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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Crustal structure beneath the central Oregon convergent margin from potential-field modeling: Evidence for a buried basement ridge in local contact with a seaward dipping backstop
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Crustal structure beneath the central Oregon convergent margin from potential-field modeling: Evidence for a buried basement ridge in local contact with a seaward dipping backstop

机译：俄勒冈州中部汇聚边缘下方的地壳结构（通过势场模拟得出）：地下埋藏的脊脊与向海浸入式止挡块局部接触的证据

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Models of magnetic and gravity anomalies along two E-W transects offshore central Oregon, one of which is coincident with a detailed velocity model, provide quantitative limits on the structure of the subducting oceanic crust and the crystalline backstop. The models indicate that the backstop-forming western edge of the Siletz terrane, an oceanic plateau that was accreted to North America approx 50 million years ago, has a seaward dip of less than 60 deg 3. Seismic, magnetic, and gravity data are compatible with no more than 2 km of subducted sediments between the Siletz terrane and the underlying crystalline crust of the Juan de Fuca plate. The data also suggest the presence of a N-S trending, 200-km-long basaltic ridge buried beneath the accretionary complex from about 43 deg N to 45 deg N. Although the height and width of this ridge probably vary along strike, it may be up to 4 km high and several kilometers wide in places and appears to be locally in contact with the Siletz terrane beneath Heceta Bank. Several models for the origin of this ridge are discussed. These include: a sliver of Siletz terrane detached from the main Siletz terrane during a late Eocene episode of strike-slip faulting; imbrication and thickening of subducted oceanic crust in place; an aseismic ridge rafted in on the subducting oceanic crust during the past 1.2 million years; and a series of ridges and/or seamounts rafted in over a longer period of time and transferred from the subducting plate to the overlying plate. The last model is the most consistent with the complicated history of local uplift, subsidence, and slope instability recorded in the ridges, basins, and banks of this part of the margin. We speculate that the massive seaward dipping western edge of the Siletz terrane in this region inhibits subduction of seamounts and sediments, resulting in fomation of buried ridge as the accumulated flotsam and jetsom of subduction. This process may also be responsible for thickening of lower accretionary complex material, over-steepening of slopes leading to massive slumping, and north-south extension through strike-slip faulting in the accretionary complex to the west of the buried ridge. Regardless of its origin, the ridge may currently be acting as an asperity inhibiting subduction.
机译：沿俄勒冈州中部两个E-W断面的磁异常和重力异常模型，其中之一与详细的速度模型相吻合，为俯冲洋壳和晶体支撑物的结构提供了定量限制。这些模型表明，形成于西勒兹地形的逆止点的西边缘是一个在大约5000万年前就被北美洲吸积的海洋高原，其向海倾角小于3度。地震，磁和重力数据是兼容的在Siletz地层与胡安德富卡板块的下层结晶壳之间的俯冲沉积物不超过2 km。数据还表明，在增生复合体的下方埋藏着从约43度N到45度N趋势的，有200 km长的NS趋势的玄武岩脊。尽管该脊的高度和宽度可能沿走向变化，但可能向上高达4公里，宽达数公里的地方，似乎与Heceta Bank下方的Siletz地形接触。讨论了该山脊起源的几种模型。其中包括：在始新世晚期走滑断层期间，从主Siletz地块中分离出的Siletz地块条;俯冲洋壳的激化和增厚;在过去的120万年中，俯冲的洋壳上漂流了一个抗震脊;一连串的山脊和/或海山在较长的时间内漂流并从俯冲板转移到上覆板。最后一个模型与在该部分边缘的山脊，盆地和河岸记录的局部隆起，沉降和边坡失稳的复杂历史最为一致。我们推测，该地区Siletz地块向西的大倾角向西倾斜，抑制了海山和沉积物的俯冲，导致了潜伏脊的积聚，形成了积聚的浮游物和俯冲的喷射。该过程还可能导致增生复合物下部材料变厚，斜坡过度加深导致大量塌陷，以及增生复合体中走滑断层向埋入山脊西部的南北延伸。无论其起源如何，洋脊目前都可能充当抑制凹凸不平的俯冲作用。

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