Metamorphic and structural evolution of the Maures-Tanneron massif (SE Variscan chain): evidence of doming along a transpressional margin

2009 ◽  
Vol 180 (3) ◽  
pp. 217-230 ◽  
Author(s):  
Yann Rolland ◽  
Michel Corsini ◽  
Antoine Demoux
Keyword(s):  
Lower Crust ◽  
Late Phase ◽  
Structural Evolution ◽  
Strike Slip ◽  
Current Situation ◽  
Metamorphic Evolution ◽  
Himalayan Belt ◽  
Slip Displacement ◽  
Regional Gradient ◽  
Major Strike

Abstract The Variscan metamorphic and structural evolution of the Maures-Tanneron massif is divided in two main post-collisional phases: (1) a MP-MT regional gradient is developed during nappe-piling process between 350 and 320 Ma, followed by (2) LP-HT regional gradient coeval with doming between 320 and 300 Ma. During this late phase, the tectonic context was dominated by E-W shortening, which produced crustal-scale upright folds and major strike-slip displacement along trans-crustal faults. Symmetric extensional fabrics are observed on the limbs of crustal-scale anticlines, and are ascribed to local accommodation of lower crust exhumation. Heat and magma transfer are allowed by these large vertical strike-slip faults, and are thought to be the cause of the late metamorphic evolution. Therefore, structures and metamorphism argue for a transpressional context at the SE branch of the Variscan chain. Comparisons with current collisional settings such as syntaxial domains of the Himalayan belt show that the timing and PT conditions of metamorphic events are similar. These observations lead us to propose that the situation of the Variscan chain during the period 320-300 Ma was still a syn-convergent setting similar to the current situation of the Himalayan-Tibet system, and that extensional movements are not the cause of, but the result of exhumation of the lower crust in this ongoing shortening context along a transpressional wrench boundary.

scholarly journals Late Palaeozoic strike-slip tectonics versus oroclinal bending at the SW outskirts of Baltica: case of the Variscan belt’s eastern end in Poland

2020 ◽  
Vol 109 (4) ◽  
pp. 1133-1160 ◽  
Author(s):  
Stanislaw Mazur ◽  
Paweł Aleksandrowski ◽  
Łukasz Gągała ◽  
Piotr Krzywiec ◽  
Jerzy Żaba ◽  
...  
Keyword(s):  
Regional Distribution ◽  
Kinematic Model ◽  
Structural Evolution ◽  
Strike Slip ◽  
Variscan Belt ◽  
Deformation Front ◽  
Fold And Thrust Belt ◽  
Isostatic Gravity ◽  
Regional Tectonic ◽  
Major Strike

AbstractGeophysical and geological data from the eastern sector of the Central European Variscan belt are presented and reviewed in the regional tectonic context. Matched filtering of isostatic gravity, guided by results of spectral analysis, along with other derivatives of gravity and magnetic fields reveal a dominant WNW–ESE-trending pre-Permian structural grain in the external zones of the Variscan belt in Poland. This trend is confirmed by regional distribution of dips in Carboniferous and Devonian strata that were penetrated by boreholes beneath Permian-Mesozoic sediments. Based on these data, two alternative concepts explaining the connection of the Variscan belt and its NE foreland, those of strike-slip tectonics versus oroclinal bending, are discussed. The WNW–ESE structural trend in the Variscan foreland is parallel to a set of major strike-slip fault zones in the area, including those of Upper Elbe, Intra-Sudetic, Odra, Dolsk and Kraków-Lubliniec. These faults are considered to convey a significant dextral displacement between Laurussia and Gondwana. The revised position of the Variscan deformation front shows a similar, uninterrupted, generally WNW–ESE trend, up to the SE border of Poland, which indicates an initial continuation of the Variscan belt into the area of the present-day Western Carpathians. The geometry of the Variscan deformation front along with the pattern of the Variscan structural grain are inconsistent with the idea of an oroclinal loop affecting the external, non-metamorphic Variscan belt. However, the data presented do not entirely rule out an oroclinal loop within the Variscan internides. The still possible options are (1) a semi-oroclinal model postulating ~ 90° bending of the Variscan tectonostratigraphic zones into parallelism with the WNW–ESE strike-slip faults or (2) an orocline limited only to the belt linking the Wolsztyn High and Moravo-Silesian non- to weakly-metamorphic fold-and-thrust belt. Regardless of the kinematic model preferred, our data indicate that structural evolution of the Polish Variscides was concluded with the end-Carboniferous NNE–SSW shortening that resulted in the present-day extent of the Variscan deformation front.

Structural evolution in the Moine of northwest Scotland: a Caledonian linked thrust system?

