SUBDUCTION TECTONICS, MAGMATISM AND SURFACE HEAT FLOW IN THE ANDEAN ARC Will Gosnold and Shan de Silva

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

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, blue, green, yellow, 240+ red

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 Afric a xlsxls or ASCII ASCII Asia xlsxls or ASCII ASCII Antar ctica Aust ralia xls xls or ASCII ASCII Nort h Amer ica xlsxls or ASCII ASCII Glob al in RTF form at Euro pe xls xls or ASCII ASCII Sout h Amer ica xlsxls or ASCII ASCII East ern North Pacifi c East ern North Pacifi c West ern North Pacifi c West ern Sout h Pacifi cWest ern Sout h Pacifi c Cont inent al Data xls xls or ASCII ASCII Easte rn Sout h Pacifi c Nort h Atlan tic Ocea n xlsxls or ASCII ASCII India n Ocea n Medi terra nean area seasMedi terra nean area seas Ocea nic Refer ence s Refer ence s Mari ne Data xls xls or ASCII ASCII Countries North America & South America Arge ntina xlsxls or ASCII ASCII Berm uda xlsxls or ASCII ASCII Bolivi a xlsxls or ASCII ASCII Brazil xlsxls or ASCII ASCII Cana da xlsxls or ASCII ASCII Chile xlsxls or ASCII ASCII Colu mbia xlsxls or ASCII ASCII Cuba xlsxls or ASCII ASCII Ecua dor xlsxls or ASCII ASCII Mexi co xlsxls or ASCII ASCII Pana ma xlsxls or ASCII ASCII Peru xlsxls or ASCII ASCII Puert o Rico xlsxls or ASCII ASCII USA xlsxls or ASCII ASCII Countries Africa Countries Europe Austria xlsxls or ASCII ASCII Bulgaria xlsxls or ASCII ASCII Czech Republic & Slovakia xlsxls or ASCII ASCII Denmark xlsxls or ASCII ASCII Finland xlsxls or ASCII ASCII France Germany xlsxls or ASCII ASCII Great Britain xls xls or ASCII ASCII Greece xlsxls or ASCII ASCII Hungary xlsxls or ASCII ASCII Ireland xlsxls or ASCII ASCII Italy xlsxls or ASCII ASCII Iceland xlsxls or ASCII ASCII Norway xlsxls or ASCII ASCII Poland xlsxls or ASCII ASCII Romania xlsxls or ASCII ASCII Spain xlsxls or ASCII ASCII Sweden xlsxls or ASCII ASCII Switzerlan d xlsxls or ASCII ASCII Countries Oceania Australia xls xls or ASCII ASCII Japan xlsxls or ASCII ASCII New Zealand xls xls or ASCII ASCII Philippines xls xls or ASCII ASCII Sumatra xlsxls or ASCII ASCII Home Continents and Oceans Africa xlsxls or ASCIIASCII Asia xlsxls or ASCIIASCII Antarctica Australia xls xls or ASCIIASCII North America xlsxls or ASCIIASCII Global in RTF format Europe xls xls or ASCIIASCII South America xlsxls or ASCIIASCII Eastern North Pacific Eastern North Pacific Western North Pacific Western South PacificWestern South Pacific Continental Data xls xls or ASCIIASCII Eastern South Pacific North Atlantic Ocean xlsxls or ASCIIASCII Indian Ocean Mediterranean area seasMediterranean area seas Oceanic References References Marine Data xls xls or ASCIIASCII

Countries North America & South America Argentina xlsxls or ASCII ASCII Bermuda xlsxls or ASCII ASCII Bolivia xlsxls or ASCII ASCII Brazil xlsxls or ASCII ASCII Canada xlsxls or ASCII ASCII Chile xlsxls or ASCII ASCII Columbia xlsxls or ASCII ASCII Cuba xlsxls or ASCII ASCII Ecuador xlsxls or ASCII ASCII Mexico xlsxls or ASCII ASCII Panama xlsxls or ASCII ASCII Peru xlsxls or ASCII ASCII Puerto Rico xlsxls or ASCII ASCII USA xlsxls or ASCII ASCII

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

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.

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

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.

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.

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 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 km 3 of ignimbrites 10 ma – emplacement of 1,500 km 3 8 ma – emplacement of 2,500 km 3 6 ma – emplacement of 5,400 km 3 4 ma – emplacement of 10,000 km 3

Sources of anomalously high heat flow 1.Long-period of conductive heating 2.Magmatism in middle and upper crust

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

Can we detect the delamination event at 13 ma?

Can we detect the delamination event at 13 ma using surface heat flow?

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

Andes Surface HFD and Intrusion Models

Cascades HFD profile

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.

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

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.

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.