along strike variations in heat flow
DESCRIPTION
Along Strike Variations in Heat Flow Shallow Thermal Structure of the Middle America Trench, Costa Rica Robert Harris, COAS Oregon State University Ingo Grevemeyer, Leibniz Institute for Marine Sciences, IFM-GEOMAR Thomas Henke, Udo Barckhausen, Christian Mueller, Soenke Neben, - PowerPoint PPT PresentationTRANSCRIPT
Along Strike Variations in Heat Flow
1. Shallow Thermal Structure of the Middle America Trench, Costa Rica
Robert Harris, COAS Oregon State UniversityIngo Grevemeyer, Leibniz Institute for Marine Sciences, IFM-GEOMARThomas Henke, Udo Barckhausen, Christian Mueller, Soenke Neben,Federal Institute for Geosciences and Natural Resources, BGRCesar R. Ranero, ICREA at Instituto de Ciencias del Mar, CSIC,
BarcelonaHeiner Villinger, University of Bremen
2. Heat Flow across Nankai along NanTroSeize Transect
Robert Harris, COAS, Oregon State UniversityFriederike Schmidt-Scheirhorn, University of BremenIODP Scientists Expedition 314/315/316
Shallow Thermal Structure of the Middle America Trench, Costa Rica
0 50 100 1500
20
40
60
80
100
120
140
160
180
Observed Gradient (°C/km)
BSR Gradient (°C/km)
0 50 100 1500
20
40
60
80
100
120
140
160
180
Observed Heat Flow (mW/m2)
BSR Heat Flow (mW/m
2)
0 10 20 30 40-40
-20
0
20
40
60
80
Deviation Obs - BSR Grad (°C/km)
Distance from Def Front (km)0 10 20 30 40-40
-20
0
20
40
60
80
Deviation Obs - BSR HF (mW/m
2)
Distance from Def Front (km)
Correlation betweenobserved and BSRderived estimates ofheat flow
Heat Flowq=k T/z
Heat Flow at Selected Areas
Mound Culebra
Heat Flow Map, Costa Rica
-87° -86° -85° -84° -83°
8°
9°
10°
11°
20
40
2040
60
80100
Heat Flow in mW/m2
Contour Interval 20 mW/m2
L
H
Table 1. Model Parameters
Unit Thermal
Conductivity
W m-1 K-1
Heat
Capacity
MJ K-1 m-3
Heat
Production
μ W m-3
Crus t (0-20 km) 2.7 -- 1.5Crus t (20-40 km) 2.7 -- 0.3Mantl e Wedge 2.9 -- 0.03Sediments 1.2 2.6 0.60Ocea nicPlate 2.9 3.3 0.03
Conclusions1. Good correlation between observed values of heat
flow and derived values of heat flow based on BSRs.2. Variations of heat flow observed along strike, likely due
to fluid flow.3. For shallow subduction zone, conductive reference
models are inadequate.
Take home points1. Variations in heat flow along strike important for better
understanding thermal regime of subduction.2. Fluid flow likely modifying temperatures along
subduction thrust3. Need to incorporate fluid flow in thermal models of
shallow subduction zone (Nusselt number approximateion, e.g., Spinelli et al.)
Heat flow along Nankai Trough
SW NEFossil Spreading
Center
0
100
200
300
Sedimentation
Heat Flow (mW/m
2)
-200 -100 0 100 200 300 400
Distance Along Trough Axis (km)
Yamano et al., 2003
Cross section of holes and seismic line along NanTroSeize Transect
Philippine Sea platemegasplay
top of subducting basement
accretionary prism
forearc basin
0
50
100
150
200
250
300
350
0
50
100
150
200
250
300
0
100
200
300
400
500
600
700
Temperature
Thermal Conductivity
Residual Temperature
C0002KumanoBasin
C0001
C0007
C0006C0008a
C0004C0008c
FrontalThrust
Thermal Resistance (m
2K/W)
Depth (m)
Depth (m)
5°C
1 °C
2 W/m/K
Shallow Megasplay
NW SE
Conclusions
1. APCT3 and DVTP provide internally consistent and high quality results.
2. Heat flow values determined from drilling are generally lower than those determined from shallow probe data, especially towards the deformation front.
3. Reconciling these lower values obtained deeper in the section with shallow probe measurements requires a concave thermal gradient.
4. Along strike variations in heat flow are observed and shallow portion of subuction thrust is not adequately modeled using conductive reference models.