1986 ◽  
Vol 123 (1) ◽  
pp. 1-11 ◽  
Author(s):  
Robert W. H. Butler
Keyword(s):  
Cross Sections ◽  
Lower Crust ◽  
Structural Evolution ◽  
Amphibolite Facies ◽  
Metamorphic Basement ◽  
Thrust System ◽  
Lower Crustal

AbstractA model is proposed whereby the Caledonian metamorphic basement-cover complex of northwest Scotland (the Moine) is considered as a linked thrust system. This system lies between the Moine thrust at its base and the Naver–Sgurr Beag slide at its top. Ductile fold and thrust zones, which developed at mid crustal levels at metamorphic grades from greenschist to amphibolite facies, are interpreted as decoupling from a detachment presently situated at relatively shallow depths. This model is illustrated by two preliminary balanced cross-sections. These imply shortening across the northwest Scottish Caledonides in excess of 130 km and probably over 200 km. When these structures are restored onto a crustal template a considerable quantity of lower crust is found to be required at depth. The most likely location for the lower crustal wedge is beneath the Grampian Highlands.

scholarly journals Structural analysis of the Rio Preto fold belt (northwestern Bahia / southern Piauí), a doubly-vergent asymmetric fan developed during the Brasiliano Orogeny

2014 ◽  
Vol 86 (3) ◽  
pp. 1101-1113 ◽  
Author(s):  
FABRÍCIO A. CAXITO ◽  
ALEXANDRE UHLEIN ◽  
LUIZ F.G. MORALES ◽  
MARCOS EGYDIO-SILVA ◽  
JULIO C.D. SANGLARD ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Structural Evolution ◽  
Shear Zones ◽  
Central Compartment ◽  
Strike Slip ◽  
Fold Belt ◽  
Main Structure ◽  
The North ◽  
Brasiliano Orogeny ◽  
Analog Models

The Rio Preto fold belt borders the northwestern São Francisco craton and shows an exquisite kilometric doubly-vergent asymmetric fan structure, of polyphasic structural evolution attributed exclusively to the Brasiliano Orogeny (∼600-540 Ma). The fold belt can be subdivided into three structural compartments: The Northern and Southern compartments showing a general NE-SW trend, separated by the Central Compartment which shows a roughly E-W trend. The change of dip of S2, a tight crenulation foliation which is the main structure of the fold belt, between the three compartments, characterizes the fan structure. The Central Compartment is characterized by sub-vertical mylonitic quartzites, which materialize a system of low-T strike slip shear zones (Malhadinha – Rio Preto Shear Zone) crosscutting the central portion of the fold belt. In comparison to published analog models, we consider that the unique structure of the Rio Preto fold belt was generated by the oblique, dextral-sense interaction between the Cristalândia do Piauí block to the north and the São Francisco craton to the south.

scholarly journals ’Taters versus Sliders: Evidence for a Long-Lived History of Strike-Slip Displacement along the Canadian Arctic Transform System (CATS)

GSA Today ◽  
2021 ◽  
Author(s):  
William McClelland ◽  
Justin Strauss ◽  
Maurice Copron ◽  
Jane Gilotti ◽  
Karol Faehnrich ◽  
...  
Keyword(s):  
Canadian Arctic ◽  
Strike Slip ◽  
History Of ◽  
Slip Displacement

scholarly journals Constraints on the rheology of the lower crust in a strike-slip plate boundary: evidence from the San Quintín xenoliths, Baja California, Mexico

Solid Earth ◽  
2017 ◽  
Vol 8 (6) ◽  
pp. 1211-1239 ◽  
Author(s):  
Thomas van der Werf ◽  
Vasileios Chatzaras ◽  
Leo Marcel Kriegsman ◽  
Andreas Kronenberg ◽  
Basil Tikoff ◽  
...  
Keyword(s):  
Grain Size ◽  
Upper Mantle ◽  
Lower Crust ◽  
Baja California ◽  
Plate Boundary ◽  
Volcanic Field ◽  
Strike Slip ◽  
Low Viscosity ◽  
The Pacific ◽  
Flow Laws

Abstract. The rheology of lower crust and its transient behavior in active strike-slip plate boundaries remain poorly understood. To address this issue, we analyzed a suite of granulite and lherzolite xenoliths from the upper Pleistocene–Holocene San Quintín volcanic field of northern Baja California, Mexico. The San Quintín volcanic field is located 20 km east of the Baja California shear zone, which accommodates the relative movement between the Pacific plate and Baja California microplate. The development of a strong foliation in both the mafic granulites and lherzolites, suggests that a lithospheric-scale shear zone exists beneath the San Quintín volcanic field. Combining microstructural observations, geothermometry, and phase equilibria modeling, we estimated that crystal-plastic deformation took place at temperatures of 750–890 °C and pressures of 400–560 MPa, corresponding to 15–22 km depth. A hot crustal geotherm of 40 ° C km−1 is required to explain the estimated deformation conditions. Infrared spectroscopy shows that plagioclase in the mafic granulites is relatively dry. Microstructures are interpreted to show that deformation in both the uppermost lower crust and upper mantle was accommodated by a combination of dislocation creep and grain-size-sensitive creep. Recrystallized grain size paleopiezometry yields low differential stresses of 12–33 and 17 MPa for plagioclase and olivine, respectively. The lower range of stresses (12–17 MPa) in the mafic granulite and lherzolite xenoliths is interpreted to be associated with transient deformation under decreasing stress conditions, following an event of stress increase. Using flow laws for dry plagioclase, we estimated a low viscosity of 1.1–1.3×1020 Pa ⋅ s for the high temperature conditions (890 °C) in the lower crust. Significantly lower viscosities in the range of 1016–1019 Pa ⋅ s, were estimated using flow laws for wet plagioclase. The shallow upper mantle has a low viscosity of 5.7×1019 Pa ⋅ s, which indicates the lack of an upper-mantle lid beneath northern Baja California. Our data show that during post-seismic transients, the upper mantle and the lower crust in the Pacific–Baja California plate boundary are characterized by similar and low differential stress. Transient viscosity of the lower crust is similar to the viscosity of the upper mantle.

