The Effect of Wedge Structure on Displacement Subduction of Piedmont Thrust Structure: A Case Study of the Southern Margin of Junggar Basin

介于复活的天山造山带与稳定的准噶尔克拉通之间的准噶尔盆地南缘前陆冲断带,是印度板块与欧亚大陆碰撞的远距离效应产物,也是新近纪以来青藏高原隆升并向北推挤的直接结果.前陆冲断带吸收了来自造山带的水平缩短构造位移量后,克拉通一侧构造趋于稳定.准噶尔盆地南缘与世界上多数前陆冲断带构造地质特征相似,通过区域地震剖面的精细构造几何学和运动学解析,发现其中的楔形构造非常典型,是前陆冲断带内部冲断构造位移量消减的主要方式之一,控制着前陆冲断带分布范围和变形方式.准噶尔盆地南缘构造变形主要由南侧的天山造山带向北逆掩冲断,但是大部分冲断构造位移量是通过楔形构造反向传递后消减.紧邻天山北麓的齐古-喀拉扎-昌吉等构造带,山前深部的楔形体沿侏罗系西山窑组煤层向北扩展过程中,部分位移量沿构造楔顶部的反冲断层向南消减,并切割上覆地层形成第一排背斜带,另一部分位移量则继续向北传递,在断坡位置引发褶皱变形,形成霍-玛-吐第二排构造带和安集海-呼图壁第三排背斜带.准噶尔盆地南缘第二、三排构造带中-新生界内部发育多个小型的构造楔型体,这些互相叠置的楔型构造横向延伸不大,加大了构造变形的复杂性和构造圈闭识别的难度.     

楔形构造在山前冲断构造位移量消减中的作用

介于复活的天山造山带与稳定的准噶尔克拉通之间的准噶尔盆地南缘前陆冲断带,是印度板块与欧亚大陆碰撞的远距离效应产物,也是新近纪以来青藏高原隆升并向北推挤的直接结果。前陆冲断带吸收了来自造山带的水平缩短构造位移量后,克拉通一侧构造趋于稳定。准噶尔盆地南缘与世界上多数前陆冲断带构造地质特征相似,通过区域地震剖面的精细构造几何学和运动学解析,发现其中的楔形构造非常典型,是前陆冲断带内部冲断构造位移量消减的主要方式之一,控制着前陆冲断带分布范围和变形方式。准噶尔盆地南缘构造变形主要由南侧的天山造山带向北逆掩冲断,但是大部分冲断构造位移量是通过楔形构造反向传递后消减。紧邻天山北麓的齐古-喀拉扎-昌吉等构造带,山前深部的楔形体沿侏罗系西山窑组煤层向北扩展过程中,部分位移量沿构造楔顶部的反冲断层向南消减,并切割上覆地层形成第一排背斜带,另一部分位移量则继续向北传递,在断坡位置引发褶皱变形,形成霍-玛-吐第二排构造带和安集海-呼图壁第三排背斜带。准噶尔盆地南缘第二、三排构造带中-新生界内部发育多个小型的构造楔型体,这些互相叠置的楔型构造横向延伸不大,加大了构造变形的复杂性和构造圈闭识别的难度。     

乌鲁木齐山前坳陷逆断裂-褶皱带及其形成机制

乌鲁木齐山前坳陷位于天山新生代再生造山带北侧,南以准噶尔南缘断裂与天山相隔,内部发育了几排逆断裂 背斜带,每一排构造带又由多个逆断裂 背斜组成。最南的齐古逆断裂 背斜带形成于中生代末,其北的玛纳斯逆断裂背斜带包含霍尔果斯、玛纳斯和吐谷鲁逆断裂背斜,形成于上新世末、早更新世初,受上、下２ 个滑脱面和断坡的控制,形成上、下２ 个背斜。再向北的独山子逆断裂背斜带由独山子、哈拉安德和安集海逆断裂背斜组成,形成于早、中更新世之间,主逆断裂向下在８ ～９ ｋｍ 深处的侏罗系中变为近水平滑脱面。此外,在独山子和吐谷鲁背斜的西北和东北还分别发育有正在形成之中的西湖和呼图壁隆起。研究了这些逆断裂 背斜带的地表和深部的构造特征、二维和三维几何学及运动学后指出,它们是在天山向准噶尔盆地扩展过程中发育于近水平滑脱面和不同断坡上的断展褶皱,独山子和安集海逆断裂 背斜的水平缩短量分别为２ ９００ ,１ ３５０ ｍ ,缩短速率分别为３９７ ,１８７ ｍ ｍ／ ａ。霍尔果斯、玛纳斯、吐谷鲁逆断裂 背斜的水平缩短量分别为５ ９００ ,６ ５００ ,６ ０００ ｍ ,相应的缩短速率分别为２０２,２２３ ,２０６ ｍ ｍ／ａ,准噶尔南缘断裂和乌鲁木齐山前坳陷第四纪?     

