Helium measurements of pore fluids obtained from the San Andreas Fault Observatory at Depth (SAFOD, USA) drill cores

Ali, S.; Stute, M.; Torgersen, T.; Winckler, Gisela; Kennedy, B. Mack

doi:10.1007/s10040-010-0645-6

Cited by 5 publications

(13 citation statements)

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“…3 He/ 4 He ratios show a similar distribution for host rocks (0.10-1.45) and veins (0.14-1.40), but increase in deformation zones (0.54-2.53). The distribution of the fluid inclusion helium isotope compositions displays a similar range as that measured in present-day fluids associated with the SAF Wiersberg and Erzinger, 2007;Ali et al, 2010). In terms of fault segments, the highest R/Ra value was observed in a San Gabriel fault sample (2.53 ± 0.80), followed by a San Andreas fault sample (1.84 ± 0.49), and a Santa Ynez one (1.44 ± 0.35).…”

Section: Noble Gases From Fluid Inclusions: Analytical Methods and Resupporting

confidence: 64%

“…Wiersberg and Erzinger (2007) found that drill mud-gas samples collected while drilling through the SAF system contained up to 12% mantle-derived helium at a depth of 3.5 km. Ali et al (2010) report similar helium isotope compositions in pore waters extracted from core taken while drilling though the SAF system. Evidence for mantle helium contributions to ground waters from the Mojave River Basin up to 35 km east from the SAF trace, has been reported by Kulongoski et al (2003) and it was suggested that this helium influx originated from the SAF as well as other secondary fault zones in the basin.…”

Section: Introductionmentioning

confidence: 64%

“…In the no-flow model of Byerlee (1990), water from the host rock is trapped in the fault zone where compressive forces raise the pressure of the trapped fluids above ambient hydrostatic pressure. If geophysics has provided indirect arguments for the potential role of fluids during seismogenic faulting (Johnson and McEvily, 1995;Unsworth et al, 1997;Zhao et al, 1996) such fluids have proven difficult to identify and sample Wiersberg and Erzinger, 2007;Ali et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

“…New approaches that can sample present-day fluids directly from recently ruptured fault zones either by sampling fluids during drilling (Wiersberg and Erzinger, 2007) or by extracting fluids from drilled cores (Shimamoto et al, 2001;Ali et al, 2010) are promising but limited in space and time. Fault zone minerals and fluid inclusions (fluids trapped in fractured minerals after healing or in secondary minerals after precipitation in fractures) associated with the active fault zones provide potential direct sampling of fault-hosted fluid.…”

Section: Introductionmentioning

confidence: 99%

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Isotopic evidence for the infiltration of mantle and metamorphic CO2–H2O fluids from below in faulted rocks from the San Andreas Fault system

et al. 2011

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To characterize the origin of the fluids involved in the San Andreas Fault (SAF) system, we carried out an isotope study of exhumed faulted rocks from deformation zones, vein fillings and their hosts and the fluid inclusions associated with these materials. Samples were collected from segments along the SAF system selected to provide a depth profile from upper to lower crust. In all, 75 samples from various structures and lithologies from 13 localities were analyzed for noble gas, carbon, and oxygen isotope compositions. Fluid inclusions exhibit helium isotope ratios ( 3 He/ 4 He) of 0.1-2.5 times the ratio in air, indicating that past fluids percolating through the SAF system contained mantle helium contributions of at least 35%, similar to what has been measured in present-day ground waters associated with the fault . Calcite is the predominant vein mineral and is a common accessory mineral in deformation zones. A systematic variation of C-and O-isotope compositions of carbonates from veins, deformation zones and their hosts suggests percolation by external fluids of similar compositions and origin with the amount of fluid infiltration increasing from host rocks to vein to deformation zones. The isotopic trend observed for carbonates in veins and deformation zones follows that shown by carbonates in host limestones, marbles, and other host rocks, increasing with increasing contribution of deep metamorphic crustal volatiles. At each crustal level, the composition of the infiltrating fluids is thus buffered by deeper metamorphic sources. A negative correlation between calcite δ 13 C and fluid inclusion 3 He/ 4 He is consistent with a mantle origin for a fraction of the infiltrating CO 2 . Noble gas and stable isotope systematics show consistent evidence for the involvement of mantle-derived fluids combined with infiltration of deep metamorphic H 2 O and CO 2 in faulting, supporting the involvement of deep fluids percolating through and perhaps weakening the fault zone. There is no clear evidence for a significant contribution from meteoric water, except for overprinting related to late weathering.

