Influences of burial process on diagenesis and high-quality reservoir development of deep-ultra-deep clastic rocks:A case study of Lower Cretaceous Qingshuihe Formation in southern margin of Junggar Basin,NW China

Taking the Lower Cretaceous Qingshuihe Formation in the southern margin of Junggar Basin as an example,the influences of the burial process in a foreland basin on the diagenesis and the development of high-quality reservoirs of deep and ultra-deep clastic rocks were investigated using thin section,scanning electron microscope,electron probe,stable isotopic composition and fluid inclusion data.The Qingshuihe Formation went through four burial stages of slow shallow burial,tectonic uplift,progressive deep burial and rapid deep burial successively.The stages of slow shallow burial and tectonic uplift not only can alleviate the mechanical compaction of grains,but also can maintain an open diagenetic system in the reservoirs for a long time,which promotes the dissolution of soluble components by meteoric freshwater and inhibits the precipitation of dissolution products in the reservoirs.The late rapid deep burial process contributed to the development of fluid overpressure,which effectively inhibits the destruction of primary pores by compaction and cementation.The fluid overpressure promotes the development of microfractures in the reservoir,which enhances the dissolution effect of organic acids.Based on the quantitative reconstruction of porosity evolution history,it is found that the long-term slow shallow burial and tectonic uplift processes make the greatest contribution to the development of deep-ultra-deep high-quality clastic rock reservoirs,followed by the late rapid deep burial process,and the progressive deep burial process has little contribution.

Action mechanisms of abnormal fluid pressure on physical properties of deep reservoirs: A case study on Jurassic Toutunhe Formation in the southern margin of Junggar Basin, NW China

Considering the action mechanisms of overpressure on physical changes in skeleton particles of deep reservoir rocks and the differences in physical changes of skeleton particles under overpressure and hydrostatic pressure, the sandstone of the Jurassic Toutunhe Formation in the southern margin of Junggar Basin was taken as an example for physical modeling experiment to analyze the action mechanisms of overpressure on the physical properties of deep reservoirs. (1) In the simulated ultra-deep layer with a burial depth of 6000-8000 m, the mechanical compaction under overpressure reduces the remaining primary pores by about a half that under hydrostatic pressure. Overpressure can effectively suppress the mechanical compaction to allow the preservation of intergranular primary pores. (2) The linear contact length ratio under overpressure is always smaller than the linear contact length ratio under hydrostatic pressure at the same depth. In deep reservoirs, the difference between the mechanical compaction degree under overpressure and hydrostatic pressure shows a decreasing trend, the effect of abnormally high pressure to resist the increase of effective stress is weakened, and the degree of mechanical compaction is gradually close to that under hydrostatic pressure. (3) The microfractures in skeleton particles of deep reservoirs under overpressure are thin and long, while the microfractures in skeleton particles of deep reservoirs under hydrostatic pressure are short and wide. This difference is attributed to the probable presence of tension fractures in the rocks containing abnormally high pressure fluid. (4) The microfractures in skeleton particles under overpressure were mainly formed later than that under hydrostatic pressure, and the development degree and length of microfractures both extend deeper. (5) The development stages of microfractures under overpressure are mainly controlled by the development stages of abnormally high pressure and the magnitude of effective stress acting on the skeleton particles. Moreover, the development stages of microfractures in skeleton particles are more than those under hydrostatic pressure in deep reservoir. The multi-stage abnormally high pressure plays an important role in improving the physical properties of deep reservoirs.

Two Contrasting Eclogite Types on the Northern Margin of the Qaidam Basin, Western China

Eclogites have been recently discovered in the Xitieshan area in the middlesegment of the northern margin of the Qaidam basin. These eclogites, together with those recognizedearlier in the Yuka area of the western segment of the northern margin of the Qaidam basin and inthe Dulan area of the eastern segment of the northern margin of the Qaidam basin, form an eclogitebelt with a length of 350 km. A comparison of the eclogites from the Yuka and Xitieshan areassuggests that they show different country rocks, microtextures, mineral assemblages, and especially,different peak temperatures, PT paths during decompression and isotopic features. Eclogites fromthe Yuka area bear evidence of prograde metamorphism, such as prograde mineral relics in garnet andgrowth zoning of garnet, and hairpin-shaped PT paths with coincidence of the baric and thermal peaksof metamorphism, which reflect rapid burial and uplift. Sm-Nd isotopic determination shows obviousSm-Nd disequilibrium, and no isochron ages of Early Paleozoic metamorphism was obtained. On thecontrary, the Xitieshan eclogite was subjected to metamorphism of higher eclogite-facies andpost-eclogite-facies temperatures, showing an obvious granulite-facies overprint. A tentative PTpath for the Xitieshan area suggests that the baric peak preceded the thermal culmination. Wholerock-garnet-omphacite Sm-Nd isotopic data give an isochron age in the Early Paleozoic. Thedifferences between the two eclogites imply their different tectonic-thermal history during theirburial and uplift.

