Shock metamorphism of quartz with initial temperatures −170 to + 1000° C     

A. J. Gratz  W. J. Nellis  J. M. Christie  W. Brocious  J. Swegle  P. Cordier 《Physics and Chemistry of Minerals》1992,19(5):267-288

Shock experiments on quartz single crystals with initial temperatures –170 to +1000°C showed that ambient temperature does not affect the type of defects formed but can lower the pressure of complete amorphization. The amount of glass recovered increases with both pressure and temperature, and the shock-induced phase transformation of quartz is temperature-activated with an apparent activation energy of <60 kj/=" mol.=" the=" phase=" transformation=" is=" localized=" along=" three=" types=" of=" transformation=" lamellae=" (narrow,=" s-shaped,=" and=" wide)=" which=" contain=" fractured=" and/or=" high-pressure=" phases.=" transformation=" lamellae=" are=" inferred=" to=" form=" by=" motion=" of=" linear=" collapse=" zones=" propagating=" near=" the=" shock=" front.=" equilibrium=" phases,=" such=" as=" stishovite,=" were=" not=" recovered=" and=" are=" probably=" not=" formed=" at=" high=" shock=" pressures:=" the=" dominant=" transformation=" mechanism=" is=" inferred=" to=" be=" solid-state=" collapse=" to=" a=" dense,=" disordered=" phase.=" melting=" occurs=" separately=" by=" friction=" along=" microfaults,=" but=" no=" high-pressure=" crystal=" phases=" are=" quenched=" in=" these=" zones.=" shock=" of=" quartz=" thus=" produces=" two=" types=" of=" disordered=" material,=" quenched=" melt=" (along=" microfaults)=" and=" diaplectic=" glass=" (in=" transformation=" lamellae);=" the=" quenched=" melt=" expands=" during=" p-t=" release,=" leaving=" it=" with=" a=" density=" lower=" than=" quartz,=" while=" recovered=" diaplectic=" glass=" has=" a=" density=" closer=" to=" that=" of=" quartz.=" at=" low=" pressures=">< 15=" gpa),=" quartz=" transforms=" mostly=" by=" shear=" melting,=" while=" at=" higher=" pressures=" it=" converts=" mostly=" along=" transformation=" lamellae.=" we=" find=" that=" shock=" paleopiezometers=" using=" microstructures=" are=" nominally=" temperature-invariant,=" so=" that=" features=" observed=" at=" impact=" craters=" and=" the=" k/t=" boundary=" require=" in=" excess=" of=" 10=" gpa=" to=" form,=" regardless=" of=" the=" target=" temperature.=" shock=" comminution=" will=" be=" much=" more=" extensive=" for=" impacts=" on=" cold=" surfaces=" due=" to=" lack=" of=" cementation=" of=" fragments=" by=" melt=" glass;=" shock=" on=" hot=" surfaces=" could=" produce=" much=" more=" glass=" than=" estimated=" from=" room-temperature=" experiments.=" because=" of=" the=" shock-impedance=" mismatch=" between=" quartz=" specimen=" and=" steel=" capsule,=" the=" incident=" shock=" wave=" reverberates=" up=" to=" a=" final=" pressure.=" the=" dynamic=" compression=" process=" is=" quasi-isentropic=" with=" high=" strain=" rates.=" preheating=" and=" precooling=" achieves=" final=" shock=" pressures=" and=" temperatures=" representative=" of=" single-shock=" states=" of=" room=" temperature=" quartz=" and=" of=" quartz=" on=" known=" planetary=" surfaces.=" stress=" histories=" were=" calculated=" by=" detailed=" 1-=" and=" 2-dimensional=" computer=" simulations.=" the=" stress=" history=" throughout=" the=" sample=" is=" relatively=" uniform,=" with=" minor=" variations=" during=" unloading.=" significant=" differences=" between=" impact=" pressures=" calculated=" by=" the=" shock-impedance-match=" method=" and=" specimen=" pressures=" calculated=" by=" computer=" simulations=" indicate=" the=" importance=" of=" modeling=" shock=" recovery=" experiments=">  相似文献   

Morphology and tectonics of the Australian-Antarctic Discordance between 123° E and 128° E     

Jeb Palmer  Jean-Christophe Sempéré  David M. Christie  Jason Phipps Morgan 《Marine Geophysical Researches》1993,15(2):121-152

