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Fluid Source (fluid + source)
Selected AbstractsUp-temperature flow of surface-derived fluids in the mid-crust: the role of pre-orogenic burial of hydrated fault rocksJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2006C. CLARK Abstract The Walter-Outalpa shear zone in the southern Curnamona Province of NE South Australia is an example of a shear zone that has undergone intensely focused fluid flow and alteration at mid-crustal depths. Results from this study have demonstrated that the intense deformation and ductile shear zone reactivation, at amphibolite facies conditions of 534 ± 20 °C and 500 ± 82 MPa, that overprint the Proterozoic Willyama Supergroup occurred during the Delamerian Orogeny (c. 500 Ma) (EPMA monazite ages of 501 ± 16 and 491 ± 19 Ma). This is in contrast to the general belief that the majority of basement deformation and alteration in the southern Curnamona Province occurred during the waning stages of the Olarian Orogeny (c. 1610,1580 Ma). These shear zones contain hydrous mineral assemblages that cut wall rocks that have experienced amphibolite facies metamorphism during the Olarian Orogeny. The shear zone rock volumes have much lower ,18O values (as low as 1,) than their unsheared counterparts (7,9,), and calculated fluid ,18O values (5,8,) consistent with a surface-derived fluid source. Hydrous minerals show a decrease in ,D(H2O) from ,14 to ,22,, for minerals outside the shear zones, to ,28 to ,40,, for minerals within the shear zones consistent with a contribution from a meteoric source. It is unclear how near-surface fluids initially under hydrostatic pressure penetrate into the middle crust where fluid pressures approach lithostatic, and where fluid flow is expected to be dominantly upward because of pressure gradients. We propose a mechanism whereby faulting during basin formation associated with the Adelaidean Rift Complex (c. 700 Ma) created broad hydrous zones containing mineral assemblages in equilibrium with surface waters. These panels of fault rock were subsequently buried to depths where the onset of metamorphism begins to dehydrate the fault rock volumes evolving a low ,18O fluid that is channelled through shear zones related to Delamerian Orogenic activity. [source] Subsurface sediment remobilization and fluid flow in sedimentary basins: an overviewBASIN RESEARCH, Issue 4 2010Mads Huuse ABSTRACT Subsurface sediment remobilization and fluid flow processes and their products are increasingly being recognized as significant dynamic components of sedimentary basins. The geological structures formed by these processes have traditionally been grouped into mud volcano systems, fluid flow pipes and sandstone intrusion complexes. But the boundaries between these groups are not always distinct because there can be similarities in their geometries and the causal geological processes. For instance, the process model for both mud and sand remobilization and injection involves a source of fluid that can be separate from the source of sediment, and diapirism is now largely discarded as a deformation mechanism for both lithologies. Both mud and sand form dykes and sills in the subsurface and extrusive edifices when intersecting the sediment surface, although the relative proportions of intrusive and extrusive components are very different, with mud volcano systems being largely extrusive and sand injectite systems being mainly intrusive. Focused fluid flow pipes may transfer fluids over hundreds of metres of vertical section for millions of years and may develop into mud volcano feeder systems under conditions of sufficiently voluminous and rapid fluid ascent associated with deeper focus points and overpressured aquifers. Both mud and sand remobilization is facilitated by overpressure and generally will be activated by an external trigger such as an earthquake, although some mud volcano systems may be driven by the re-charge dynamics of their fluid source. Future research should aim to provide spatio-temporal ,injectite' stratigraphies to help constrain sediment remobilization processes in their basinal context and identify and study outcrop analogues of mud volcano feeders and pipes, which are virtually unknown at present. Further data-driven research would be significantly boosted by numerical and analogue process modelling to constrain the mechanics of deep subsurface sediment remobilization as these processes can not be readily observed, unlike many conventional sediment transport phenomena. [source] Towards ground truthing exploration in the central Arctic Ocean: a Cenozoic compaction history from the Lomonosov RidgeBASIN RESEARCH, Issue 2 2010M. O'Regan ABSTRACT The Integrated Ocean Drilling