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Objective: 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 4He, through the continental crust.. Project Description: Sedimentary rocks and oil ... continued below

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Torgerson, Thomas & Kennedy, B. M. March 25, 2011.

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Objective: 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 4He, 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 4He 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 4He, 3He 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 ([iNg]sample/[iNg]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 base covering many geologic environments, we have determined that the log normal mean of the radiogenic 4He flux across the Earth’s continental crust is 4.18 x 1010 4He atoms m-2 s-1. Furthermore, it was found that the range of the continental 4He degassing flux increases with decreasing time and space scales. The statistics can be interpreted as reflecting natural variability and suggest that the mechanisms transporting the crustal helium degassing flux contain a high degree of both spatial and temporal variability. This estimate of the log normal mean of the continental degassing flux of 4He is approximately equivalent to the radiogenic production rate for 4He in the whole crust. Large scale vertical mass transport in continental crust is estimated as scaled values of the order 10-5 cm2s-1 for helium (over 2Byr and 40km vertically) vs. 10-2 cm2s-1 for heat. This rate of mass transport requires not only release of He from the solid phase via diffusion, fracturing or comminution; but also an enhanced rate of mass transport facilitated by some degree of fluid advection. This further implies a separation of heat and mass during transport.

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  • Report No.: DOE/FG/95ER14528
  • Grant Number: FG02-95ER14528
  • DOI: 10.2172/1010436 | External Link
  • Office of Scientific & Technical Information Report Number: 1010436
  • Archival Resource Key: ark:/67531/metadc837262

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Office of Scientific & Technical Information Technical Reports

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  • March 25, 2011

Added to The UNT Digital Library

  • May 19, 2016, 3:16 p.m.

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  • March 14, 2018, 2:22 p.m.

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Torgerson, Thomas & Kennedy, B. M. technical report and journal articles, report, March 25, 2011; United States. (digital.library.unt.edu/ark:/67531/metadc837262/: accessed November 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.