Heat flow, arc volcanism, and subduction in northern Oregon

摘要: A total of 75 heat flow measurements are presented for the part Oregon Cascade Range and surrounding provinces, including Willamette Valley, High Lava Plains, Deschutes-Umatilla Plateau, Blue Mountains, between 43°30′ 45°05′N. The data document a major change in regional from values 40±2 mW m−2. Western Valley provinces to 100±5 m−2 along boundary provinces. This variation has half width approximately 10 km appears be exactly same whole study area (a strike length over 150 km). coincides with line hot springs occurs 20–30 west axis where andesite stratovolcanoes Mount Jefferson Three Sisters occur. corresponds steep gravity gradient about an amplitude −25 mGal. Both sets can explained by hot, low-density region 60 wide crust below 7–10 km. source is probably zone temporary residence magmas melting off subduction zone. Such crustal staging chambers may commonly involved complex petrologic evolution andesites granitic rocks volcanic arcs. ratio apparent intrusive extrusive ranges 1:1 counting volcanism 10:1 or 50:1 if only andesitic rhyolitic volcanics included. overall pattern consistent active Juan de Fuca plate under Pacific Northwest. absorption continental outer arc sinking occurrence high associated documented. lack earthquakes Northwest related proximity ridge fact that several kilometers sediment overlie basaltic basement it begins subducted, so already at minimum temperature 100°–200°C. During Oligocene Miocene edge was least 40–60 its present position. last 6–10 m.y. decreased subnormal values. effectiveness as sink thus clearly demonstrated. eastward migration might proposed rotation due Basin spreading.