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. Arcnate 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 decollement 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-Uriimqi 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 decollement 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.

Major breakthrough of Well Gaotan 1 and exploration prospects of lower assemblage in southern margin of Junggar Basin, NW China

Well Gaotan 1 was tested a high yield oil and gas flow of more than 1 000 m^3 a day in the Cretaceous Qingshuihe Formation,marking a major breakthrough in the lower assemblage of the southern margin of Junggar Basin. The lower assemblage in the southern margin of the Junggar Basin has favorable geological conditions for forming large Petroleum fields, including:(1) Multiple sets of source rocks, of which the Jurassic and Permian are the main source rocks, with a large source kitchen.(2) Multiple sets of effective reservoirs,namely Cretaceous Qingshuihe Formation, Jurassic Toutunhe Formation and the Khalza Formation etc.(3) Regional thick mudstone caprock of Cretaceous Tugulu Group, generally with abnormally high pressure and good sealing ability.(4) Giant structural traps and litho-stratigraphic traps are developed. The northern slope also has the conditions for large-scale litho-stratigraphic traps.(5) Static elements such as source rocks, reservoirs and caprocks are well matched, and the dynamic evolution is suitable for large oil and gas accumulation. The lower assemblage of the southern margin of the Junggar Basin has three favorable exploration directions, the Sikeshu Sag in the west part, the large structures in the middle and eastern part, and the northern slope.

Geological factors associated with unsuccessful exploration wells in the northern margin of the Qaidam basin

We investigated the geological factors associated with unsuccessful exploration wells in the northern margin of the Qaidam basin to better understand their cause.The structural situation,the hydrocarbon accumulation mechanism and unsuccessful well data collected from 1996 to 2005 were studied.The results show that the main geological factors associated with unsuccessful exploration wells are a lack of effective source rocks and a lack of effective traps,as well as the migration-accumulation conditions that exist in this area.The basin was reformed by Meso-Cenozoic tectonic evolution.Multi-stage tectonic activities have both positive and negative effects on hydrocarbon accumulation.Source rocks distribution,effective migration channels,effective traps and the tectonic evolution effects on hydrocarbons should be the key objects for further studies.

Lithofacies paleogeography restoration and its significance of Jurassic to Lower Cretaceous in southern margin of Junggar Basin,NW China

In view of the difficulties in the study of lithofacies paleogeography and the low reliability of the distribution range of sedimentary sand bodies in the prototype basin caused by less deep drilling, complex seismic imaging and low degree of exploration in the southern margin of Junggar Basin, NW China. A new method based on the source to sink idea was used to restore lithofacies paleogeography and predict glutenite distribution. In the restoration, apatite fission track age was used to define range and uplift time of macro-provenance;the range of provenance area and the migration process of lake shoreline were restored based on the quantitative relationship between gravel diameter and transportation distance, tectonic shortening and other geological parameters;drilling cores and field outcrop sedimentary structures were analyzed, and a series of maps of lithofacies paleogeographic evolution and distribution range of glutenite bodies were compiled. It is concluded that from Early Jurassic to Early Cretaceous, in the southern margin of Junggar Basin, the provenance area gradually expanded from south to north, the lake basin expanded, shrunk and expanded, and the paleoclimate changed from humid to drought to humid. The western section always had proximal fan delta deposits from the southern ancient Tianshan provenance developed, and in the middle and eastern sections, the provenance areas evolved from far source to near source, mainly river-delta, braided delta, fan delta and other sediments developed. The boundary between provenance areas of the western and middle sections is speculated to be Hongche fault zone. In an angle open to the northwest with the current basin edge line, the restored ancient lake shoreline controlled the heterogeneity of reservoirs in the delta plain belt and delta front belt on its both sides. The ancient lake shoreline, current stratigraphic denudation line and current basin margin line limit the types and scope of favorable reservoirs.This understanding provides an important geological basis for oil and gas exploration in the deep lower source-reservoir assemblage at the southern margin of Junggar Basin.

