Newly Discovered Ca. 163 Ma OIB-Type Diabase Dike from the Shiquanhe Ophiolites, Western Tibet

Objective The Shiquanhe ophiolite is an important tectonic belt in western Tibet. It has been debated whether the Shiquanhe ophiolite represents an allochthonous nappe derived from the Bangong-Nujiang suture zone to the north or the

Lacustrine shale oiliness influenced by diabase intrusions in the Paleogene Funing Formation,Subei Basin,China

The research on the correlation between hydrocarbon accumulations and magmatic activities has always attracted aroused much wide attention.Existing research has primarily the hydrocarbon generations capability of source rocks and the quality of reservoirs by diabase intrusions.whereas,rare systematic research has been conducted on the oiliness and enrichment mechanism.To be specific,the diabase intrusive zone,the contact metamorphic zone and the normal shale zone of the Funing Formation in the Gaoyou Sag,Subei Basin were taken as the object of this study.Moreover,in this study,the hydrocarbon generation quality,reservoir quality,and oil-bearing quality of diabase-metamorphic zone-normal shale were evaluated using X-ray diffractions,argon ion polishing-field emission scanning electron microscope,energy spectrum,rock slice/light-sheet microscopic observations,organic geochemical tests,N_(2) gas adsorption and 2D NMR tests.The results indicated that the intrusive zone,the metamorphic zone,and the normal zone were formed in order by the degree of effect of diabase intrusions.Secondly,the oil content of different parts exhibited significant heterogeneity due to the baking effect of diabase,and the metamorphic zone had the significantly better oil-bearing nature than the intrusive zone.Lastly,a distribution model was proposed for the diabase intrusive zone-metamorphic zone-normal surrounding rock zone.

An Important Spreading Event of the Neo-Tethys Ocean during the Late Jurassic and Early Cretaceous: Evidence from Zircon U-Pb SHRIMP Dating on Diabase in Nagarze, Southern Tibet

Widely distributed in Gyangzê-Chigu area, southern Tibet, NW- and nearly E-W-trending diabase（gabbro）-gabbro diorite dykes are regarded as the product of the large-scale spreading of the late Neo-Tethys Ocean. In order to constrain the emplacement age of these dykes, zircons of two samples from diabases in Nagarzê were dated by using the U-Pb SHRIMP method. Two nearly the same weighted mean ^206pb/^23SU ages were obtained in this paper, which are 134.9±1.8 Ma （MSWD=0.65） and 135.5 ± 2.1 Ma （MSWD=1.40）, respectively. They not only represent the crystallization age of the diabase, but also documented an important spreading event of the Neo-Tethys Ocean during the late Jurassic and early Cretaceous. This dating result is of great significance to reconstruct the temporal framework of the late Neo-Tethys Ocean in the Qinghai-Tibet Plateau.

Geochemical Characteristics and Genesis of the Luxi-Xianrenzhang Diabase Dikes in Xiazhuang Uranium Orefield, Northern Guangdong Province

The Luxi-Xianrenzhang diabase dikes were emplaced into the eastern part of the Guidong composite granitoids in northern Guangdong Province at the end of the Early Cretaceous. They show tholeiitic features, enrichment in large ion lithophile elements, slight enrichment in light rare earth elements, depletion in Zr and Hf, and basically no depletion in Nb and Ta and no Eu anomaly. They are similar to intraplate basalt in terms of trace element characteristics. They have high εNd（t） values （3.6-4.9）, initial ^87Sr/^86Sr ratios （0.70530-70641） and δ^18O values and Dupal anomaly of Pb isotope compositions. Their Sr-Nd, Pb-Sr, Pb-Nd and Pb-Pb isotopes plot between DMM and EMII, with Pb similar to EMII, Nd relatively close to DMM and Sr in between. This profile suggests that the diabase dikes studied were derived from partial melting of a mantle source that had been subjected to metasomatism by fluids originated from a subduction zone under a tectonic environment of crustal extension and lithosphere thinning in the late Yanshanian.