准噶尔盆地南缘前陆冲断带形成时间的初步厘定

一般认为生长地层的时代就是构造形成的时代（Suppe等,1992;Shaw 等,1994）.准噶尔盆地南缘前陆冲断带发育地表可见的三排构造带：以齐古-喀拉扎背斜-清水河构造为主的第一排构造、以霍尔果斯-玛纳斯-吐谷鲁背斜为主的第二排构造、以独山子-安集海背斜-呼图壁背斜为主的第三排构造,卷入三排构造的地层有侏罗系、白垩系、第三系和第四系,形成了现今复杂的地貌地形和地层分布,三排构造带的形成时间对油气评价和油气勘探意义重大.     

准噶尔盆地南缘褶皱冲断带断裂输导石油效率评价

为了评价准噶尔盆地南缘褶皱冲断带断裂输导原油效率,通过定义断裂输导系数和分析原油成藏过程有效性,建立了断裂输导石油效率评价方法。评价结果表明,断裂输导系数沿着褶皱冲断带呈带状分布,高效断裂输导区主要位于托斯台背斜、独山子背斜、安集海背斜、霍尔果斯背斜及其以南、吐谷鲁背斜、清水河断鼻和齐古背斜等地区。高效断裂输导区内,第一排构造带断裂输导效率最高,第二排构造带次之,第三排构造带相对最低。研究区独山子油田、霍尔果斯油田、吐谷鲁油田、齐古油田等均分布在高效断裂输导范围内,表明高效断裂输导是准南褶皱冲断带原油成藏的重要条件之一。     

河流阶地演化与构造抬升速率——以天山北麓晚第四纪河流作用为例

构造地貌学重点关注构造和地表过程对于地形地貌演化的差异化作用,构造活动速率则是评估这种影响的一个重要指标。利用河流阶地数据计算河流下切速率从而约束构造抬升速率是常用的方法,但由于阶地成因复杂,这一方法具有不确定性。对于山前河流地貌序列,基于背斜段与未变形段的阶地拔河高度差以及阶地面形成年龄,计算得到的河流下切速率可在一定程度上消除气候等因素的影响,因此可用于估算背斜自阶地形成以来的平均抬升速率。基于该方法,本文通过研究天山北麓乌鲁木齐河、塔西河、玛纳斯河、金钩河、安集海河及奎屯河等河流在背斜段发育的主要阶地,分析了背斜抬升速率及其时空特征。天山北麓发育3排逆断裂-背斜带,结果表明位于第Ⅱ排逆断裂-背斜带的吐谷鲁背斜自约13ka以来的抬升速率为3.52mm/a,同时期霍尔果斯背斜构造抬升速率为4.8mm/a,玛纳斯背斜东端的抬升速率相对较小,为<2mm/a; 第Ⅲ排构造带中的独山子背斜全新世抬升速率仅为1.2~1.9mm/a。这可能表明,自山前向盆地方向晚第四纪背斜抬升速率大致呈减小趋势,与背斜地壳缩短量的空间分布规律基本一致。更多的阶地年龄数据有助于更好地揭示天山北麓晚第四纪背斜构造活动特征。     

天山北麓活动背斜带的变形特征

天山中段北麓发育有3排受逆断裂控制的背斜带,对这些构造带的研究有助于认识天山及其前陆盆地晚新生代构造变形的机理.基于地层变形分析,并结合前人的研究成果,从整体上探讨了这3排构造带的变形时间与基本模式.分析表明,天山北麓第Ⅰ排构造带的托斯台背斜自中新世褶皱作用明显;第Ⅱ排构造带吐谷鲁背斜于约6.0Ma开始生长,伴随发育同构造沉积即生长地层;第Ⅲ排构造带独山子背斜发育时间应晚于约2.6Ma.这一变形时间序列揭示天山北麓3排逆断裂-褶皱带的构造变形具有向前陆盆地逐步扩展的特征,并伴随产生幅度不等的地壳缩短.天山北麓约8～15km的地壳缩短总量表明,晚新生代以来构造驱动沿约130km宽的山麓带是相对均一的.     

