A Novel Three-stage Tectonic Model for Mississippi Valleytype Zn-Pb Deposits in Orogenic Fold-and-Thrust Belts

Mississippi Valley-type(MVT) Zn-Pb deposits predominantly form within both orogenic forelands and fold-andthrust belts, yet the mineralization process within the latter tectonic setting remains inadequately understood. This study, through a comprehensive review of MVT deposits across global fold-and-thrust belts, introduces a novel model elucidating the mineralization process in the context of tectonic belt evolution. It is demonstrated that during the stage Ⅰ, regional compression is introduced by early stages of plate convergence, causing the folding and thrusting and creating structural or lithological traps such as evaporite diapirs and unconformity-related carbonate dissolution-collapse structures. Thereafter, in stage Ⅱ, hydrocarbons begin to migrate and accumulate within these traps, where reduced sulfur is generated through thermochemical or bacterial sulfate reduction concurrent with or preceding Zn-Pb mineralization. In the subsequent stage Ⅲ, as plate convergence persists, the regional stress transitions from compression to transpression or extension. Under these conditions, steeply-dipping extensional faults are generated, facilitating the ascent of metalliferous brines into early-formed structural or lithological traps. Precipitation of Zn and Pb sulfides occurs through the mixing of Zn-Pb-transporting fluids with pre-existing reduced sulfur or by interaction with hydrocarbons.

Petrogenesis and Tectonic Implications of the Early Triassic Nianzi Adakitic Granite Unit in the Yanshan Fold and Thrust Belt:New Constraints from U-Pb Geochronology and Sr-Nd-Hf Isotopes

The Nianzi granite unit,which includes the Nianzi,Xiaolianghou and Xiawopu granitic intrusions,is a significant component of the northern part of the North China Craton(NCC)and is situated in the Yanshan fold and thrust belt(YFTB).However,there is still debate regarding the tectonic evolutionary history of the YFTB during the late Permian to Triassic period,specifically regarding the timing of subduction and collision between the NCC and the Paleo-Asian Ocean.The Nianzi granite unit exhibits unique petrological,geochronological and geochemical signatures that shed light on the tectonic evolutionary history of the YFTB.This study presents detailed petrology,whole-rock geochemistry,together with Sr-Nd isotopic,zircon U-Pb dating and Lu-Hf isotopic data of the granites within the Nianzi granite unit.Our findings demonstrate that the granites primarily consist of subhedral K-feldspar,plagioclase,quartz,minor biotite and hornblende,with accessory titanite,apatite,magnetite and zircon.Zircon U-Pb dating indicates that the Xiaolianghou granite was emplaced at 247.5±0.62 Ma.Additionally,the adakitic characteristics of the Nianzi,Xiawopu and Xiaolianghou granitic intrusions,such as high Sr and Ba contents and high ratios of Sr/Y and(La/Yb)N,combined with negative Sr-Nd and Lu-Hf isotopes(87Sr/86Sr)i=0.705681–0.7057433,εNd(t)=−21.98 to−20.97,zirconεHf(t)=−20.26 to−9.92,as well as the I-type granite features of high SiO_(2),Na_(2)O and K_(2)O/Na_(2)O ratios,enriched Rb,K,Sr and Ba,along with depleted Th,U,Nb,Ta,P and Ti,suggest that the Nianzi granitic unit was mainly derived from the partial melting of a thickened lower crust containing hydrous,calc-alkaline to high-K calc-alkaline,mafic to intermediate metamorphic rocks.In light of these parameters,we further integrate our data with previous studies and conclude that the Nianzi granitic unit was generated in a post-collisional extensional environment during the Early Triassic.

