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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS017 Oral Presentation 2363
Evolution of shallow crustal thermal structures from subduction to
collision in Taiwan Region
Dr. Wu-Cheng Chi
Institute of Earth Sciences Academia Sinica IASPEI
Donald L. Reed
We study crustal thermal evolution by examining heat flow patterns along a convergent boundary from
a young subduction zone to a more structurally-mature collision zone. More than 8000 km of seismic
profiles covering a region of 45,000 km2 offshore southern Taiwan show wide spread bottom simulating
reflectors (BSRs). We derived 1107 BSR-based heat flows before combining additional 42 published
offshore thermal probe data and 86 onland heat flow data to document the shallow forearc thermal
structures from the subduction zone to the collision zone. In the subduction zone geothermal gradient
ranges mostly within 30 to 80 oC/km, and decreases toward the ridge due to intensive dewatering at
the toe, sediment blanketing effect, topographic effect, cooling from the subducting plate, and other
processes. The temperature-depth relation derived from BSRs in the initial collision zone can be
explained by a model with a maximum vertical steady-state flow rate of 6.7 mm/yr, suggesting possible
upward fluid migration at the shallow depths. The heat flow reduction from blanketing effect can be
reduced up to 50% due to fast sedimentation rates near the continental slope. The geothermal
gradients range mostly from 30 to 90 oC/km in the collision zone, and increase, instead of decrease,
toward the ridge, possibly caused by exhumation, erosion, topographic-induced ground water
circulation, and some upper mantle processes related to collision. Heat flow in collision zone ranges
from 80 to 250 mW/m2. The high heat flow in collision zone correlates with shallower seismicity zone
and high seismic attenuation. While the lower heat flow in the subduction zone might allow the
earthquakes rupture to greater depth. The drastic increase in heat flow along the ridge from subduction
to collision zone may cause overestimates in exhumation rates if a constant 30 oC/km geothermal
gradient was used in fission track studies.
Keywords: heat flow, collision zone, bsr