Permeability and Protest in Lane 49: Entangling Materialities of Place with Housing Activism in Shanghai

Since China’s implementation of a neo‐liberal housing regime, housing activism has boomed. Whilst activism is ultimately in place, as increasingly recognised within protest work, there is limited reflection upon how permeable material histories are entangled with the throwntogetherness of place as a site for protest. Employing ethnography over three months, this article follows the emergence, organisation and implementation of housing activism in Lane 49, a public housing community in downtown Shanghai. Utilising feminist geography and feminist political theorisations of material permeability this article contributes to Chinese geographies of protest, providing a local epistemology of housing activism which demonstrates the importance of drawing materiality into understandings of activist tactics. The article also contributes to radical geographies of protest by deconstructing the idea of public protest in a public place and thus offering opportunities to demonstrate how, through blurring public‐private binaries, protest can emerge and survive in authoritative governance regimes.     

Permeability of the continental crust: dynamic variations inferred from seismicity and metamorphism

The variation of permeability with depth can be probed indirectly by various means, including hydrologic models that use geothermal data as constraints and the progress of metamorphic reactions driven by fluid flow. Geothermal and metamorphic data combine to indicate that mean permeability ( k ) of tectonically active continental crust decreases with depth ( z ) according to log  k  ≈ −14–3.2 log  z , where k is in m² and z in km. Other independently derived, crustal-scale k – z relations are generally similar to this power-law curve. Yet there is also substantial evidence for local-to-regional-scale, transient, permeability-generation events that entail permeabilities much higher than these mean k – z relations would suggest. Compilation of such data yields a fit to these elevated, transient values of log  k  ≈ −11.5–3.2 log  z , suggesting a functional form similar to that of tectonically active crust, but shifted to higher permeability at a given depth. In addition, it seems possible that, in the absence of active prograde metamorphism, permeability in the deeper crust will decay toward values below the mean k – z curves. Several lines of evidence suggest geologically rapid (years to 10³ years) decay of high-permeability transients toward background values. Crustal-scale k – z curves may reflect a dynamic competition between permeability creation by processes such as fluid sourcing and rock failure, and permeability destruction by processes such as compaction, hydrothermal alteration, and retrograde metamorphism.     

The application of failure mode diagrams for exploring the roles of fluid pressure and stress states in controlling styles of fracture-controlled permeability enhancement in faults and shear zones

Permeability enhancement associated with deformation processes in faults and shear zones plays a key role in facilitating fluid redistribution between fluid reservoirs in the crust. Especially in high fluid flux hydrothermal systems, fracture-controlled permeability can be relatively short-lived, unless it is repeatedly regenerated by ongoing deformation. Failure mode diagrams in pore fluid factor and differential stress space, here termed λ–σ failure mode diagrams, provide a powerful tool for analysing how fluid pressure and stress states drive failure, associated permeability enhancement and vein styles during deformation in faults and shear zones. During fault-valve behaviour in the seismogenic regime, relative rates of recovery of pore fluid factor, differential stress and fault cohesive strength between rupture events impact on styles of veining and associated, fracture-controlled permeability enhancement in faults and shear zones. Examples of vein-rich fault zones are used to illustrate how constraints can be placed, not just on fluid pressure and stress states at failure, but also on the fluid pressurization and loading paths associated with failure and transitory permeability enhancement in faults and shear zones. This provides insights about when, during the fault-valve cycle, various types of veins can form. The use of failure mode diagrams also provides insights about the relative roles of optimally oriented faults and misoriented faults as hydraulically conductive structures. The analysis highlights the dynamics of competition between fluid pressures and loading rates in driving failure and repeated permeability regeneration in fracture-controlled, hydrothermal systems.     

Changes in fluid pathways in a calcite vein mesh (Natih Formation,Oman Mountains): insights from stable isotopes