天山北缘前陆冲断带形成时间的地层学证据

乌鲁木齐附近天山北缘喀拉扎背斜及其周缘的地层学分析表明，上中新统一上新统昌吉河群(N1-2ch)(相当于独山子组N1-2d)是喀拉扎山地区发育的生长地层，是喀拉扎背斜形成时的同构造沉积层序．这个结论表明、包括喀拉扎背斜在内的天山北缘第一排前陆冲断构造带形成于晚中新一上新世时期．     

呼图壁至乌苏一带新构造变形特征及油气勘探方向预测

以覆盖北天山山前呼图壁至乌苏一带的四景 L andsat TM卫星遥感图像的地质解译为基础 ,结合野外实地考察所获取的地质资料以及烃源岩的生烃和排烃的盆地模拟分析结果 ,对呼图壁—乌苏地区第二、三排构造带上新世以来的新构造运动变形特征、背斜和断裂构造的形成时代以及油气勘探方向进行分析和预测。该区第二、三排背斜构造的变形非常强烈 ,它们的构造变形始于上新世末期 ,早更新世末期是新构造变形最强烈的时期 ,这些背斜构造带在中更新世早期已基本形成。第二排背斜构造带的构造变形强于第三排构造带。有利烃源岩安集海河组的排烃高峰期在距今 0 .3Ma左右 ,晚于背斜构造的形成时期 ,其生成和排出的油气很有可能聚集于这些背斜构造中。发育于背斜构造核部或北翼一侧的逆冲断裂构造为油气的垂向运移提供了良好通道 ,但也可能导致油气的逸散和破坏。综合分析表明第三排背斜构造带中的西湖背斜、独南背斜、安集海背斜和呼图壁背斜具有良好的油气勘探前景     

天山北缘河流阶地形成及构造变形定量分析

新生代以来,北天山山前发育了3排冲断褶皱带。新生代晚期一系列河流普遍穿过这3排冲断褶皱带并发育了三级河流阶地。在最新构造活动的影响下,河流阶地普遍发生变形,遭受抬升。利用光释光及14C年代学方法确定了塔西河三级阶地的形成年龄,并实际测量了三级阶地的高程。结果表明吐谷鲁背斜的构造抬升速率在32．85-28．75 ka问为9．50-12．57 mm／a,12-13 ka间为9．67-14．5 mm／a,全新世则增至10．79-23．44mm／a,天山基底的平均隆升速率达到3．39-3．86mm／a。通过对天山最高一级夷平面、野外实测侏罗纪地层高程及天山发育的煤层的相对隆升速率的研究则表明天山自24 Ma以来平均的隆升速率约为0．085-0．146 mm／a。结合对北天山其他主要河流阶地的观察及研究可以看出自晚更新世一全新世以来,天山北缘的最新构造活动具有不断加快的特征。     

构造运动和气候变化对天山北麓奎屯河阶地发育的影响作用

奎屯河出天山后,强烈下切形成深达300m的河谷,在河谷两侧发育多级河流阶地。在遥感解译和野外测量的基础上,获得了河流阶地平面分布图和阶地位相图。根据奎屯河阶地的平面特征与剖面特征,将河流阶地由新到老分为T1,T2,T3,T4和T5等5组。前人用 10Be测年数据认为T4阶地堆积于深海氧同位素(MIS)第2阶段,奎屯河强烈下切开始于MIS 2后期,形成于距今1.3万年; 本文14C年龄数据说明T2阶地形成于 3100±40kaB.P.,其发育与亚北方期的偏凉气候有关; 根据河流平均下切速率估算T3阶地形成于10.6kaB.P.,其发育可能与新仙女木冷期有关。因此,认为阶地发育明显受控于气候变化。在独山子背斜区,T4阶地相对于T3阶地的抬升量为12m,隆起速率为5mm/a,T3阶地以来的拱曲抬升量为13m,隆起速率为1.2mm/a,反映末次冰期以后,独山子背斜隆起速率早期较大,晚期明显变小。独山子断层将T2阶地垂直错断3.7m,断层垂直活动速率为1.09~1.14mm/a,与同时段背斜隆起的速率相近,说明该时段隆起量主要由独山子断层垂直活动所引起,背斜拱曲变形有限。奎屯河T5阶地的3个小阶地反映独山子背斜向南扩展,造成抬升下切与下降淤积区的界线随时间向南侧迁移。奎屯河西岸T4阶地面上的羽状阶地陡坎反映在T4阶地发育期间,发生5次上游下切与下游堆积区的界线向下游迁移事件,这可能受独山子背斜间歇性隆起的影响,更可能是西南侧托斯台背斜抬升影响的结果。独山子背斜南翼在T3阶地形成以后发生4次曲流向北迁移的事件,在时间上与独山子断层全新世古地震时间相关,说明受独山子背斜隆起中心在奎屯河东岸的影响,奎屯河发生向西转弯,独山子断层多次活动,伴随背斜的隆起,引发河流4次弯曲和曲流向背斜轴部的4次迁移事件。     