Quantitative identification of coal-type gas and oil-type gas in source-mixed gas at the northern margin of Qaidam Basin

The current study tested the gas component and carbon isotopic composition of gas samples from 6 oilgas fields at the northern margin of Qaidam Basin, and established a chart to quantitatively identify the mixing ratio of source-mixed gas. Besides, this research quantitatively investigated the natural gas generated by different types of organic matter. The results show that different ratios of source-mixed gas exist in the 6 oil-gas fields at the northern margin of Qaidam Basin. Among them, Mabei has the highest mixing ratio of coal-type gas, followed by Nanbaxian, Mahai, Lenghu-4, Lenghu-3 and Lenghu-5, with the ratios of coal-type gas 91%, 87%, 83%, 66%, 55% and 36%, respectively. Lenghu-3 and Lenghu-4 oil-gas fields were mainly filled by coal-type gas earlier. For Lenghu-3, the gas was mainly generated from low matured source rocks in lower Jurassic Series of Lengxi sub-sag. For Lenghu-4, the gas was mainly generated from humus-mature source rocks in lower Jurassic Series of the northern slope of Kunteyi sub-sag. Gas in Lenghu-5 was mainly later filled oil-type gas, which was generated from high matured sapropelics in lower Jurassic Series of Kunteyi sub-sag. Earlier filled coal-type gas was the main part of Mahai, Nanbaxian and Mabei oil-gas fields. Gas source of Mahai was mainly generated from high mature humics in lower Jurassic Series of Yibei sub-sag; for Nanbaxian, the gas was mainly generated from high matured humics in middle-lower Jurassic Series of Saishiteng sub-sag; for Mabei, the gas was mainly generated from humus-mature source rocks in middle Jurassic Series of Yuqia sub-sag.

Characteristics and genesis of clay minerals in the northern margin of the Qaidam Basin

In order to develop appropriate reservoir protection measures in the northern margin of the Qaidam Basin and improve its oil and gas recovery efficiency,characteristics of clay minerals from eleven clay rock samples from the northern margin of the Qaidam Basin were investigated using X-ray diffraction analysis,the Scanning Electron Microscope（SEM）and energy spectrum analysis.Clay mineral composition and distribution characteristics of the main hydrocarbon reservoirs,i.e.,from the Jurassic and Paleogene-Neogene,were explored.We analyzed the main factors which affected these attributes.The results show that the major clay minerals in the northern margin are chlorite,kaolinite,illite,smectite and illite/smectite inter-stratified minerals.Illite is the most widely spread clay mineral in this area. Chlorite is mainly found in the entire Neogene and in shallow horizons of the Paleogene.Smectite is enriched in the shallow Paleogene-Neogene.There are large amounts of kaolinite and illite/smectite inter-stratified minerals in the Jurassic.The major factors affecting the different development of clay minerals in the region are properties of parent rocks,paleoclimate and paleowater media conditions, diagenesis transformation,tectonic and terrain conditions.

THE SEQUENCE OF PALEOENVIRONMENTAL CHANGES SINCE ABOUT 4KA B.P., RECORDED BY NIYA SECTION IN SOUTHERN MARGIN OF TARIM BASIN

Through synthetic researches of multi-index geological records of Niya section, which are of high resolution in southern margin of Tarim Basin, this paper has reconstructed the sequences of paleoclimate in this region during historical times (since about 4000a B.P.). During the last 4000 years, the area has experienced alternations of relative cold-moisture and relative warm-dry periods. Three evident cold-moisture periods and three warm-dry periods are identifing. The study shows that the human activities have an intimate relation with the evolution of paleoclimate in the southern Xinjiang. Paleoclimate has played very important role in influencing human being′s agricultural activities.