Structural Variation between the Western and Eastern Kuqa Fold-and-thrust Belt,China:Insights from Seismic Interpretation and Analog Modeling

The Kuqa fold-and-thrust belt exhibits apparent structural variation in the western and eastern zone.Two salt layer act as effective decollements and influence the varied deformation.In this study,detailed seismic interpretations and analog modeling are presented to construct the suprasalt and subsalt structures in the transfer zone of the middle Kuqa and investigate the influence of the two salt layers.The results reveal that the relationship of the two salt layers changes from separated to connected,and then overlapped toward the foreland in the transfer zone.Different structural models are formed in the suprasalt and subsalt units due to the interaction of the two salt layers.The imbricate thrust faults form two broom-like fault systems in the subsalt units.The suprasalt units develop detached folds terminating toward the east in the region near the orogenic belt.Whereas,two offset anticlines with different trends develop at the frontal edge of the lower salt layer and the trailing edge of the upper salt layer,respectively.According to exploration results in this region,the relationship between suprasalt and subsalt structures has an influence on hydrocarbon accumulation.We believe that the connected deformation contains high-risk plays while the decoupled deformation contains well-preserved plays.

The Sequence of Magmatic-Tectonic Events and Orogenic Processes of the Yanshan Belt, North China

This paper emphasizes that the interactive constraints of geology and isotopic dating is the best approach to construct the geological event sequence, and has compiled 106 data of reasonable isotopic ages for the igneous rocks of the Yanshan belt. We propose a sequence of mgmatic-tectonic events in the Jurassic-Cretaceous Yanshan orogen of North China. Five orogenic episodes are divided, (1) pre-and initial orogenic episode (Early Jurassic); (2) early orogenic episode (Middle Jurassic); (3) peak orogenic episode (Late Jurassic); (4) late orogenic episode (early Early Cretaceous), and (5) post-orogenic episode. Each episode is a short cycle, all of the orogenic processes construct a longer cycle, and they, in general, followed a counter-clockwise (ccw) PTt path. Finally, it is suggested that the Yanshanian movement was so intensive that the magmatism and tectonic deformation had involved all the lithosphere thickness and the late-Achaean-formed cratonic lithosphere had been significantly reworked.

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.

Thermal Evolution of Plutons and Uplift Process of the Yanshan Orogenic Belt

Abstract: Thermochronological dating was used to study the thermal evolution of the Mesozoic plutons and uplift history of the Yanshan orogenic belt. The results show that the cooling history of the plutons is complicated, corresponding to the inhomogeneous uplift process of the Yanshan orogenic belt. The Panshan granite cooled fast during 226.48–204.95 Ma at a rate of 10.22°C/Ma after its emplacement at a depth of about 10 km, and its fast uplift occurred in about 96–35 Ma at an average rate of 0.115 mm/a. The Wulingshan pluton cooled fast during 132–127.23 Ma at a rate of 94.34°C/Ma, and its rapid uplift occurred in 86–45 Ma at an average rate of 0.186 mm/a. The Yunmengshan granite cooled fast during 143–120.99 Ma at a rate of 19.51°C/Ma, and its rapid uplift occurred in 106–103.95 Ma and 20–0.0 Ma at a rate of 1.06 mm/a and 0.15 mm/a respectively. The Sihetang granite-gneiss uplifted rapidly since 13 Ma at an average rate of 0.256 mm/a. The Badaling granite uplifted rapidly since 6 Ma at an average rate of 0.556 mm/a. The Cenozoic uplift of the Yanshan Mountains can be well correlated to the rifting process of the surrounding basins.

Indosinian Foreland Fold-and-Thrust Belt Bordering Yunnan and Guangxi, China

Recent discoveries of ophiolites indicate that there must be a Palaeotethyan geosuture zone bordering China and Vietnam, which separates the Vietbac block from the South China subcontinent. The Indosinian foreland fold-and-thrust belt bordering Yunnan and Guangxi provided further evidence for the palaeotethysides. The oceanic crust was subducted southwestwards while the magmatic arc migrated northeastwards, and the continent-arc collision occurred in the Late Triassic with the thrusting being extended towards the north or northeast. The features of thrust-nappe structure are discussed, which proved the continental margin of the Palaeotethyan ocean there to be a complicated one. A face-to-face collision occurred first along the NW-striking segment and then along the ENE-striking segment accompanied by transpression or oblique thrusting occurring along the NW-striking one.