Simulation for the Controlling Factors of Structural Deformation in the Southern Margin of the Junggar Basin

According to the differences of structural deformation characteristics, the southern margin of the Junggar basin can be divided into two segments from east to west. Arcuate thrust-and-fold belts that protrude to the north are developed in the eastern segment. There are three rows of en echelon thrust-and-fold belts in the western segment. Thrust and fold structures of basement-involved styles are developed in the first row, and décollement fold structures are formed from the second row to the third row. In order to study the factors controlling the deformation of structures, sand-box experiments have been devised to simulate the evolution of plane and profile deformation. The planar simulation results indicate that the orthogonal compression coming from Bogeda Mountain and the oblique compression with an angle of 75° between the stress and the boundary originating from North Tianshan were responsible for the deformation differences between the eastern part and the western part. The Miquan-ürümqi fault in the basement is the pre-existing condition for generating fragments from east to west. The profile simulation results show that the main factors controlling the deformation in the eastern part are related to the décollement of Jurassic coal beds alone, while those controlling the deformation in the western segment are related to both the Jurassic coal beds and the Eogene clay beds. The total amount of shortening from the Yaomoshan anticline to the Gumudi anticline in the eastern part is ~19.57 km as estimated from the simulation results, and the shortening rate is about 36.46%; that from the Qingshuihe anticline to the Anjihai anticline in the western part is ~22.01 km as estimated by the simulation results, with a shortening rate of about 32.48%. These estimated values obtained from the model results are very close to the values calculated by means of the balanced cross section.     

Crustal Shortening on the Margins of the Tien Shan,Xinjiang, China

We present the results of mapping selected cross-sections across the margins of the Chinese Tien Shan, an intracontinental mountain belt that formed in response to the India-Eurasia collision. This belt contains significant lateral variation in topography, structure, and stratigraphy at all scales, and our estimated rates of shortening also reveal a distribution of shortening that varies laterally. At the largest scale, it consists of two major high mountain ranges in the west that merge eastward into a complex, single high mountain belt with several distinct ranges, then separates farther eastward into several low mountain ranges in the south and a single narrow high mountain range in the north. Active fold-and-thrust belts along parts of the north and south flanks of the Tien Shan involve only Mesozoic and Cenozoic sedimentary cover, which varies in both stratigraphy and structure from east to west. The southern fold-and-thrust belt decreases in width and complexity from west to east and ends before reaching Korla. The northern belt begins near the longitude where the southern belt ends, and increases in width and complexity from west to east. Within these two fold-and-thrust belts are both E-W and N-S variations in stratigraphy at the scale of the fold-and-thrust belts and across individual structures. All these variations make it very difficult to generalize either structure or stratigraphy within the Tien Shan or within local areas.

Four maps and cross-sections, two across each of the northern and southern fold-and-thrust belts, imply different magnitudes of shortening. In the eastern part of the northern belt, a cross-section along the southern part of the Hutubi River yields shortening of 6.2 km, and a section to the north across the Tugulu anticline yields shortening of 5.5 km. The two parts of the cross-section cannot be added because the Tugulu anticline lies 20 km west of the Hutubi River, and diminishes greatly in amplitude toward the Hutubi River. In the western part of the northern belt, cross-sections require 4.6 to 5.0 km of shortening at Tuositai and 2.12 to 2.35 km across the Dushanzi anticline. The Tuositai structure lies south of the Dushanzi anticline, but shortening in these two areas also cannot be summed, because they seem to be separated by a N-trending strike-slip fault. In the western part of the southern fold-and-thrust belt, an incomplete cross-section along the Kalasu River suggests shortening of 12.1 to 14.1 km. If the estimated shortening of 6 to 7 km in the Qiulitage anticline, which we did not map, is added, the total shortening in this cross-section would be ～18 to 21 km. To the east, a complete cross-section at Boston Tokar yielded shortening of 10.3 to 13.0 km.

