Heat flow in the Southern Chile Forearc controlled by large-scale tectonic processes

Villar Munoz, Luica, Diaz Naveas, J. and Behrmann, Jan H. (2012) Heat flow in the Southern Chile Forearc controlled by large-scale tectonic processes [Poster] In: The Lübeck Retreat, Collaborative Research SFB 574 Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters, 23.-25.05.2012, Lübeck.

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From north to south, the Southern Chile forearc is affected by the subduction of the aseismic Juan
Fernandez Ridge, a number of major oceanic fracture zones on the downgoing Nazca Plate, the
active Chile Ridge spreading center, and underthrusting of the Antarctic Plate. The tectonic structure
is characterized by intense deformation of the lower continental slope within a variably wide
accretionary wedge. In places the middle and upper slope is affected by out-of-sequence
overthrusting and by normal faulting. In the area of the Chile Triple Junction at 46°S latitude most of
the forearc is destroyed by subduction erosion, to be rebuilt further south by sediment offscraping and
accretion from the Antarctic Plate.
The Southern Chile forearc has been intensively explored by reflection seismic surveys, and has been
drilled by the Ocean Drilling Program during two expeditions (ODP Leg 141 - Behrmann et al., 1992;
ODP Leg 202 – Mix et al., 2003). The widespread occurrence of gas hydrates has been known for
some time. Regarding the analysis of reflection seismic sections we have used data of R/V SONNE
Expeditions 101 and 161, R/V VIDAL GORMAZ Expeditions VG02 and VG06, and R/V ROBERT
CONRAD Cruises RC2901 and RC2902. Using bottom water temperature data obtained from the
World Ocean Data Base (NOAA) and an acoustic velocity model constrained from the seismic
sections, and measurements of temperature, thermal conductivity and acoustic velocity from ODP
boreholes, we use the position of the Bottom Simulating Reflector (BSR) in reflection seismic sections
to estimate the heat flow through the forearc in an area between 32°S and 47°S latitude.
Heat flow in most of the upper and middle continental slope is on the order of 50-80 mWm-2. This is
normal for continental basement and overlying slope sediments, and is true also for those parts in the
south of the area that are being underthrusted by hot, young oceanic crust. The middle and lower
slopes, however, in some places display up to 50% increased heat flow. Here the sea floor is
underlain by zones of active deformation and accretionary wedge building. This observation cannot
be easily reconciled with models of conductive heat transfer, but is an indication that advecting pore
fluids from deeper in the subduction zone may transport a substantial part of the heat there. The size
of the anomalies indicates that fluid advection and outflow at the sea floor is diffuse rather than being
restricted to individual fault structures, or mud volcanoes and mud mounds, as is the case in other
convergent margins.
A large area with higher heat flow correlate in space with tectonic phenomena, however. On the lower
slope above the subducting Chile Ridge at 46°S, values of up to 280 mWm-2 indicate that the
overriding South American Plate is effectively heated by subjacent zero-age oceanic plate material on
a regional scale.
Behrmann, J.H., Lewis, S.D., Musgrave R., et al. (1992) Proceedings of the Ocean Drilling Program, Initial Reports, 141. Ocean
Drilling Program. College Station, TX
Mix, A.C., Tiedemann, R., Blum, P., et al. (2003) Proceedings of the Ocean Drilling Program Initial Reports, 202. Ocean Drilling
Program, College Station, TX.

Document Type: Conference or Workshop Item (Poster)
Keywords: Geodynamics
Research affiliation: OceanRep > SFB 574 > C5
OceanRep > SFB 574
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
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Date Deposited: 21 Sep 2012 11:12
Last Modified: 21 Sep 2012 11:12
URI: http://eprints.uni-kiel.de/id/eprint/15337

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