A dynamic model of extension in the Baltimore Canyon Trough Region
A dynamic model of extension in the Baltimore Canyon Trough Region
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DOI：
10.1029/91tc03012
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发表时间：
1992-04
期刊：
影响因子：
4.2
通讯作者：
D. Harry;D. Sawyer
中科院分区：
文献类型：
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作者：
D. Harry;D. Sawyer
在北大西洋中部的巴尔的摩峡谷海槽地区的伸展动力学模型表明，裂谷进行了两个阶段，并控制横向偏移预先存在的弱点内中地壳和上地幔阿巴拉契亚造山带。地壳的弱点被假设为导致薄皮逆冲断层在阿巴拉契亚前陆，和上地幔的弱点，阿巴拉契亚腹地的地壳增厚的结果。在裂谷作用的早期阶段（225-185 Ma），地壳和地幔的伸展轨迹位于各自的预弱化区内，并由下地壳的剪切带以类似于整个岩石圈简单剪切的方式连接。此时上地壳的伸展和减薄导致阿巴拉契亚皮埃蒙特晚三叠世-早侏罗世裂谷盆地的形成，并导致水平压力梯度的发展，从而驱动下地壳中广泛的韧性流动。压力梯度也可能影响了岩浆的运输，将东部巴尔的摩峡谷海槽下方产生的熔体移动到更西边的三叠纪盆地。在裂谷作用的晚期（185-175 Ma），由于上涌的软流圈的热弱化作用，地壳的伸展作用移到了上地幔薄弱层之上。地壳和地幔的伸展轨迹重合，裂陷方式类似于整个岩石圈的纯剪切。地壳伸展轨迹的变化伴随着三叠纪盆地沉降和火山活动的停止，巴尔的摩峡谷海槽快速沉降的开始，以及将巴尔的摩峡谷海槽下的高度薄地壳与三叠纪盆地省下的中度薄地壳分离的基底枢纽区的形成。延伸越来越集中在巴尔的摩峡谷海槽东部边缘之下，直到海底扩张开始，大约5千万年。在裂谷开始后由此产生的共轭边缘是不对称的，包括三叠纪盆地在内的大部分地区都滞留在北美板块上。
A dynamic model of extension in the Baltimore Canyon trough region of the central North Atlantic indicates that rifting proceeded in two stages and was controlled by laterally offset preexisting weaknesses within the middle crust and upper mantle beneath the Appalachian orogen. The crustal weakness is hypothesized to result from thin-skinned thrust faulting in the Appalachian foreland, and the upper mantle weakness results from crustal thickening beneath the Appalachian hinterland. During the early stages of rifting (225–185 Ma), the loci of extension in the crust and mantle lie within the respective preweakened regions and are connected by a shear zone in the lower crust in a manner similar to whole lithosphere simple shear. Extension and thinning of the upper crust at this time results in the formation of Late Triassic-Early Jurassic rift basins in the Appalachian Piedmont and in the development of a horizontal pressure gradient which drives widespread ductile flow in the lower crust. The pressure gradient may also have influenced magma transport, moving melt generated beneath the eastern Baltimore Canyon trough into the more westerly Triassic basin province. During the late stages of rifting (185–175 Ma), extension in the crust shifts to a position overlying the preexisting upper mantle weakness as a result of thermal weakening by the upwelling asthenosphere in this region. The loci of extension in the crust and mantle are then coincident, and the style of rifting becomes similar to whole lithosphere pure shear. The shift in the locus of crustal extension is accompanied by the cessation of subsidence and volcanism in the Triassic basins, the onset of rapid subsidence in the Baltimore Canyon trough, and the formation of a basement hinge zone separating the highly thinned crust beneath the Baltimore Canyon trough from moderately thinned crust beneath the Triassic basin province. Extension becomes increasingly focused beneath the eastern edge of the Baltimore Canyon trough until the onset of seafloor spreading, approximately 50 m.y. after rifting began. The resulting conjugate margins are asymmetric, with most of the region encompassing the Triassic basins stranded on the North American plate.