Role of melt during deformation in the deep crust   总被引：1，自引：0，他引：1  

Cameron Davidson  Stefan M. Schmid  Lincoln S. Hollister 《地学学报》1994,6(2):133-142

Deformation in the deep crust is strongly influenced by the presence of melt. Injected melt (or magma) weakens the crust because strain will tend to localize where melt is present. The amount of strain a pluton may accommodate is dependent on the length of time it takes for a pluton to crystallize and the strain rate. For plutons that intrude into rocks which are near the solidus temperature of the melt, crystallization times can be quite long (> 1Myr).
Partial melting of deep crustal rocks can lead to melt-enhanced embrittlement. This occurs because the volume change for most melting reactions is positive. Therefore, when the rate of melt production outpaces the rate at which melt can leave the system, the melt pressure increases. Eventually, the melt pressure may become sufficiently high that the melting rocks behave in a brittle fashion and fracture.
Conjugate sets of dilatant shear fractures filled with melt occur in migmatite from the Central Gneiss belt (Canada); this suggests that melt-enhanced embrittlement occurred in these rocks. An expression which relates the magnitude of differential stress to the angle between conjugate dilatant shear fractures is derived. Assuming that migmatite has a small tensile strength, differential stresses are ≤ 20 MPa in migmatitic rocks at the time melt-enhanced embrittlement occurs. The occurrence of melt-enhanced embrittlement shows that a switch in deformation mechanism from plastic flow to cataclasis is possible in the deep crust during melting. Furthermore, repeated episodes of melt-enhanced embrittlement in migmatitic rocks may be an efficient mechanism for extracting melt from partially melted terrains.  相似文献   

Phase relationships in granulitic metapelites from the Ivrea-Verbano zone (Northern Italy)     

R. Schmid  B. J. Wood 《Contributions to Mineralogy and Petrology》1976,54(4):255-279

Paragneisses of the Ivrea-Verbano zone exhibit over a horizontal distance of 5 km mineralogical changes indicative of the transition from amphibolite to granulite facies metamorphism. The most obvious change is the progressive replacement of biotite by garnet via the reaction: a $${\text{Biotite + sillimanite + quartz }} \to {\text{ Garnet + K - feldspar + H}}_{\text{2}} {\text{O}}$$ which results in a systematic increase in the modal ratio g = (garnet)/(garnet + biotite) with increasing grade. The systematic variations in garnet and biotite contents of metapelites are also reflected by the compositions of these phases, both of which become more magnesian with increasing metamorphic grade. The pressure of metamorphism has been estimated from the Ca₃Al₂Si₃O₁₂ contents of garnets coexisting with plagioclase, sillimanite and quartz. These phases are related by the equilibrium: b $$\begin{gathered} 3 CaAl_2 {\text{Si}}_{\text{2}} {\text{O}}_{\text{8}} \rightleftharpoons Ca_3 Al_2 {\text{Si}}_{\text{3}} {\text{O}}_{{\text{12}}} + 2 Al_2 {\text{SiO}}_{\text{5}} + {\text{SiO}}_{\text{2}} \hfill \\ plagioclase garnet sillimanite quartz \hfill \\ \end{gathered} $$ which has been applied to these rocks using the available data on the mixing properties of plagioclase and garnet solid solutions. Temperature and f _{H 2O} estimates have been made in a similar way using thermodynamic data on the biotite-garnet reaction (a) and the approximate solidus temperatures of paragneisses. Amphibolite to granulite facies metamorphism in the Ivrea-Verbano zone took place in the P-T ranges 9–11 kb and 700–820 °C. The differences in temperature and pressure of metamorphism between g= 0 and g = 1 (5 kms horizontal distance) were less than 50° C and approximately 1 kb. Retrogression and re-equilibration of garnets and biotites in the metapelites extended to temperatures more than 50° C below and pressures more than 1.5 kb below the peak of metamorphism, the degree of retrogression increasing with decreasing grade of the metamorphic “peak”. The pressure and temperature of the peak of metamorphism are not inconsistent with the hypothesis that the Ivrea-Verbano zone is a slice of upthrusted lower crust from the crust-mantle transition region, although it appears that the thermal gradient was too low for the zone to represent a near-vertical section through the crust. The most reasonable explanation of the granulite facies metamorphism is that it arose through intrusion of mafic rocks into a region already undergoing recrystallisation under amphibolite facies conditions.  相似文献   