DIWA TYPE OF GOLD MINERALIZATION IN THE YINSHAN-YANSHAN-LIAO-JI ORE BELT,CHINA

This studied gold ore belt is giant and very important in China. Its regional tectonics and evolutional process are complicated. There are a few of view points on its geotec-tonic attribute in the Mesozoic and Cenozoic eras and on the type of its some gold ore deposits, especially, on one hosted in the pre-diwa geological bodies. On the basis of the diwa theory, the author discussed the regionalization, and its evolutional process, and some features of diwa tectono-magmatism and diwa type of gold mineralization in this belt. The author proposed that(1)the main body zone is a part of the diwa regime in the Mesozoic and Cenozoic eras, and(2)the diwa tectono-magmatism had a series of features such as universalism and violence, newborn, reform and superimposition, joining, inheritance, multiperiodic activity, complica-tion and so on. The gold mineralization formed in the diwa regime are called diwa type of golddeposits.In this paper the diwa type of endogenetic gold mineralization products hosted in the pre-diwa geological bodies in this zone is discussed in detail.

山东省萤石矿成矿地质条件及勘查开发现状

山东省萤石矿床类型主要有热液充填石英-萤石脉型、重晶石-萤石型、萤石-铅锌硫化物型3种,主要分布在胶北隆起区和胶南隆起区,其分布轮廓主要受位于两个隆起区西侧的郯庐断裂带控制。区内断裂构造发育,提供良好的成矿空间条件。山东省萤石矿的成矿来源主要是岩浆活动形成的富含Ca、F等元素的热水溶液,与中生代燕山晚期的岩浆活动关系密切。截至2021年底,山东省查明萤石矿产地13处,累计查明萤石矿石量为975.9万t,矿物量(CaF_(2))为334.61万t;保有萤石矿石量为519.17万t,矿物量(CaF_(2))为176.8万t,均已停采。

Source model of the 2018 M_(w)7.5 Papua New Guinea earthquake constrained by InSAR measurements: Insight into a blind rupture beneath the New Guinea Highlands

The Southern Highland Fold and Thrust Belt(SHFTB),the boundary of the Australian plate and the New Guinea Highland block,significantly contributes to the convergent deformation along the plate bound-ary.However,due to the lack of observation data,the detailed slip pattern of the SHFTB and the orogenic mechanism beneath the New Guinea Highlands remains controversial.On 25 February 2018,the M_(w)7.5 Papua New Guinea(PNG)earthquake struck the southeastern segment of the SHFTB.The detailed rupture characteristics of this event is significant for further clarifying the inter-seismic slip pattern along the SHFTB.Here,the coseismic deformation field of this earthquake was obtained using high-resolution ALOS-2 satellite images.We find that the 2018 M_(w)7.5 PNG earthquake ruptured a large-scaled fault(SHFTB)extending to the lower crust(deeper than 20 km)beneath the New Guinea Highlands,with a dip angle of 24°.The slips on the fault plane are equivalent to moment magnitudes of M_(w)7.51.Three major asperities with thrust-dominated slip of up to 3.94 m are detected on the fault plane.This finding implies that the slip pattern on the eastern segment of the SHFTB is dominated by thrust,rather than with significant sinistral movement,as previously reported.The tectonic deformation across the New Guinea Highlands is possibly concentrated on the large-scale fault SHFTB and primarily controls the intra-continental orogeny in the central Papua New Guinea.

