Applications of twin analysis to studying meteorite impact structures

Schedl, Andrew

doi:10.1016/j.epsl.2006.02.018

Cited by 14 publications

(15 citation statements)

References 42 publications

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“…). The formation of calcite twins during impact has been reported for natural impacts, as well as impact experiments by several authors (e.g., Robertson and Grieve ; Langenhorst ; Schedl ; Lindgren et al. ).…”

Section: Discussionmentioning

confidence: 53%

Subsurface deformation of experimental hypervelocity impacts in quartzite and marble targets

Winkler

Luther

Poelchau

et al. 2018

Meteorit & Planetary Scien

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Two impact cratering experiments on nonporous rock targets were carried out to determine the influence of target composition on the structural mechanisms of subsurface deformation. Projectiles of 2.5 mm diameter were accelerated to ~5 km s−1 and impacted onto blocks of marble or quartzite. Subsurface deformation was mapped and analyzed on the microscale using thin sections of the bisected craters. Additionally, both experiments were modeled and the calculated strain zones underneath the craters were compared to experimental deformation features. Microanalysis shows that the formation of radial, tensile, and intragranular cracks is a common response of both nonporous materials to impact cratering. In the quartzite target, the subsurface damage is additionally characterized by highly localized deformation along shear bands with intense grain comminution, surrounded by damage zones. In contrast, the marble target shows closely spaced calcite twinning and cleavage activation. Crater diameter and depth as well as the damage lens underneath the crater are unexpectedly smaller in the marble target compared to the quartzite target, which is in contradiction to the marble's much weaker compressive and tensile strengths. However, numerical models result in craters that are similar in size as well as in strain accumulation at the end of transient crater formation, indicating that current models should still be viewed cautiously when compared to experimental details.

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Section: Discussionmentioning

confidence: 53%

Subsurface deformation of experimental hypervelocity impacts in quartzite and marble targets

Winkler

Luther

Poelchau

et al. 2018

Meteorit & Planetary Scien

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“…This technique is widely applied to infer paleostress orientations in various terrestrial settings (Tourneret and Laurent, 1990;González-Casado and García-Cuevas, 1999;González-Casado et al, 2006;Schedl, 2006) and has also been successfully employed to explore stress relationships in a carbonaceous chondrite (Lindgren et al, 2011). Here, we used the classic e-twin stress analysis method of Turner (1953Turner ( , 1962 to determine the orientation of the maximum compression (r 1 ) that acted on the sample to form the calcite twins.…”

Section: Calcite Twin Stress Analysismentioning

confidence: 99%

The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts

Lindgren

Hanna

Dobson

et al. 2015

Geochimica et Cosmochimica Acta

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Petrographic analysis of eight CM carbonaceous chondrites (EET 96029, LAP 031166, LON 94101, MET 01072, Murchison, Murray, SCO 06043, QUE 93005) by electron imaging and diffraction, and X-ray computed tomography, reveals that six of them have a petrofabric defined by shock flattened chondrules. With the exception of Murchison, those CMs that have a strong petrofabric also contain open or mineralized fractures, indicating that tensional stresses accompanying the impacts were sufficient to locally exceed the yield strength of the meteorite matrix. The CMs studied span a wide range of petrologic subtypes, and in common with Rubin (2012) we find that the strength of their petrofabrics increases with their degree of aqueous alteration. This correspondence suggests that impacts were responsible for enhancing alteration, probably because the fracture networks they formed tapped fluid reservoirs elsewhere in the parent body. Two meteorites that do not fit this pattern are MET 01072 and Murchison; both have a strong petrofabric but are relatively unaltered. In the case of MET 01072, impact deformation is likely to have postdated parent body aqueous activity. The same may also be true for Murchison, but as this meteorite also lacks fractures and veins, its chondrules were most likely flattened by multiple low intensity impacts. Multiphase deformation of Murchison is also revealed by the microstructures of calcite grains, and chondrule-defined petrofabrics as revealed by X-ray computed tomography. The contradiction between the commonplace evidence for impact-deformation of CMs and their low shock stages (most belong to S1) can be explained by most if not all having been exposed to multiple low intensity (i.e., <5 GPa) shock events. Aqueous alteration was enhanced by those impacts that were of sufficient intensity to open high permeability fracture networks that could connect to fluid reservoirs.

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“…Attempts have also been made to quantify shock effects in carbonates using X-ray diffraction (XRD) and electron spin resonance (ESR) (Polanskey and Ahrens 1994;Skála and Jakeš 1999;Skála et al 2002;Burt et al 2005); however, calibration of the observed effects with respect to shock pressure remains ambiguous so that these methods remain qualitative at present. Recently, the first detailed application of twin analysis in calcite has been used to quantify shock pressures in carbonates from Serpent Mound, USA (Schedl 2006). Given that low shear stresses of ∼10 MPa are required for twinning in calcite (Schedl 2006), this technique may prove a useful shock indicator for carbonates at relatively low shock levels.…”

Section: Introductionmentioning

confidence: 99%

Impact metamorphism of CaCO₃‐bearing sandstones at the Haughton structure, Canada

Osinski

2007

Meteorit & Planetary Scien

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Abstract— Impact‐metamorphosed CaCO3‐bearing sandstones at the Haughton structure have been divided into 6 classes, based to a large extent on a previous classification developed for sandstones at Meteor Crater. Class 1a sandstones (<3 GPa) display crude shatter cones, but no other petrographic indications of shock. At pressures of 3 to 5.5 GPa (class 1b), porosity is destroyed and well‐developed shatter cones occur. Class 2 rocks display planar deformation features (PDFs) and are characterized by a “jigsaw” texture produced by rotation and shear at quartz grain boundaries. Calcite shows an increase in the density of mechanical twins and undergoes micro‐brecciation in class 1 and 2 sandstones. Class 3 samples display multiple sets of PDFs and widespread development of diaplectic glass, toasted quartz, and symplectic intergrowths of quartz, diaplectic glass, and coesite. Textural evidence, such as the intermingling of silicate glasses and calcite and the presence of flow textures, indicates that calcite in class 3 sandstones has undergone melting. This constrains the onset of melting of calcite in the Haughton sandstones to > 10 < 20 GPa. At higher pressures, the original texture of the sandstone is lost, which is associated with major development of vesicular SiO2 glass or lechatelierite. Class 5 rocks (>30 GPa) consist almost entirely of lechatelierite. A new class of shocked sandstones (class 6) consists of SiO2‐rich melt that recrystallized to microcrystalline quartz. Calcite within class 4 to 6 sandstones also underwent melting and is preserved as globules and euhedral crystals within SiO2 phases, demonstrating the importance of impact melting, and not decomposition, in these CaCO3‐bearing sandstones.

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Applications of twin analysis to studying meteorite impact structures

Cited by 14 publications

References 42 publications

Subsurface deformation of experimental hypervelocity impacts in quartzite and marble targets

Subsurface deformation of experimental hypervelocity impacts in quartzite and marble targets

The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts

Impact metamorphism of CaCO₃‐bearing sandstones at the Haughton structure, Canada

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Applications of twin analysis to studying meteorite impact structures

Cited by 14 publications

References 42 publications

Subsurface deformation of experimental hypervelocity impacts in quartzite and marble targets

Subsurface deformation of experimental hypervelocity impacts in quartzite and marble targets

The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts

Impact metamorphism of CaCO3‐bearing sandstones at the Haughton structure, Canada

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Impact metamorphism of CaCO₃‐bearing sandstones at the Haughton structure, Canada