Descriptive nomenclature and classification of pyroclastic deposits and fragments     

Priv.doz. Dr. R. Schmid 《International Journal of Earth Sciences》1981,70(2):794-799

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Plan for the swiss randomized hail suppression experiment. Design of Grossversuch IV     

B. Federer  A. Waldvogel  W. Schmid  F. Hampel  E. Rosini  D. Vento  P. Admirat  J. F. Mezeix 《Pure and Applied Geophysics》1978,117(3):548-571

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Activity-composition relationships for pyrope-grossular garnet   总被引：1，自引：0，他引：1  

B. J. Hensen  R. Schmid  B. J. Wood 《Contributions to Mineralogy and Petrology》1975,51(3):161-166

Activity coefficients () for grossular in pyrope-grossular garnet have been determined experimentally using the divariant assemblage garnet-anorthite-sillimanite (kyanite)-quartz. Values of for garnets with 10–12 mole % grossular have been obtained at 1000 °, 1100 °, 1200 ° and 1300 ° C at pressures between 15 and 21 Kb. The data are consistent with a symmetrical regular solid model for grossular-pyrope solid solutions. The interaction parameter (W) increases linearly with decreasing temperature and is given by W = 7460-4.3 T cals (T in °K). A solvus in the pyrope-grossular solid solution is predicted with a temperature of critical mixing of 629°C±90 ° C.  相似文献   

Plio-Pleistocene transpressional reactivation of Paleozoic and Paleogene structures in the Rhine-Bresse transform zone (northern Switzerland and eastern France)     

M.?GiamboniEmail author  K.?Ustaszewski  S.?M.?Schmid  M.?E.?Schumacher  A.?Wetzel 《International Journal of Earth Sciences》2004,93(2):207-223

Pliocene to recent uplift and shortening in the southern Rhinegraben is documented by deformation of Pliocene fluvial gravels, deposited on a nearly planar surface, as well as by progressive deflection and capture of rivers. This deformation is suggested to result from thick-skinned tectonic movements as evidenced by observations on seismic records, which demonstrate a spatial coincidence between en-échelon anticlines at the surface and faults located in the crystalline basement. These findings contradict the often invoked thin-skinned tectonism in the recent tectonic history of the Rhinegraben. In particular the transfer zone between the Rhinegraben and the Bressegraben is very suitable for reactivation under the present day stress field. Thick-skinned reactivation of faults in the basement is also expressed by focal plane mechanisms of recent earthquakes showing strike-slip- rather than reverse faulting characteristics. This is of importance for the densely populated and industrialised southern Rhinegraben, previously affected by large earthquakes in historical times (e.g. Basel 1356).  相似文献   

Estimation of elevation-dependent satellite antenna phase center variations of GPS satellites   总被引：16，自引：7，他引：9  

R. Schmid  M. Rothacher 《Journal of Geodesy》2003,77(7-8):440-446

A method for the estimation of the phase center variations of GPS satellite antennas using global GPS data is presented. First estimations have shown an encouraging repeatability from day to day and between satellites of the same block. Thus, two different satellite antenna patterns for Block II/IIA and for Block IIR with a range of about 4 cm and an accuracy of less than 1 mm could be found. The present approach allows the creation of a consistent set of receiver and satellite antenna patterns and phase center offsets. Thereby, it is possible to switch from relative to absolute phase center variations without a scale problem in global networks. This changeover has an influence on troposphere parameters, reduces systematic effects due to uncorrect antenna modeling and should diminish the elevation dependence of GPS results. AcknowledgmentsThe authors thank Prof. G. Seeber (University of Hannover) and Dr. G. Wübbena (Geo++ GmbH) and their groups for their kindness in making available the absolute field calibration results derived from robot measurements.  相似文献   

Reef development on a deepening platform: two Early Cretaceous coralgal patch reefs (Catí, Llàcova Formation, eastern Spain) compared     