The Australian-Antarctic Discordance (AAD) is an anomalously deep and rugged zone of the Southeast Indian Ridge (SEIR) between 120° E and 128° E. The AAD contains the boundary between the Indian Ocean and Pacific Ocean isotopic provinces. We have analyzed SeaMarc II bathymetric and sidescan sonar data along the SEIR between 123° E and 128° E. The spreading center in the AAD, previously known to be divided into several transform-bounded sections, is further segmented by nontransform discontinuities which separate distinct spreading cells. Near the transform which bounds the AAD to the east, there is a marked change in the morphology of the spreading center, as well as in virtually every measured geochemical parameter. The spreading axis within the Discordance lies in a prominent rift valley similar to that observed along the Mid-Atlantic Ridge, although the full spreading rate within the AAD is somewhat faster than that of slow-spreading centers (~ 74 mm a^–1 vs. 0–40 mm a^–1). The AAD rift valleys show a marked contrast with the axial high that characterizes the SEIR east of the AAD. This change in axial morphology is coincident with a large (~ 1 km) deepening of the spreading axis. The segmentation characteristics of the AAD are analogous to those of the slow-spreading Mid-Atlantic Ridge, as opposed to the SEIR east of the AAD, which exhibits segmentation characteristics typical of fast-spreading centers. Thus, the spreading center within and east of the AAD contains much of the range of global variability in accretionary processes, yet it is a region free from spreading rate variations and the volumetric and chemical influences of hotspots. We suggest that the axial morphology and segmentation characteristics of the AAD spreading centers are the result of the presence of cooler than normal mantle. The presence of a cool mantle and the subsequent diminution of magma supply at a constant spreading rate may engender the creation of anomalously thick brittle lithosphere within the AAD, a condition which favor, the creation of an axial rift valley and of thin oceanic crust, in agreement with petrologic studies. The morphologies of transform and non-transform discontinuities within the Discordance also possess characteristics consistent with the creation of anomalously thick lithosphere in the region. The upper mantle viscosity structure which results from lower mantle temperatures and melt production rates may account for the similarity in segmentation characteristics between the AAD and slow-spreading centers. The section of the AAD which overlies the isotopic boundary is associated with chaotic seafloor which may be caused by an erratic pattern of magmatism and/or complex deformation associated with mantle convergence. Finally, the pattern of abyssal hill terrain within a portion of the AAD supports previous models for the formation of abyssal hills at intermediate- and slow-spreading ridges, and provides insights into how asymmetric spreading is achieved in this region.  相似文献   

Petrologic consequences of rift propagation on oceanic spreading ridges     

John M. Sinton  Douglas S. Wilson  David M. Christie  Richard N. Hey  John R. Delaney 《Earth and Planetary Science Letters》1983,62(2):193-207

The production of anomalously differentiated lava compositions at several mid-ocean spreading centers can be attributed to magmatic processes associated with propagating rifts. The degree of differentiation attained by magmas beneath oceanic spreading ridges depends mainly on the balance between cooling rate and the supply rate of new magma to shallow chambers. Low supply rates and moderate cooling rates allow advanced degrees of closed-system fractionation to occur. High supply rates result in open systems in which magma compositions are buffered by frequent replenishment with new hot magma. Propagating rift tips are a special class of ridge-transform intersection in which the balance between cooling and supply rates is conducive to the development of advanced degrees of differentiation over an expanded length of ridge. This balance is affected by the spreading rate, the propagation rate of the rift, the length of the bounding transform and proximity to hotspots. Maximum compositional variability and maximum degree of differentiation occur within 50 km of propagating rift tips and subsequently diminish with increasing distance. Rifts that propagate through plates in directions approximating their absolute motion relative to the lower mantle are characterized by the presence of anomalously differentiated lavas over longer ridge segments than are rifts that propagate against their absolute motion. Geochemical anomalies may persist, though changing in degree and extent, for several million years on ridge segments that stop propagating. The concept of “magnetic telechemistry” is generally supported by our study, but in the vicinity of hotspots, magnetic anomaly amplitude may be controlled more by bathymetric and/or thickened magnetic layer effects than by geochemistry.  相似文献   

