Laboratory simulation of explosive volcanic loading and implications for the cause of the K/T boundary

Gratz, A. J.; Nellis, W. J.; Hinsey, N.

doi:10.1029/92gl01289

Cited by 11 publications

(2 citation statements)

References 26 publications

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“…The model can account for the apparent lack of control that shock propagation direction exerts on the orientation of PDFs (Figure 8) The results of this study also emphasize a critical point regarding mosaicism as a diagnostic indicator of shock damage in silicates. Gratz et al [1992] suggest that their unconfined experiments on granite support the contention that volcanic explosions with peak pressures below 15 GPa cannot generate shock-induced microstructures.…”

Section: Discussionmentioning

confidence: 72%

The microstructural response of quartz and feldspar under shock loading at variable temperatures

Huffman¹,

Brown²,

Carter³

et al. 1993

J. Geophys. Res.

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Shock recovery experiments were carried out on Westerly granite and Hospital Hill quartzite targets in the peak pressure range 8 to 25 GPa, preshock temperatures of 25 ø, 450 ø, and 750øC and pulse durations of 2 to 7 gs using internally heated momentum traps and explosive plane wave generators. Optical and transmission electron microscopy analyses of quartz and feldspar shocked at 25øC revealed the previously documented progression, with increasing pressure: (1) fracturing; (2) planar fractures and shock mosaicism; (3) shock mosaicism and planar deformation features (PDFs); and (4) isotropization. This same sequence is observed for experiments at elevated preshock temperature but with specific microstructures occurring at lower pressures than those in previous experiments at room temperature. At 750øC, strong shock mosaicism, partially thermally recovered, is characteristic of feldspar shocked to 8 GPa, whereas 15 GPa is required for its development in quartz and for the generation of PDFs in both minerals. The results suggest that threshold pressures for formation of the various microstructures and phases are expected to vary systematically as a function of the preshock temperature of the target material. We suggest that PDFs are generated in the shock transition by progressive, heterogeneous, phase transformation of the crystal structure to form dense glass or high pressure polymorphs. The onset pressures for PDFs in specific crystallographic orientations is not influenced strongly by temperature, but the character of the PDFs does change as preshock temperature is increased at the same peak shock stress. The change from multiple sets of thin PDFs at low temperature to thicker single sets of PDFs at moderate temperature, and finally to complete isotropization at high tempera tures, reflects a change in the phase transformation mechanism as a function of temperature. In contrast, development of shock mosaicism in quartz and feldspar occurs throughout the duration of shock loading and is better developed at elevated temperatures where the kinetics are enhanced by the additional thermal energy in the target. crostructures in known volcanic rocks, diatremes, and landslides [Carter et al., 1990; Officer and Carter, 1991] and the apparent differences between these features and classic impactinduced microstructures [Alexopoulos eta/., 1988] indicates that the endogenous microstructures, if of a legitimate shock origin, must be generated in an environment that is quite different from impact. Microstructural data from recent shock recovery experiments on Hospital Hill quartzite and Westerly granite [Reimold and Hiirz, 1986a, b; Huffman et al., 1990] and single crystal quartz [Langenhorst et al., 1992; Gratz et al., ] indicate that preshock temperature may be of fundamental importance to the character of high-strain-rate microstructures at specific peak shock pressures. These observations then raise the question as to what other parameters might influence microstructural development in the dynamic range. Temperature, st...

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Section: Discussionmentioning

confidence: 72%

The microstructural response of quartz and feldspar under shock loading at variable temperatures

Huffman¹,

Brown²,

Carter³

et al. 1993

J. Geophys. Res.

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“…Similarly, there is no physical basis for the production of strong shock waves by volcanic explosions. Volcanic "explosions" are sustained decompression events (de Silva et al, 1990;Gratz et al, 1992b), with maximum overpressures of <0.5 GPa (Self et al, 1979;Wilson et al, 1980). Considering the totally different physical conditions in volcanic explosions, it is unrealistic to assume that volcanic explosions could produce isotropic lamellae, such as PDFs.…”

Section: Comparison Of Shock-metamorphosed and Endogenically Deformedmentioning

confidence: 99%

Shock metamorphism of quartz in nature and experiment: II. Significance in geoscience*

