ◽  
pp. 1-16 ◽  
Author(s):  
J. V. A. Keller ◽  
M. P. Coward
Keyword(s):  
Field Studies ◽  
Geometrical Model ◽  
Northern Apennines ◽  
Tyrrhenian Sea ◽  
Tectonic Model ◽  
Detachment Faults ◽  
Fold And Thrust Belt ◽  
Internal Zone ◽  
Extensional Faulting ◽  
Seismic Lines

AbstractField studies on the island of Elba and seismic lines from the Northern Tyrrhenian Sea, Italy, indicate that major extensional displacements were accommodated along east-dipping low-angle detachment faults. The rifting and subsidence in the Northern Tyrrhenian Sea basin have followed convergence and collision of the Corso-Sardinian block and the Apulian microplate. This collisional episode produced the Northern Apennines fold-and-thrust belt. Major extensional faults cut down-section through the stratigraphy and pre-existing west-dipping thrust faults. West-dipping thrusts can also be reactivated and form antithetic faults to the east-dipping detachments. Brittle deformation conditions predominated during the extensional phase. The geometry, internal structure and the fabrics (brittle and penetrative) associated with a well-exposed low-angle extensional detachment in Elba are presented in this paper. A geometrical model for the brittle extensional faulting is presented in which regional extension was accommodated on a system consisting of two sets of simultaneously active antithetic faults. The east-dipping detachment faults appear to have started at steeper angles, based on field and seismic observations, and rotated counter-clockwise to lower dips. Due to this rotation, and for space accommodation, antithetic west-dipping faults formed and rotated clockwise. A tectonic model is proposed whereby slowing of the convergence between Apulia and Corsica, as well as Tethys oceanic crust and Apulian crust subduction, led to the delamination of the Apulian litho-spheric mantle away from the crust. Accompanying asthenospheric upwelling and intrusion at the crust—mantle interface beneath the Tyrrhenian Sea caused late orogenic crustal stretching in the Northern Apennines internal zone.

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