Gosnold IASPEI

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HEAT FLOW TRANSECTS ACROSS THE CASCADES AND ANDES MAGMATIC ARCS : 

HEAT FLOW TRANSECTS ACROSS THE CASCADES AND ANDES MAGMATIC ARCS Will Gosnold University of North Dakota, USA Valiya M. Hamza Observatorio Nacional, Rio de Janeiro, Brazil

Overview: 

Overview HFD data Data treatment Characteristics of each HFD profile Tectonic history Tectonic models

Slide3: 

The Global Heat Flow Database of the International Heat Flow Commission Click on the globe to enter                                                                                                                                                                                                   Global Heat Flow ( mW m^2) : 0-40 violet, 40-80 blue, 80-120 green, 120-240 yellow, 240+ red www.heatflow.und.edu

Slide4: 

13-08-2004 Under Construction! We are in the process of uploading data so they can be downloaded as Microsoft Excel 97 spreadsheets or as ASCII files by selecting from the tables below. Not all files are on the server. Continents and Oceans Countries North America & South America   Countries Africa Countries Europe Countries Oceania Home Continents and Oceans www.heatflow.und.edu

Slide5: 

Countries North America & South America   www.heatflow.und.edu

Slide6: 

Residual Heat Flow Density contour map of South America (Hamza et al., 2005)

Slide7: 

Locations of active volcanoes (red triangles) and heat flow sites in South America. Light blue sites are in low-angle subduction area; purple sites are in the high angle subduction area.

Slide10: 

The data were smoothed using a 10-point running mean of heat flow density vs. distance from the volcanic front.

Slide11: 

In the Andes region of steep subduction, HFD increases sharply to >250 mW m-2 at the volcanic front and the high HFD region extends about 200 km behind the VF. At 300 km behind the VF, HFD has declined to 60 mW m-2. HFD is relatively stable in the back arc basins as well as in Precambrian regions to the east, with values in the range of 60 to 80 mW m-2.

Slide12: 

In the Andes region with sub-horizontal subduction, the transition from magmatic arc to craton is indistinguishable from normal crustal HFD variability due to age and radioactive heat production.

Slide13: 

The transect across the Cascades between latitudes 45 N to 49 N shows a narrow band of high HFD over the volcanic arc followed by a gradual increase in HFD from 60 mW m-2 to 80 mW m-2 over a distance of about 800 km. In the region of the Idaho Batholith, between 800 km and 1150 km, HFD is about 80 mW m-2.

Slide14: 

The zone of high HFD is about 300 km wide in the steeply subducting section of the Andean arc and <100 km wide in the Cascade arc. HFD variability in the flat subduction zone is indistinguishable from variability due to crustal age and radioactive heat production.

Tectonic scheme for Altiplano-Puna Volcanic Complex: 

Tectonic scheme for Altiplano-Puna Volcanic Complex 30 ma - Crustal doubling 13 ma – Delamination event 10 ma – Initiation of pulsed emplacement of upper to mid-crustal magmas which fueled eruption of at least 30,000 km3 of ignimbrites 10 ma – emplacement of 1,500 km3 8 ma – emplacement of 2,500 km3 6 ma – emplacement of 5,400 km3 4 ma – emplacement of 10,000 km3

Slide16: 

Temperature contours 13 my after delamination. Magma emplacement in the upper crust is necessary to account for observed heat flow. meters meters meters meters

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Can we detect the delamination event at 13 ma?

Slide18: 

Can we detect the delamination event at 13 ma? NO.

Slide19: 

Plate rollback with counter flow at subduction velocity Plate rollback with counter flow at half subduction velocity Plate rollback with no counter flow

Slide22: 

Andes Surface HFD and Intrusion Models

Slide23: 

Cascades HFD profile

Slide24: 

Locations of active volcanoes (red triangles) and HFD sites in South America. Light blue sites are in low-angle subduction area; purple sites are in the high angle subduction area.

Slide25: 

Locations of HFD sites (purple circles) and active Volcanoes (red triangles) in Cascade range.

Slide26: 

Conclusions In all cases, the high HFD belt coincides with the zone of active volcanism and the amplitude of the HFD anomaly appears to correlate with the angle of subduction. Variable width of the high HFD zones is interpreted to be related to differences in thickness and composition of the local crust, and to the duration of subduction.

Slide27: 

The sharpness of changes in HFD is due to magma emplacement within the past 4 my. The overprint of near surface magmatism masks the thermal effects of delamination. Special acknowledgement of volcanologist Shanaka deSilva for consultation on volcano-tectonic history.

Slide29: 

6 my after delamination 10 my after delamination

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