Grieve

Langenhorst

Stöffler

1996

Meteorit & Planetary Scien

353

440

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Abstract— The occurrence of shock metamorphosed quartz is the most common petrographic criterion for the identification of terrestrial impact structures and lithologies. Its utility is due to its almost ubiquitous occurrence in terrestrial rocks, its overall stability and the fact that a variety of shock metamorphic effects, occurring over a range of shock pressures, have been well documented. These shock effects have been generally duplicated in shock recovery experiments and, thus, serve as shock pressure barometers. After reviewing the general character of shock effects in quartz, the differences between experimental and natural shock events and their potential effects on the shock metamorphism of quartz are explored. The short pulse lengths in experiments may account for the difficulty in synthesizing the high‐pressure polymorphs, coesite and stishovite, compared to natural occurrences. In addition, post‐shock thermal effects are possible in natural events, which can affect shock altered physical properties, such as refractive index, and cause annealing of shock damage and recrystallization. The orientations of planar microstructures, however, are unaffected by post‐impact thermal events, except if quartz is recrystallized, and provide the best natural shock barometer in terms of utility and occurrence. The nature of planar microstructures, particularly planar deformation features (PDFs), is discussed in some detail and a scheme of variations in orientations with shock pressure is provided. The effect of post‐impact events on PDFs is generally limited to annealing of the original glass lamellae to produce decorated PDFs, resulting from the exsolution of dissolved water during recrystallization. Basal (0001) PDFs differ from other PDF orientations in that they are multiple, mechanical Brazil twins, which are difficult to detect if not partially annealed and decorated. The occurrence and significance of shock metamorphosed quartz and its other phases (namely, coesite, stishovite, diaplectic glass and lechatelierite) are discussed for terrestrial impact structures in both crystalline (non‐porous) and sedimentary (porous) targets. The bulk of past studies have dealt with crystalline targets, where variations in recorded shock pressure in quartz have been used to constrain aspects of the cratering process and to estimate crater dimensions at eroded structures. In sedimentary targets, the effect of pore space results in an inhomogeneous distribution in recorded shock pressure and temperature, which requires a different classification scheme for the variation of recorded shock compared to that in crystalline targets. This is discussed, along with examples of variations in the relative abundances of planar microstructures and their orientations, which are attributed to textural variations in sedimentary target rocks. Examples of the shock metamorphism of quartz in distal ejecta, such as at the K/T boundary, and from nuclear explosions are illustrated and are equivalent to that of known impact structures, except with ...

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Multiple factors in the origin of the Cretaceous/Tertiary boundary: the role of environmental stress and Deccan Trap volcanism

Glasby

Kunzendorf²

1996

Geol Rundsch

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A review of the scenarios for the Cretaceous/ Tertiary (K/T) boundary event is presented and a coherent hypothesis for the origin of the event is formulated. Many scientists now accept that the event was caused by a meteorite impact at Chicxulub in the Yucatan Peninsula, Mexico. Our investigations show that the oceans were already stressed by the end of the Late Cretaceous as a result of the long-term drop in atmospheric CO2, the long-term drop in sea level and the frequent development of oceanic anoxia. Extinction of some marine species was already occurring several million years prior to the K/T boundary. The biota were therefore susceptible to change. The eruption of the Deccan Traps, which began at 66.2 Ma, coincides with the K/T boundary events. It erupted huge quantities of H2SO4, HCl, CO2, dust and soot into the atmosphere and led to a significant drop in sea level and marked changes in ocean temperature. The result was a major reduction in oceanic productivity and the creation of an almost dead ocean. The volcanism lasted almost 0.7 m.y. Extinction of biological species was graded and appeared to correlate with the main eruptive events. Elements such as Ir were incorporated into the volcanic ash, possibly on soot particles. This horizon accumulated under anoxic conditions in local depressions and became the marker horizon for the K/T boundary. An oxidation front penetrated this horizon leading to the redistribution of elements. The eruption of the Deccan Traps is the largest volcanic event since the Permian-Triassic event at 245 Ma. It followed a period of 36 m.y. in which the earth's magnetic field failed to reverse. Instabilities in the mantle are thought to be responsible for this eruption and therefore for the K/T event. We therefore believe that the K/T event can be explained in terms of the effects of the Deccan volcanism on an already stressed biosphere. The meteorite impact at Chicxulub took place after the onset of Deccan volcanism. It probably played a regional, rather than global, role in the K/T extinction.

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Laboratory simulation of explosive volcanic loading and implications for the cause of the K/T boundary

Cited by 11 publications

References 26 publications

The microstructural response of quartz and feldspar under shock loading at variable temperatures

The microstructural response of quartz and feldspar under shock loading at variable temperatures

Shock metamorphism of quartz in nature and experiment: II. Significance in geoscience*

Multiple factors in the origin of the Cretaceous/Tertiary boundary: the role of environmental stress and Deccan Trap volcanism

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