Calculating long-term shortening rates from these four cross-sections is difficult, because the time of initiation of deformation is poorly known. In the Kalasu River area of the southern belt, there is evidence that limited shortening of 2 to 4 km occurred in the early Miocene, if major thickness changes in deposition of conglomerate unit 3b are interpreted to be growth strata. Geological evidence suggests that most of the shortening began in both belts after the beginning of the deposition of the thick conglomerate unit shown as lower Quaternary on Chinese geological maps. Strata within the middle part of these conglomerates were deposited during the growth of the folds. Presence of Equus near the base of similar conglomerates indicates a Quaternary age, but the fossil localities are far from most of our cross-sections, and the contemporaneity of the rocks remains in question. The beginning of conglomerate deposition may be controlled by climate change, and if so, the beginning of conglomerate deposition may be generally contemporaneous throughout the region at ～2.5 Ma. Deformation began at some time after the onset of conglomerate deposition, but this time is not well constrained. Thus we have calculated shortening rates for 2.5, 1.6, and 1.0 Ma that should bracket maximum and minimum slip rates. These calculations yield the following ranges in the northern fold-and-thrust belt: southern Hutubi River = 2.5 to 6.2 mm/yr; Tugulu anticline = 2.1 to 5.5 mm/yr; Tuositai anticline = 1.8–2.0 to 4.6–5.0 mm/yr; and Dushanzi anticline = 0.8 to 2.1–2.4 mm/yr; and in the southern fold-and-thrust belt: Kalasu River = 4.6–5.6 (including the Qiulitage anticline = 7.2–8.4) to 12.1–14.1 (including Qiulitage anticline = 18–21) mm/yr; and at Boston Tokar = 4.1–5.2 to 10.3–13.1 mm/yr. If 2 to 4 km of shortening occurred in the Kalasu River section during early Miocene time, the long-term rates for Quaternary time are 3.2–4.8 (including Qiulitage anticline = 5.6–7.6) to 8.1–12.1 (including Qiulitage anticline = 14–19) mm/yr.

Calculation of the shortening rate across the entire width of the Tien Shan is difficult because of the rapid lateral variations in structure and because of active deformation within the range, which we have not studied. The cross-sections at Boston Tokar in the south and Tuositai in the north lie along the same longitude. Adding the shortening rates in these areas would yield a minimum range (using 2.5 Ma as the initiation time) of 5.7 to 7.2 mm/yr. If deformation began at 1.6 or 1.0 Ma, the range of shortening rates would be 10–11.2 mm/yr to 14.9–18.1 mm/yr, respectively. Because the first indication of structural growth with the mapped areas occurs above the base of the conglomerates at the top of the stratigraphic succession, a minimum shortening rate greater than 5.7 to 7.2 mm/yr is more likely.

Both the marginal fold-and-thrust belts have a thin-skinned geometry with the drcollement at -6 to 10 km and within Mesozoic and Cenozoic sedimentary rocks. Toward the interior of the range the decollement must pass into the Paleozoic basement rocks and steepen beneath the flanks of the range. The structural style is similar to that in the Laramide Rocky Mountains and the California Transverse Ranges. The highest parts of the Tien Shan are adjacent to areas of active shortening. Such a relation might suggest that the major uplift of the Tien Shan is very young, mostly latest Cenozoic or Quaternary in age. The shortening across the Tien Shan is inhomogeneous and spatially distributed.     

