Hydrocarbon Geological Conditions and Exploration Potential of Mesozoic–Paleozoic Marine Strata in the South Yellow Sea Basin

No substantial breakthroughs have been made in hydrocarbon exploration of the South Yellow Sea Basin.It is believed that the Mesozoic-Paleozoic marine sedimentary formation in the South Yellow Sea Basin is similar to that in the Sichuan Basin.Therefore,outcrop,drilling,and seismic data were determined and compared with the research results on petroleum geological conditions in the Yangtze land area,and the hydrocarbon geological conditions were analyzed comprehensively from multiple aspects,such as basin evolution and main source rocks,reservoir characteristics,preservation conditions,and structural traps.The results show that two main stages in the South Yellow Sea Basin(the stable evolution stage of the Mesozoic-Paleozoic marine basin and the Mesozoic-Cenozoic tectonic reformation and basin formation stage)were important for the development and evolution of four sets of main source rocks.Reservoirs dominated by carbonate rocks,three sets of capping beds with good sealing capability,relatively weak magmatic activity,and multiple types of structural traps jointly constituted relatively good hydrocarbon-reservoir-forming conditions.There were four sets of main source-reservoir-cap assemblages and three possible hydrocarbon reservoir types(primary residual-type hydrocarbon reservoir,shallow reformed-type hydrocarbon reservoir,and composite-type hydrocarbon reservoir)developed in the marine strata.It is concluded that the marine strata in the South Yellow Sea Basin have relatively good hydrocarbon potential.The Laoshan Uplift is characterized by stable structure,complete preserved source reservoir cap assemblage,and large structural traps,and thus it is the preferred prospect zone for marine Paleozoic hydrocarbon exploration in this area.

Dynamic simulation of differential accumulation history of deep marine oil and gas in superimposed basin:A case study of Lower Paleozoic petroleum system of Tahe Oilfield,Tarim Basin,NW China

According to the complex differential accumulation history of deep marine oil and gas in superimposed basins,the Lower Paleozoic petroleum system in Tahe Oilfield of Tarim Basin is selected as a typical case,and the process of hydrocarbon generation and expulsion,migration and accumulation,adjustment and transformation of deep oil and gas is restored by means of reservoine-forming dynamics simulation.The thermal evolution history of the Lower Cambrian source rocks in Tahe Oilfield reflects the obvious differences in hydrocarbon generation and expulsion process and intensity in different tectonic zones,which is the main reason controlling the differences in deep oil and gas phases.The complex transport system composed of strike-slip fault and unconformity,etc.controlled early migration and accumulation and late adjustment of deep oil and gas,while the Middle Cambrian gypsum-salt rock in inner carbonate platform prevented vertical migration and accumulation of deep oil and gas,resulting in an obvious"fault-controlled"feature of deep oil and gas,in which the low potential area superimposed by the NE-strike-slip fault zone and deep oil and gas migration was conducive to accumulation,and it is mainly beaded along the strike-slip fault zone in the northeast direction.The dynamic simulation of reservoir formation reveals that the spatio-temporal configuration of"source-fault-fracture-gypsum-preservation"controls the differential accumulation of deep oil and gas in Tahe Oilfield.The Ordovician has experienced the accumulation history of multiple periods of charging,vertical migration and accumulation,and lateral adjustment and transformation,and deep oil and gas have always been in the dynamic equilibrium of migration,accumulation and escape.The statistics of residual oil and gas show that the deep stratum of Tahe Oilfield still has exploration and development potential in the Ordovician Yingshan Formation and Penglaiba Formation,and the Middle and Upper Cambrian ultra-deep stratum has a certain oil and gas resource prospect.This study provides a reference for the dynamic quantitative evaluation of deep oil and gas in the Tarim Basin,and also provides a reference for the study of reservoir formation and evolution in carbonate reservoir of paleo-craton basin.

