Landward vergence and oblique structural trends in the Oregon margin accretionary prism: Implications and effect on fluid flow

MacKay, Mary E.; Moore, G. F.; Cochrane, Guy R.; Moore, J. Casey; Kulm, L. D.

doi:10.1016/0012-821x(92)90108-8

Cited by 167 publications

(134 citation statements)

References 26 publications

Supporting

Mentioning

127

Contrasting

Order By: Relevance

“…Although fluid venting and gas hydrate processes are well documented, the seismically opaque mounts and ridges on seismic profiles were only initially interpreted as mud volcanoes [MacKay et al, 1992]. A more detailed study, however, suggests that tectonic shortening causes the formation of plunging anticlines along which fluid venting and carbonate precipitation occurs [e.g., Suess et al, 1999].…”

Section: A3 Cascadia Margin/oregon Washingtonmentioning

confidence: 99%

Significance of Mud Volcanism

Kopf

2002

Reviews of Geophysics

746

646

View full text Add to dashboard Cite

Mud volcanism and diapirism have puzzled geoscientists for ∼2 centuries. They have been described onshore and offshore in many places on Earth, and although they occur in various tectonic settings, the majority of the features known to date are located in compressional tectonic scenarios. This paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described. Mud volcanoes show variable geometry (up to tens of kilometers in diameter and several hundred meters in height) and a great diversity regarding the origin of the fluid and solid phases. Gas (predominantly methane), water, and mud may be mobilized at subbottom depth of only a few meters but, in places, can originate from several kilometers depth (with minor crustal or mantle input). The possible contribution of mud extrusion to global budgets, both from quiescent fluid emission and from the extrusive processes themselves, is important. In regions where mud volcanoes are abundant, such as the collision zones between Africa and Eurasia, fluid flux through mud extrusion exceeds the compaction‐driven pore fluid expulsion of the accretionary wedge. Also, quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and, hence, to greenhouse climate.

show abstract

Section: A3 Cascadia Margin/oregon Washingtonmentioning

confidence: 99%

Significance of Mud Volcanism

Kopf

2002

Reviews of Geophysics

746

646

View full text Add to dashboard Cite

show abstract

“…In contrast to VIM, the COM exhibits extensive thrusting at the deformation front of the accretionary wedge (Snavely, 1987;Moore et al, 1990;MacKay et al, 1992). A result of this is a focused pore fluid expulsion along fracture zones at the COM.…”

Section: Introductionmentioning

confidence: 99%

Organic Geochemistry of Gases, Fluids, and Hydrates at the Cascadia Accretionary Margin

Whiticar¹,

Hovland²,

Kastner³

et al. 1995

Proceedings of the Ocean Drilling Program, 146 Part 1 Scientific Results

View full text Add to dashboard Cite

The drilling during Ocean Drilling Program Leg 146 at the accretionary margin complexes off Vancouver Island, Canada (VIM), and Oregon, U.S.A (COM), addressed specific geochemical relationships and phenomena associated with fluid, gas, and heat fluxes generated by the compressive forces. Of particular importance were the occurrence of hydrates and formation of thermogenic hydrocarbons. In most cases, the geochemistry of the hemipelagic sediments is dominated by steady-and nonsteady-state diagenetic reactions, including sulfate reduction (Sites 888 and 891), and methanogenesis and methanotrophy (Sites 888-892). However, these shallow (<600 mbsf) sediments are also clearly and extensively influenced by pervasive and active fracture COM migration of deeper seated thermogenic hydrocarbons at the VIM and COM, respectively. The origin of bacterial and thermogenic gases is confirmed by their molecular and stable carbon isotope signatures. In many cases, the occurrence of C 2 + hydrocarbons delineates the fault zones.Only disseminated macrocrystalline hydrate, not massive hydrate, was encountered during Leg 146. Based on the carbon isotope signature, the hydrate is of bacterial origin and identical to that of the surrounding sediment free gas. Thermogenic gas hydrates were not encountered. The discrepancy between the location of the bottom-simulating reflector (BSR) and the base of hydrate stability may be caused by the presence of other gases or fluid constituents in the hydrate lattice. The amount of free gas inferred by the vertical seismic profiler (VSP) below the BSR may be due to the incomplete upward cryo-distillation of gases. This vertical shift could be created by (1) the change in bottom-water temperatures between glacial and interglacial, and (2) a pressure drop caused by sea-level change and accretionary uplift. The presence of hydrogen sulfide in the methane hydrates at Site 892 was unexpected and results from the rapid incorporation of H 2 S into hydrates, protecting them from reaction, (e.g., formation of iron monosulfides.)

show abstract

“…Estimates of the total amount of gas nenta,1 •nargin, either by offscraping at the deformation stored in this reservoir are very dependent on tim an-front or by being underplated beneath the accretionary swer to this question. Most rccc•t studies indicate that, complex some tens of kilometers east of the deformation free gas beneath the BSR is genorally the primary fac-front [MacKay et al, 1992;MacKay, 1995]. tot controlling reflection amplitude [e.g., Miller et al, As is the case in many accretionary complexes world-1991; Baugs et al, 1993; Siagh et ol., 1993], although wide, this enviromnent has resulted in the extensive this layer was widely thought to be only a few me-presence of gas hydrate.…”

Section: Introductionmentioning

confidence: 99%

Estimating the thickness of the free gas zone beneath Hydrate Ridge, Oregon continental margin, from seismic velocities and attenuation

Tréhu¹,

Flueh²

2001

J. Geophys. Res.

View full text Add to dashboard Cite

Abstract. Recent Ocean Drilling Program (ODP) results in the Oregon accretionary prism and on the Blake Ridge indicate that the zone containing free gas beneath the hydrate-bearing near-surface sediments is considerably thicker than previously thought. In this paper, we present results from travel time inversion of refracted seismic waves that show very low (<1.85 km/s) velocities extending for 500-600 m beneath the base of the gas hydrate stability zone in Hydrate Ridge on the Oregon continental margin near ODP site 892. The low-velocity near-surface layer extends across Hydrate Ridge and beneath the adjacent continental slope to the east. Because Pliocene sediments are exposed at the crest of Hydrate Ridge in an erosional setting, we suggest that these low velocities indicate the extent of a zone of dispersed free gas rather than recent sedimentation. Strong frequency-dependent attenuation of amplitudes is observed for _P waves crossing this zone. Amplitude spectra, referenced to spectra for similar accretionary complex paths that do not cross the interpreted gassy layer, indicate a very low _P wave quality factor (Qp) within this zone, with Qp --12 compared to Qp >100 in the "normal" accretionary complex sediments west of Hydrate Ridge. These results suggest that refraction seismic techniques are a powerful way to constrain the depth to which free gas is present in sediments beneath the hydrate stability zone. Defining the extent of the free gas zone is an important factor for estimating the total volume of gas present and for evaluating its impact on slope stability and potential contribution to global climate change.

show abstract

Landward vergence and oblique structural trends in the Oregon margin accretionary prism: Implications and effect on fluid flow

Cited by 167 publications

References 26 publications

Significance of Mud Volcanism

Significance of Mud Volcanism

Organic Geochemistry of Gases, Fluids, and Hydrates at the Cascadia Accretionary Margin

Estimating the thickness of the free gas zone beneath Hydrate Ridge, Oregon continental margin, from seismic velocities and attenuation

Contact Info

Product

Resources

About