Program's Expedition 302, the Arctic Coring Expedition (ACEX), recovered the first Cenozoic sedimentary sequence from the central Arctic Ocean. ACEX provided ground truth for basin scale geophysical interpretations and for guiding future exploration targets in this largely unexplored ocean basin. Here, we present results from a series of consolidation tests used to characterize sediment compressibility and permeability and integrate these with high-resolution measurements of bulk density, porosity and shear strength to investigate the stress history and the nature of prominent lithostratigraphic and seismostratigraphic boundaries in the ACEX record. Despite moderate sedimentation rates (10,30 m Myr,1) and high permeability values (10,15,10,18 m2), consolidation and shear strength measurements both suggest an overall state of underconsolidation or overpressure. One-dimensional compaction modelling shows that to maintain such excess pore pressures, an in situ fluid source is required that exceeds the rate of fluid expulsion generated by mechanical compaction alone. Geochemical and sedimentological evidence is presented that identifies the Opal A,C/T transformation of biosiliceous rich sediments as a potential additional in situ fluid source. However, the combined rate of chemical and mechanical compaction remain too low to fully account for the observed pore pressure gradients, implying an additional diagenetic fluid source from within or below the recovered Cenozoic sediments from ACEX. Recognition of the Opal A,C/T reaction front in the ACEX record has broad reaching regional implications on slope stability and subsurface pressure evolution, and provides an important consideration for interpreting and correlating the spatially limited seismic data from the Arctic Ocean. [source] Contrasting paleofluid systems in the continental basement: a fluid inclusion and stable isotope study of hydrothermal vein mineralization, Schwarzwald district, GermanyGEOFLUIDS (ELECTRONIC), Issue 2 2007B. BAATARTSOGT Abstract An integrated fluid inclusion and stable isotope study was carried out on hydrothermal veins (Sb-bearing quartz veins, metal-bearing fluorite,barite,quartz veins) from the Schwarzwald district, Germany. A total number of 106 Variscan (quartz veins related to Variscan orogenic processes) and post-Variscan deposits were studied by microthermometry, Raman spectroscopy, and stable isotope analysis. The fluid inclusions in Variscan quartz veins are of the H2O,NaCl,(KCl) type, have low salinities (0,10 wt.% eqv. NaCl) and high Th values (150,350°C). Oxygen isotope data for quartz range from +2.8, to +12.2, and calculated ,18OH2O values of the fluid are between ,12.5, and +4.4,. The ,D values of water extracted from fluid inclusions vary between ,49, and +4,. The geological framework, fluid inclusion and stable isotope characteristics of the Variscan veins suggest an origin from regional metamorphic devolatilization processes. By contrast, the fluid inclusions in post-Variscan fluorite, calcite, barite, quartz, and sphalerite belong to the H2O,NaCl,CaCl2 type, have high salinities (22,25 wt.% eqv. NaCl) and lower Th values of 90,200°C. A low-salinity fluid (0,15 wt.% eqv. NaCl) was observed in late-stage fluorite, calcite, and quartz, which was trapped at similar temperatures. The ,18O values of quartz range between +11.1, and +20.9,, which translates into calculated ,18OH2O values between ,11.0, and +4.4,. This range is consistent with ,18OH2O values of fluid inclusion water extracted from fluorite (,11.6, to +1.1,). The ,D values of directly measured fluid inclusion water range between ,29, and ,1,, ,26, and ,15,, and ,63, and +9, for fluorite, quartz, and calcite, respectively. Calculations using the fluid inclusion and isotope data point to formation of the fluorite,barite,quartz veins under near-hydrostatic conditions. The ,18OH2O and ,D data, particularly the observed wide range in ,D, indicate that the mineralization formed through large-scale mixing of a basement-derived saline NaCl,CaCl2 brine with meteoric water. Our comprehensive study provides evidence for two fundamentally different fluid systems in the crystalline basement. The Variscan fluid regime is dominated by fluids generated through metamorphic devolatilization and fluid expulsion driven by compressional nappe tectonics. The onset of post-Variscan extensional tectonics resulted in replacement of the orogenic fluid regime by fluids which have distinct compositional characteristics and are related to a change in the principal fluid sources and the general fluid flow patterns. This younger system shows remarkably persistent geochemical and isotopic features over a prolonged period of more than 100 Ma. [source] | ||||||||||