Chemical etching of deformation sub-structures in quartz     

M. W. Wegner  J. M. Christie 《Physics and Chemistry of Minerals》1983,9(2):67-78

Chemical etching of dislocations has been studied in natural and synthetic quartz single crystals, in deformed synthetic quartz and in naturally and experimentally deformed quartzites. The ability of different etchants to produce polished or preferentially etched surfaces on quartz is described. Dislocation etching was achieved on all crystal planes examined by using a saturated solution of ammonium bifluoride as the etchant. Appropriate etching times were determined for etching quartzites for grain size, subgrain boundaries, deformation lamellae, dislocations and twins. Growth and polished surfaces of synthetic single crystal quartz were similarly etched and dislocation etch pits, characteristic of various orientations were found. The use of ammonium bifluoride proved to be expecially advantageous for the basal plane, producing a polished surface with etch pits, suitable for dislocation etch pit counting. “Double” etch pits have been found on Dauphiné twin boundaries on the basal plane and the first order prism, using this etchant. Slip lines and deformation bands were suitably etched on deformed synthetic crystal surfaces for identification of the slip planes. Other acidic etchants have been explored and their application to the study of deformation structures in quartz crystals is discussed.  相似文献   

Exsolution in terrestrial and lunar plagioclases revealed by chemical etching     

M. W. Wegner  R. E. Jones  J. M. Christie 《Contributions to Mineralogy and Petrology》1978,65(3):283-291

A new chemical etching technique reveals fine scale exsolution structures on polished surfaces of plagioclases in the bytownite and labradorite range. A very obvious blue and locally brown stain is produced (by the action of citric acid) in growth zones of a restricted range of compositions on etched surfaces. The blue-stained zones contain very fine grooves, corresponding to the traces of thin exsolution lamellae. Exsolution features have been revealed in this way in plagioclases in a terrestrial diabase, lunar basalts and an amphibolite. Compositions of the exsolved areas found by microprobe analysis represent averages of the matrix and exsolution lamellae. Analytical methods with higher spatial resolution are required to determine the composition of the lamellae. This etching method permits easy optical identification of compositional zoning and of fine scale exsolution over relatively large areas and is therefore complementary to other techniques.  相似文献   

Preferential chemical etching of terrestrial And lunar olivines     

M. W. Wegner  J. M. Christie 《Contributions to Mineralogy and Petrology》1974,43(3):195-212

A new chemical etching technique has been developed to study defect structures in terrestrial and lunar olivine crystals. Dislocations, low-angle dislocation boundaries, dislocation arrays and pile-ups have been observed on the (010, (100), and (001) faces of both polished and cleaved naturally deformed single crystal olivine, on various orientations of crystals in dunite, and in an experimentally deformed olivine crystal. Etching of Apollo 12 igneous rocks revealed dislocations and radiation damage tracks in lunar olivine. Dislocation etching of the (001) face of olivine is reported for the first time in this paper.  相似文献   

Chemical etching of dislocations in forsterite     

M. W. Wegner  J. M. Christie 《Contributions to Mineralogy and Petrology》1976,59(2):131-140

Chemical etching of pure melt-grown forsterite crystals is reported here for the first time. Cleaved forsterite crystals of known purity, and polished sections of the same crystals have been successfully etched revealing dislocations, subgrain boundaries, inclusions and growth imperfections.  相似文献   

Comparison of quartz microfabric with strain in recrystallized quartzite     

David M. Miller  John M. Christie 《Journal of Structural Geology》1981,3(2):129-141

The relationship between quartz c-axis microfabric and strain is examined in six specimens of recrystallized quartzite conglomerate in which strain was measured using pebble shapes. Four rocks subjected to plane strain display a direct relationship between the strength of preferred orientation and the strain intensity. The c-axis distributions in these rocks, as well as a rock subjected to moderate extensional strain, are crossed-girdles with maxima near the intermediate principal strain axis and connecting girdles at acute angles to the direction of maximum shortening. A rock subjected to moderate flattening strain has several maxima clustered near the direction of maximum shortening and a weak connecting girdle through the intermediate principal strain axis.These results are generally similar to those of other studies comparing strain and tectonite fabrics and also with experimental and computer simulation studies of fabrics. The degree of preferred orientation is related to total strain, and therefore microfabrics in quartzites may be cautiously interpreted as qualitative indicators of strain intensity. Uncertainties are greater, however, for correlations of fabric patterns with shapes of the strain ellipsoid. An observed increase in recrystallized grain sizes with increasing strain suggests that flow stress was lower in the more strained rocks.  相似文献   

The effects of water vapour and oxides of nitrogen on ozone and temperature structure of the stratosphere     

