摘要:

For the better part of 2 decades, it has been known that dewatering of sediments accreted to or subducted beneath accretionary wedges is a fundamental aspect of the subduction‐accretion process. Yet, evidence for fluid flow in modern accretionary wedges is largely secondary and based on the presence of geochemical and/or thermal anomalies [e.g.,Vrolijk et al., 1991]; the analysis of seismic velocity as an indicator of porosity, which suggests a progressive loss of pore volume in a landward direction [e.g.,Bray and Karig, 1985]; and the occurrence of secondary sediment microstructures characteristic of fluid movement [e.g.,Maltman et al., 1992].The only quantitative measurements of fluid expulsion at surface vents are based on submersible‐deployed, seepage‐meter data [e.g.,Carson et al., 1990], and these results—coupled with the surface area of the vents—indicate flow rates significantly greater than can be supported by steadystate dewatering [Le Pichon et al., 1992]. The fluid budgets and mass fluxes associated with accretion are poorly constrained. Results of previous drilling suggest two distinct modes of fluid flow: channelized flow along fault zones (primarily the décollement [e.g.,Mascle and Moore, 1990]) or diffuse flow, which is apparently accommodated by a pervasive fracture permeability [e.g.,Taira et

ISSN:0002-8606    

DOI:10.1029/93EO00459

年代:1993

数据来源: WILEY

摘要:

Reliable age information on Quaternary volcanic events is difficult to obtain because14C dating generally does not extend beyond 45,000 years, and recent applications of40Ar/39Ar methods—proven techniques for older lavas—suggest that dating events younger than approximately 100,000 years will be problematic. Because of the gap left in coverage by these traditional techniques, attention has turned to alternative chronometers, such as thermoluminescence, surface exposure dating using the build‐up of cosmogenic nuclides, U‐series disequilibria, and desert varnish. This research has received impetus and funding because of the importance of young igneous processes in evaluating volcanic hazards, related questions of seismicity, and radioactive waste disposal.These new techniques need to be calibrated against each other using identical samples, which is being done in several volcanic fields throughout the southwestern United States [e.g.,Anthony and Poths, 1992]. One such area, the Zuni‐Bandera volcanic field near Grants, N. Mex., was the site of a field conference [Laughlin et al., 1993] held from April 26 to 28, to report on recent determinations of flow chronology based on14C,3He,40Ar/39Ar, and U‐series techniques. An informal group to continue research on correlated samples was als

ISSN:0002-8606    

DOI:10.1029/93EO00489

年代:1993

数据来源: WILEY