Outcrop-scale tomography: Insights into the 3D structure of multiphase boudins

Hagke, Christoph von; Bamberg, Bob; Virgo, Simon; Urai, János

doi:10.1016/j.jsg.2018.02.014

Cited by 11 publications

(6 citation statements)

References 53 publications

(79 reference statements)

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“…Many authors regard slab rollback as having caused isobaric heating and Barrovian metamorphism (M 2 ) of previous HP‐LT rocks, due to increased basal heating from the upwelling asthenosphere (e.g., Jolivet et al, 2013; Jolivet & Brun, 2010). However, a crustal thickening model has been proposed by Lamont et al (2019) and Searle and Lamont et al (2019) who argue for compression as a result of continent‐continent collision between Cyclades/Adria and Eurasia as the cause of M 2 ‐M 3 kyanite‐sillimanite grade metamorphism on Naxos, based on isoclinal upright folds within the Naxos core, a clockwise prograde P ‐ T ‐ t paths of kyanite grade gneisses and migmatites, and evidence for horizontal constriction and vertical extension within the core of Naxos migmatite dome (Lamont et al, 2019; Virgo et al, 2018; von Hagke et al, 2018). Lamont et al (2019) suggested a switch from overall compression to extension occurred at circa 15 Ma, timing that coincides with a two‐fold decrease in the Africa‐Eurasia convergence rate (DeMets et al, 2015).…”

Section: Geology Of Tinos and The Cycladic Blueschist Unitmentioning

confidence: 99%

The Cycladic Blueschist Unit on Tinos, Greece: Cold NE Subduction and SW Directed Extrusion of the Cycladic Continental Margin Under the Tsiknias Ophiolite

et al. 2020

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High pressure-low temperature (HP-LT) metamorphic rocks structurally beneath the Tsiknias Ophiolite make up the interior of Tinos Island, Greece, but their relationship with the overlying ophiolite is poorly understood. Here, new field observations are integrated with petrological modeling of eclogite and blueschists to provide new insight into their tectonothermal evolution. Pseudomorphed lawsonite-, garnet-, and glaucophane-bearing schists exposed at the highest structural levels of Tinos (Kionnia and Pyrgos Subunits) reached~22-26 kbar and 490-520°C under water-saturated conditions, whereas pseudomorphed lawsonite-and aegirine-omphacite bearing eclogite reached~20-23 kbar and 530-570°C. These rocks are separated from rocks at deeper structural levels (Sostis Subunit) by a top-to-SW thrust. The Sostis Subunit records P-T conditions of~18.5 kbar and 480-510°C and is overprinted by pervasive top-toNE shearing that developed during exhumation from (M 1) blueschist to (M 2) greenschist facies conditions of~7.3 ± 0.7 kbar and 536 ± 16°C. These P-T-D relationships suggest that the Cycladic Blueschist Unit represents a discrete series of tectonometamorphic subunits that each experienced different tectonic and thermal histories. These subunits were buried to variable depths and sequentially extruded toward the SW from a NE dipping subduction zone. The difference in age and P-T conditions between the HP-LT rocks and the overlying metamorphic sole of the Tsiknias Ophiolite suggests that this NE dipping subduction zone was active between circa 74 and 46 Ma and cooled at a minimum rate of 1.2-1.5°C/km/Myr prior to continent-continent collision between Eurasia and Adria/Cyclades. Plain Language Summary High pressure-low temperature metamorphic rocks make up the interior of Tinos Island, Greece and underlie an ancient piece of oceanic crust and mantle (Tsiknias Ophiolite). The rocks that make up Tinos were once mudstones and limestones deposited on the NE margin of the Cycladic-Adriatic continent and were deeply buried in a subduction zone. In this work, we investigate the structures and mineralogy of the Tinos high-pressure rocks and find they were buried to variable depths (80-60 km) and reached temperatures of 500-550°C. These packages of rock were then emplaced against each other during their return journey toward the surface after subduction ended. We document evidence for circa 25 Myr (ca. 74 and 46 Ma) of subduction prior to continent-continent collision (between Eurasia and Adria/Cyclades) on Tinos and that this records the closure of an ancient ocean to the NE of the Cyclades.

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Section: Geology Of Tinos and The Cycladic Blueschist Unitmentioning

confidence: 99%

The Cycladic Blueschist Unit on Tinos, Greece: Cold NE Subduction and SW Directed Extrusion of the Cycladic Continental Margin Under the Tsiknias Ophiolite

et al. 2020

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“…1b-e), with marine or lacustrine carbonates and mudstones being the most common. Examples include LES in such disparate salt basins as the Barents Sea, the Permian Basin of Europe, the Pyrenees and Betics of Spain, the Levant Basin in the eastern Mediterranean, the Red Sea and Gulf of Suez, the Oman salt basins, the Precaspian Basin, the Kuqa Basin of China, the Flinders Ranges of Australia, La Popa Basin in Mexico, the Paradox Basin of the southwestern (SW) US, and the salt basins of Nova Scotia (e.g., Dalgarno and Johnson, 1968;Hite and Buckner, 1981;Dekker, 1985;Wade and MacLean, 1990;Lawton et al, 2001;Peters et al, 2003;Volozh et al, 2003;Chen et al, 2004;Bosworth et al, 2005;Geluk, 2007a;Cámara and Flinch, 2017;Flinch and Soto, 2017;Rowan and Lindsø, 2017). Siliciclastic layers can also include siltstones, sandstones, and even conglomerates (e.g., Paradox Basin; Rasmussen, 2014).…”