Geochronology,Geochemistry and Petrogenesis of Diabase Dyke Swarms in East Tianshan,Xinjiang,NW China

Diabase dyke swarms are widespread in the East Tianshan and Beishan regions. LA-ICP-MS zircon U-Pb ages of these diabase vary from 305 Ma to 278 Ma, showing that these dykes were formed during Late Carboniferous-Early Permian magmatism. All diabase samples are subalkali calc-alkali, characterized by slight LREE and LILEs enrichment, and weak negative Ti, Nb and Ta anomalies. The diabase samples have positive ＊＇Nd（t）values （〉＋3）, high Sr isotopic compositions （initial 87Sr/S6Sr values=0.7030-0.7097）, and large variation of Pb isotopic compositions, indicating they were derived from a deplete mantle source. Regional geology and geochemistry evidences indicate that these diabase dyke swarms were generated in a lithosphere extensional setting and had the same magma sources. Initial magmas may be a mixture of depleted asthenosphere mantle and enriched lithospheric mantle during rapid magma ascending.

Geochronology and Tectonic Implications of Diabase Intruded Into Xiangshan Group in the Southeastern Alxa Block, NW China

The southeastern Alxa Block(i.e.,the Hexi Corridor)is a tectonic junction between the North China Block(NCB)to the east,the Alxa Block to the north,and the western Qinling–North Qilian Orogenic Belt to the southwest(Fig.1).The southeastern Alxa Block had undergone

A new type of micro-disseminated gold deposits in association with diabase found in Yunnan and Guizhou provinces and Guangxi Zhuang Autonomous Region——Their geological characteristics and metallogenic conditions

With the continuous development of gold ore prospecting and exploration in recent years a new type of micro-disseminated gold deposits have been found in the regions of Southwest Guizhou Province and Northwest Guangxi Zhuang Autonomous Region,with the orebodies directly occurring in diabase or in the contact zone between diabase and strata.The orebodies are strictly controlled by fault structures.The discovery of this type of gold deposits has brought about new prospects for gold ore prospecting in the Yunnan-Guizhou-Guangxi Golden Triangle region.From the preliminary analysis of the geological characteristics of the Qiaoxiang gold deposit in Wangmo County,in combination with the results of research work in the adjacent areas in recent years,this paper roughly described the geological characteristics and metallogenic conditions of this type of gold ore deposits with an attempt to make more and more geologists pay enough attention to this type of gold ore deposits,so as to promote gold ore prospecting in Guizhou Province to develop toward a variety of types of gold deposits in all round way.

Geochemical characteristics of diabase in Songshan district of Henan, China

In order to understand the dynamic background,the mantle source region characteristic and magma evolution of the diabase in Henan Songshan region and the mineral composition in the area,we have done a systematic study about the mineralogical characteristics and geochemical characteristics of the diabase.Mineralogy research of the diabase in the studied area shows that the diabase have complex mineral compositions,the main rock forming minerals are plagioclase and augite,other minerals in the

Geochemistry and Petrogenesis of Diabase Dykes in the Northern Part of EDC, Karnataka, India: Implication for Sulfide Metal Exploration

Northern part of Eastern Dharwar Craton (EDC) in Karnataka is essentially a granitoid country, frequently intruded by diabase dykes of varied dimensions. Compositionally, majority of them are constituted by pyroxene and plagioclase and less frequently they are olivine-bearing types. One of the major dykes near Thinthini is intensely altered and contains sulfide mineralization brought out by episodic hydrothermal process. Geochemically they are slightly on the higher side of silica content, except the olivine bearing dykes. Their sulfur endowment is also higher. Various discrimination diagrams suggest that they are broadly tholeiitic in composition formed from the less differentiated magma derived from mantle at relatively greater depth and intruded into the granitic rocks which in turn were formed in a subduction setting. The structural deformation prior to and post dating dyke intrusion as deciphered from detailed field studies, alteration of country rocks and hydrothermal activity in the area provide a good background to explore sulfide and other associated metals and also to understand the likely extension of the known mineralized zones.

