Fluids in accretionary prisms

Moore, J. Casey; Vrolijk, Peter

doi:10.1029/92rg00201

Cited by 528 publications

(357 citation statements)

References 134 publications

(80 reference statements)

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“…7). The presence of chemoautotrophic benthic biological communities is commonly interpreted as a tracer of active fluid flow out of the seabed (Suess et al, 1985;Le Pichon et al, 1987;Boulegue et al, 1987;Moore and Vrolijk, 1992). Since the first in situ observation of biological communities related to cold seeps on the Oregon accretionary margin (Suess et al, 1985), similar observations have been reported from active erosional margins (Cadet et al, 1987;Sibuet et al, 1988) as well as from active accretionary margins (Le Pichon et al, 1987, 1990.…”

Section: Dating Of Rock Samplessupporting

confidence: 52%

Slope instabilities at an active continental margin: large-scale polyphase submarine slides along the northern Peruvian margin, between 5 °S and 6 °S

et al. 1995

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A mega-submarine slide was evidenced along the Peruvian margin during a Seabeam survey of the R/V Charcot (Bourgois et al., 1986). The debris-slide was initially interpreted as the result of the slope failure occurring along a seaward curved scarp, and extending from east to west, along the line of maximum slope. Complementary bathymetric data obtained from the R/V Sonne survey conducted to the north and to the south of the previous surveyed area has resulted in the identification of large-scale polyphase submarine slides involving a total surface of about 1000 km', between latitudes 5"lSS and 6"05'S. Using Seabeam and Hydrosweep multibeam echosounder data in combination with deep-sea submersible observations, three distinct slope-failure types related to three main stages have been revealed. The three sliding phases occurred roughly along the same trend, orientated N230", and are therefore mainly controlled by the N80" orientation of the subducting Nazca plate.( 1) The first phase of slope failure is documented by a debris-avalanche deposit, which extends from the lower slope down to 5 km within the trench floor. The deposit originates from the northern wall of a wide valley located along the upper slope. (2) The second phase of slope failure is characterized by a debris-avalanche, with a crescent-shaped scar, located along the middle slope and a hummocky deposit covering the lower slope and extending up to 10 km across the trench. The volume of rock involved in this event is estimated to some 250 km3. The slope failure is assumed to be related to an oversteepening of the middle slope induced by a rollover deformation. (3) The third phase of slope failure corresponds to a translational sliding block and a toppling block with volumes of 6 km3 and 13 km3, respectively. The seismic energy produced during the seismic cycle has greatly increased fracturation and fluids buildup along the area previously weakened by a rollover fold. A restricted N-S folding is observed in the vicinity of the trench, to the north of the two debris-avalanche deposits. It may have formed in relation to the local compression limited to the subduction of the Nazca plate. Sliding and folding thus document the paradox between the compressive regime in the lower plate and the extensional regime in the upper part of the upper plate. IntroductionMost of the large-scale submarine landslides recognised worldwide occur either along intraplate volcanic alignments or along active continental margins. They include landslides along the steep submerged volcanic slopes of the Hawaiian islands (Lipman et al., 1988;Moore et al., 1989), the large landslides from Tristan da Cunha (South Atlantic island) and from El Hierro (Canary islands) described by Holcomb and Searle (1991), the volcanic debris-avalanche along the submerged flank of the Fournaise volcano off the Reunion island (L&at et al., 1989;Cochonat et al., 1990), the giant submarine slide on the northern slope of Puerto Rico island and the giant submarine slump along the northern Chile co...

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Section: Dating Of Rock Samplessupporting

confidence: 52%

Slope instabilities at an active continental margin: large-scale polyphase submarine slides along the northern Peruvian margin, between 5 °S and 6 °S

et al. 1995

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“…Smectite also plays a critical role in the overall fluid budget of a subduction zone (Moore and Vrolijk, 1992). At low temperatures, interstitial-water molecules are transferred to interlayer sites in clay minerals as volcanic ash and volcanic-rock fragments are altered to smectite.…”

Section: Thematic Backgroundmentioning

confidence: 99%

Clay mineralogy and clay geochemistry in the vicinity of the décollement zone, northern Barbados Ridge

