Formation of high‐pressure metabasites in the southern Appalachian Blue Ridge via Taconic continental subduction beneath the Laurentian margin
Formation of high‐pressure metabasites in the southern Appalachian Blue Ridge via Taconic continental subduction beneath the Laurentian margin
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南阿巴拉契亚蓝岭通过劳伦山脉边缘下的塔科大陆俯冲形成高压变碱岩
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
D. Moecher
中科院分区：
文献类型：
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作者：
E. Anderson;D. Moecher
解释蓝岭南部榴辉岩、退变质榴辉岩、橄榄岩和混合岩基底片麻岩的构造模型，认为蓝岭东部（EBR）和蓝岭西部（WBR）之间的小洋盆闭合。在这个“仰冲蛇绿岩”模型中，方济各会类型的洋壳向东俯冲到皮埃蒙特弧下发生在弧仰冲到劳伦特边缘之前。在EBR-WBR边界附近发现的千米级榴辉岩体被引用作为仰冲蛇绿岩/增生岛弧模型的证据。然而，基于蓝岭西部、中部和东部高压变基性岩矿物化学的温压估算表明，榴辉岩和麻粒岩是中温型（550-900°C），与仰冲蛇绿岩模型不一致。洋中脊玄武岩俯冲到大陆边缘和岛弧之下，温度很少超过550°C。本研究的热压比较和重新审查深地震剖面从蓝岭允许向西俯冲的大陆材料下劳伦特在塔科尼奥伦提斯，现在保存在中部和东部蓝岭构造省的megamélange模型。从蓝岭高压变基性岩确定的P-T路径与先前从加里东和华力西榴辉岩确定的P-T路径相似。热压相似性意味着大陆碰撞、大陆地壳俯冲至50-65公里深处，然后迅速排出的共同构造历史。
Tectonic models that account for the occurrence of eclogite, retrograde eclogite, peridotite, and migmatitic basement gneisses in the southern Blue Ridge invoke closure of a small ocean basin between the eastern Blue Ridge (EBR) and western Blue Ridge (WBR). In this “obducted ophiolite” model, Franciscan‐type, eastward subduction of oceanic crust beneath the Piedmont arc occurred prior to obduction of the arc onto the Laurentian margin. The discovery of kilometer‐scale eclogite bodies near the EBR‐WBR boundary are cited as evidence for obducted ophiolite/accreted island arc models. However, thermobarometric estimates based on mineral chemistry from HP metabasites of the western, central, and eastern Blue Ridge indicate that eclogites and granulites are medium‐temperature type (550–900°C), inconsistent with the obducted ophiolite model. Mid‐ocean ridge basalt subducted beneath continental margins and island arcs rarely reaches temperatures in excess of 550°C. Thermobarometric comparisons of the present study and a reexamination of deep seismic profiles from the Blue Ridge allow for a model of westward subduction of continental material beneath Laurentia during the Taconic orogeny that produced a megamélange now preserved in the central and eastern Blue Ridge tectonic provinces. P‐T paths determined from Blue Ridge HP metabasites are similar to P‐T paths determined previously from Caledonian and Variscan eclogites. Thermobarometric similarities imply a common tectonic history of continental collision, subduction of continental crust to depths of 50–65 km, followed by rapid eduction.