燕山构造带东段中生界盆地页岩油气地质研究现状与展望

中国陆相盆地页岩油资源丰富,是我国未来油气增储上产的重要战略接替领域。燕山构造带东段(辽西地区)中生界盆地群页岩油气资源丰富,但尚处于油气勘探空白区,落实其勘探前景势成必然。基于研究区勘探的实际情况,并通过与国内外典型页岩油气盆地石油地质条件对比,综合沉积体系以及烃源岩地球化学参数分析等,明确了燕山构造带东段中生界盆地群页岩油气的资源潜力。研究结果表明:(1)下侏罗统北票组和下白垩统九佛堂组均发育连续厚层的暗色泥页岩,为主力烃源岩层位;(2)烃源岩的总有机碳(TOC)含量均值为1%~4%,以Ⅱ_(1)型或Ⅱ_(2)干酪根为主,且指示热演化成熟度的镜质体反射率(Ro)普遍高于0.6%,具有良好的油气潜力;(3)两套烃源岩层系均富含火山碎屑成分,脆性矿物含量较高,具有良好的可改造性。针对陆相含油气盆地页岩油气勘探存在的问题,首先讨论了赋存页岩油气重要载体的碳酸盐质细粒沉积岩的多源成因机制与油气富集类型,其中研究区以火山热液型和混源型甜点为主;另外探讨了火山-湖泊作用对有机质的富集效应,认为火山灰的输入提升了有机质的富集效力。同时,根据以往的勘探实践经验,提出原型盆地恢复技术和“天-地-钻”三位一体技术是解决复杂造山带油气勘探(特别是密植山区)中面临的诸多问题的关键。

渤海湾盆地中部428构造带近S-N向走滑断裂的形成时期及其在中生代期间的调节转换作用

渤海湾盆地中部428构造带自印支期以来经历了多期次构造运动叠加改造过程,区域内发育了大量的近S-N向与近EW向褶皱、断层构造,并控制了潜山的形成。然而目前对428构造带的研究仅局限于探索区域内潜山构造成因及其油气圈闭特性,对区域内的断裂系统,尤其是发育的大量近S-N向断裂的形成时期及其后期演化过程中所起到的调控作用尚不明确。鉴于此,为明确其形成时期、探索其对区域构造格局演化模式所产生的影响,基于前人的研究成果,以石臼坨凸起东侧428构造带为主要研究对象,通过对该区域典型的地震剖面进行精确解析,对其展开了系统性的研究。研究结果表明:(1) 428构造带与石臼坨凸起东侧连接处存在一条近S-N向走滑断裂;(2)该走滑断裂的形成最早可追溯至印支期。根据古生界褶皱和薄底构造的分布特征可知,该走滑断裂最初为近E-W向逆冲推覆断裂的侧向断坡;(3)近S-N向走滑断裂阻挡了燕山期NWW向的逆冲推覆作用,从而控制古生界和中生界大量协调褶皱的发育。而近E-W向断裂表现为压扭性质,控制了中生界雁列式褶皱的形成。基于以上认识,认为该近S-N向走滑断裂在印支-燕山期均起到了重要的调控作用,是一个重要的调节转换带。

燕山板内变形带侏罗纪主要构造事件

对燕山地区中生代板内变形的研究进展进行了总结,确定翁文灏75年前识别和提出的燕山运动A幕、B幕和中间幕发生在侏罗纪。侏罗纪的构造变形最终塑造了东西向燕山褶皱-冲断带的格架。通过对典型盆地的分析,燕山运动A幕以髫髻山组安山岩之下的角度不整合为标志,时限为160Ma±5Ma前,时期为中侏罗世龙门期—九龙山期,时代推测在175～160Ma之间。中间幕以髫髻山组和兰旗组火山岩为代表,时代约在165～156Ma之间。B幕强烈的冲断形成了土城子组和后城组的粗碎屑堆积,时限在135Ma±1Ma前,时代为156～139Ma。白垩纪早期,区域变形逐渐以伸展为主,古地理—古环境明显改变,火山喷发频繁、强烈,构造变形较弱。显然,早白垩世的构造发展已不属于燕山运动的范畴。燕山运动A幕是燕山板内变形带最主要的构造事件,也是东亚构造体制转变的标志。