Geochemistry and Geochronology of OIB-type Early Jurassic Magmatism in the Zhangguangcai Range, NE China, as a Result of Continental Back-arc Extension

The Zhangguangcai Range in the Xing’an(Hinggan) Mongolian Orogenic Belt, NE China, contains Early Jurassic(c. 188 Ma) Dabaizigou(DBZG) porphyritic dolerite. Compared with other island-arc mafic rocks, the DBZG dolerite is characterized by high trace-element contents, relatively weak Nb and Ta enrichments, and no Zr, Hf or Ti depletions, similar to OIB-type rocks. Analysed rocks have(87Sr/86Sr)i ratios of 0.7033–0.7044, relatively uniform positive εNd(t) values of 2.3–3.2 and positive εHf(t) values of 8.5–17.1. Trace-element and isotopic modelling indicates that the DBZG mafic rocks were generated by partial melting of asthenospheric mantle under garnet-to spinel-facies conditions. The occurrence of OIB-like mafic intrusion suggests significant upwelling of the asthenosphere in response to lithospheric attenuation caused by continental rifting. These processes occurred in an incipient continental back-arc environment in the upper plate of a palaeo-Pacific slab subducting W–NW beneath East Asia.

Mesoproterozoic Nuna Supercontinent and the Geomagnetic Field in Light of Recent Paleomagnetic Data from Diabase Dykes of Finland

The number of good quality paleomagnetic data of the Mesoproterozoic supercontinent Nuna(e.g.Columbia,Hudsonland)has increased in recent years enabling more reliable global continental reconstructions(e.g Hoffman

辽宁第Ⅳ金刚石成矿带东部潘家沟辉绿岩中铬铁矿的矿物化学特征及其意义

辽宁省永宁地区因发现原生金刚石而被划分为辽宁第Ⅳ金刚石成矿带,但尚未厘定出金刚石的来源,有必要加强对与金刚石伴生的指示矿物的研究。对该成矿带东部潘家沟地区辉绿岩中选获的铬铁矿开展电子探针成分分析,并与辽宁典型金伯利岩管中的铬铁矿成分进行对比,以探讨该地区铬铁矿的成因及其与金刚石的关系。根据铬铁矿样品电子探针背散射图像显示的粒径、形态及熔蚀特征,以及铬铁矿电子探针成分测试显示的高Cr、富Mg、低Al及贫Ti的特征,推测该地区的铬铁矿来自地幔捕掳晶,属于镁铬铁矿亚类,主要为镁铁-铬铝铁亚种和镁铁-铬铝亚种。计算得到铬铁矿的形成温度为1 252~1 307℃,与前人报道的瓦房店典型金伯利岩中铬铁矿的形成温度基本一致,也接近金刚石的形成温度,表明潘家沟地区辉绿岩中铬铁矿的成因与金刚石关系密切,该地区具有良好的金刚石成矿潜力和找矿前景。研究成果对潘家沟地区金刚石原生矿的勘查及探明该地区金刚石的来源具有指导意义。

我国原生金刚石矿找矿勘查实践与研究新进展

2013年召开的“全国金刚石找矿勘查现场研讨会”,标志着我国新一轮原生金刚石矿找矿勘查工作的开始。近十年以来,原生金刚石矿找矿勘查实践与研究取得了一系列新进展:安徽栏杆地区和辽宁瓦房店地区新增一批原生金刚石资源量,进一步提升了我国金刚石资源保障能力;新划分出辽宁第Ⅳ金刚石成矿带和山东平邑—费县金刚石成矿带,在全国多个地区发现了新的找矿线索,进一步拓展了金刚石原生矿的找矿空间;进一步完善了构造解析-三维建模-工程验证、高分辨率遥感信息提取等综合找矿方法,形成了深部找矿和发现隐伏岩体的新思路;含矿岩体成因研究、金伯利岩(钾镁煌斑岩)侵位模型、金刚石原产地研究等取得了新认识;年代学研究表明,我国含金刚石母岩的成矿时代从古生代延伸到晚中生代,具有显著的多期次成矿特征。此外,文章根据近十年来金刚石找矿勘查与研究取得的新进展及存在的新问题,提出了今后原生金刚石找矿勘查与研究的相关建议。

