Progressive orocline formation in the Eastern Pontides–Lesser Caucasus

The Eastern Pontides–Lesser Caucasus fold–thrust belt displays a peculiar northwards arc-shaped geometry that was defined as an orocline in earlier studies. The Lesser Caucasus was affected by two main tectonic events that could have caused orocline formation: (1) Paleocene–Eocene collision of the South Armenian Block with Eurasia; and (2) Oligocene–Miocene Arabia–Eurasia collision. We tested the hypothesis that the Lesser Caucasus is an orocline and aimed to time the formation of this orocline. To determine the vertical axis rotations, 37 sites were sampled for palaeomagnetism in rocks of Upper Cretaceous–Miocene age in Georgia and Armenia. In addition, we compiled a review of c. 100 available datasets. A strike test was applied to the remaining datasets, which were divided into four chronological sub-sets, leading us to conclude that the Eastern Pontides–Lesser Caucasus fold–thrust belt forms a progressive orocline. We concluded that: (1) some pre-existing curvature must have been present before the Late Cretaceous; (2) the orocline acquired part of its curvature after the Paleocene and before the Middle Eocene as a result of South Armenian Block–Eurasia collision; and (3) about 50% of the curvature formed after the Eocene and probably before the Late Miocene, probably as a result of Arabia–Eurasia collision.东庞提斯-小高加索褶皱冲断带呈现出独特的向北弧形几何形态，早年研究中将其定义为构造弯山（orocline）。小高加索地区受两期主要构造事件影响，这两期事件可能促成了构造弯山的形成：（1）古新世-始新世南亚美尼亚地块与欧亚大陆的碰撞；（2）渐新世-中新世阿拉伯板块与欧亚大陆的碰撞。本研究验证了“小高加索属于构造弯山”这一假说，并旨在确定该构造弯山的形成时间。为确定垂直轴旋转量，研究团队在格鲁吉亚与亚美尼亚境内的晚白垩世-中新世时代岩石中完成了37个采样点的古地磁（palaeomagnetism）取样。此外，研究团队整合了约100套已公开数据集的综述成果。研究对剩余数据集进行了走向测试，并将其划分为四个年代学子集，最终得出结论：东庞提斯-小高加索褶皱冲断带属于渐进式构造弯山。本研究最终得出三点结论：（1）晚白垩世之前便已存在一定的初始弯曲形态；（2）受南亚美尼亚地块-欧亚大陆碰撞事件影响，该构造弯山的部分弯曲形成于古新世之后、中始新世之前；（3）约50%的弯曲形态形成于始新世之后、晚中新世之前，其成因大概率为阿拉伯板块-欧亚大陆碰撞事件。