Stefan Gtz  Hannes Lser  Dieter U. Schmid 《Cretaceous Research》2005,26(6):864-881

Two coralgal patch reefs of the Hauterivian Llàcova Formation (Maestrat Basin, eastern Spain), exposed at two consecutive stratigraphic levels within a single section, have been studied to document taxonomic implications of a changing environment. These two reefal palaeocommunities differ substantially in coral taxonomic composition, microbialite formation pattern and in abundance and composition of encrusters and bioeroders. Of a total of 14 coral species, just one (Stylina parvistella) occurs in both reefs, yet is abundant in the (lower) reef A and rare, occurring near the reef base, in the reef B assemblage. Reef A is dominated by a phototrophic fauna and coral species with small corallites and imperforate septa (a stylinid-thamnasteriid-heterocoeniid-actinastreid association), along with an encruster association dominated by Bacinella and Lithocodium. Reef B is characterised by a balanced phototrophic-heterotrophic fauna that gradually passes into a heterotrophic-dominated assemblage. During this latest growth stage, microsolenid corals dominated the assemblage. The encruster fauna is characterised by sponges, polychaetes and bryozoans. Moderate deepening during a transgressive systems tract (TST) depositional sequence and elevated nutrient supply are interpreted to represent the driving environmental parameters that caused faunal compositions to differ between these two reefal palaeocommunities. Nine coral taxa, previously known only from younger (Barremian–Cenomanian) strata, have been identified, namely Dimorphocoenia? rudis, Eocomoseris raueni, Eocomoseris sp., Holocoenia jaccardi, Latusastrea irregularis, Mesomorpha sp., Microsolena kugleri, Polyphylloseris mammillata and Polyphylloseris sp. This observation emphasises the importance of the Hauterivian Stage as a period of evolutionary transition in Late Jurassic–Cretaceous coral faunas.  相似文献   

The EUCOR-URGENT Project     

J. H. Behrmann  P. A. Ziegler  S. M. Schmid  B. Heck  M. Granet 《International Journal of Earth Sciences》2005,94(4):505-506

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Electrokinetic remediation of an electroplating site: design and scale-up for an in-situ application in the unsaturated zone   总被引：1，自引：0，他引：1  

S. Wieczorek  H. Weigand  M. Schmid  C. Marb   《Engineering Geology》2005,77(3-4):203-215

In-situ electrokinetic remediation of contaminated soils requires integrated approaches and adequately engineered setups to control relevant mass fluxes. Based on laboratory findings, this study presents the design of a pilot-scale remediation at an operating electroplating site. The fine-textured soil developed from Jurassic limestone exhibits a chromium, copper, nickel, and zinc contamination down to depths of more than 4 m. The feasibility of an electrokinetic remediation in the unsaturated zone was tested in a lab-scale experiment with subsoil material sampled at the site. The electrodes were placed in water-impermeable, ion-selective membrane wells. This construction allows the necessary watering of the electrodes, maintains unsaturated conditions in the soil compartment, and enables the transfer of contaminant ions into the wells. In addition, the soil is protected from pH changes caused by water electrolysis at the electrodes. The setup includes a watering and drainage system to compensate the electroosmotic water flux and impede desiccation of the anodic region. With a direct current of 70 V and an electric field strength of 2.2 V cm⁻¹, contaminant removal rates amounted up to 27% and 66% (w/w) of the initial zinc/copper and chromium/nickel concentrations. Copper, nickel, and zinc accumulated in the cathode well, while chromate species were enriched in the anode well. Given the successful lab-scale remediation, the pilot plant was designed for the in-situ treatment of a soil volume of 12 m³ below a production hall. A power of 500 V DC at a maximum current of 30 A is supplied by a transformer rectifier. This yields an electric field strength comparable to the lab-scale experiment and thereby similar contaminant transport velocities. A vacuum distillation unit is employed for process water reuse and to control electrolyte conductivity. To cope with chlorine gas generation at the anodes a gas absorber unit is employed. According to the lab-scale results, about 2, 9, 9, and 15 kg zinc, chromium, copper, and nickel, respectively, are expected to be removed from the field plot during an operation time of 10 months.  相似文献