Tectonic evolution of the Dabashan orocline, central China: Insights from the superposed folds in the eastern Dabashan foreland

The Dabashan orocline is situated in the northwestern margin of the central Yangtze block,central China.Previous studies have defined the orthogonal superposed folds growing in its central-western segment thereby confirming its two-stage tectonic evolution history.Geological mapping has revealed that more types of superposed folds have developed in the eastern segment of the orocline,which probably provides more clues for probing the structure and tectonic history of the Dabashan orocline.In this paper,based on geological mapping,structural measurements and analyses of deformation,we have identified three groups of folds with different trends （e.g.NW-,NE-and nearly E-trending folds） and three types of structural patterns of superposed folds in the eastern Dabashan foreland （e.g.syn-axial,oblique,and conjunctional superposed folds）.In combination with geochronological data,we propose that the synaxial superposed folds are due to two stages of ～N-S shortening in the west and north of the Shennongjia massif,and that oblique superposed folds have been resulted from the superposition of the NW-and NE-trending folds onto the early ～ E-W folds in the east of the Shennongjia massif in the late Jurassic to early Cretaceous.The conjunctional folds are composed of the NW-and NE-trending folds,corresponding to the regional-scale dual-orocline in the eastern Sichuan as a result of the southwestward expansion of the Dabashan foreland during late Jurassic to early Cretaceous,coeval with the northwestward propagation of the Xuefengshan foreland.Integration of the structure and geochronology of the belt shows that the Dabashan orocline is a combined deformation belt primarily experiencing a twostage tectonic evolution history in Mesozoic,initiation of the Dabashan orocline as a foreland basin along the front of the Qinling orogen in late Triassic to early Jurassic due to collisional orogeny,and the final formation of the Dabashan orocline owing to the southwestward propagation of the Qinling orogen during late Jurassic to early Cretaceous intra-continental orogeny.Our studies provide some evidences for understanding the structure and deformation of the Dabashan orocline.

Formation of Natural Bitumen and its Implication for Oil/gas Prospect in Dabashan Foreland

Natural bitumen is the evolutionary residue of hydrocarbon of sedimentary organic matter. Several kinds of bitumen with different occurrences, including bitumen in source rock, migration bitumen filled in fault, oil-bed bitumen and paleo-reservoir bitumen, are distributed widely in the Dabashan foreland. These kinds of bitumen represent the process of oil/gas formation, migration and accumulation in the region. Bitumen in source rock fiUed in fractures and stylolite and experienced deformation simultaneously together with source rock themselves. It indicated that oil/gas generation and expelling from source rock occurred under normal buried thermal conditions during prototype basin evolution stages prior to orogeny. Occurrences of bitumen in source rock indicated that paleo- reservoir formation conditions existed in the Dabashan foreland. Migration bitumen being widespread in the fault revealed that the fault was the main channel for oil/gas migration, which occurred synchronously with Jurassic foreland deformation. Oil-bed bitumen was the kind of pyrolysis bitumen that distributed in solution pores of reservoir rock in the Dabashan foreland depression, the northeastern Sichuan Basin. Geochemistry of oil-bed bitumen indicated that natural gas that accumulated in the Dabashan foreland depression formed from liquid hydrocarbon by pyrolysis process. However, paleo-reservior bitumen in the Dabashan forleland was the kind of degradation bitumen that formed from liquid hydrocarbon within the paleo-reservior by oxidation, alteration and other secondary changes due to paleo-reservior damage during tectonics in the Dabashan foreland. In combination with the tectonic evolution of the Dabashan foreland, it is proposed that the oil/gas generated, migrated and accumulated to form the paleo-reservoir during the Triassic Indosinian tectonic movement. Jurassic collision orogeny, the Yanshan tectonic movement, led to intracontinental orogeny of the Dabashan area accompanied by geofluid expelling and paleo-reservoir damage in the Dabashan foreland. The present work proposed that there is liquid hydrocarbon exploration potential in the Dabashan foreland, while there are prospects for the existence of natural gas in the Dabashan foreland depression.

