札格羅斯造山帶基爾庫克弧凹之構造演化及活動性

札格羅斯造山帶是阿爾卑斯－喜馬拉雅造山系統的一部分，由阿拉伯板塊及歐亞板塊間的陸－陸碰撞所生成。造山帶前方的前陸盆地是世界上重要的產油區之一，位於造山帶西北方的基爾庫克弧凹所含之油氣儲藏量約佔盆地總儲量的18 %，但其油氣探勘程度相較於中東其他國家較低，故若能對此區域的構造演化模式有更完整的了解，應有助於增加油氣探勘的準確性。本研究可分為兩個部分，第一部分利用MOVE軟體回復前人所發表的構造平衡剖面，探討長期構造演化歷史，結果顯示此處的構造大致遵循由東北向西南傳遞的順時序（in-sequence）演化，且基盤逆衝斷層多未穿出沈積層出露至地表，而是向上連結至區域的基底滑脫層。剖面在回復後共產生了約16.3公里的縮短量，縮短率約7 %，不同構造區的地層縮短量大致由後陸向前陸方向遞減，此外後陸之基盤斷層所產生的水平壓縮量與沈積層中因滑脫褶皺作用所產生的地層縮短量非常接近，然而前陸之基盤斷層所產生的水平壓縮量卻未完全反映於此處的沈積層之中，此現象反映了縮短量會沿滑脫層向前陸傳遞的情形。在研究的第二部分，利用小基線子集法（Small Baseline Subset）處理D-InSAR之資料，對研究區域內主要的構造進行地表變形觀測，此部分的結果顯示山前斷層及基爾庫克斷層周圍有明顯的地表變形特徵，其上盤地表分別以約10 mm/yr及20 mm/yr的速率抬升，代表此二構造屬於基爾庫克地區近年來具有較高活動性的構造。最後綜合兩部分的研究結果，與地震活動分布進行比較，可歸納出此處由東北向西南擴展的活躍造山運動，使源自脆－塑性轉換帶的基盤斷層大致以順時序的模式參與變形，這些基盤斷層向上連結至基底滑脫層，使縮短量沿著滑脫層向前陸傳遞，使沈積層產生滑脫褶皺。而基盤的構造活動所產生之地層縮短量尚未完全反映至前陸的變形之中，然而前陸現今的構造活動性有提升的趨勢，說明了地層的水平縮短仍然在持續，且較大的變形應會沿軟弱岩層發生。

關鍵字

平衡剖面；札格羅斯造山帶；基爾庫克弧凹； InSAR ；小基線子集法

並列摘要

Zagros orogen is part of the Alpine-Himalayan orogenic system and is formed as a result of collision between Arabian Plate and Eurasia Plate. Foreland basin of Zagros orogen is one of the most important petroleum-rich area in the world. Kirkuk recess in the northwestern part of the Zagros orogen contains 18% of oil and gas storage of the whole foreland basin. Therefore, a more complete understanding of structural evolution should be helpful to increase the accuracy of oil and gas exploration. This study can be divided into two parts, first we use MOVE software to restore the balanced cross section in order to investigate the long-term structural evolution. The result shows that the deformation propagated from northeast to southwest, which reflects the in-sequence evolution of low angle basement-rooted thrusts. Moreover, these thrusts don’t penetrate the sedimentary cover but connected upward to the basal detachment layer. After the restoration, the cross section gives shortening around 16.3 km, with a shortening rate of about 7%. Shortening in different structural zone roughly decrease from hinterland to foreland. Moreover, horizontal compression caused by basement thrusts is closed to shortening caused by detachment folds in the hinterland, while horizontal compression caused by basement thrusts in the foreland is not fully reflected in the sedimentary layer, this implies that shortening will be propagated toward foreland along the detachment layer. In the second part of the study, we use Small Baseline Subset (SBAS) technique to deal with D-InSAR data, in order to analyze temporal surface deformation across main fault-related folding within recent years. The result shows that there is obvious deformation pattern around the Kirkuk Fault and Mountain Front Fault, with uplift rate of about 10 mm/yr and 20 mm/yr. As the result, we consider these two structures are relative active in Kirkuk recess in recent years. Finally, we combine the results above and compare with the distribution of seismic activity. It can be concluded that the active orogenic movement propagating from northeast to southwest makes the in-sequence evolution of basement thrusts. These basement thrusts are connected upwards to the basal detachment layer, so that shortening is transferred along the detachment layer to foreland, causing detachment folds formed in the sedimentary cover. Shortening caused by structures in the basement has not yet been fully reflected in the deformation of the foreland. However, the current structural activity of foreland has a tendency to increase, indicating that horizontal shortening of the stratum is still continuing, and larger deformation should occur along weak formations.