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Section: Noble Gases From Fluid Inclusions: Analytical Methods and Resupporting

confidence: 64%

Section: Introductionmentioning

confidence: 64%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Isotopic evidence for the infiltration of mantle and metamorphic CO2–H2O fluids from below in faulted rocks from the San Andreas Fault system

et al. 2011

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“…In cases where wells are not available or the specific yield of the formation is too small, rock samples have been collected and stored in evacuated stainless steel vessels. Over time (often weeks to months) gases dissolved in the pore fluids accumulate in the headspace and can subsequently be extracted for measurement (Osenbruck et al, 1996(Osenbruck et al, , 1998Ali et al, 2010).…”

Section: Sampling and Analysis Sampling Methodsmentioning

confidence: 99%

technical report and journal articles

2011

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GENERAL OVERVIEWObjective: This project seeks to improve the application of noble gas isotope studies to multiphase fluid processes in the Earth's crust by (1) identifying the important noble gas carrier phases in sediments to address the processes that have led to the observed enrichment and depletion patterns in sedimentary rocks and fluids, (2) examine the mechanisms by which such noble gas patterns are acquired, trapped and subsequently released to mobile crustal fluids, and (3) evaluate the time and length scales for the transport of noble gas components, such as radiogenic 4 He, through the continental crust.. Project Description:Sedimentary rocks and oil field gases typically are enriched in heavy noble gases: Xe/Ar ratios of ~10-10,000 times the ratio in air have been observed that cannot be explained by adsorption hypotheses. Laboratory experiments designed to isolate sedimentary phases for noble gas analysis are conducted to identify the carrier phase(s). It has been observed that radiogenic 4 He accumulates in confined aquifer waters at rates that exceed the rate of local production and approaching the whole crustal production rate. A literature evaluation of 4 He, 3 He crustal fluxes is being conducted to evaluate crustal scale mass transport in terms of the rate, mechanisms, temporal and spatial variability and the role played by tectonic processes. Results:The laboratory study has concentrated on noble gas abundances in a variety of sedimentary silica samples. We have found that, in general, samples of inorganic silica have noble gas abundances that are consistent with occlusion of air-saturated water in fluid inclusions and lack requisite enrichment/depletion factors needed to explain the noble gas inventory in oil field fluids. However, numerous replicate analyses of noble gases extracted from silica spicules from live sponges (Calyxnicaeensis) show significantly enriched Ar, Kr, and Xe concentrations ([ i Ng] sample /[ i Ng] asw > 1), but with very little if any mass dependence in the acquisition and trapping of Ar, Kr and Xe. Noble gases in silica samples from the (diatomaceous) Monterey Formation (Elk Hills oil field, CA) and an Atlantic box core were found to be somewhat depleted with respect to the sponge spicule, fractionated in a fashion favoring the heavy noble gases, and approach the compositions that have been observed in bulk deep sea sediments. We suspect that the differences in noble gas absolute and relative abundances between the sponge spicule samples and the more evolved diatomaceous samples are related to either (1) fundamental differences in the biologically controlled mineralization or (2) postdepositional effects related to the progressive crystallization of amorphous silica (e.g. opal-A) to more ordered structures. Laboratory cultured diatoms and box core sea sediment samples collected as a function of depth within the sediment column have been processed for analysis of the silica phases to address these questions.Through a statistical evaluation using a global data bas...

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