Simulation experiment on hydrocarbon generating potential of various source rocks on the northern margin of the Qaidam Basin,Qinghai,China

The northern margin of the Qaidam Basin is one of the main oil-gas exploration areas in western China,where source rocks are composed mostly of Middle and Lower Jurassic dark mud shale,carbargillite and coal. A large number of subsurface and outcrop samples differing in lithology with different types of organic matter were selected for resource evaluation,research and calculation. And among them,13 samples were used for simulation experiment on hydrocarbon generating potential of various source rocks. At first,two kinds of heating modes were compared through simulation experiment,including single temperature-step heating and continual heating. Perhaps,the process of hydrocarbon generation and expulsion occurred naturally between a close system and an open system. In addition,the first heating mode was convenient,and all its reaction products were involved in the whole thermal evolution,and the final simulation experimental results were basically in consistency with the natural evolution trend. Therefore,the first heating mode was adopted and the hydrocarbon yield of every sample was worked out. Accord-ing to the type and lithology of organic matter and the hydrocarbon yield of samples for simulation experiment,hy-drocarbon generation and expulsion mode with three kinds of lithology and five types of source rock has been estab-lished to provide the basis for hydrocarbon generation evaluation,research and resource calculation.

Formation conditions and exploration direction of large and medium gas reservoirs in the Junggar Basin, NW China

The Junggar Basin is rich in oil but lacks natural gas, which is inconsistent with its geological background of natural gas. Based on the analysis of main source kitchens, and the evaluation of geological setting and controlling factors of gas accumulation, it is proposed that three significant fields for gas exploration should be emphasized. The first field is the Carboniferous volcanic rocks. The Carboniferous residual sags and large-scale reservoirs were developed in three active continental margins, i.e., the southeastern, northeastern and northwestern active continental margins. Gas accumulation is controlled by the favorable reservoir-caprock combinations composed of volcanic rocks and their superimposed lacustrine mudstones in the Upper Wuerhe Formation. Dinan, Eastern and Zhongguai uplifts are three favorable directions for natural gas exploration. The second field is the Lower combinations in the southern margin of Junggar Basin. Rows of structural traps were developed in this area with ideal preservation conditions and space-time configuration for trap-source combinations. Sets of clastic reservoirs and overpressured mudstones formed perfect reservoir-caprock combinations which are the main exploration direction for Jurassic coal-type gas reservoirs in this area. The seven large structural traps in the middle-east section are recently the most significant targets. The last field is the Central Depression. Large hydrocarbon generating centers, i.e., Mahu, Fukang and Shawan sags, were developed in this area, their source rocks were deeply buried and at highly-mature stage. Thus the Central Depression is a favorable exploration direction for Permian high-over mature gas fields(reservoirs). Great attentions should be paid to two types of targets, the deeply–buried structures and structural-lithologic traps. Based on three main gas systems, gas exploration is suggested be strengthened within three fields and on three levels.

Double Difference Location of the Mainshock and Aftershocks of the Hutubi MS6.2 Earthquake That Occurred on December 8,2016

The mainshock and aftershocks of the Hutubi M_S6.2 earthquake on December 8,2016 were relocated by applying the double difference method, and we relocated 477 earthquakes in the Hutubi region. The earthquake relocation results show that the aftershocks are distributed in the east-west direction towards the north side of the southern margin of the Junggar Basin fault,and are mainly distributed in the western region of the mainshock. The distance between the mainshock after relocation and the southern margin of the Junggar Basin fault is obviously shortened. Combined with the focal mechanism and the spatial distribution of the mainshock and aftershocks,it is inferred that the southern margin of the Junggar Basin fault is the main seismogenic structure of the Hutubi earthquake.

柴达木盆地北缘断裂锡铁山-阿木尼克山段第四纪晚期古地震活动性

柴达木盆地北缘断裂带是青藏高原北部的一条区域性活动断裂带,构成了柴达木盆地北部和祁连山的边界断裂,研究其第四纪晚期古地震活动对于理解柴达木盆地北缘断裂带地震复发周期、地震危险性等具有重要意义。通过地质考察、遥感解译、探槽开挖及OSL地质测年、古地震期次分析等,对柴达木盆地北缘断裂(锡铁山-阿木尼克山段)古地震事件进行了研究。研究表明:探槽剖面共揭露了5次比较可靠的古地震事件,发震时间分别为:事件E1距今约60 a;事件E23.1±0.3~3.4±0.3 ka;事件E37.5±0.3~8.1±0.3 ka;事件E410.1±0.4~11.4±0.4 ka;事件E512.1±0.4~12.8±0.4 ka。利用古地震逐次限定法认为柴达木盆地北缘断裂(锡铁山-阿木尼克山段)地震复发周期为2.6~3.4 ka。阿木尼克山段最新离逝时间为60年前,锡铁山段最新离逝时间为3.1±0.3 ka,分析认为柴达木盆地北缘断裂锡铁山段未来遭遇破坏性地震的可能性大于阿木尼克山段。该结果可以更好地了解柴达木盆地北缘断裂的古地震期次、复发间隔等,对地震预报预测及评价该断裂未来地震危险性具有一定的指导意义。