Chinese Continental Blocks in Global Paleocontinental Reconstruction during Paleozoic and Mesozoic

The Cambrian to Cretaceous paleomagnetic data from Chinese continental and adjacent blocks were collected using principles to obtain reliable and high-precision paleomagnetic data and to pay attention to the similarity of paleobiogeography and the coordination of tectonic evolution.The Chinese continental blocks were laid up on the reconstruction of proposed global paleocontinents with almost the same scale.Thus,it can be clearly recognized that the global continents,including Chinese continental blocks,range along latitudes on the southern side of the equator during the Early Paleozoic. In the Paleozoic,Chinese continental blocks were still located among the Laurentia,Siberia and Gondwana plates,following the fast moving of the Siberia Plate northwards,the amalgamation in a north-south direction at the western parts of the Laurentia and Gondwana plates,and the Iapetus and Rheic Oceans were subducted,eventually to form a uniform Pangea in the Late Paleozoic.The Australian and Indian plates of Eastern Gondwana moved and dispersed gradually southwards, continued to extend the Paleo-Tethys Ocean.The Chinese continental and adjacent blocks were still located in the Paleo-Tethys Ocean,preserved the status of dispersion,gradually moving northwards, showing characteristics of ranging along a north-south orientation until the Permian.In addition,a series of local collisions happened during the Triassic,and consequently most of the Chinese continental blocks were amalgamated into the Pangea,except for the Gangdise and Himalayan blocks. There was a counter-clockwise rotation of the Eastern Asian continent in the Jurassic and northwards migration of the Chinese continent in varying degrees during the Cretaceous,but the Himalayan and Indian plates did not collide into the Chinese continent during this period.

Paleozoic and Mesozoic Basement Magmatisms of Eastern Qaidam Basin,Northern Qinghai-Tibet Plateau:LA-ICP-MS Zircon U-Pb Geochronology and its Geological Significance

The eastern margin of the Qaidam Basin lies in the key tectonic location connecting the Qinling, Qilian and East Kunlun orogens. The paper presents an investigation and analysis of the geologic structures of the area and LA-ICP MS zircon U-Pb dating of Paleozoic and Mesozoic magmatisms of granitoids in the basement of the eastern Qaidam Basin on the basis of 16 granitoid samples collected from the South Qilian Mountains, the Qaidam Basin basement and the East Kunlun Mountains. According to the results in this paper, the basement of the basin, from the northern margin of the Qaidam Basin to the East Kunlun Mountains, has experienced at least three periods of intrusive activities of granitoids since the Early Paleozoic, i.e. the magmatisms occurring in the Late Cambrian （493.1±4.9 Ma）, the Silurian （422.9±8.0 Ma-420.4±4.6 Ma） and the Late Permian-Middle Triassic （257.8±4.0 Ma-228.8＋1.5 Ma）, respectively. Among them, the Late Permian - Middle Triassic granitoids form the main components of the basement of the basin. The statistics of dated zircons in this paper shows the intrusive magmatic activities in the basement of the basin have three peak ages of 244 Ma （main）, 418 Ma, and 493 Ma respectively. The dating results reveal that the Early Paleozoic magmatism of granitoids mainly occurred on the northern margin of the Qaidam Basin and the southern margin of the Qilian Mountains, with only weak indications in the East Kunlun Mountains. However, the distribution of Permo-Triassic （P-T） granitoids occupied across the whole basement of the eastern Qaidam Basin from the southern margin of the Qilian Mountains to the East Kunlun Mountains. An integrated analysis of the age distribution of P-T granitoids in the Qaidam Basin and its surrounding mountains shows that the earliest P-T magmatism （293.6-270 Ma） occurred in the northwestern part of the basin and expanded eastwards and southwards, resulting in the P-T intrusive magmatism that ran through the whole basin basement. As the Cenozoic basement thrust system developed in the eastern Qaidam Basin, the nearly N-S-trending shortening and deformation in the basement of the basin tended to intensify from west to east, which went contrary to the distribution trend of N-S-trending shortening and deformation in the Cenozoic cover of the basin, reflecting that there was a transformation of shortening and thickening of Cenozoic crust between the eastern and western parts of the Qaidam Basin, i.e., the crustal shortening of eastern Qaidam was dominated by the basement deformation （triggered at the middle and lower crust）, whereas that of western Qaidam was mainly by folding and thrusting of the sedimentary cover （the upper crust）.

