Variations in temperature gradients identify active faults in the Oregon accretionary prism

Zwart, Gretchen; Moore, J. Casey; Cochrane, Guy R.

doi:10.1016/0012-821x(95)00244-7

Cited by 57 publications

(55 citation statements)

References 20 publications

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“…5, 6) are consistent with the presence of a convective system, with higher values near zones of fluid discharge. However, elsewhere in similar circumstances, such as off Oregon [26], the conductive heat flow is similar to that predicted by plate cooling models. A recent global compilation has shown that conductive heat flow near trenches is not systematically lower than in crust of the same age away from trenches and does not appear to decrease as lithosphere approaches trenches [27].…”

Section: Discussionsupporting

confidence: 65%

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Low heat flow from young oceanic lithosphere at the Middle America Trench off Mexico

Minshull

Bartolomé

Byrne

et al. 2005

Earth and Planetary Science Letters

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Seismic reflection profiles across the Middle America Trench at 208N show a high amplitude bottom simulating reflector interpreted as marking a phase transition between methane hydrate and free gas in the pore space of both accreted and trench sediments. We determine the depth of the hydrate-gas phase boundary in order to estimate the geothermal gradient and hence the heat flow beneath the trench and the frontal part of the accretionary wedge which overlies the downgoing plate. After correction for sedimentation, heat flow values in the trench and through the accretionary wedge are only about half of the values predicted by plate cooling models for the 10 Ma subducting lithosphere. There is no systematic correlation between heat flow in the accretionary wedge and distance from the trench. A comparison with heat flow predicted by a simple analytical model suggests that there is little shear heating from within or beneath the wedge, despite the high basal friction suggested by the large taper angle of the wedge. The geothermal gradient varies systematically along the margin and is negatively correlated with the frontal slope of the wedge. Some local peaks may be attributed to channelised fluid expulsion. D

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Section: Discussionsupporting

confidence: 65%

“…3), since in some cases heat flow reaches a local maximum over inferred thrust faults, as observed commonly elsewhere in accretionary wedges [e.g., 18,26]. However, the accreted sediments are sufficiently deformed that it is generally difficult to identify such faults.…”

Section: Discussionmentioning

confidence: 97%

Low heat flow from young oceanic lithosphere at the Middle America Trench off Mexico

Minshull

Bartolomé

Byrne

et al. 2005

Earth and Planetary Science Letters

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“…Active faults are considered to be paths for pore fluid flow as fractures may have produced relatively permeable zones along the fault planes. Heat flow anomalies have actually been detected in the vicinity of active faults on the landward side of trenches, such as the Cascadia, Barbados, and Nankai subduction zones (e.g., Zwart et al 1996;Foucher et al 1990;Kinoshita et al 2003), though they are thrust faults under a compressive stress field.…”

Section: Possible Causes Of the High Heat Flow On The Seaward Slopementioning

confidence: 97%

High heat flow anomalies on an old oceanic plate observed seaward of the Japan Trench

Yamano

Kinoshita

Gotô

2007

Int J Earth Sci (Geol Rundsch)

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Thirty-three new measurements on the seaward slope and outer rise of the Japan Trench along a parallel of 38°45 0 N revealed the existence of high heat flow anomalies on the subducting Pacific plate, where the seafloor age is about 135 m.y. The most prominent anomaly with the highest value of 114 mW/m 2 is associated with a small mound on the outer rise, which was reported to be a kind of mud volcano. On the seaward slope of the trench, heat flow is variable: high (70-90 mW/m 2 ) at some locations and normal for the seafloor age (about 50 mW/m 2 ) at others. The spatial variation of heat flow may be related to development of normal faults and horst/graben structures due to bending of the Pacific plate before subduction, with fluid flow along the fault zones enhancing the vertical heat transfer. Possible heat sources of the high heat flow anomalies are intra-plate volcanism in the last several million years like that discovered recently on the Pacific plate east of the Japan Trench.

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“…In spite of uncertainties and natural variability in these parameters, apparent thermal gradients calculated from BSR depths can provide insights into subsurface temperature structure and indirectly into patterns of fluid flow [e.g., Yamano et al, 1982;Bangs et al, 1993;Yuan et al, 1996;Pecher et al, 1996;Zwart et al, 1996]. We calculated the apparent thermal gradient assuming hydrostatic pressure, a sediment P wave velocity of 1.73 km/s (measured by interval velocity analysis; Figure 7), a seafloor temperature of 2.5°C (as was measured near the escarpment during ROV dives; Figure 8), and the phase boundary for pure methane hydrate in water of 3.5% salinity (as determined experimentally by Maekawa et al [1995]).…”

Section: Fluid Flow Inferred From Variations In Bsr Depth and Seafloomentioning

confidence: 99%

Seismic and seafloor evidence for free gas, gas hydrates, and fluid seeps on the transform margin offshore Cape Mendocino

et al. 2003

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[1] Seismic data and seafloor samples indicate the presence of free gas, gas hydrate, and fluid seeps south of the Gorda Escarpment, a topographic feature that marks the eastern end of the Gorda/Pacific transform plate boundary southwest of Cape Mendocino, California. In spite of high sedimentation rates and high biological productivity, direct or indirect indicators of gas hydrate presence had not previously been recognized in this region, or along transform margins in general. Gas is indicated by a bottom simulating reflection (BSR) observed near the Gorda Escarpment, by ''bright spots'' and ''gas curtains'' scattered throughout the sedimentary basin to the south, and by d C and d18 O isotopes of carbonates, which are similar to those recovered from other hydrate-bearing regions. The BSR reflection coefficient of À0.13 ± 0.04 and interval velocities as low as 1.38 km/s indicate that free gas is present beneath the BSR. Local shallowing of the BSR toward the north facing Gorda Escarpment and beneath a channel near the crest suggests fluid flow toward the seafloor. Integrating these various observations, we suggest a scenario in which methane is formed in thick Miocene and Pliocene deposits of organicrich sediments that fill the marginal basin south of the transform fault. Dissolved and free gas migrates toward the escarpment along stratigraphic horizons, resulting in hydrate formation and in channels, slumps and chemosynthetic communities on the face of the escarpment. We conclude that the BSR appears where hydrate-bearing sediments are uplifted because of current triple junction tectonics.

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Variations in temperature gradients identify active faults in the Oregon accretionary prism

Cited by 57 publications

References 20 publications

Low heat flow from young oceanic lithosphere at the Middle America Trench off Mexico

Low heat flow from young oceanic lithosphere at the Middle America Trench off Mexico

High heat flow anomalies on an old oceanic plate observed seaward of the Japan Trench

Seismic and seafloor evidence for free gas, gas hydrates, and fluid seeps on the transform margin offshore Cape Mendocino

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