Hydrodynamic Evolution and Hydrocarbon Accumulation in the Dabashan Foreland Thrust Belt,China

There are two plays in the Dabashan foreland tectonic belt： the upper and the lower plays. The lower play experienced one sedimentary hydrodynamic stage, two burial hydrodynamic stages, two tectonic hydrodynamic stages and two infiltration hydrodynamic stages from the Sinian to the Cenozoic, while the upper play had one sedimentary hydrodynamic stage, one burial hydrodynamic stage, two tectonic hydrodynamic stages and one infiltration hydrodynamic stage from the Permian to the Cenozoic. Extensive flows of both sedimentary water, including hydrocarbons, and deep mantle fluid occurred in the Chengkou faults during collision orogeny in the Middle-Late Triassic Indosinian orogeny, and fluid flow was complicated during intracontinental orogeny in the Middle-Late Jurassic. In addition to these movements, infiltration and movement of meteoric water took place in the Chengkou faults, whereas in the covering-strata decollement tectonic belt, extensive sedimentary water flow （including hydrocarbons） occurred mainly in the Zhenba and Pingba faults. During the stage of rapid uplift and exhumation from the Cretaceous to the Cenozoic, the fluid flow was characterized mainly by infiltration of meteoric water and gravity-induced flow caused by altitude difference, whereas sedimentary water flow caused by tectonic processes was relatively less significant. Sedimentary water flow was more significant to the lower play in hydrocarbon migration and accumulation during collision orogeny in the Middle-Late Triassic Indosinian orogeny, but its influence is relatively slight on the upper play. On one hand, hydrodynamics during intracontinental orogeny in the Middle-Late Jurassic adjusted, reformed or oven destroyed oil reservoirs in the lower play; on the other hand, it drove large amounts of hydrocarbons to migrate laterally and vertically and is favorable for hydrocarbon accumulation. Infiltration hydrodynamics mainly adjusted and destroyed oil reservoirs from the Cretaceous to the Cenozoic.

Physical Modeling of Fold-and-Thrust Belt Evolution and Triangle Zone Development:Dabashan Foreland Belt(Northeast Sichuan basin,China) as an Example

Triangle zones, generally found in foreland fold-and-thrust belts, serve as favorable objects of petroleum exploration. Taking the Dabashan foreland belt as an example, we studied the formation and development of triangle zones, and investigated the effect of d^collements and the mechanical contrast of lithology by employing the method of physical modeling. Four experimental models were conducted in the work. The results showed that ＇sand wedges＇ grew episodically, recorded by deformational length, height and slope angle. The height versus shortening rate presented an S-shape curve, and uplifting occurred successively in the direction of the foreland belt. During the formation of the triangle zone, layer-parallel shortening took place at the outset; deformation decoupling then occurred between the upper and lower brittle layers, divided by a middle-embedded silicone polymers layer. The upper brittle layers deformed mainly by folding, while the lower sand layers by thrusting. As shortening continued, the geometry of a triangle zone was altered. We consider that the triangle zone in the Dabashan foreland belt was modified from an early one based on available seismic profiles and the experimental results. In addition, dccollements and mechanical contrast impose significant influence on structural development, which can directly give rise to structural discrepancies. More d^collements and obvious mechanical contrast between brittle layers can promote the coupling between the upper and lower brittle layers. Basal d^collement controls the whole deformation and decreases the slope angle of the wedge, while roof d^collement determines whether a triangle zone can be formed.

Structural features and deformational ages of the northern Dabashan thrust belt

A large-scale pop-up structure occurs at the front of the northern Dabashan thrust belt （NDTB）, bound by the NNE-dipping Chengkou fault to the south, and the SSW-dipping Gaoqiao fault to the north. The pop-up structure shows different features along its strike as a direct reflection of the intensity of tectonic＂ activity. To the northwest, the structure is characterized by a two-directional thrust system forming a positive flower-like structure. In contrast, the southeastern part is composed of the vertical Chengkou fault and a series of N-directed backthrusts, showing a semi-flower-like structure. We present results from Ar-Ar dating of syntectonic microthermal metamorphic sericite which show that the Chengkou fault experienced intense deformation during the mid-Mesozoic Yanshanian epoch （about 143.3 Ma）, causing rapid uplift and thrusting of the northern Dabashan thrust belt. During the propagation of this thrust, a series of backthrusts formed because of the obstruction from the frontier of Dabashan thrust belt, leading to the development of the pop-up structure.