Late Paleozoic to Mesozoic Intrusions Distribution in the North Sanjiang Orogenic Belt,Southwest China:Evidence from Zircon U-Pb Dating and Geochemistry

A mosaic of terranes or blocks and associated Late Paleozoic to Mesozoic sutures are characteristics of the north Sanjiang orogenic belt （NSOB）. A detailed field study and sampling across the three magmatic belts in north Sanjiang orogenic belt, which are the Jomda-Weixi magmatic belt, the Yidun magmatic belt and the Northeast Lhasa magmatic belt, yield abundant data that demonstrate multiphase magmatism took place during the late Paleozoic to early Mesozoic. 9 new zircon LA-ICP-MS U-Pb ages and 160 published geochronological data have identified five continuous episodes of magma activities in the NSOB from the Late Paleozoic to Mesozoic： the Late Permian to Early Triassic （c. 261-230 Ma）; the Middle to Late Triassic （c. 229-210 Ma）; the Early to Middle Jurassic （c. 206-165 Ma）; the Early Cretaceous （c. 138-110 Ma） and the Late Cretaceous （c. 103-75 Ma）. 105 new and 830 published geochemical data reveal that the intrusive rocks in different episodes have distinct geochemical compositions. The Late Permian to Early Triassic intrusive rocks are all distributed in the Jomda-Weixi magmatic belt, showing arc-like characteristics; the Middle to Late Triassic intrusive rocks widely distributed in both Jomda-Weixi and Yidun magmatic belts, also demonstrating volcanic-arc granite features; the Early to Middle Jurassic intrusive rocks are mostly exposed in the easternmost Yidun magmatic belt and scattered in the westernmost Yangtza Block along the Garze-Litang suture, showing the properties of syn-collisional granite; nearly all the Early Cretaceous intrusive rocks distributed in the NE Lhasa magmatic belt along Bangong suture, exhibiting both arc-like and syn-collision-like characteristics; and the Late Cretaceous intrusive rocks mainly exposed in the westernmost Yidun magmatic belt, with A-type granite features. These suggest that the co-collision related magmatism in Indosinian period developed in the central and eastern parts of NSOB while the Yanshan period co-collision related magmatism mainly occurred in the west area. In detail, the earliest magmatism developed in late Permian to Triassic and formed the Jomda-Wei magmatic belt, then magmatic activity migrated eastwards and westwards, forming the Yidun magmatic bellt, the magmatism weakend at the end of late Triassic, until the explosure of the magmatic activity occurred in early Cretaceous in the west NSOB, forming the NE Lhasa magmatic belt. Then the magmatism migrated eastwards and made an impact on the within-plate magmatism in Yidun magmatic belt in late Cretaceous.

OIL AND GAS GENERATION OF MESOZOIC MARINE SOURCE ROCK IN QIANGTANG BASIN, TIBET PLATEAU, CHINA

Tibet plateau is a vast hydrocarbon\|bearing region which is the biggest in area, the lowest in exploration and the poorest in knowing, especially, knowing a little for Mesozoic marine petroleum geology problem (particularly for Mesozoic marine source rock) in Chinese land. The research of oil and gas generation for Mesozoic marine source rock have been accomplished on basis of a large number of data for source rock samples appeared on the weather (29 items, about 4000 samples, 23976 sample times and 200000 data) in Tibet Plateau. Full text is composed of following four parts:1\ Regional geology\;Summarized regional geology briefly, emphasized on regional structures, sedimentary facies and stratum characteristics related closely with source rock.