柴北缘尕海南山晚志留世—晚泥盆世火山岩浆组合对早古生代造山后伸展时限的约束

柴达木盆地北缘(柴北缘)构造带经历了早古生代的大洋俯冲到大陆俯冲,形成了广为人知的柴北缘超高压变质带。早古生代造山带何时开始垮塌一直存在争论,火山岩和侵入岩作为深地岩石探针能为约束地壳活动提供关键制约。应用锆石LA–ICP–MS U–Pb年代学和Lu–Hf同位素方法对柴北缘东段尕海南山地区出露的牦牛山组火山碎屑岩和侵入其中的花岗岩开展研究。锆石U–Pb年代学结果显示,牦牛山组火山碎屑岩的形成时代约为423 Ma,侵入其中的花岗岩的形成时代为370 Ma,表明火山岩喷发的年龄在晚志留世,后期侵入的花岗岩结晶年龄为晚泥盆世;锆石Lu–Hf同位素结果显示,晚志留世熔结凝灰岩ε_(Hf)(t)值集中在–11.5~–8.3,其两阶段Hf模式年龄集中在1945~2133 Ma,显示火山岩主要源于古老地壳物质熔融;而晚泥盆世侵入的花岗岩的ε_(Hf)(t)值分布在3.9~9.1,其两阶段的Hf模式年龄集中在792~1118 Ma,显示花岗岩主要源于中—新元古代地壳物质的部分熔融。结合对区域地质、岩石学等资料的综合分析认为,晚志留世—早泥盆世时期,大陆深俯冲导致的强烈造山作用造成柴北缘地壳发生明显加厚,加厚的欧龙布鲁克地壳基底发生部分熔融,形成了该时期的火山岩;晚泥盆世时期,加厚地壳的拆沉作用导致软流圈地幔上涌,引发区域地壳伸展,上涌的软流圈物质与地壳相互作用并发生部分熔融作用。因此区域牦牛山组形成时代跨度较大,不能笼统地用牦牛山组代表造山结束的时限,晚泥盆世岩浆岩的出现才预示着柴北缘地区进入显著的地壳伸展状态。

鄂尔多斯盆地南缘麟游-淳化地区平凉组礁滩体沉积特征及分布预测

鄂尔多斯盆地南缘平凉期发育规模生物礁滩型储层,目前对该区的研究主要集中在礁滩体的类型、成因、区域演化等方面,而对礁滩体的地球物理预测尚未开展系统研究。为了提高礁滩体的预测精度,建立礁滩体储层地震预测方法,通过野外露头实地踏勘,结合岩心及分析测试等资料,对镶边台地高能环境下的生物礁滩发育特征进行研究。通过已知井的井震响应特征,建立礁滩体正演模型,同时开展流体活动性、地震纹理属性分析,形成研究区礁滩体储层的地震预测方法。结果表明:鄂尔多斯盆地南缘平凉组主要发育碳酸盐岩台地边缘-浅水陆棚沉积体系;礁滩体主要分布于台地边缘亚相,多期叠置;高亮体和纹理属性对礁滩体的预测效果最好,2种方法的联合应用大大提高了礁滩体预测精度。研究成果为台缘带礁滩体平面分布规律预测和鄂尔多斯盆地南缘平凉组礁滩体的勘探开发奠定基础。

