Migrated Multichannel Seismic-Reflection Records across the Peru Continental Margin

New heat-flow values were obtained in the central Peru Trench area during site surveys and drilling of Ocean Drilling Program (ODP) Leg 112 by measuring temperatures with ordinary surface heat-flow probes and in the drill holes and by estimating from bottom-simulating reflectors resulting from gas hydrates. The values determined by these methods are consistent with each other within the limits of error. When combined with existing data, heat-flow distribution from the trench to the coast was delineated. Heat flow is lower than 40 mW/m 2 at the bottom of the trench and 40 to 50 mW/m 2 on the landward slope. The low heat flow at the trench bottom can be explained partly by a high sedimentation rate. Heat flow is variable about where the Mendana Fracture Zone meets the trench. This low heat flow might result from hydrothermal circulation in the fracture zone, which some scientists believe is a new propagating rift. On the landward slope, no significant difference in heat flow is recognized between the northern side and the southern side of the fracture zone, in spite of differences in the age of the subducting plate and the tectonic history. Heat flow on the landward slope may be slightly higher than that in most other subduction zones.

Section: Estimating From Gas Hydrate Bsrsmentioning

confidence: 99%

Heat-Flow Studies in the Peru Trench Subduction Zone

Yamano¹,

Uyeda²

1990

“…The upper slope is characterized by largescale normal faulting (von Huene and Miller, 1988) and smallerscale faulting observed in cores (for example, Sample 112-679D-7H-7,1-18 cm; see Suess, von Huene, et al, 1988, p. 173), indicating a predominantly brittle deformation. The lower slope is less clearly imaged in seismic profiles, but evidence exists for landward-dipping thrust faults, typical of an accretionary complex.…”

Section: Introductionmentioning

confidence: 99%

“…The upper-and lower-slope regions have distinctively different tectonic characters. The upper slope has undergone uplift, subsidence, and noncompressional deformation since at least the Miocene, whereas the lower slope consists of an accretionary wedge and is dominated by compressional tectonics (von Huene and Miller, 1988).…”

Section: Introductionmentioning

confidence: 99%

Controls on Physical Properties of Peru Continental Margin Sediments and Their Relationship to Deformation Styles

Hill¹,

Marsters²

1990

The state of a sediment undergoing deformation depends upon its initial properties at the time of deposition and its subsequent stress history (including diagenetic changes) during burial. Sediment facies classification can be used to determine the variation in initial properties and the relative control this variation has on properties during burial. On the Peru continental margin, three main facies have been identified: laminated diatomaceous mud, massiveto-bioturbated diatomaceous mud, and terrigenous mud. These facies exhibit a gradation in properties, with the laminated diatomaceous mud having very high liquid limit, water content, and shear strength, compared to the terrigenous facies, and with the massive-to-bioturbated facies showing intermediate properties. The properties of the diatomaceous sediments are interpreted to result from a strong particle framework provided by the diatom frustules, which support a high proportion of the sediment load. Dolomitization during burial appears to enhance particle framework strength and results in a heterogeneous sediment column. The development of numerous rupture or fault surfaces, as commonly observed in upper-slope cores from Leg 112, is interpreted as the result of strain-softening during deformation. Scaly cleavage, observed at depth in lower-slope cores, is interpreted to result from strain-hardening behavior that takes place during deformation at greater burial depth.

“…In a midslope position, the Yaquina Basin is perched on a foundered, intensely fractured continental plateau. Patchy, elongate, lower-slope basins are ponded behind the crest of a stunted accretionary complex (Trench-Slope Break or "TSB") at the leading edge of the continental block (Hussong et al, 1976;von Huene and Miller, 1988;Moore and Taylor, 1988).…”

Section: Structural and Stratigraphic Settingmentioning

confidence: 99%

“…7). Site 685 is positioned on the narrow accretionary prism along the landward wall of the trench, above a major thrust fault imaged in seismic-reflection records (von Huene and Miller, 1988) and therefore in the pathway of fluids ascending from the subduction zone that may have interacted with the descending oceanic crust. Orogenesis and accelerated convergence during late Miocene time (Cande, 1985;Pardo-Casas and Molnar, 1987) may have intensified onshore erosion, shelf bypassing, and trench sedimentation; the seaward growth, deformation, and dewatering of the accretionary complex; and the ascent of buried pore lilt;] 550 (mM) normal seawater chlorinity < 400 to 550 (mM) freshwater influence > 1000 to 550 (mM) brine influence Figure 11.…”

Section: MMmentioning

confidence: 99%

Carbonate Cementation of Granular and Fracture Porosity: Implications for the Cenozoic Hydrologic Development of the Peru Continental Margin

Suess¹,

Thornburg²

1990

The evolution of pore fluids migrating through the forearc basins, continental massif, and accretionary prism of the Peru margin is recorded in the sequence of carbonate cements filling intergranular and fracture porosities. Petrographic, mineralogic, and isotopic analyses were obtained from cemented clastic sediments and tectonic breccias recovered during Leg 112 drilling. Microbial decomposition of the organic-rich upwelling facies occurs during early marine diagenesis, initially by sulfate-reduction mechanisms in the shallow subsurface, succeeded by carbonate reduction at depth. Microcrystalline, authigenic cements formed in the sulfate-reduction zone are 13 C-depleted (to -20.1% c PDB), and those formed in the carbonate-reduction zone are 13 C-enriched (to +19.0%c PDB). Calcium-rich dolomites and near-stoichiometric dolomites having uniformly heavy S 18 0 values (+2.7 to +6.6%c PDB) are typical organic decomposition products. Quaternary marine dolomites from continental-shelf environments exhibit the strongest sulfate-reduction signatures, suggesting that Pleistocene sea-level fluctuations created a more oxygenated water column, caused periodic winnowing of the sediment floor, and expanded the subsurface penetration of marine sulfate.We have tentatively identified four exotic cement types precipitated from advected fluids and derived from the following diagenetic environments: (1) meteoric recharge, (2) basalt alteration, (3) seafloor venting and (4) hypersaline concentration. Coarsely crystalline, low-magnesium (Lo-Mg) calcite cements having pendant and blocky-spar morphologies, extremely negative S 18 0 values (to -7.5%o PDB), and intermediate S 13C values (-0.4%c to +4.6%c PDB) are found in shallow-marine Eocene strata. These cements are evidently products of meteoric diagenesis following subaerial emergence during late Eocene orogenic movements, although the strata have since subsided to greater than 4,000 m below sea level. Lo-Mg calcite cements filling scaly fabrics in the late Miocene accretionary prism sediments are apparently derived from fluids having lowered magnesium/calcium (Mg/Ca) and 18Q/16Q rat j os; suc h fl u id s m ay have reacted with the subducting oceanic crust and ascended through the forearc along shallow-dipping thrust faults. Micritic, high-magnesium (Hi-Mg) calcite cements having extremely depleted 5 13 C values (to -37.3%c PDB), and a benthic fauna of giant clams (Calyptogena sp.) supported by a symbiotic, chemoautotrophic metabolism, provide evidence for venting of methane-charged waters at the seafloor. Enriched 518 0 values (to +6.6%c PDB) in micritic dolomites from the continental shelf may be derived from hypersaline fluids that were concentrated in restricted lagoons behind an outer-shelf basement ridge, reactivated during late Miocene orogenesis.