We present a structural, microstructural, and stable isotope study of a calcite vein mesh within the Cretaceous Natih Formation in the Oman Mountains to explore changes in fluid pathways during vein formation. Stage 1 veins form a mesh of steeply dipping crack‐seal extension veins confined to a 3.5‐m‐thick stratigraphic interval. Different strike orientations of Stage 1 veins show mutually crosscutting relationships. Stage 2 veins occur in the dilatant parts of a younger normal fault interpreted to penetrate the stratigraphy below. The δ¹⁸O composition of the host rock ranges from 21.8‰ to 23.7‰. The δ¹³C composition ranges from 1.5‰ to 2.3‰. This range is consistent with regionally developed diagenetic alteration at top of the Natih Formation. The δ¹⁸O composition of vein calcite varies from 22.5‰ to 26.2‰, whereas δ¹³C composition ranges from ?0.8‰ to 2.1‰. A first trend observed in Stage 1 veins involves a decrease of δ¹³C to compositions nearly 1.3‰ lower than the host rock, whereas δ¹⁸O remains constant. A second trend observed in Stage 2 calcite has δ¹⁸O values up to 3.3‰ higher than the host rock, whereas the δ¹³C composition is similar. Stable isotope data and microstructures indicate an episodic flow regime for both stages. During Stage 1, formation of a stratabound vein mesh involved bedding‐parallel flow, under near‐lithostatic fluid pressures. The ¹⁸O fluid composition was host rock‐buffered, whereas ¹³C composition was relatively depleted. This may reflect reaction of low ¹³C CO₂ derived by fluid interaction with organic matter in the limestones. Stage 2 vein formation is associated with fault‐controlled fluid flow accessing fluids in equilibrium with limestones about 50 m beneath. We highlight how evolution of effective stress states and the growth of faults influence the hydraulic connectivity in fracture networks and we demonstrate the value of stable isotopes in tracking changes in fluid pathways.     

A permeability‐change model for water‐level changes triggered by teleseismic waves

Although many hydrologic changes induced by teleseismic waves have been reported, the mechanism(s) responsible for the changes are usually not known. Permeability changes induced by seismic strains are often invoked to explain changes in water level. Using water‐level data in Taiwan after the 2008 Wenchuan earthquake, we show here that the observations cannot be properly explained by previously proposed models of postseismic permeability changes. A new model is required in which the postseismic permeability decreases exponentially as a function of time, with a time constant of <3 min, which is appreciably shorter than inferred from earlier studies. The result may have important implications for pore‐sealing mechanism(s).     

Evolution of porosity, permeability and fluid pressure in dilatant faults post-failure: implications for fluid flow and mineralization

Mineralization of brittle fault zones is associated with sudden dilation, and the corresponding changes in porosity, permeability and fluid pressure, that occur during fault slip events. The resulting fluid pressure gradients cause fluid to flow into and along the fault until it is sealed. The volume of fluid that can pass through the deforming region depends on the degree of dilation, the porosity and permeability of the fault and wall rocks, and the rate of fault sealing. A numerical model representing a steep fault cutting through a horizontal seal is used to investigate patterns of fluid flow following a dilatant fault slip event. The model is initialized with porosity, permeability and fluid pressure representing the static mechanical state of the system immediately after such an event. Fault sealing is represented by a specified evolution of porosity, coupled to changes in permeability and fluid pressure, with the rate of porosity reduction being constrained by independent estimates of the rate of fault sealing by pressure solution. The general pattern of fluid flow predicted by the model is of initial flow into the fault from all directions, followed by upward flow driven by overpressure beneath the seal. The integrated fluid flux through the fault after a single failure event is insufficient to account for observed mineralization in faults; mineralization would require multiple fault slip events. Downward flow is predicted if the wall rocks below the seal are less permeable than those above. This phenomenon could at least partially explain the occurrence of uranium deposits in reactivated basement faults that cross an unconformity between relatively impermeable basement and overlying sedimentary rocks.     

A vector of high‐temperature paleo‐fluid flow deduced from mass transfer across permeability barriers (quartz veins)

Quartz veins acted as impermeable barriers to regional fluid flow and not as fluid‐flow conduits in Mesoproterozoic rocks of the Mt Painter Block, South Australia. Systematically distributed asymmetric alteration selvedges consisting of a muscovite‐rich zone paired with a biotite‐rich zone are centered on quartz veins in quartz–muscovite–biotite schist. Geometric analysis of the orientation and facing of 126 veins at Nooldoonooldoona Waterhole reveals a single direction along which a maximum of all veins have a muscovite‐rich side, irrespective of their specific individual orientation. This direction represents a Mesoproterozoic fluid‐flow vector and the veins represent permeability barriers to the flow. The pale muscovite‐rich zones formed on the downstream side of the vein and the dark biotite‐rich zones mark the upstream side. The alteration couplets formed from mica schist at constant Zr, Ga, Sc, and involved increases in Si, Na, Al and decreases in K, Fe, Mg for pale alteration zones, and inverse alteration within dark zones. The asymmetry of the alteration couplets is best explained by the pressure dependence of mineral–fluid equilibria. These equilibria, in combination with a Darcian flow model for coupled advection and diffusion, and with permeability barriers imposed by the quartz veins, simulate the pattern of both fluid flow and differential, asymmetric metasomatism. The determined vector of fluid flow lies along the regional foliation and is consistent with the known distribution of regional alteration products. The presence of asymmetric alteration zones in rock containing abundant pre‐alteration veins suggests that vein‐rich material may have generally retarded regional fluid flow.     