扬子北缘大洪山地区新元古代辉长辉绿岩中单斜辉石成因及其构造意义

为进一步解析扬子地块北缘新元古代造山作用过程,本文对扬子地块北缘大洪山造山带~820Ma辉长辉绿岩中的单斜辉石进行了岩相学和原位主微量元素分析,共识别出三类单斜辉石:Ⅰ类单斜辉石核部和边部结晶温度分别为1159~1192℃、1162~1187℃,结晶压力分别为0.16~0.44GPa、0.31~0.52GPa;Ⅱ类单斜辉石结晶温度为1145~1179℃,结晶压力为0.27~0.53GPa;Ⅲ类单斜辉石结晶温度为1118~1150℃,结晶压力为0.09~0.35GPa。三类单斜辉石反演获得的母岩浆含水量分别为1.6%~2.4%、1.7%~2.2%、0.9%~2.1%。三类单斜辉石结晶于岩浆演化的不同阶段:早期基性岩浆形成了高Mg#值的Ⅰ类单斜辉石核部;随着岩浆结晶演化,形成低Mg#值的Ⅰ类单斜辉石边部和Ⅱ类单斜辉石;岩浆演化晚期伴随地壳混染,形成Ⅲ类单斜辉石。综合研究表明扬子地块北缘大洪山辉长辉绿岩形成于弧后盆地背景。

西藏驱龙铜钼矿床辉绿岩地球化学、锆石U-Pb年龄及地质意义

冈底斯岩浆带位于西藏中部,是新特提斯洋形成、俯冲、消减以及印度大陆和欧亚大陆碰撞的产物,记录了中-新生代“构造-岩浆-成矿”过程和地质演变。驱龙铜钼矿床位于冈底斯岩浆带的东段,以超大规模斑岩型铜钼矿产而闻名。矿床内出露中侏罗统叶巴组火山岩,古近纪和中新世花岗岩类侵入岩,以及辉绿岩脉等脉岩。基性-中基性岩脉是探索地球深部动力学演变和幔源物质属性的重要窗口,是反演地幔物质化学组成和物理化学条件的直接研究对象。文章以冈底斯岩浆带东段驱龙铜钼矿床内辉绿岩为研究对象,在锆石U-Pb同位素年龄和全岩主量、微量及稀土元素特征分析的基础上,探讨辉绿岩的形成时代、源区属性和产出环境,浅析研究区古近纪构造背景,以期为冈底斯岩浆带古近纪基性岩浆活动和区域构造演化提供约束性数据支撑。锆石LA-ICP-MS U-Pb定年结果显示,辉绿岩成岩年龄为(58.9±1.1)Ma,属古新世晚期,与驱龙铜钼成矿作用(16.9~15.8 Ma)无成因联系。辉绿岩属钙碱性系列,高铝(Al_(2)O_(3)=15.43%~18.42%)、贫钾(K_(2)O=0.02%~1.39%)、低钛(TiO_(2)=0.74%~1.05%),相对富集Rb、Th、U、La、Sr和亏损Nb、P和Ti,稀土元素配分曲线呈弱右倾平环状,无负Eu异常,显示弧岩浆的特征。分析认为,研究区辉绿岩形成于冈底斯岩浆活动的第三阶段(65~41 Ma),是在印度大陆和欧亚大陆初始碰撞的背景下,俯冲的新特提斯洋板片发生断离折返,幔源岩浆底侵下地壳,使得岩石圈地幔部分熔融形成的基性岩浆快速上侵的产物。

云南个旧卡房辉绿岩墙锆石U-Pb年龄、地球化学特征及其岩石圈伸展作用

【研究目的】卡房辉绿岩成因与成岩构造环境的探索对研究个旧地区构造岩浆演化具有重要的科学意义。【研究方法】本文基于LA-ICP-MS锆石U-Pb年龄、全岩地球化学和Sr-Nd-Pb同位素分析等方法研究卡房辉绿岩墙的形成年代、地球化学特征及地质意义。【研究结果】锆石U-Pb地质年代学研究表明卡房辉绿岩侵位年龄为77 Ma,年龄为2409 Ma、2616 Ma、290 Ma的继承锆石指示个旧地区存在新太古代和古元古代构造热事件形成的变质基底以及早二叠世的岩浆活动。卡房辉绿岩属于钾玄岩系列,以低硅、高钾、高钛、高镁为特征,富集Rb、K、Sr等大离子亲石元素,亏损Nb、Ta、Zr、Hf等高场强元素,具有与洋岛玄武岩相似的稀土和微量元素分布特征。卡房辉绿岩具有较高的初始^(87)Sr/^(86)Sr同位素比值(0.70782~0.70791)和正的εNd(t)值(2.07~2.29);初始铅同位素组成中,(^(206)Pb/^(204)Pb)t=18.286~18.465,(^(207)Pb/^(204)Pb)t=15.668~15.717,(208Pb/^(204)Pb)t=37.763~38.830。Sr-Nd-Pb同位素特征指示卡房辉绿岩岩浆源区具有富集地幔(EM2)特征。【结论】卡房辉绿岩成岩机制为在伸展构造背景下,上涌的软流圈地幔底侵富集岩石圈地幔。在岩石圈地幔60~120 km深度,石榴石二辉橄榄岩经过5%~15%的部分熔融,形成了卡房辉绿岩的初始岩浆,在岩浆侵位过程中同化混染下地壳物质并经过较弱的分离结晶作用形成了卡房辉绿岩。