Origin of Paleofluids in Dabashan Foreland Thrust Belt:Geochemicai Evidence of ^(13)C,^(18)O and ^(87)Sr/^(86)Sr in Veins and Host Rocks

In the last ten years, with important discoveries from oil and gas exploration in the Dabashan foreland depression belt in the borderland between Shanxi and Sichuan provinces, the relationship between the formation and evolution of, and hydrocarbon accumulation in, this foreland thrust belt from the viewpoint of basin and oil and gas exploration has been studied. At the same time, there has been little research on the origin of fluids within the belt. Based on geochemical system analysis including Z values denoting salinity and research on δ13C, δ18O and S7Sr/S6Sr isotopes in the host rocks and veins, the origin of paleofluids in the foreland thrust belt is considered. There are four principal kinds of paleofluid, including deep mantle-derived, sedimentary, mixed and meteoric. For the deep mantle-derived fluid, the δ13C is generally less than -5.0‰PDB, δ18O less than -10.0‰PDB, Z value less than 110 and 87Sr/86Sr less than 0.70600; the sedimentary fluid is mainly marine carbonate- derived, with the δ13C generally more than -2.0‰PDB, 18δO less than -10.0‰PDB, Z value more than 120 and STSr/S6Sr ranging from 0.70800 to 0.71000; the mixed fluid consists mainly of marine carbonate fluid （including possibly a little mantle-derived fluid or meteoric water）, with the j13C generally ranging from -2.0‰ to -8.0‰PDB, δ18O from -10.0‰ to -18.0‰ PDB, Z value from 105 to 120 and 87Sr/86Sr from 0.70800 to 0.71000; the atmospheric fluid consists mainly of meteoric water, with the δ13C generally ranging from 0.0‰ to -10.0‰PDB, δ18O less than -8.0%rPDB, Z value less than 110 and 87Sr/86Sr more than 0.71000. The Chengkou fault belt encompasses the most complex origins, including all four types of paleofluid; the Zhenba and Pingba fault belts and stable areas contain a simple paleofluid mainly of sedimentary type; the Jimingsi fault belt contains mainly sedimentary and mixed fluids, both consisting of sedimentary fluid and meteoric water. Jurassic rocks of the foreland depression belt contain mainly meteoric fluid.

北大巴山汉江流域地貌特征及其构造意义

北大巴山地区位于青藏高原向东扩张的前缘地带,研究该区域水系流域的构造地貌特征以及构造活动程度的空间分布,探讨研究区的新构造运动和地貌演化阶段,有助于理解该地区地貌演化对青藏高原新生代隆升的响应。同时,也能在一定程度上限定青藏高原向东扩张的范围。基于ASTER GDEM数据,提取了研究区流域的面积高程积分值(HI)及曲线(HC)、标准化河长坡降指标(SL/K)和Hack剖面、流域盆地不对称度(AF)、河谷宽高比(VF)、盆地延伸率(Re)等地貌指数,分析流域地貌特征。结果表明,研究区48个子流域中有46个面积高程积分小于0.5且积分曲线呈“S”型和下凹型,表明北大巴山地区处于地貌演化阶段的壮年-老年期。综合5种地貌指数分析,揭示研究区主要断裂都具有构造活动性,其中宁陕断裂和城口-房县断裂的构造活动性较强,安康断裂的活动性较弱。这表明青藏高原的向东扩张已经影响到了北大巴山地区的构造变形和现代地貌的演化过程。

志留系泥页岩滑脱层对大巴山前陆冲断带构造样式的影响——基于物理模拟研究

大巴山前陆冲断带处于秦岭造山带与四川盆地的过渡区,是四川盆地大中型油气藏探明储量的主要分布区,也是盆山耦合研究的典型区。该地区发育三套主要滑脱层,前人研究多以底层寒武系泥页岩和顶层上三叠统膏盐岩作为区域主控滑脱层,认为中间层志留系滑脱层使褶皱冲断带的构造样式复杂化,但是中间滑脱层对大巴山前陆冲断带的具体影响研究较少。本文通过物理模拟设计两组实验、四个模型,探讨了相同厚度的硅胶和玻璃微珠作为基底滑脱层时,中间滑脱层对于模型整体构造样式的影响,分析了其与基底及沉积盖层的相互作用。实验结果显示:①硅胶作基底滑脱层时,正向逆冲断层和反向逆冲断层数量相当,反冲断层多为自基底逆冲的断层。玻璃微珠作为基底滑脱层时,存在中间滑脱层的体系以正向逆冲断层为主,反冲断层多为浅部小型断层;②中间滑脱层的引入降低了整个体系的强度,使体系中构造变形更加复杂,模型中出现脱耦现象。中间滑脱层对前陆方向的变形起主导作用,促进了模型远端前陆方向的传播,垂向上沉积载荷的增大激活了中间滑脱层对挤压端构造样式的影响;③模拟表明,该地区志留系滑脱层使剖面出现脱耦,寒武系基底滑脱层为摩擦滑脱层,上三叠统之上发育较薄沉积盖层。