Comparisons on Mineralogy and Lithology between Paleozoic Marine and Lacustrine Dolostones, Northern China

1 Introduction Dolomite[Ca Mg(CO3)2],a common mineral in carbonate rocks,can be found in various geological settings from Precambrian to modern age,and is widely reported in almost all sedimentary and digenetic

MARINE SOURCE ROCKS AND THEIR DEPOSITIONAL CONDITIONS OF MESOZOIC—CENOZOIC IN THE GAMBA—TINGRE BASIN,SOUTH TIBET:ORGANIC GEOCHEMICAL STUDY

The Gamba—Tingri basin lies in south Tethys Himalaya subzone. It is 400km in length from east to west, and 30～50km in width from north to south. The basin is mainly made up of marine Mesozoic and Lower Cenozoic, i.e., Jurassic, Cretaceous, and Lower Tertiary. Its total strata are more than 3100m in thickness. The passive continental margin of the India plate developed during Jurassic—Cretaceous after a Triassic rifting stage. Collision took place between the India and the Eurasian plate during the latest Cretaceous and earliest Tertiary (Liu and Einsele, 1994), which resulted in a Tertiary residual basin.The Jurassic stratigraphic system in the Gamba—Tingri basin were not carried out until recently (Wan et al., 1999), which is divided into three formations, i.e.., Pupuga Fm., Nieniexiongla Fm., and Menkadun Fm.. The Cretaceous and Tertiary stratigraphic system is after Wan (1985) and Xu et al.(1990), which the Cretaceous is divided into six formations: Dongsan Fm., Chaqiela Fm., Lengqingle Fm., Xiawuchubo Fm., Jiubao Fm., and Zongshan Fm, whereas the Tertiary is divided into Jiabula Fm. Zongpu Fm., and Zhepure Fm.

Reservoir Volcanic Rocks: Geology and Geochemistry, the Mesozoic Non-marine Songliao Basin, NE China

The reservoir volcanic rocks in Songliao Basin include the Lower Cretaceous (K1yc Form.,114～135 Ma, acidic rocks) and the Upper Jurassic (J3hs Form., 145～158 Ma, intermediate rocks). Vesicles coupled with faults make the volcanic reservoir spaces which do not as badly getting worse with buried depth as those of sediments generally doing. The flood rhyolites of the Lower Cretaceous cover ca. 100 000 km2 with relict thickness from 100 m to more than 1 000 m. They are high-silica, rich in aluminum and potassium, high REE contents with large negative Eu anomalies, thus believed also be formed by the large-scale sialic crust partial-melting. The andesitic rocks of the Upper Jurassic are rich in Al and K, but with lower REE contents and minor negative Eu anomalies, as well as dispersal patterns of HREE. They are believed to be produced by progressively shallower partial-melting where the fractionation of garnet and/or zircon may be involved. The most probable heat sources provided for the long-lasting volcanisms in the Songliao Basin is the subduction of the Okhotsk plate.

Evidences for Late Paleozoic and Mesozoic Basaltic Magmatism in Southwestern Cameroon and Implications for Correlations between the Gulf of Guinea in Africa and Northeast Brazil

Late Paleozoic and Mesozoic basaltic dikes were recently identified in Southwestern Cameroon in a ca.200km corridor of NE-SW trend that includes the Cameroon Line and corresponds,in a prebreak-up reconstitution of

Petrogenesis of the Paleozoic and Mesozoic Volcanic Rocks in Northwest China

Recently,we carried out the National Nature Science Foundation of China （No.41273033） and Special Fund for Basic Scientific Research of Central Colleges （No.310827153407） and made some advances as follows.

Control of Earth system evolution on the formation and enrichment of marine ultra-deep petroleum in China