晚新生代以来天山南、北麓冲断作用的定量分析

利用地表地质、二维地震和钻、测井资料建立了两条横穿天山南、北麓库车河地区和金钩河—安集海河地区的构造剖面,从几何学和运动学的角度探讨新生代以来不同序次台阶状逆断层及其相关褶皱的叠加过程、以及叠加过程中断层形态、褶皱形态与位移量之间的定量关系。生长地层和生长不整合分析表明,上新世早期(4.2～5Ma)可能是天山南、北麓新生代冲断褶皱的主要形成期,发育自天山内部的台阶状逆断层在向两侧沉积盆地扩展过程中形成多个滑脱面和断坡,断层位移在断坡位置引发褶皱变形,从而形成南北方向背斜带成排分布的构造格局。在天山南麓库车河剖面中,控制库车地区构造变形的三条台阶状逆断层位移量分别为5.7km、6.3km和18km,它们的活动时代由老到新,而位移量却逐渐增大,反映新生代以来天山南麓的冲断作用可能存在一个加速的过程。按上述数值计算,渐新世(23Ma)以来的缩短速率为1.3mm/a,上新世(5.2±0.2Ma)以来的缩短速率为3.6mm/a。在天山北麓金钩河—安集海河剖面中,山前深部楔形体内的断层位移量为16.9km,但只有6km的位移量沿中上侏罗统西山窑组煤层内的滑脱面向北传递至第二排背斜带,而至第三排背斜带,位移量已递减为0.22～0.29km。以上新世早期(4.2～5Ma)作为构造活动时间,计算出该剖面上、下构造层上新世以来的缩短速率为2.6～3.1mm/a和3.8～4.5mm/a,其中下构造层内的山前深部楔形体、霍尔果斯深层背斜和安集海背斜的缩短速率分别为3.9～4.6mm/a、1.2～1.4mm/a和0.04～0.38mm/a,这说明由于断层位移量在向北传递过程中不断被褶皱作用吸收或沿反冲断层向南消减,各排背斜带的变形强度由南向北依次减弱。     

北天山山前安集海河阶地形成的时代及意义

北天山山前几条主要河流普遍发育河谷阶地。安集海河发育６～８级阶地,通过年代测定及区域对比,可得出安集海河阶地形成于中更新世晚期一晚更新世早期（约１２～１４万年左右）。第四纪以来构造活动及气候变化控制着河流下切和侧蚀作用的进行,安集海河阶地的形成和发育明显受第四纪晚期构造活动和气候变化等因素的影响。     

独山子背斜的几何学运动学数字模拟

独山子背斜位于准噶尔盆地南缘西段,是北天山逆冲推覆带在前陆盆地山前形成的断层相关褶皱。本文以横跨背斜的过井地震剖面为蓝本,用钻井数据、相邻地震剖面和地表形态为约束,运用断层相关褶皱模型对独山子背斜进行几何学定量分析,以建立合理的与实际接近的构造模型; 提取构造特征参数进行基于Trishear模型的运动学定量模拟,选取与实际数据吻合度最高的构造形态为独山子背斜的最佳几何模型。模拟数据表明:独山子背斜为前翼呈三角剪切的断层传播褶皱; 背斜变形从喜马拉雅山晚期更新统(Q1-3)沉积期间开始形成并生长,平均推覆速率为0.18 mm/a; 全新统沉积期间(Q4)推覆活动强度达到最大值,平均推覆速率为 4.64 mm/a。形成独山子背斜所需的总推覆位移量为5 600 m左右,第四纪期间的平均推覆速率约为0.19 mm/a。     

呼图壁背斜构造模型和成因机制

呼图壁背斜位于准噶尔盆地南缘褶皱—冲断带的北部,属于天山向准噶尔盆地下方逆冲带的最前缘。基于全新的高精度三维地震资料,本文揭示了呼图壁背斜具有上下分层变形的特点,背斜发育双层滑脱的构造形态,浅层主要以古近系紫泥泉子组的石膏质泥岩为滑脱面,与上覆的古近系和新近系地层产生滑脱背斜;深层主要以侏罗系的八道湾组和西山窑组的煤层为区域性的滑脱面,产生侏罗系和上覆地层的断背斜构造,深浅层滑脱叠置,总缩短量达1 210 m。受二叠系隆凹构造格局的影响,石炭—二叠系古凸起对新生界的变形具有定形、定位的作用。利用ADS法定量分析和研究表明呼图壁背斜的形成经历了前期弱挤压构造运动,发育时间在新近纪,约23 Ma,后期为强烈的挤压构造运动,时间在7 Ma左右,呼图壁背斜的发育与南缘天山的期次隆起具有很好的响应。

     

天山北缘晚新生代快速变形时间的确定及其成藏意义

生长地层分析及区域研究成果表明天山北缘冲断带晚新生代快速变形主要形成于10～7Ma以来。10Ma以来准南前陆冲断带持续扩展,形成现今地表可见的三排褶皱冲断带,其构造形成时间明显晚于天山南缘,显示印-藏碰撞引起的区域构造变形由南向北传播的特征。10Ma以来的变形强度显示天山北缘乌鲁木齐以西—齐古背斜地区的构造变形相对较弱,向两侧剥蚀作用、构造变形有所增强。晚新生代快速变形与晚期成藏匹配良好,决定冲断带前缘是油气成藏的有利部位,而山前构造带的剥蚀、隆升强烈,构造变形较弱的构造(带)应是早期成藏得以保存的有利部位。