Tectonothermal Evolution of the Eastern Tibetan Plateau Foreland: Fission-Track Thermochronology of the Southern Dabashan Fold-Thrust Belt

Apatite fission-track dating and thermal-history modeling were carried out on samples from the Dabashan （大巴山）, a fold-thrust belt, northeast of the Sichuan （四川） Basin and east of the Tibetan Plateau. A first cooling event in the Late Cretaceous is followed by a prolonged period of ther- mal stability with exhumation rates of 〈0.025 mm/a, as determined from age vs. elevation relationships. The preservation of age vs. elevations relationships and the lack of distinct age changes across tectonic structures indicate that the Dabashan fold-thrust belt formed prior to the Late Cretaceous, consistent with the current view of Triassic-Early Cretaceous shortening. Relatively short mean track lengths （-12 μm） indicate that the samples remained in the partial annealing zone for a prolonged time. The knick points in the best-fitting temperature-time models suggest that the onset of late-stage accelerated cooling commenced at 〈11 Ma. Related exhumation rates are 0.3-0.2 mm/a assuming geothermal gra- dients of 20 and 30 ℃/km. We speculate that this late-stage event results from eastward growth of the Tibetan Plateau and overstepping of the Sichuan Basin, it is likely responsible for the youthful mor- phology of the Dabashan.

Oil/Gas Migration and Aggregation in Intra-Continental Orogen Based on Numerical Simulation: A Case Study from the Dabashan Orocline, Central China

Geofluid, driven by tectonic stress, can migrate and aggregate in geological body. Thus, numerical simulation has been widely used to rebuild paleo-tectonic stress field and probe oil/gas （one type of geofluid） migration and aggregation. Based on geological mapping, structural data, and mechanical parameters of rocks, we reconstruct the traces for gas/oil migration and aggregation in Dabashan intra-continental orogen using numerical simulation. The study shows that gas/oil, obviously dominated by late Middle Jurassic-Early Cretaceous paleo-tectonic stress field that is characterized by NE-SW shortening in the Dabashan thrust belt and SW-emanating shortening in its foreland belt, massively migrate from the Dabashan thrust belt to its foreland belt, that is, NE to SW, resulting in the formation of some probable favorable areas for oil/gas mainly along the Tiexi -Wuxi fault, in some superposed structure （e.g., Zhenba , Wanyuan , Huangjinkou , and Tongnanba areas）, and in the Zigui Basin. Thus, our study shows that numerical simulation can be effectively applied to study oil/gas migration and aggregation in intra-continental orogen and provided some significant evidences for oil/gas exploration.

Mesozoic uplift of the Dabashan and Micangshan-Hannan Dome in the South Qinling orogenic belt

The topographic evolution of continental orogens is important for understanding continental orogenic processes,geodynamic mechanisms,and climatic and environmental changes.The Qinling Orogen is a major orogenic belt in China,and its uplift history can provide insights into the tectonic configuration and geodynamics of China and East Asia.Previous studies have shown that the Dabashan and Micangshan-Hannan Dome(MHD)in the South Qinling orogenic belt were uplifted during the Mesozoic.However,the magnitude of the uplift remains unclear.In this study,using sedimentary records in the northern Sichuan Basin and lithospheric flexural modeling,we estimated the magnitude of Mesozoic uplift of the Dabashan and MHD,along with the effective elastic thickness(Te)of the Sichuan Basin.The Dabashan and MHD were uplifted by approximately 1220 and 880 m during the Middle Jurassic and Early Cretaceous,respectively.Therefore,we propose that the present-day elevation of the Dabashan and MHD is primarily the result of Mesozoic uplift.The differences in the duration and amount of uplift between different tectonic units indicate that the uplift processes and driving mechanisms in the South Qinling orogenic belt were different in the Mesozoic and Cenozoic.Mesozoic uplift was the result of convergence of the North China and South China blocks advanced from east to west,whereas Cenozoic uplift was driven by ongoing indentation of the Indian Plate into Eurasia from southwest to northeast.The lithospheric strength of the northern Sichuan Basin was weakened from the Middle Jurassic to Early Cretaceous,and Tedecreased from 73 to 57 km.This may have been caused by the flexure-related bending stresses in the lithosphere that developed due to the large topographic loading.