scholarly journals Geology, Geochronology and Geochemistry of Weilasituo Sn-Polymetallic Deposit in Inner Mongolia, China

Minerals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 104 ◽  
Author(s):  
Fan Yang ◽  
Jinggui Sun ◽  
Yan Wang ◽  
Junyu Fu ◽  
Fuchao Na ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Lower Crust ◽  
Structural Evolution ◽  
Magma Source ◽  
Crustal Material ◽  
Quartz Porphyry ◽  
Polymetallic Deposit ◽  
High Concentrations ◽  
Great Xing’An Range ◽  
Lower Crustal

The recently discovered Weilasituo Sn-polymetallic deposit in the Great Xing’an Range is an ultralarge porphyry-type deposit. The mineralization is closely associated with an Early Cretaceous quartz porphyry. Analysis of quartz porphyry samples, including zircon U-Pb dating and Hf isotopies, geochemical and molybdenite Re-Os isotopic testing, reveals a zircon U-Pb age of 138.6 ± 1.1 Ma and a molybdenite Re-Os isotopic age of 135 ± 7 Ma, suggesting the concurrence of the petrogenetic and metallogenic processes. The quartz porphyry has high concentrations of SiO2 (71.57 wt %–78.60 wt %), Al2O3 (12.69 wt %–16.32 wt %), and K2O + Na2O (8.85 wt %–10.44 wt %) and A/CNK ratios from 0.94–1.21, is mainly peraluminous, high-K calc-alkaline I-type granite and is relatively rich in LILEs (large ion lithophile elements, e.g., Th, Rb, U and K) and HFSEs (high field strength elements, e.g., Hf and Zr) and relatively poor in Sr, Ba, P, Ti and Nb. The zircon εHf(t) values range from 1.90 to 6.90, indicating that the magma source materials were mainly derived from the juvenile lower crust and experienced mixing with mantle materials. Given the regional structural evolution history, we conclude that the ore-forming magma originated from lower crust that had thickened and delaminated is the result of the subduction of the Paleo–Pacific Ocean. Following delamination, the lower crustal material entered the underlying mantle, where it was partially melted and reacted with mantle during ascent. The deposit formed at a time of transition from post-orogenic compression to extension following the subduction of the Paleo–Pacific Ocean.

Proterozoic geological evolution of the northern Vestfold Hills, Antarctica

1991 ◽  
Vol 128 (4) ◽  
pp. 307-318 ◽  
Author(s):  
C. W. Passchier ◽  
R. F. Bekendam ◽  
J. D. Hoek ◽  
P. G. H. M. Dirks ◽  
H. de Boorder
Keyword(s):  
Large Scale ◽  
Structural Evolution ◽  
Shear Zones ◽  
Granulite Facies ◽  
Strike Slip ◽  
Amphibolite Facies ◽  
Tectonic Event ◽  
Vestfold Hills ◽  
Two Phases ◽  
Brittle Faulting

AbstractThe presence of polyphase shear zones transected by several suites of dolerite dykes in Archaean basement of the Vestfold Hills, East Antarctica, allows a detailed reconstruction of the local structural evolution. Archaean and early Proterozoic deformation at granulite facies conditions was followed by two phases of dolerite intrusion and mylonite generation in strike-slip zones at amphibolite facies conditions. A subsequent middle Proterozoic phase of brittle normal faulting led to the development of pseudotachylite, predating intrusion of the major swarm of dolerite dykes around 1250 Ma. During the later stages and following this event, pseudotachylite veins were reactivated as ductile, mylonitic thrusts under prograde conditions, culminating in amphibolite facies metamorphism around 1000–1100 Ma. This is possibly part of a large-scale tectonic event during which the Vestfold block was overthrust from the south. In a final phase of strike-slip deformation, several pulses of pseudotachylite-generating brittle faulting alternated with ductile reactivation of pseudotachylite.

Sign in / Sign up

Export Citation Format

Share Document