Geophysical Observations of Slope Deposits, Middle America Trench off Guatemala.

von Huene, Roland, Ladd, J. and Norton, I. (1982) Geophysical Observations of Slope Deposits, Middle America Trench off Guatemala. Open Access Initial Reports of The Deep Sea Drilling Project, 67 . pp. 719-732. DOI 10.2973/dsdp.proc.67.138.1982.

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Slope deposits drilled during Leg 67 were later detailed in redisplayed seismic-reflection records. These deposits are
of significantly lower seismic velocity and probably lower density than the underlying basement. This relationship indicates
a contact between rocks of differing consolidation rather than a continuous sedimentary sequence. The slope
deposits cover basement terranes of three different topographies. The shelf edge is an arch whose seaward flank forms a
steep (up to 15°) upper slope. The midslope area has a rugged topography covered by thick slope deposits. The lower
slope is relatively smooth except where broken locally by benches. The upper and middle slope areas are associated with
strong magnetic anomalies and rare, landward-dipping reflections truncated by the rough surface. The rough midslope
topography may reflect erosion succeeding the Paleocene uplift of this area and at least local subsidence in the early
Miocene. Slope deposits covered the Trench landward slope, contemporaneous with the increased arc volcanism indicated
by ash layers and with the present period of subduction.
The subducting ocean crust and sediment of the Cocos Plate has a linear horst and graben topography of hundreds
of meters relief that disappears beneath the landward slope of the Trench without disturbing its topography. This
passive assimilation of oceanic material without significant accretion in the late Neogene argues for significant decoupling
at the front of the subduction zone.
A base of gas-hydrate reflection is evident in many of the redisplayed seismic records off Guatemala. These reflections
are most common where slope deposits are thick; the reflections have not been identified in the underlying
acoustic basement. This observation is consistent with the geochemical evidence that gas hydrate has its source in the organic-
rich slope sediment. The hydrate depth and the temperature measurements in drill holes indicate a temperature
gradient of 30°C/km.

Document Type: Article
Keywords: Slope deposits, Guatemala, Middle America Trench, IPOD drilling
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.2973/dsdp.proc.67.138.1982
Projects: DSDP
Date Deposited: 10 Oct 2016 13:38
Last Modified: 10 Oct 2016 13:38

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