Tectonic rotation in the western South-Dabashan orogenic belt in late Mesozoic

A paleomagnetic study was carried out on Early-Middle Jurassic sediments in the Zhenba area, the western South-dabashan orogenic belt. Stepwise thermal demagnetization isolated the characteristic high temperature component (HTC) (D=37.1°,I=46.1°, α95=10.1°), which passed the fold test. By comparing the corresponding pole of HTC (57.6°N, 196.6°E, A95=9.9°) with coeval reference poles for the Sichuan basin, we detected a 26.5°±9.0° clockwise rotation of the study area relative to the stable Sichuan basin. We interpret that this rotation was caused by obstruction of the Hannan block during thrusting of the Dabashan, and occurred around Early Cretaceous.

川东北大巴山地区油气保存条件综合分析

大巴山前构造带经历了多期构造运动,油气的保存条件复杂。通过对川东北大巴山地区构造形态和断裂特征、地层出露情况及盖层发育特征等进行综合分析,结合已有地层水矿化度数据和油气显示情况为约束,综合分析大巴山地区油气保存条件。研究结果表明:(1)大巴山地区保存条件整体较差,由于北大巴山地区构造带断裂破碎作用强烈,断裂分布密集,大气水下渗作用强烈,水型以NaHCO_(3),Na_(2)SO_(4)型为主,出露地层以震旦系—志留系为主,油气藏保存条件受到严重影响,为油气保存不利区域;(2)但因受到不同断裂带的强烈破碎作用和抬升剥蚀作用,大巴山地区油气保存条件有明显的分带性和分段性,往盆地内方向过渡区域构造变形强度逐渐减弱,断裂数量减少,水型以MgCl_(2),Na_(2)SO_(4)型为主,出露地层以泥盆系—二叠系为主,油气保存条件整体逐渐变好;(3)南大巴山前陆冲断带铁溪—巫溪隐伏断裂盆地方向受到中下三叠统的膏盐岩和侏罗系泥质岩盖层的封盖作用,大气水下渗被阻挡,出露地层多为三叠系以上地层,断裂分布较少,水型以CaCl_(2)为主,为油气保存有利区域。

南秦岭-大巴山地区下寒武统沉积层状钡矿床成因机制研究

为理清沉积层状重晶石、毒重石矿床成因机制及其差异成矿的控制因素,对南秦岭-大巴山地区下寒武统地层中不同成矿特征的钡矿床开展了矿物学和碳-硫-氧-锶同位素地球化学分析。结果显示,该区内沉积钡矿床有以重晶石为主或以毒重石为主的类型;矿石中碳酸盐矿物具有负的碳同位素组成(δ^(13)C_(Carb)为-26.1‰~-6.3‰),重晶石具有非常大的硫、氧同位素分馏(δ^(34)SBrt为25.1‰~62.2‰,δ^(18)O_(Brt)为12.2‰~18.9‰和δ^(18)O/δ^(34)S≈0.1),反映成矿时有强烈的甲烷驱动微生物硫酸盐还原作用;毒重石等碳酸盐矿物和重晶石的锶同位素组成较为一致,都具有宽的^(87)Sr/^(86)Sr变化范围(0.7070~0.7103)和低的^(87)Sr/^(86)Sr值(~0.7070),指示成矿流体可能是与基性-超基性岩有关的富金属热液,热液流体在运移过程中与碎屑地层相互作用使其^(87)Sr/^(86)Sr值变大。综合研究认为,南秦岭-大巴山地区下寒武统沉积层状钡矿床的形成是富钡等热液流体引入缺氧盆地的结果,甲烷驱动的硫酸盐还原作用导致局部水体中硫酸根和碳酸根浓度的变化是钡离子以重晶石和/或毒重石形成的主控因素。

大巴山革命精神内涵及当代启示

大巴山精神是川陕红军精神的区域表达,是大巴山地区振兴发展的精神财富,其形成发展富有特定的历史渊源、文化性格和实践基础“,信念坚定、不怕牺牲“”实事求是、排难创新“”男女平等、妇女解放“”智勇坚定、不胜不休”构成新时代大巴山精神的本质内涵。大巴山精神应该成为中国共产党革命精神谱系中重要内容。

