Abrupt thermal transition reveals hydrothermal boundary and role of seamounts within the Cocos Plate

Fisher, A. T.; Stein, Carol A.; Harris, Robert N.; Wang, Kelin; Silver, Eli A.; Pfender, M.; Hutnak, M.; Cherkaoui, A.; Bodzin, R.; Villinger, Heinrich

doi:10.1029/2002gl016766

Cited by 136 publications

(239 citation statements)

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“…The Cocos plate has a complex tectonic history in the Ticoflux II area, comprising basalt crust generated at the EPR (East pacific Rise) at fast spreading rates and at the CNS (Cocos-Nasca Spreading Center) at intermediate spreading rates. The heat-flow measured on EPR generated crust is typically 90% below theoretical heat-flow predicted by the conductive lithosphere model, suggesting that cooling has been strongly accelerated by the circulation of hydrothermal fluids (Vacquier and Sclater, 1967;Von Herzen and Uyeda, 1963;Fisher et al, 2003). In contrast, the heat flow of CNS generated crust is in good agreement with calculated conductive heat-flow values.…”

Section: Regional Settingsupporting

confidence: 65%

“…1a). The aim of this expedition was to study the impact of low temperature ridgeflank hydrothermal activity on the cooling rate of the Cocos plate consisting of a 18-24 Ma-old crust (Fisher et al, 2003). The Cocos plate has a complex tectonic history in the Ticoflux II area, comprising basalt crust generated at the EPR (East pacific Rise) at fast spreading rates and at the CNS (Cocos-Nasca Spreading Center) at intermediate spreading rates.…”

Section: Regional Settingmentioning

confidence: 99%

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Characterization of metalliferous sediment from a low-temperature hydrothermal environment on the Eastern Flank of the East Pacific Rise

et al. 2008

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Metalliferous deposits are described from the eastern flank of the East Pacific Rise (EPR) offshore Costa Rica, close to a basaltic seamount called "Dorado high".Based on heat-flow data and porewater profiles, the site is an area of active low temperature hydrothermal discharge. We focus on the mineralogical and chemical analyses from a 124 cm long gravity core (GC50), located on the north-western slope of the 100 m high Dorado high. In this core, the sediments consist of detrital clay minerals as well as authigenic minerals such as zeolites, apatites, and Fe/Mn-rich oxyhydroxides. In contrast, the reference sediments from adjacent areas without hydrothermal activity are olive gray hemipelagic muds composed of volcanic glass particles, clay minerals, siliceous microfossils, and some detrital quartz and feldspar.Bulk sediment chemistry and chemical enrichment factors calculated with respect to the reference sediment indicate that the most important chemical changes occurred at the base of the core from 100 to 124 cm bsf, with strong enrichments in MnO, CaO, P 2 O 5 , and Fe 2 O 3 . These enrichments are correlated with the occurrence of authigenic Fe-oxyhydroxide (goethite) and Mn oxide (todorokite and vernadite, at 100 cm bsf), and hydrothermal apatite (110-124 cm bsf). In the upper section of the core from 12 to 70 cm, the sediment is composed of abundant smectite and authigenic phillipsite, and only minor chemical changes can be observed with respect to the reference sediments.The ubiquitous presence of phillipsite suggests that the entire sedimentary column of core GC50 was first affected by diagenesis. However, below 70 cm bsf, these phillipsites are partially dissolved and Fe oxides occur from 110 to 124 cm, followed 2 upward by Mn oxides at 100 cm. This transition from Fe to Mn rich sediments can be interpreted in terms of an upward increasing redox potential. PAAS-normalized REE patterns of GC50 sediments present clearly negative Ce and positive Y anomalies inherited from seawater at the base of core GC50. These anomalies decrease upward, which we interpret together with the transition from Fe to Mn-rich sediments by an upward migrating low temperature hydrothermal fluid. Thus, after a first stage of diagenesis, the discharge of a low temperature hydrothermal fluid occurred through the sedimentary column, leading to the precipitation of hydrothermal compounds that are lacking towards the surface.

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Section: Regional Settingsupporting

confidence: 65%

Section: Regional Settingmentioning

confidence: 99%

Characterization of metalliferous sediment from a low-temperature hydrothermal environment on the Eastern Flank of the East Pacific Rise

et al. 2008

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“…The transition between the low and high heat flow generally correlates with the extension of the plate suture but is also influenced by the proximity of seamounts (Fisher et al, 2003) and appears relatively abrupt. High wavenumber variations in the heat flow data are interpreted as focused fluid flow through the margin near the deformation front (Harris et al, 2010a(Harris et al, , 2010b. …”

mentioning

confidence: 99%

“…These profiles show strong variations along strike consistent with regional heat flow data on the incoming Cocos plate. Along the margin underthrust by EPR crust, heat flow is low (Langseth and Silver, 1996;Fisher et al, 2003;Hutnak et al, 2007), whereas along the margin underthrust by CNS crust, heat flow is generally high. The transition between the low and high heat flow generally correlates with the extension of the plate suture but is also influenced by the proximity of seamounts (Fisher et al, 2003) and appears relatively abrupt.…”

mentioning

confidence: 99%

“…Along the margin underthrust by EPR crust, heat flow is low (Langseth and Silver, 1996;Fisher et al, 2003;Hutnak et al, 2007), whereas along the margin underthrust by CNS crust, heat flow is generally high. The transition between the low and high heat flow generally correlates with the extension of the plate suture but is also influenced by the proximity of seamounts (Fisher et al, 2003) and appears relatively abrupt. High wavenumber variations in the heat flow data are interpreted as focused fluid flow through the margin near the deformation front (Harris et al, 2010a(Harris et al, , 2010b.…”