Taking the Paleozoic of the Sichuan and Tarim basins in China as example,the controlling effects of the Earth system evolution and multi-spherical interactions on the formation and enrichment of marine ultra-deep petroleum in China have been elaborated.By discussing the development of“source-reservoir-seal”controlled by the breakup and assembly of supercontinents and regional tectonic movements,and the mechanisms of petroleum generation and accumulation controlled by temperature-pressure system and fault conduit system,Both the South China and Tarim blocks passed through the intertropical convergence zone(ITCZ)of the low-latitude Hadley Cell twice during their drifts,and formed hydrocarbon source rocks with high quality.It is proposed that deep tectonic activities and surface climate evolution jointly controlled the types and stratigraphic positions of ultra-deep hydrocarbon source rocks,reservoirs,and seals in the Sichuan and Tarim basins,forming multiple petroleum systems in the Ediacaran-Cambrian,Cambrian-Ordovician,Cambrian-Permian and Permian-Triassic strata.The matching degree of source-reservoir-seal,the type of organic matter in source rocks,the deep thermal regime of basin,and the burial-uplift process across tectonic periods collectively control the entire process from the generation to the accumulation of oil and gas.Three types of oil and gas enrichment models are formed,including near-source accumulation in platform marginal zones,distant-source accumulation in high-energy beaches through faults,and three-dimensional accumulation in strike-slip fault zones,which ultimately result in the multi-layered natural gas enrichment in ultra-deep layers of the Sichuan Basin and co-enrichment of oil and gas in the ultra-deep layers of the Tarim Basin.

阿拉善-华北北缘晚古生代-早中生代岩浆作用:对古亚洲洋俯冲-闭合过程的制约

位于中亚造山带南部的阿拉善-华北北缘地区保存了丰富的晚古生代-早中生代岩浆记录,为理解古亚洲洋从俯冲至闭合的构造演化过程提供了关键信息。本文对位于内蒙古西部的甘其毛都地区的4个侵入体进行了岩相学、地球化学、锆石U-Pb年代学和Lu-Hf同位素分析。锆石U-Pb定年表明这些岩体分别形成于早二叠世(283±3Ma、273±5Ma、272±5Ma)和中三叠世(238±3Ma)。早二叠世岩体以石英闪长岩和闪长玢岩为主,富集轻稀土与大离子亲石元素,亏损高场强元素Nb、Ta等,Hf同位素显著亏损(-4.0~+15.6)。它们可能是由俯冲板片流体交代地幔楔部分熔融形成的基性岩浆经分离结晶演化而成。中三叠世侵入体为花岗闪长岩,轻重稀土元素强烈分异,锆石ε_(Hf)(t)值均为正值(+5.0~+8.5),可能代表了碰撞造山阶段新生下地壳物质部分熔融的产物。在此基础之上,本文系统收集并分析了阿拉善-华北北缘地区晚古生代-早中生代岩浆岩的时空分布规律与地球化学特征,以限定其构造背景与深部动力学过程。结合前人研究成果提出:石炭纪时期,古亚洲洋向南俯冲至阿拉善-华北克拉通之下并不断向北后撤;至早二叠世,俯冲板片转变为前进式俯冲,整体处于挤压环境,发育大规模岩浆活动与弧背前陆盆地;早-中三叠世,古亚洲洋闭合,阿拉善-华北克拉通沿索伦缝合带与北侧的中亚弧增生体系发生碰撞-拼贴。

Paleomagnetic results of Paleozoic and Mesozoic rocks from Xingshan-Zigui section in Hubei Province, South China

The paleomagnetic reconnaissance study of the Paleozoic and Mesozoic sedimentary rocks from the Yangtze Block (YZB) was made to conduct the Apparent Polar Wander Path (APWP) of the YZB during the Phanerozoic. A total of 825 samples from 84 sites were collected from a continuous section along the Xiangxi River valley in Xingshan and Zigui counties in Hubei Province, northern margin of the YZB. Stepwise thermal/alternating demagnetization isolated well defined characteristic magnetization (ChRM) at a higher temperature in most of the samples, and relatively thermal stability and high coercivity were revealed from these samples. All the ChRMs can pass the fold and/or reversal tests, suggesting that they are probably primary. Therefore, new pole positions are presented for the YZB.