燕山板内造山带中段中生代构造格局与构造演化

燕山板内造山带中段中生代构造格局由近东西向丰宁-隆化断裂、古北口-平泉断裂和密云-喜峰口-青龙断裂及马兰峪背斜组成。丰宁-隆化断裂为由北向南的低角度逆冲断层经后期改造而形成。古北口-平泉断裂系由柳河-承德县断层、乌龙矶-小料北沟断层、寿王坟-大杖子-下杖子断层组成的断裂系统,在剖面上呈正花状构造,具右行斜压性质,活动时代为148～132Ma。密云-喜峰口-青龙断裂为一右行走滑断裂。马兰峪背斜不具有变质核杂岩的构造组合特征,深部岩浆活动主导的、基底薄弱带控制的断块差异隆升可能是其形成的重要机制。三叠系砾岩中的砾石绝大多数具再生砾石特征,主要来自石炭系—二叠系,其中火山岩砾石的年代(240～248Ma)表明其沉积时间应明显小于240Ma。下板城盆地北部及西部王家店-小梁后盆地原所谓的早侏罗世南大岭组火山岩的时代分别为161Ma和126～127Ma。因此,原标志印支期变形的角度不整合的时代已被否定,印支运动构造表现需重新认识。

燕山地区土城子组划分、时代与盆地性质探讨

燕山地区土城子组分布广泛,顶底清晰,是本区最具特色的岩石地层单位之一。区域地质对比研究表明,燕山西部土城子组与燕山中东部土城子组在地层、时代上有较大的不同,西部盆地中髫髻山组火山岩不发育或很少发育,土城子组在地层划分上常包含九龙山组或髫髻山期火山岩,时代为中晚侏罗世（J2—J3）;东部盆地普遍发育髫髻山组火山岩浆或火山-沉积地层,土城子组划分与层型剖面一致。古生物化石和同位素年龄研究表明：土城子组时限在156-139Ma之间,属于晚侏罗世—早白垩世。土城子期盆地沉积的不对称性,相分布特征,古水流等指示其形成在一个挤压作用下的陆内火山-沉积盆地环境。

辽西地区燕山板内造山带东段中生代逆冲推覆构造

本文厘定并阐述了辽西地区燕山中生代板内造山带东段发育的逆冲推覆构造的宏观构造格局、运动学特征、形成时代和形成过程;探讨了形成该构造体系的区域构造背景及其大地构造意义。该区的逆冲构造系统由6条主干逆冲断层组成。分布于西北和东南缘的两条最外缘道冲断层走向为ENE,居于其间的逆冲断层呈NNE—NE,而且,向东北和南西方向这些断层具有汇合的趋势。在东北端收敛于凌源—东官营子断裂(“内蒙地轴”南缘断裂)上,而在西南端则汇拢于大屯—锦州断裂及其西延的密云—喜峰口断裂。总体上构成一个类似于双重构造(duplex)的巨型逆冲系统。该区边冲作用始于中侏罗世之前,于侏罗纪末达到高峰并基本形成了本区的推覆构造格局。本区逆冲断层系统,总体逆冲方向指向南东,与燕山板内造山带中段、西段以向北、北西逆冲为主的逆冲推覆构造明显不同。结合燕山中段发现的近东西向右行走滑断裂系统及其与本区逆冲推覆构造体系的时-空关系分析,指出本区逆冲推覆构造的形成,是沿燕山东西向构造带右行走滑作用因构造方向的改变发生构造转换的结果。

