Chemically induced fracturing in alkali feldspar     

K. S. Scheidl  A. -K. Schaeffer  E. Petrishcheva  G. Habler  F. D. Fischer  J. Schreuer  R. Abart 《Physics and Chemistry of Minerals》2014,41(1):1-16

Fracturing in alkali feldspar during Na⁺–K⁺ cation exchange with a NaCl–KCl salt melt was studied experimentally. Due to a marked composition dependence of the lattice parameters of alkali feldspar, any composition gradient arising from cation exchange causes coherency stress. If this stress exceeds a critical level fracturing occurs. Experiments were performed on potassium-rich gem-quality alkali feldspars with polished (010) and (001) surfaces. When the feldspar was shifted toward more sodium-rich compositions over more than about 10 mole %, a system of parallel cracks with regular crack spacing formed. The cracks have a general (h0l) orientation and do not correspond to any of the feldspar cleavages. The cracks are rather oriented (sub)-perpendicular to the direction of maximum tensile stress. The critical stress needed to initiate fracturing is about 325 MPa. The critical stress intensity factor for the propagation of mode I cracks, K _Ic, is estimated as 2.30–2.72 MPa m^1/2 (73–86 MPa mm^1/2) from a systematic relation between characteristic crack spacing and coherency stress. An orientation mismatch of 18° between the crack normal and the direction of maximum tensile stress is ascribed to the anisotropy of the longitudinal elastic stiffness which has pronounced maxima in the crack plane and a minimum in the direction of the crack normal.  相似文献   

2021 JGS best paper award and the editors’ choice paper volume 24(1)     

Fischer  Manfred M.  Paez  Antonio  Staufer-Steinnocher  Petra 《Journal of Geographical Systems》2022,24(1):1-4

Journal of Geographical Systems -  相似文献   

An experimental determination of chlorine isotope fractionation in acid systems and applications to volcanic fumaroles     

Z.D. Sharp  T.P. Fischer  M. Halick 《Geochimica et cosmochimica acta》2010,74(1):264-1053

The δ³⁷Cl values of volcanic fumarole gases and bubbling springs were measured from the Central American and the Kurile arcs. Low temperature gas samples from the Central American arc have δ³⁷Cl values generally between −2 and 2‰, whereas high-temperature fumaroles (>100 °C) range from 4 to 12‰, with several outliers. This is in contrast to the high-temperature fumaroles from the Kurile island Kudryavy which have slightly positive δ³⁷Cl values, averaging 0.8‰ (±0.6, 1σ), and from our previous work on Izu and Mariana arc samples in which the δ³⁷Cl values of fumarole and ash samples are similar to each other and negative. Assuming that the source for the high-T Central American fumaroles has typical subduction δ³⁷Cl values (−2.5 to 1‰), then there must be a large Cl isotope fractionation in the near-surface fumarolic system. The most likely fractionation mechanism for the high δ³⁷Cl values is between Cl⁻_aq − HCl(g), but published theoretical fractionation for this pair is only ∼1.5‰, insufficient to explain the large range of values observed in the fumaroles. Three experiments were undertaken in order to identify a process that could cause the wide range of δ³⁷Cl values observed in the high-temperature fumaroles. Results are the following: (1) A sub-boiling equilibration experiment between aqueous chloride and HCl gas had , in agreement with the theoretical calculations. (2) Evaporation of HCl(g) from hydrochloric acid at room temperature had fractionation in the opposite sense, with a . (3) A ‘synthetic fumarole’ gave large positive fractionations up to 9‰, with ³⁷Cl strongly partitioned into the vapor phase. The ‘fumarole’ experiments were made by bubbling dry air through boiling hydrochloric acid in an Erlenmeyer flask, and collecting the evolved HCl(g) in a second ‘downstream’ flask filled with distilled water. This extreme enrichment is likely due to a distillation process in which ³⁷Cl-enriched HCl(g) is stripped from the hydrochloric acid followed by a significant fraction of the light HCl(g) redissolving into the constantly condensing water vapor on the walls of the first flask. This distillation experiment creates a Cl isotope fractionation that is the same order of magnitude as observed in the high-temperature fumaroles in Central America. These results suggest that there must be a H₂O liquid-vapor region in the sub-surface fumarole conduit where light Cl is stripped from the HCl gas as it passes through the fumarole. Similar ³⁷Cl enrichments are expected in fossil epithermal boiling systems.  相似文献   

Time-window-based filtering method for near-surface detection of leakage from geologic carbon sequestration sites     

Lehua Pan  Jennifer L. Lewicki  Curtis M. Oldenburg  Marc L. Fischer 《Environmental Earth Sciences》2010,60(2):359-369

We use process-based modeling techniques to characterize the temporal features of natural biologically controlled surface CO₂ fluxes and the relationships between the assimilation and respiration fluxes. Based on these analyses, we develop a signal-enhancing technique that combines a novel time-window splitting scheme, a simple median filtering, and an appropriate scaling method to detect potential signals of leakage of CO₂ from geologic carbon sequestration sites from within datasets of net near-surface CO₂ flux measurements. The technique can be directly applied to measured data and does not require subjective gap filling or data-smoothing preprocessing. Preliminary application of the new method to flux measurements from a CO₂ shallow-release experiment appears promising for detecting a leakage signal relative to background variability. The leakage index of ±2 was found to span the range of biological variability for various ecosystems as determined by observing CO₂ flux data at various control sites for a number of years.  相似文献