Analysis of the Wallowa-Baker terrane boundary: Implications for tectonic accretion in the Blue Mountains province, northeastern Oregon
Analysis of the Wallowa-Baker terrane boundary: Implications for tectonic accretion in the Blue Mountains province, northeastern Oregon
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瓦洛瓦-贝克地体边界分析：对俄勒冈州东北部蓝山省构造增生的影响
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
Kenneth Johnson
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作者：
J. Schwartz;A. Snoke;C. Frost;Calvin G. Barnes;L. Gromet;Kenneth Johnson
贝克地体，暴露于俄勒冈州东北部的蓝山省，是一个长寿命的古代（古生代晚期-中生代早期）增生杂岩，具有相关的前弧。这个复合地形位于瓦洛瓦和奥尔兹费里岛弧地形之间。贝克地体的北缘是一个宽阔的带（约25公里宽），由断界的瓦叠板和变质火成岩和变质沉积岩片组成，断裂成埃尔克霍恩岭泥质岩的燧石-泥质岩混杂岩。构造单元内的变质岩在231 ~ 226 Ma之间结晶，具有较低的初始87 Sr/ 86 Sr比值（0.7033 ~ 0.7034）和正的初始e Nd值（+7.7 ~ +8.5）。硅质泥质岩的初始87 Sr/ 86 Sr值在0.7073 ~ 0.7094之间，初始e Nd值在−4.7 ~−7.8之间。我们将这个广阔的叠瓦状断裂带解释为一个基本的构造边界，它将远端瓦洛瓦岛弧地体与贝克增生复杂地体分开。我们认为，这一地块边界是一个广泛的叠瓦构造带的一个例子，该叠瓦构造带由板块和弧形地壳片组成，在构造上混合在一个增生杂岩中，为赤道中部印度太平洋地区摩鹿加海边缘发育的实际弧-弧碰撞带提供了陆地上的古代模拟。
The Baker terrane, exposed in the Blue Mountains province of northeastern Oregon, is a long-lived, ancient (late Paleozoic–early Mesozoic) accretionary complex with an associated forearc. This composite terrane lies between the partially coeval Wallowa and Olds Ferry island-arc terranes. The northern margin of the Baker terrane is a broad zone (>25 km wide) of fault-bounded, imbricated slabs and slices of meta-igneous and metasedimentary rocks faulted into chert-argillite melange of the Elkhorn Ridge Argillite. Metaplutonic rocks within tectonic units in this zone crystallized between 231 and 226 Ma and have low initial 87 Sr/ 86 Sr ratios (0.7033–0.7034) and positive initial e Nd values (+7.7 to +8.5). In contrast, siliceous argillites from the chert-argillite melange have initial 87 Sr/ 86 Sr values ranging from 0.7073 to 0.7094 and initial e Nd values between −4.7 and −7.8. We interpret this broad, imbricate fault zone as a fundamental tectonic boundary that separates the distal, Wallowa island-arc terrane from the Baker accretionary-complex terrane. We propose that this terrane boundary is an example of a broad zone of imbrication made up of slabs and slices of arc crust tectonically mixed within an accretionary complex, providing an on-land, ancient analogue to the actualistic arc-arc collisional zone developed along the margins of the Molucca Sea of the central equatorial Indo-Pacific region.