地壳与弱化岩石圈地幔的相互作用:以燕山造山带为例

燕山造山带中生代发育4期钙碱性火山活动,它们的源区组成都是受壳幔相互作用的制约,其中髫髻山组和义县组分布广泛,具有代表性．髫髻山组岩性比较单一,地球化学参数变化范围小,岩浆的AFC作用不强烈,源区成分不复杂．依据Kay et al．(1991)的方法,估算了早-中侏罗世燕山地区的地壳厚度为40-45 km.髫髻山组粗安岩是在加厚的地壳 (40-45 km)条件下,源区是含角闪石的石榴石麻粒岩+底侵的基性岩的壳幔过渡带熔融形成．义县组火山岩的源区为下地壳+岩石圈地幔,地幔组分较髫髻山组增加．研究区中生代早期地壳开始加厚,发生下地壳拆沉,进入流变学性质改变了的“弱化的岩石圈地幔”,二者发生作用．岩石圈地幔在中生代晚期受到流体、熔体、地幔矿物中活化的分子水、剪切构造作用,以及温、压条件改变的影响,导致岩石圈地幔发生不均一的局部弱化,为容纳拆沉的下地壳提供了优化场所．推测弱化岩石圈地幔出现于135 Ma以后燕山地区发育的小型拉伸盆地之下,以及对应的小型软流圈底辟体之上．上述模型可以与俯冲带的楔形地幔与俯冲洋壳的相互作用相对比．

华北地台北缘燕辽钼(铜)成矿带矿床地质特征及动力学背景

华北地台北缘是中国重要的多金属成矿带,中段部位钼(铜)矿床的分布受区域EW向、NE向、NNE向断裂的联合控制。成矿带东端辽西地区以钼矿为主,西端冀北地区以铜(钼)矿为主。钼矿床的形成与燕山期中酸性小侵入体关系密切,矿床多产于花岗斑岩体之中或内外接触带中,矿床类型以斑岩型、斑岩_矽卡岩型、矽卡岩型为主。同位素研究表明,钼(铜)矿床成矿物质及成矿流体主要来源于下地壳或与太古代结晶基底有关的花岗岩;钼矿的形成主要与中生代富硅、富钾质花岗岩有关,而与铜矿成因有关的花岗岩酸碱度相对较低。成矿年代学研究表明,燕辽钼(铜)成矿带大规模成矿作用发生于180Ma左右和140Ma左右2个时期,其对应的成矿动力学背景分别为华北板块与西伯利亚板块后碰撞造山阶段和中国东部构造体制大转折晚期。

燕山中段盘山花岗岩体锆石SHRIMP U-Pb年龄测定及其构造意义

位于燕山陆内造山带中段南缘的蓟县盘山花岗岩体由狼家峪、官庄、东罗庄和小盘山4个侵入单元组成,并发育侵入期后含斑石英二长岩脉,发育环绕岩体分布的周缘向斜并侵蚀早期东西向蓟县断裂。对前3个侵入单元及岩体西侧围岩中的顺层侵入的含斑石英二长岩脉等4件样品的锆石U-Pb(SHRIMP)定年结果为,年龄值界于203-207Ma,表明盘山花岗岩体侵位于三叠纪末期。这个年龄结果进一步限定了燕山陆内造山带东西向褶皱、逆冲/逆掩断层系统形成时代的上限,显示其形成时代为印支期。

辽西牛营子地区晚三叠世逆冲构造

燕山陆内造山带侏罗纪的构造及其研究已广为报道,但确凿的三叠纪构造分析明显不足。对辽西凌源牛营子地区详细的构造地质调查揭示该区晚三叠世晚期存在的逆冲构造。盆地东部中侏罗世郭家店组之下覆盖着一套晚三叠世道冲叠瓦构造,其运动指向:黄土坡以西逆冲叠瓦构造由西向东推覆;黄土坡以北弧形断裂由北向南道冲,为派生的运动。逆冲断裂带控制的槽地之中发育同逆冲期邓杖子组灰岩—白云岩质角砾砾岩。我们的资料表明,邓杖子组时代应属晚三叠世晚期,与晚三叠世老虎沟组基本是连续过渡的。原定牛营子盆地早—中侏罗世地层是倒置的,正常的晚三叠世—中侏罗世地层序列自下而上应为老虎沟组、邓杖子组、水泉沟组、郭家店组。晚三叠世晚期逆冲构造事实的确定说明,燕山陆内造山带至少从晚三叠世起就经历了强烈的变形,其早期变形历史对于认识区域构造演化和陆内变形的发展过程具有重要意义。