准噶尔盆地南缘侏罗系八道湾组富藻类体煤系源岩的发现及其沉积背景

通过沉积有机质中生物标志化合物组合分析,并结合荧光显微组分镜检结果,本研究首次在准噶尔盆地南缘建功剖面下侏罗统八道湾组上段识别出一套富藻类有机质输入的煤系沉积。该套煤系源岩主体处于低成熟–成熟早期演化阶段,镜质组反射率为0.5%~0.6%;有机碳(TOC)含量主要介于2.0%~4.0%之间,局部发育碳质泥岩和煤线;生烃潜量(S_(1)+S_(2))值普遍为3.0~5.0 mg/g,碳质泥岩段最高达18.4 mg/g;氢指数(HI)主要为100~150 mg/g,碳质泥岩段达280 mg/g,属于Ⅱ2型有机质。沉积有机质中生物标志化合物组合表现为姥鲛烷优势,中、短链正构烷烃含量较高,C_(27)~C_(29)规则甾烷呈“V”型分布,Ts、C_(29)Ts、C_(30)H藿烷含量较高,C同位素组成较轻。全岩荧光显微镜镜检结果表明,源岩中壳质组主要为孢子体和藻类(屑)体。结合沉积背景综合判断,该套富藻类体煤系沉积形成于水体较深的湖泊沼泽化早期阶段,浮游藻类等低等水生生物对沉积有机质存在显著贡献,有望成为区域潜在的优质烃源岩。

基于核磁共振动态截止值理论的致密砂砾岩储层渗透率评价方法

准噶尔盆地南缘深层清水河组致密砂砾岩储层为该区的重要勘探领域,渗透率是评价致密砂砾岩储层的关键参数。为提高此类储层渗透率计算精度,基于核磁共振实验,分析致密砂砾岩岩心饱和水及离心核磁共振横向弛豫时间(T_(2))谱,明确致密砂砾岩孔隙中流体的赋存形态及渗流规律,提出常规核磁共振渗透率计算方法的不足,并且提出核磁共振动态截止值的概念。基于核磁共振动态截止值,将储层孔隙空间划分为3类:自由流体孔、毛细管半束缚孔、完全束缚孔;分析了渗透率与不同孔隙类型之间的相关关系:致密砂砾岩储层渗透率与自由流体孔孔隙度、核磁总孔隙度、毛细管半束缚孔的T_(2)几何平均值呈正相关关系,与完全束缚孔流体饱和度呈负相关关系。构建基于不同孔隙类型渗透率模型,计算渗透率与岩心实验渗透率之间的相对误差小于9.0%。该方法提高了致密砂砾岩储层渗透率的计算精度,且在准噶尔盆地南缘深层清水河组致密砂砾岩储层评价中具有广泛的应用前景。

基于离散元数值模拟的构造变形机制分析方法——以准噶尔盆地南缘为例

受多期构造运动影响,准噶尔盆地南缘前陆冲断褶皱带具横向东西分段、南北分带,纵向构造叠置的变形特征。但该区构造变形机制及样式的不同认识在一定程度上制约了油气勘探的深入。为探究准南缘新生代以来构造变形机制及其变形过程,本文利用高精度地震、钻井和岩石力学等资料,根据实际地质条件,重点考虑滑脱层的数量、强度及厚度变化,结合滑脱层纵向组合、横向分布范围及同沉积作用、先存构造等因素,共设计了10组模型,并采用离散元数值模拟方法开展了对比实验。实验结果表明,滑脱层强度、厚度及其组合主要控制冲断褶皱带构造纵向叠置关系及构造样式,滑脱层分布及同沉积作用主要控制其横向变形范围,先存构造主要影响后期构造的继承性发育。在此基础上,分段开展了多因素组合模拟实验并与实际地震剖面进行对比,重构了准南缘构造变形过程,揭示了新生代以来其构造变形机制,即先存断裂、古凸起、三套不同性质滑脱层纵向叠置关系和同沉积作用共同控制了西段构造的形成与演化,“下强上弱”“下薄上厚”两套纵向叠置滑脱层控制了中段构造的形成与演化,先存断裂及单套较弱滑脱层控制了东段构造的形成与演化。该方法可为类似的复杂构造变形区提供参考。

柴北缘孤山一带侵入岩U-Pb年代学约束及构造环境特征

研究区位于祁连山脉南西部,岩体呈不规则的残块状、条带状混杂侵入于早元古代达肯大坂群中—深变质岩中,现已变质为中细粒二云花岗片麻岩。岩石中TiO_(2)质量分数为0.61%,Al_(2)O_(3)质量分数为12.5%,Na_(2)O和K_(2)O质量分数共7.43%,Fe_(2)O_(3)质量分数为0.94%,具有高Ti、Al、Fe和富钾的特征。锆石U-Pb加权平均值为766.1 Ma±5.4 Ma,侵位于新元古代南华纪。侵位方式为被动的岩墙扩张,为火山弧型花岗岩,形成于同碰撞构造环境,可能为I-S型花岗岩。