Structural evolution of the northwestern Zagros, Kurdistan Region, Iraq: Implications on oil migration
Structural evolution of the northwestern Zagros, Kurdistan Region, Iraq: Implications on oil migration
复制标题
伊拉克库尔德斯坦地区扎格罗斯西北部的构造演化：对石油运移的影响
作者：
Csontos László;Sasvári Ágoston;P. Tamas;Kósa László;Azad T. Salae;A. Athar
伊拉克库尔德斯坦地区的研究区域跨越南部低地和北方褶皱叠瓦状扎格罗斯山脉之间的重要地形/结构边界。它还包括北方扎格罗斯构造方向的显著变化，从一般的西北-东南“扎格罗斯”走向到东西“金牛座”走向。在山区（中生代-古近纪）和低地（新近纪）进行的地质测绘和结构观察得出以下结论。(1)最古老的变形记录是一个层平行缩短，再加上西南向的剪切，其次是主要的折叠约。10公里波长和CA。1,000米振幅。即使是上中新世-上新世Bakhtiari组，在某些地方也有陡峭的倒转岩层，向斜保存了新近纪-上新世的同构造地层。盒状褶皱与脊部塌陷、核部内冲和系统节理组的形成有关。(2)在主要褶皱的南翼，可以观察到不同偏移的逆冲断层。南翼和北方翼的逆冲断层被认为是主褶皱期间主要隆升的原因。(3)雁列式褶皱接力样式表明，沿EW向段沿着为左旋剪切，沿NW向段沿着为右旋剪切。(4)对条纹状断层面的快速定性分析表明，从NE-SW到N-S的缩短趋势是可变的，一些罕见的NW-SE缩短都与逆冲断层有关。(5)该地区的总体构造背景与欧亚大陆下的阿拉伯边缘向东北向北的扩张有关。CA。30°弯曲的山脉可能是由阿拉伯边缘的原始形状，或由在北方的东西向的预先存在的构造带。几个观察结果表明，有没有造山带弯曲（即主要旋转）的不同部分的链，但结构简单地塑造在其本地扶壁（几乎）根据目前的方向。然而，不能排除不同节段中的有限量的刚体旋转。不断变化的缩短方向在西北-东南扎格罗斯和东西金牛座弧段上产生了几个结构组合，其中许多仍然保存下来。(6)在上白垩统和古新统灰岩中，沥青大量渗漏是由于这些地层的裂缝或地槽造成的。许多这些沥青填充的空隙与上述晚新生代-近期缩短-褶皱过程有关;因此，油气向这些空隙中的迁移被解释为非常年轻。这与早期关于该地区晚白垩世大规模破裂和烃类流失的观点相矛盾。
The studied area in Kurdistan Region of Iraq lies across an important topographic/structural boundary between the southern lowlands and the northern, folded and imbricated Zagros Mountains. It also encompasses a prominent change in structural orientation of the northern Zagros, from a general NW-SE “Zagros” to an E-W “Taurus” trend. Geological mapping and structural observations, both in the mountains (Mesozoic–Palaeogene) and in the lowlands (Neogene), led to the following conclusions. (1) The oldest recorded deformation is a layer-parallel shortening, coupled with southwest-vergent shear that was followed by major folding of ca. 10 km wavelength and ca. 1,000 m amplitude. Even the Upper Miocene–Pliocene Bakhtiari Formation has steep to overturned beds in some parts, and synclines preserve syn-tectonic strata of Neogene–Pliocene age. Box folding is associated with crestal collapse, internal thrusting in the core and with formation of systematic joint sets. (2) On the southern limb of the major folds, thrusting of variable offset can be observed. The thrusts on the southern and northern limbs are considered responsible for the major uplift during main folding. (3) En-échelon fold-relay patterns suggest left-lateral shear along the EW-oriented segment and right-lateral shear along the NW-oriented segment. (4) A quick-look qualitative analysis of striated fault planes suggests a variable shortening trend from NE-SW to N-S, and some rare NW-SE shortening all associated with thrust faults. (5) The general structural setting of the area is linked to the north-eastwards to northwards propagation of the Arabian Margin beneath Eurasia. The ca. 30° bend in the mountain chain may be explained by the original shape of the Arabian Margin, or by pre-existing tectonic zones of E-W orientation in the northern part. Several observations suggest that there was no oroclinal bending (i.e. major rotation) of different parts of the chain, but the structures simply molded on their local buttress (almost) according to present orientations. However, a limited amount of rigid-body rotation in the different segments cannot be ruled out. The changing shortening directions generated several structural combinations on both the NW-SE Zagros and the E-W Taurus segments of the arc, many of which are still preserved. (6) Spectacular bitumen seepage in Upper Cretaceous and Palaeocene limestone originates from fractures or geodes of these formations. Many of these bitumen-filled voids are linked to the above-described Late Neogene–Recent shortening-folding process; therefore hydrocarbon migration into these voids is interpreted to be very young. This contradicts earlier ideas about massive Late Cretaceous breaching and bleeding off of hydrocarbons in this region.