• Effect of mineralogy on friction-dilation relationships for simulated faults: Implications for permeability evolution in caprock faults

      Zhang, Fengshou; An, Mengke; Zhang, Lianyang; Fang, Yi; Elsworth, Derek; Univ Arizona, Dept Civil & Architectural Engn & Mech (CHINA UNIV GEOSCIENCES, BEIJING, 2020-03)
      This paper experimentally explores the frictional sliding behavior of two simulated gouges: one, a series of quartz-smectite mixtures, and the other, powdered natural rocks, aiming to evaluate and codify the effect of mineralogy on gouge dilation and frictional strength, stability, and healing. Specifically, velocity-stepping and slide-hold-slide experiments were performed in a double direct shear configuration to analyze frictional constitutive parameters at room temperature, under normal stresses of 10, 20, and 40 MPa. Gouge dilation was measured based on the applied step-wise changes in shear velocity. The frictional response of the quartz-smectite mixtures and powdered natural rocks are affected by their phyllosilicate content. Frictional strength and healing rates decrease with increasing phyllosilicate content, and at 20 wt.% a transition from velocity-weakening to velocity-strengthening behavior was noted. For both suites of gouges, dilation is positively correlated with frictional strength and healing rates, and negatively correlated with frictional stability. Changes in the permeability of gouge-filled faults were estimated from changes in mean porosity, indexed through measured magnitudes of gouge dilation. This combined analysis implies that the reactivation of caprock faults filled with phyllosilicate-rich gouges may have a strong influence on permeability evolution in caprock faults.
    • Thermo-tectonic history of the Junggar Alatau within the Central Asian Orogenic Belt (SE Kazakhstan, NW China): Insights from integrated apatite U/Pb, fission track and (U–Th)/He thermochronology

      Glorie, S.; Otasevic, A.; Gillespie, J.; Jepson, G.; Danišík, M.; Zhimulev, F.I.; Gurevich, D.; Zhang, Z.; Song, D.; Xiao, W.; et al. (CHINA UNIV GEOSCIENCES, BEIJING, 2019-05-31)
      The Junggar Alatau forms the northern extent of the Tian Shan within the Central Asian Orogenic Belt (CAOB) at the border of SE Kazakhstan and NW China. This study presents the Palaeozoic-Mesozoic post-collisional thermo-tectonic history of this frontier locality using an integrated approach based on three apatite geo-/thermochronometers: apatite U-Pb, fission track and (U-Th)/He. The apatite U-Pb dates record Carboniferous-Permian post-magmatic cooling ages for the sampled granitoids, reflecting the progressive closure of the Palaeo-Asian Ocean. The apatite fission track (AFT) data record (partial) preservation of the late Palaeozoic cooling ages, supplemented by limited evidence for Late Triassic (similar to 230-210 Ma) cooling and a more prominent record of (late) Early Cretaceous (similar to 150-110 Ma) cooling. The apatite (U-Th)/He age results are consistent with the (late) Early Cretaceous AFT data, revealing a period of fast cooling at that time in resulting thermal history models. This Cretaceous rapid cooling signal is only observed for samples taken along the major NW-SE orientated shear zone that dissects the study area (the Central Kazakhstan Fault Zone), while Permian and Triassic cooling signals are preserved in low-relief areas, distal to this structure. This distinct geographical trend with respect to the shear zone, suggests that fault reactivation triggered the Cretaceous rapid cooling, which can be linked to a phase of slab-rollback and associated extension in the distant Tethys Ocean. Similar conclusions were drawn for thermochronology studies along other major NW-SE orientated shear zones in the Central Asian Orogenic Belt, suggesting a regional phase of Cretaceous exhumation in response to fault reactivation at that time. (C) 2019, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.