Underwood¹,

Deng²

1997

Proceedings of the Ocean Drilling Program, 156 Scientific Results

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Fine-grained sediments recovered during Leg 156 of the Ocean Drilling Program contain assemblages of clay minerals that change considerably with depth. Key structural and stratigraphic features within the toe of the northern Barbados accretionary prism include the basal décollement and a sharp boundary between lithologic Units II and III; this lithologic boundary occurs within the décollement zone. We analyzed three size fractions (4−8 µm, 1−4 µm, and <1 µm) by X-ray diffraction and obtained chemical data from the <1-µm size fractions by scanning electron microscopy coupled with energy dispersive spectroscopy. Relative proportions of expandable clay minerals increase significantly, but erratically, near the top of the décollement zone. Proportions of discrete smectite and smectite-rich illite/smectite (I/S) mixed-layer clays decrease steadily down the décolle-ment zone. The base of the décollement zone is characterized by unusually high concentrations of illite. These changes in clay mineralogy influence the shear strength of claystones at the deformation front and help control the position of the décollement.Relative abundances of illite within all lithofacies units increase in coarser size fractions, and this trend is consistent with a detrital source. Kaolinite does not display any systematic partitioning within Unit II, but its proportions increase in the finer size fractions within Unit III. The smectite content of Unit II increases with decreasing grain size; Unit III shows the opposite trend between particle size and % smectite. Bentonite-like samples probably originated through in situ alteration of disseminated volcanic ash, but we believe that the pyroclastic material was mixed into a background sediment that already contained abundant detrital smectite. Illitic mixed-layer clays within the underthrust domain (Unit III) also appear to be detrital in origin. Correlations among both % smectite and % kaolinite and most major-element oxides are statistically significant, but correlations for illite are not. Expandable clays vary considerably in their chemical make-up; the most common type appears to be a Mg-poor, K-rich, Fe-Al-beidellite. We rely upon actualistic provenance connections for late Quaternary clays to guide our interpretations of Miocene and Oligocene sediment dispersal. If these analogues are valid, then the proto-Orinoco and protoAmazon Rivers were the most important detrital sources for the older hemipelagic and turbidite deposits of Barbados Ridge.

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“…The ¢rst-order implication of uniform L/S ratios would be that there is no signi¢cant di¡erence between the composition of sediment-derived C that makes it into the magma generation zone in Costa Rica versus Nicaragua. One possible explanation is that the uniformly high values re£ect loss of organic C by thermal decomposition in the forearc (see [35]). This would be consistent with the occurrence of methane-rich seeps, o¡-shore mud volcanoes and methane hydrate zones in the forearc region of the Central American arc, as well as at arcs worldwide [36].…”

Section: Sources Of Comentioning

confidence: 99%

Contrasting He–C relationships in Nicaragua and Costa Rica: insights into C cycling through subduction zones

Shaw

Hilton

Fischer

et al. 2003

Earth and Planetary Science Letters

162

160

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We report 3 He/ 4 He ratios, relative He, Ne, and CO 2 abundances as well as N 13 C values for volatiles from the volcanic output along the Costa Rica and Nicaragua segments of the Central American arc utilising fumaroles, geothermal wells, water springs and bubbling hot springs. CO 2 / 3 He ratios are relatively constant throughout Costa Rica (av. 2.1U10 10 ) and Nicaragua (av. 2.5U10 10 ) and similar to arcs worldwide (V1.5U10 10 ). N 13 C values range from 36.8x (MORB-like) to 30.1x (similar to marine carbonate (0x)). 3 He/ 4 He ratios are essentially MORBlike (8 þ 1 R A ) with some samples showing evidence of crustal He additions^water spring samples are particularly susceptible to modification. The He^CO 2 relationships are consistent with an enhanced input of slab-derived C to magma sources in Nicaragua ((L+S)/M = 16; where L, M and S represent the fraction of CO 2 derived from limestone and/or marine carbonate (L), the mantle (M) and sedimentary organic C (S) sources) relative to Costa Rica ((L+S)/ M = 10). This is consistent with prior studies showing a higher sedimentary flux to the arc volcanics in Nicaragua (as traced by Ba/La, 10 Be and La/Yb). Possible explanations include: (1) offscraping of the uppermost sediments in the Costa Rica forearc, and (2) a cooler thermal regime in the Nicaragua subduction zone, preserving a higher proportion of melt-inducing fluids to subarc depths, leading to a higher degree of sediment transfer to the subarc mantle. The absolute flux of CO 2 from the Central American arc as determined by correlation spectrometry methods (5.8U10 10 mol/yr) and CO 2 / 3 He ratios (7.1U10 10 mol/yr) represents approximately 14^18% of the amount of CO 2 input at the trench from the various slab contributors (carbonate sediments, organic C, and altered oceanic crust). Although the absolute flux is comparable to other arcs, the efficiency of CO 2 recycling through the Central American arc is surprisingly low (14^18% vs. a global average of V50%). This may be attributed to either significant C loss in the forearc region, or incomplete decarbonation of carbonate sediments at subarc depths. The implication of the latter case is that a large fraction of C (up to 86%) may be transferred to the deep mantle (depths beyond the source of arc magmas). ß

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Fluids in accretionary prisms

Cited by 528 publications

References 134 publications

Slope instabilities at an active continental margin: large-scale polyphase submarine slides along the northern Peruvian margin, between 5 °S and 6 °S

Slope instabilities at an active continental margin: large-scale polyphase submarine slides along the northern Peruvian margin, between 5 °S and 6 °S

Clay mineralogy and clay geochemistry in the vicinity of the décollement zone, northern Barbados Ridge

Contrasting He–C relationships in Nicaragua and Costa Rica: insights into C cycling through subduction zones

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