龙王沟辉绿岩矿废弃地生态修复技术研究

龙王沟辉绿岩矿为历史遗留矿山,早期开采技术水平低下,环保意识不强,造成了严重的矿山地质环境及生态环境问题。为达到保护生态环境,以及减少或避免矿山目前已形成的裸露采坑问题对当地生态环境进一步破坏的目的,对龙王沟辉绿岩矿废弃地进行了生态修复治理研究。针对项目区现状特征,提出项目治理工程措施和土地复垦措施技术方案,经比较分析确定了优选技术方案,并对生态修复工程分项进行了设计。项目实施后,生态效益、社会效益、经济效益显著。

渤海湾盆地临南洼陷沙三段辉绿岩地球化学特征及其构造意义

辉绿岩作为一种重要的非常规油气储集单元,其形成和分布通常受控于大地构造背景。笔者以渤海湾盆地临南洼陷沙三段辉绿岩为研究对象,采用岩石学、地球化学和Sr-Nd同位素地球化学等方法,探讨辉绿岩地球化学特征及其地球动力学背景。研究结果表明,辉绿岩属于富钠碱性玄武岩系列,高铝低钛,大离子亲石元素(Rb、Ba、Pb、Sr)和轻稀土元素富集,高场强元素(Th、U)相对亏损,显示Eu正异常。研究区辉绿岩源于不同壳幔端元相互混合的软流圈地幔。辉绿岩的形成与板内岩浆活动有关,且岩浆侵位过程中发生与地壳物质的混染,是大陆伸展构造背景下的产物。渤海湾盆地新生代伸展属于主动裂谷环境,软流圈地幔上涌与太平洋板块向欧亚板块俯冲和板内地幔柱的形成密切相关。

Plume-lithosphere interaction in the Comei Large Igneous Province: Evidence from two types of mafic dykes in Gyangze, south Tibet, China

Two suites of mafic dykes,T1193-A and T1194-A,outcrop in Gyangze area,southeast Tibet.They are in the area of Comei LIP and have indistinguishable field occurrences with two other dykes in Gyangze,T0902 dyke with 137.7±1.3 Ma zircon age and T0907 dyke with 142±1.4 Ma zircon age reported by Wang YY et al.(2016),indicating coeval formation time.Taking all the four diabase dykes into consideration,two different types,OIB-type and weak enriched-type,can be summarized.The“OIB-type”samples,including T1193-A and T0907 dykes,show OIB-like geochemical features and have initial Sr-Nd isotopic values similar with most mafic products in Comei Large Igneous Provinces(LIP),suggesting that they represent melts directly generated from the Kerguelen mantle plume.The“weak enriched-type”samples,including T1194-A and T0902 dykes,have REEs and trace element patterns showing withinplate affinity but have obvious Nb-Ta-Ti negative anomalies.They show uniform lowerεNd(t)values(−6‒−2)and higher 87Sr/86Sr(t)values(0.706‒0.709)independent of their MgO variation,indicating one enriched mantle source.Considering their closely spatial and temporal relationship with the widespread Comei LIP magmatic products in Tethyan Himalaya,these“weak enriched-type”samples are consistent with mixing of melts from mantle plume and the above ancient Tethyan Himalaya subcontinental lithospheric mantle(SCLM)in different proportions.These weak enriched mafic rocks in Comei LIP form one special rock group and most likely suggest large scale hot mantle plume-continental lithosphere interaction.This process may lead to strong modification of the Tethyan Himalaya lithosphere in the Early Cretaceous.