Middle Yangtze sea-basin over Paleozoic-Mesozoic transition——Sedimental continuity and environmental catastrophe

On the centimeter scale of lithologic change, we conduct poly-statistic analysis on the sedimentary behavior and dynamic features of the stratigraphic sequence from upper Dalong formation to lower Daye formation, which across the Permian-Triassic boundary in East Hubei. From the perspective of stochastically dynamic system, the depositional process of upper Dalong formation can be regarded as a stable Markovian process with weakly stratigraphic correlation and randomly lithologic alteration. Compared to it, the depositional process of lower Daye formation was unstable Markovian process with much closer stratigraphic correlation and ordered lithologic change. As for the replacement style of the sedimental cycle, the former was chaotic, while the latter was periodical. Otherwise, although the overall depositional process of the two formations was continuous, their dynamic characteristics were obviously different. So this P-T sedimental boundary can also be regarded as a dynamic limit. It was a kind of depositional reaction in response to a catastrophic alteration when the geological environment was in continuous change but came over a certain threshold state.

Palynofloral changes in the Upper Paleozoic and Mesozoic of the Deocha-Pachami area, Birbhum Coalfield, West Bengal, India

The study of Upper Paleozoic and Mesozoic palynomorphs in three boreholes from the Deocha-Pachami area, Birbhum Coalfield, West Bengal, India, has allowed dating of the Talchir, Barakar, Dubrajpur, and Rajmahal formations, and revealed many hiatuses. The lowermost unit, the Talchir Formation, yielded earliest Permian palynomorphs. The Barakar Formation, which includes coal-bearing strata, was previously dated as Early Permian. However, data presented herein indicate an Early Permian to earliest Triassic age for this unit,containing actually the Karharbari, Barakar s.s., Kulti, and Ranigang formations as well as the basal part of the Panchet Formation. The overlying Dubrajpur Formation is Jurassic (Callovian to Tithonian), with an unconformity at its base. The uppermost Dubrajpur Formation is Tithonian-Berriasian. The palynomorphs from the intertrappeans within the Rajmahal Formation suggest an Early Cretaceous age. The revised ages of the Barakar and Dubrajpur formations are of major regional significance. The distribution patterns of spore-pollen may provide a broad spectrum of paleoclimate during Permian, Late Jurassic, and Early Cretaceous times, as there is no record of marine signatures in the study area.

地球系统演化对中国海相超深层油气形成与富集的控制作用

以四川盆地和塔里木盆地古生界为例,详细论述了地球系统演化和多圈层相互作用对中国海相超深层油气形成与富集的控制作用。通过探讨超大陆散聚和区域构造运动控制下的盆地“源-储-盖”叠置发育和匹配程度,以及温压系统和断裂输导体系控制的油气生成和富集机制,发现华南和塔里木陆块同步漂移过程中,两次经过低纬度哈德里环流带的热带辐合区(ITCZ),均形成了优质烃源岩;提出深部构造活动和地表气候演变共同控制了四川盆地和塔里木盆地超深层烃源岩、储层和盖层的类型和发育层位,形成了埃迪卡拉系—寒武系、寒武系—奥陶系、寒武系—二叠系和二叠系—三叠系的多个油气系统。源-储-盖匹配程度、烃源岩母质类型、盆地深部热体制和跨构造期埋深-隆升过程,联合控制油气从生成到富集的全过程,形成了台缘带近源充注成藏、高能滩远源断裂连通成藏、走滑破裂带立体成藏3种油气富集模式,最终促使四川盆地超深层多层系天然气富集和塔里木盆地超深层油气共富集。

济阳坳陷沾化东部古—中生界潜山构造样式与成藏模式

济阳坳陷古—中生界潜山经历多期挤压、伸展、走滑及剥蚀等构造作用的叠加,以沾化东部潜山为例,利用丰富的钻井与地震资料,在潜山构造层划分的基础上,剖析了潜山构造演化及构造特征,总结了潜山构造样式,建立了油气成藏模式。研究结果表明,晚古生代以来,在多期不同方向、不同性质构造运动的作用下,沾化东部古—中生界潜山经历了4期挤压作用、2期伸展作用、2期走滑作用、4期剥蚀作用,形成了高位、中位和低位3类潜山,发育了伸展、挤压、走滑与剥蚀4类9种构造样式。依据构造样式及潜山地层残留和上覆盖层的差异,建立了3类潜山成藏模式,其油气来源、油气富集层段及富集特征各不相同,其中高位潜山斜坡带上古生界与中生界、中位潜山下古生界和低位潜山中紧靠油源的潜山各层系油气成藏条件最为有利,油气富集程度高,是研究区下一步重点勘探对象。