英德市大杷山矿区地质特征分析

英德市大杷山矿区范围内累计查明水泥用灰岩矿资源储量395877.7kt;其中控制的内蕴经济资源量(332)96337.2kt,推断的内蕴经济资源量(333)299540.5kt。矿区矿石主要平均化学成分:CaO 50.58%,MgO 0.92%。矿体的埋藏浅,地形条件利于地表水自然排泄,矿区水文地质条件简单,矿体及围岩的稳定性好,工程地质条简单,矿山开采将对地形地貌和地质环境造成较明显的影响,环境地质条件中等;矿床开采技术条件属于以环境地质问题为主的中等矿床(Ⅱ-3)类型。

大巴山前陆盆地形成及演化与油气勘探潜力分析

根据野外地质调查、地震资料解释以及大量岩心分析化验等资料 ,探讨了大巴山前陆盆地的形成及演化 ,分析了油气勘探潜力。研究结果表明 ,大巴山前陆盆地形成始于燕山中幕 ,盆地演化经历了J1 J12 陆内坳陷湖盆阶段、J22 J3 前陆盆地阶段、K1 N盆地萎缩阶段以及喜马拉雅期最终定型阶段。大安寨段和凉高山组两套优质烃源岩的有机质丰度高 ,有机质类型以Ⅱ1型和Ⅱ2 型为主。侏罗系发育大安寨段、凉高山组自生自储型和下沙溪庙组下生上储型 3套生储盖组合。有利勘探区带包括大巴山前冲断带、川北凹陷带和川中低隆起带。

秦岭造山带大巴山弧形构造带中生代构造变形

大巴山构造带位于秦岭造山带南部,一直被认为是华北、扬子板块碰撞带前陆逆冲-推覆构造带。研究表明,位于城口—房县断裂之南的大巴山弧形构造带,经历了两次明显的叠加变形过程。大巴山弧形构造带由轴向弧形延伸的线状褶皱与弧形弯曲的逆冲断层组成(D2),是南大巴山主期变形产物。弧形构造带西段褶皱轴向为北北西—近南北向,叠加在先前轴向近东西向的开阔宽缓的褶皱(D1)之上,形成典型横跨叠加构造。弧形构造带中段和东段,褶皱轴向逐渐转变为近东西向。构造填图显示,在弧形带形成之前,发生过一期轴向北东到北北东向褶皱为主的变形(D1)。据变形序列、卷入的地层以及区域构造关系判断,西段与中、东段D1变形时代均为晚三叠世—早侏罗世,很可能与华北、扬子的碰撞相关。而相关的地质、同位素年代学及磷灰石裂变径迹资料显示,大巴山弧形构造带主期变形(D2)的变形时代为晚侏罗世—早白垩世(160～110Ma),所以大巴山弧形构造带记录了两期不同系统构造变形的叠加,这对研究秦岭造山带的演化,具有重要意义。

四川盆地北部大巴山山前带构造样式与变形机制

利用最新的地震和地表地质资料,对四川盆地北部大巴山山前构造进行综合解释。按构造样式差异,将大巴山山前构造带划分出3个构造带:通江—黄金口西NW向潜伏断褶带、五宝场—铁山坡NW—NE向构造交汇带及温泉井—奉节近EW向构造带;其对应的前缘构造样式分别为反冲断层型、褶皱滑脱型及双向冲断—褶皱型。中生代以来的构造变形主要有2期:印支晚期,以NE向褶皱作用为主;燕山中、晚期—喜马拉雅期,以NW向冲断—褶皱作用为主。大巴山前缘构造受不同方向挤压应力联合作用的控制。

大巴山前陆弧形构造带形成机理分析

基于野外观察和构造测量,论述了大巴山前陆弧形构造带的基本构造特征,包括弧形带展布特征、分带特征、分段特征、分层特征、构造变形样式、叠加变形特征和古构造应力场特征等,在此基础上探讨了大巴弧形成的主要控制因素。指出大巴弧形成的机理不同于经典的碰撞造山模式,该弧形构造带经历了古生代大陆边缘伸展裂陷初始期、中晚三叠世碰撞造山雏形期和中晚侏罗世陆内造山定型期。造山作用前的古大陆边缘伸展作用及其产生的不规则边界形态对弧形带的形成起到了决定作用。其中先成的城口-房县弧形断裂带不仅控制了早古生代沉积-岩浆作用,同时成为大巴弧形成的主导边界条件,而弧形带两端的基底隆起也起到了重要的限制作用。根据实际地质资料设计的简单沙箱模型模拟了这个弧形带的形成条件和过程。