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Expedition 344 summary

Li¹,

Malinverno²,

Torres³

et al. 2013

Proceedings of the IODP

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Expedition 344 summaryProc. IODP | Volume 344 2 from velocity-strengthening to velocity-weakening friction, and shear becomes localized. The onset of seismogenic behavior is correlated with the intersection of the 100°-150°C isotherm and the subduction thrust (Hyndman et al., 1997;Oleskevich et al., 1999). With increasing depth down the subduction thrust, the frictional characteristics undergo a second transition either due to the juxtaposition with the forearc mantle or because the rocks are heated to 350°-450°C and can no longer store elastic stresses needed for rupture. Transitional regions between the three zones have conditional stability and can host rupture but are generally not thought to be regions where large earthquakes initiate.Although this three-zone two-dimensional view of the subduction thrust provides a reasonable framework, it is simplistic. Rupture models for large subduction earthquakes suggest significant fault plane heterogeneity in slip and moment release that in three dimensions is characterized as patchiness (Bilek and Lay, 2002). Additionally, we now know the transition zone from stable to unstable sliding is not simple but hosts a range of fault behaviors that includes creep events, strain transients, slow and silent earthquakes, and low-frequency earthquakes (Peng and Gomberg, 2010;Beroza and Ide, 2011;Ide, 2012).Fundamentally unknown are the processes that change fault behavior from stable sliding to stick-slip behavior. Understanding these processes is important for understanding earthquakes, the mechanics of slip, and rupture dynamics. For a fault to undergo unstable slip, fault rocks must have the ability to store elastic strain, be velocity weakening, and have sufficient stiffness. Hypotheses for mechanisms leading to the transition between stable and unstable slip invoke temperature, pressure, and strain-activated processes that lead to downdip changes in the mechanical properties of rocks. These transitions are also sensitive to fault zone composition, lithology, fabric, and fluid pressures.The composition of the material in the fault zone and its contrast with the surrounding wall rock play a key role in rock frictional behavior. The frictional state of the incoming sediment changes progressively with increasing temperature and pressure as it travels downdip. Important lithologic factors influencing friction are composition, fabric, texture, and cementation of rocks, as well as fluid pore pressure (Bernabé et al., 1992;Moore and Saffer, 2001;Beeler, 2007;Marone and Saffer, 2007;Collettini et al., 2009). For example, fault rocks with high phyllosilicate content are generally weaker than rocks with low phyllosilicate content (Ikari et al., 2011). Sediment properties including porosity, permeability, consolidation state, and alteration history also exert a strong influence on fault zone behavior. At erosive margins, where the plate boundary cuts into the overriding plate, the composition and strength of the upper plate is also important (McCaffrey, 1993).Field observations and la...

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Seafloor basalt alteration and chemical change in the ultra thinly sedimented South Pacific

Zhang

Smith-Duque

2014

Geochem Geophys Geosyst

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Determining the relationship between ocean floor basalt alteration and sedimentation is fundamental to understanding how oceanic crust evolves with time. Ocean floor basalts recovered at IODP Sites U1365 (100 Ma) and U1368 (13.5 Ma) in the South Pacific have been subjected to remarkably low sedimentation rates (0.71 and 1.1 m/Myr 21 , respectively). We report detailed petrographic and geochemical analysis of basalt cores from these sites in order to investigate what impact sediment insulation has on seafloor alteration beyond 10-15 Myr of ocean crust formation. Both sites exhibit low-temperature (<150 C) alteration (e.g., iron-hydroxides, carbonate, and quartz) within a predominantly oxidative regime, albeit with markedly different alteration styles and intensity. Alteration at Site U1365, which is predominantly composed of sheet flows, occurs mainly near sheet flow boundaries and fractures. In contrast, Site U1368 comprises interlayered pillows and thin sheet flows that have been subjected to relatively even levels of alteration. Variation of alteration style and intensity between Sites U1365 and U1368 appear closely tied to lithology and crustal structure. Although alteration-induced elemental changes at both sites are similar in, e.g., increasing K, Rb, U, Ba, and Fe 31 and decreasing Fe 21 , Ca, and Ni, they show distinct differences in Th, which is significantly decreased at Site U1365 but relatively constant at Site U1368. At both sites enrichment of LREEs relative to HREEs is ascribed to alteration. The greater vein abundance and notably higher Fe 31 /TiO 2 , K 2 O/TiO 2 , LOI/TiO 2 , and Rb/TiO 2 ratios of representative samples at Site U1365 compared to Site U1368 are attributed to increased alteration intensity. This is mirrored by greater overall chemical change (Fe 2 O 3 , FeO, CaO, K 2 O, Li, Rb, Pb, and U) observed at Site U1365 than those of Site U1368 and other DSDP/ODP sites between 6 and 46 Ma. Since both Sites U1365 and U1368 endured only minimal sedimentation, we attribute the differences in overall chemical change across the two sites to duration of exposure to seawater.

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Abrupt thermal transition reveals hydrothermal boundary and role of seamounts within the Cocos Plate

Cited by 136 publications

References 29 publications

Characterization of metalliferous sediment from a low-temperature hydrothermal environment on the Eastern Flank of the East Pacific Rise

Characterization of metalliferous sediment from a low-temperature hydrothermal environment on the Eastern Flank of the East Pacific Rise

Expedition 344 summary

Seafloor basalt alteration and chemical change in the ultra thinly sedimented South Pacific

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