Krishna Rao  V. R.  Christie  A. D. 《Pure and Applied Geophysics》1973,106(1):1498-1519

Summary A steady-state mean meridional model of the stratosphere is used to investigate the effects of water vapour and nitrogen oxides on ozone and temperature distributions in the stratosphere. The Chapman classical photochemical scheme for ozone is extended to include the dominant reactions involving hydrogen compounds and nitrogen oxides. The ozone and temperature changes are studied under radiative-photochemical equilibrium conditions and in a model incorporating both transport and radiative-photochemical processes. It is found that both hydrogen and nitrogen reactions contribute to substantial decreases in ozone and temperature under photochemical equilibrium conditions, but the computed distribution do not resemble those observed. The effect of transport processes is to reduce the deviations in the ozone mixing ratio and temperature with the computed distributions having many features in common with the observations. It is found that the ozone and temperature respond more readily to the arbitrary increase of nitrogen oxides than to that of water vapour.  相似文献   

Shock Metamorphism of Deformed Quartz     

Andrew J. Gratz  James Tyburczy  John Christie  Thomas Ahrens  Peter Pongratz 《Physics and Chemistry of Minerals》1988,16(3):221-233

Deformed, synthetic quartz containing a dislocation density of 2.9 ± 1.9 × 10⁸/cm² and abundant bubbles and small inclusions was shocked to peak pressures of 12 and 24 GPa. The resultant material was inhomogeneously deformed and extremely fractured. The 12 GPa sample contained large regions lacking apparent shock deformation, suggesting that the original microstructure of a quartz target may be distinguished in low-stress shocks with minimal annealing. No change in dislocation density was caused by shock loading except in regions containing shock lamellae, where the dislocation density was lowered. Generally the same types of microstructures were induced by shock of deformed quartz as by shock of relatively defect-free as-grown crystals. Glass-filled veins were abundant, especially at lower stresses, and contained angular fragments of quartz welded together. Microfaults formed on \({{\{ 10\bar 11\} } \mathord{\left/ {\vphantom {{\{ 10\bar 11\} } {\{ 01\bar 11\} }}} \right. \kern-0em} {\{ 01\bar 11\} }}\) and \({{\{ 11\bar 22\} } \mathord{\left/ {\vphantom {{\{ 11\bar 22\} } {\{ 1\bar 212\} }}} \right. \kern-0em} {\{ 1\bar 212\} }}\) , inclined close to 45° to the shock propagation direction. Curviplanar features occurred in groups, with contrast indicating Moiré patterns, twins, and stacking faults or related structures; most were interpreted as fractures, possibly welded together with glass. Regions containing shock lamellae sets were present. Lamellae sets were uncommon at 12 GPa, but distributed every few microns at 24 GPa. Lamellae occurred in a spectrum of habits ranging from 35–1500 Å in thickness, from 35 Å upward in spacing, and from closely-packed parallel sets to networks of diverse orientations; some lamellae were not parallel-sided, but wedge-shaped with basal and \({{\{ 10\bar 13\} } \mathord{\left/ {\vphantom {{\{ 10\bar 13\} } {\{ 01\bar 13\} }}} \right. \kern-0em} {\{ 01\bar 13\} }}\) edges, Thick lamellae were connected to glassy veins, and the wedge-shaped type generally narrowed away from veins; they also subdivided and merged along their length. Lamellae were dominantly basal at 12 GPa, and at 24 GPa on \({{\{ 10\bar 12\} } \mathord{\left/ {\vphantom {{\{ 10\bar 12\} } {\{ 01\bar 12\} }}} \right. \kern-0em} {\{ 01\bar 12\} }}\) , with poles normal to the shock direction. We propose that they are not shear features, but rather glass-filled tensile fractures. Vitrification was widespread, especially at 24 GPa, apparently more so than in shock of as-grown material. This suggests that index of refraction is not an appropriate shock paleopiezometer, as it depends on the defect structure of the starting material. Neither lamella width nor spacing was correlated with shock stress; however, the criterion of multiple glass lamellae sets as indications of shock deformation and its intensity are consistent with our measurements. Dislocation density was lowered in lamellae-containing and glassy areas, possibly removed by nucleation of and absorption by lamellae. No high-pressure phases were observed. Based on the complete set of observed features, it appears that shock deformation in quartz is primarily brittle-melt deformation, with an important role played by hot, fluid silica.  相似文献