Structural controls on hydrothermal flow in a segmented rift system, Taupo Volcanic Zone, New Zealand

Vigorous hydrothermal convection transfers 10 times the average continental heat flow through the central Taupo Volcanic Zone (TVZ), a region of active extension (approximately 8 mm year^?1) and productive rhyolitic volcanism. Over 20 high‐temperature (>250°C) geothermal fields occur within Quaternary pyroclastic basins, with convective circulation to depths of 7–8 km presumably extending through basement rocks. Parallel‐striking normal faults, fractures and dikes dissect the convective regime, interacting with fluids to either enhance or restrict flow according to the relative permeability of structure and host rock. In the basement, high bulk permeability is maintained by focussed flow through faults and associated fractures well oriented for reactivation in the prevailing stress field. In contrast, distributed flow through fault‐bounded compartments prevails within Quaternary basins, masking any signal of deeper structural control. Exceptions occur where more competent rocks are exposed at the surface. As in narrow magmatic rifts elsewhere, the extensional fabric is partitioned into discrete rift segments linked along strike by accommodation zones. Eighty per cent of TVZ geothermal fields correlate spatially with rift architecture, with 60% located in accommodation zones. We suggest that segmented rift fabrics generate bulk permeability anisotropy that is to some extent predictable, with rift segments characterized by enhanced axial flow, and accommodation zones characterized by locally enhanced vertical permeability that is tectonically maintained. This provides a plausible explanation for the common occurrence of geothermal fields within accommodation zones and their notable absence within densely faulted rift segments. Maintenance of structural permeability in zones of active hydrothermal precipitation necessarily requires repeated brittle failure. Geothermal plumes therefore exploit tectonically maintained permeability within accommodation zones, with rift segments functioning mostly as drawdown regions. The influence of rift architecture on flow paths has important implications for geothermal extraction and epithermal mineral exploration within the TVZ and other structurally segmented hydrothermal systems, both active and extinct.     

云冈石窟顶部土层水盐分布特征研究

可溶盐是石质文物风化的重要原因,其聚集、运移与水密不可分。石窟顶部土层中的盐是云冈石质文物内部盐分的重要来源,因而研究石窟顶部土层中的水盐分布特征对未来减小可溶盐在石质文物内部的聚集具有十分重要的意义。本研究对云冈石窟顶部不同位置、不同深度土层的饱和渗透系数、含水率、孔隙比、可溶盐含量进行了系统的分析测试,并结合取土位置的坡度和植被覆盖率,研究了云冈石窟顶部土层中水盐分布特征。结果表明:植被覆盖率越高,土体含水量越高;坡度越大,土体含水率越低;土体孔隙比与饱和渗透系数呈线性关系。植被覆盖率、坡度及土体的渗透性能是影响石窟顶部土层水盐分布的主要原因。     

Physical properties of carbonate fault rocks,fucino basin (Central Italy): implications for fault seal in platform carbonates

We documented the porosity, permeability, pore geometry, pore type, textural anisotropy, and capillary pressure of carbonate rock samples collected along basin‐bounding normal faults in central Italy. The study samples consist of one Mesozoic platform carbonate host rock with low porosity and permeability, four fractured host rocks of the damage zones, and four fault rocks of the fault cores. The four fractured samples have high secondary porosity, due to elongated, connected, soft pores that provide fluid pathways in the damage zone. We modeled this zone as an elastic cracked medium, and used the Budiansky–O'Connell correlation to compute its permeability from the measured elastic moduli. This correlation can be applied only to fractured rocks with large secondary porosity and high‐aspect ratio pores. The four fault rock samples are made up of survivor clasts embedded in fine carbonate matrices and cements with sub‐spherical, stiff pores. The low porosity and permeability of these rocks, and their high values of capillary pressure, are consistent with the fault core sealing as much as 77 and 140 m of gas and oil columns, respectively. We modeled the fault core as a granular medium, and used the Kozeny–Carmen correlation, assigning the value of 5 to the Kozeny constant, to compute its permeability from the measured porosities and pore radii. The permeability structure of the normal faults is composed of two main units with unique hydraulic characteristics: a granular fault core that acts as a seal to cross‐fault fluid flow, and an elastic cracked damage zone that surrounds the core and forms a conduit for fluid flow. Transient pathways for along‐fault fluid flow may form in the fault core during seismic faulting due to the formation of opening‐mode fractures within the cemented fault rocks.