叠合盆地深层海相油气差异富集历史的动态模拟——以塔河油田下古生界含油气系统为例

以塔里木盆地塔河油田下古生界含油气系统为例,针对叠合盆地深层海相油气复杂的差异富集历史,采用成藏动力学模拟方法进行深层油气的生排烃、运聚和调整改造的历史恢复。研究表明:①塔河油田下寒武统烃源岩的热演化史反映出不同构造带的生排烃过程及其强度具有明显不同,是导致深层油气相态差异的主要原因。②走滑断裂和不整合面等构成的复合输导体系控制深层油气早期运移聚集和后期调整,中寒武统台内膏盐岩阻止深层油气的垂向运聚,致使深层油气呈现明显的“断控”特征,其中北东向走滑断裂带和深层油气运移低势区叠加有利于汇聚成藏,且主要沿北东向走滑断裂带呈串珠状分布。③成藏动态模拟揭示“源-断-缝-膏-保”时空配置控制塔河深层油气的差异富集,奥陶系经历多期充注、垂向运聚、侧向调整改造的成藏历史,深层油气一直处于运移聚集和逸散的动态平衡中。④油气残留量统计显示塔河油田深层奥陶系鹰山组和蓬莱坝组仍具有较好的勘探开发潜力,超深层中上寒武统具有一定的油气资源前景。研究为塔里木盆地深层油气的动态定量评价提供了参考依据,也可以为古老克拉通盆地碳酸盐岩相关油气成藏演化的研究提供借鉴。

华北克拉通北缘张家口地区古生代-中生代岩浆岩锆石氧逸度对金成矿的制约

华北克拉通北缘张家口地区是我国重要的金矿集区,区内金矿床普遍富碲,金成矿与岩浆岩具有密切成因联系。本文通过对张家口地区古生代-中生代岩浆岩锆石氧逸度进行分析,评价各岩浆岩成矿潜力,从而对金和碲的物质来源及矿床成因进行约束。锆石Ce^(4+)/Ce^(3+)、Ce-U-Ti、Ce/Nd和Eu_(N)/Eu_(N)^(*)等氧逸度计算方法获得的区内岩浆岩氧逸度总体趋势一致,结合地质特征及各氧逸度计适用性,本文认为锆石Ce-U-Ti氧逸度计更为可靠。张家口地区岩浆岩氧逸度从高到低依次为青羊沟花岗岩(平均ΔFMQ=+4.4)、张家口组流纹岩(平均ΔFMQ=+3.2)、水泉沟碱长正长岩(平均ΔFMQ=+2.6)、伟晶岩脉(平均ΔFMQ=+2.5)、上水泉花岗岩(平均ΔFMQ=+1.5)、响水沟花岗岩(平均ΔFMQ=+1.4)、象山花岗闪长岩(平均ΔFMQ=+1.2)。中高氧逸度(硫化物-硫酸盐转变阶段)有利于Au、Te的迁移富集。水泉沟碱长正长岩、伟晶岩脉及青羊沟花岗岩等岩体与东坪和大白阳金矿床成矿流体的氧逸度范围一致,其出溶的岩浆流体氧逸度高,携带迁移Au、Te等元素的能力强,成矿潜力较大。水泉沟碱性岩锆石微量元素具有Eu_(N)/Eu_(N)^(*)>0.3、10000×(Eu_(N)/Eu_(N)^(*))/Y>1、(Ce/Nd)/Y>0.01、Dy/Yb<0.3及(Eu_(N)/Eu_(N)^(*))/Y与(Ce/Nd)/Y呈正相关的特点,具有成矿岩体的特征。锆石氧逸度及微量元素组成显示水泉沟碱性岩具有很好的Au-Te成矿潜力,而上水泉花岗岩的成矿潜力较差,张家口地区富碲金矿床应与水泉沟碱性岩具有密切成因联系。