Section: Introductionmentioning

confidence: 99%

Deformation of intrasalt competent layers in different modes of salt tectonics

Rowan

Urai

Fiduk³

et al. 2019

Solid Earth

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Abstract. Layered evaporite sequences (LESs) comprise interbedded weak layers (halite and, commonly, bittern salts) and strong layers (anhydrite and usually non-evaporite rocks such as carbonates and siliciclastics). This results in a strong rheological stratification, with a range of effective viscosity up to a factor of 105. We focus here on the deformation of competent intrasalt beds in different endmember modes of salt tectonics, even though combinations are common in nature, using a combination of conceptual, numerical, and analog models, and seismic data. In bedding-parallel extension, boudinage of the strong layers forms ruptured stringers, within a halite matrix, that become more isolated with increasing strain. In bedding-parallel shortening, competent layers tend to maintain coherency while forming harmonic, disharmonic, and polyharmonic folds, with the rheological stratification leading to buckling and fold growth by bedding-parallel shear. In differential loading, extension and the resultant stringers dominate beneath suprasalt depocenters, while folded competent beds characterize salt pillows. Finally, in passive diapirs, stringers generated by intrasalt extension are rotated to near vertical and encased in complex folds during upward flow of salt. In all cases, strong layers are progressively removed from areas of salt thinning and increasingly disrupted and folded in areas of salt growth as deformation intensifies. The varying styles of intrasalt deformation impact seismic imaging of LES and associated interpretations. Ruptured stringers are often visible where they have low dips, as in slightly extended salt layers or beneath depocenters, but are poorly imaged in passive diapirs due to steep dips. In contrast, areas of slightly to moderately shortened salt typically have well-imaged, mostly continuous intrasalt reflectors, although seismic coherency decreases as deformation intensifies. Similarly, wells are most likely to penetrate strong layers in contractional structures and salt pillows, less likely in extended salt because they might drill between stringers, and unlikely in tall passive diapirs because the stringers are near vertical. Thus, both seismic and well data may be interpreted to suggest that diapirs and other areas of more intense intrasalt deformation are more halite rich than is actually the case.

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“…2b and d, 5). Interestingly, thinner layers tend to rupture less during layer-parallel extension than thicker layers (von Hagke et al, 2018). 10…”

Section: Thickness and Strengthmentioning

confidence: 99%

Deformation of intrasalt competent layers in different modes of salt tectonics

Rowan

Urai

Fiduk³

et al. 2019

Preprint

Self Cite

View full text Add to dashboard Cite

Abstract. Layered evaporite sequences (LES) comprise interbedded weak layers (halite and, commonly, bittern salts) and strong layers (anhydrite and usually non-evaporite rocks such as carbonates and siliciclastics). This results in a strong rheological stratification, with a range of effective viscosity up to a factor of 105. We focus here on the deformation of competent intrasalt beds in different modes of salt tectonics using a combination of conceptual, numerical and analog models, and seismic data. In bedding-paralell extension, boudinage of the strong layers forms ruptured stringers, within a halite matrix, that become increasingly isolated with increasing strain. In bedding-parallel shortening, competent layers tend to maintain coherency while forming harmonic, disharmonic, and polyharmonic folds, with the rheological stratification leading to buckling and fold growth by bedding-parallel shear. In differential loading, extension and the resultant stringers dominate beneath suprasalt depocenters while folded competent beds characterize salt pillows. Finally, in tall passive diapirs, stringers generated by intrasalt extension are rotated to near vertical in tectonic melanges during upward flow of salt. In all cases, strong layers are progressively removed from areas of salt thinning and increasingly disrupted and folded in areas of salt growth as deformation intensifies. The varying styles of intrasalt deformation impact seismic imaging of LES and associated interpretations. Ruptured stringers are often visible where they have low dips, as in slightly extended salt layers or beneath depocenters, but are usually not imaged in tall passive diapirs due to steep dips. In contrast, areas of slightly to moderately shortened salt typically have well imaged, mostly continuous intrasalt reflectors, although seismic coherency decreases as deformation intensifies. Similarly, wells are most likely to penetrate strong layers in contractional structures and salt pillows, less likely in extended salt because they might drill between stringers, and unlikely in tall passive diapirs because the stringers are near-vertical. Thus, both seismic and well data may be interpreted to suggest that diapirs and other areas of more intense intrasalt deformation are more halite rich than is actually the case.

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Outcrop-scale tomography: Insights into the 3D structure of multiphase boudins

Cited by 11 publications

References 53 publications

The Cycladic Blueschist Unit on Tinos, Greece: Cold NE Subduction and SW Directed Extrusion of the Cycladic Continental Margin Under the Tsiknias Ophiolite

The Cycladic Blueschist Unit on Tinos, Greece: Cold NE Subduction and SW Directed Extrusion of the Cycladic Continental Margin Under the Tsiknias Ophiolite

Deformation of intrasalt competent layers in different modes of salt tectonics

Deformation of intrasalt competent layers in different modes of salt tectonics

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