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阿拉善地块早古生代岩浆作用的成因研究，对理解阿拉善地块与古亚洲洋相互作用过程至关重要。本文在阿拉善地块中部新识别出一中志留世花岗岩体(噶顺花岗岩),其锆石U-Pb年龄为432Ma,以高Sr低Y为特征，属弱过铝质、中钾-高钾钙碱性花岗岩，εHf (t)=-8.8～-19.4,形成于古老下地壳岩石的部分熔融。本文同时总结了阿拉善地块其他晚奥陶世-早泥盆世岩浆岩的成分特征，发现阿拉善地块早古生代岩浆岩在成因上可分为两类：类型I,侵位于晚奥陶世-早中志留世，为典型幔源弧岩浆岩，形成于俯冲流体交代地幔楔的部分熔融；类型II,侵位于中晚志留世-早泥盆世，普遍高Sr低Y,形成于古老中基性地壳岩石的部分熔融。纵观阿拉善地块整个早古生代的岩浆作用，在晚奥陶世-早中志留世→中晚志留世-早泥盆世→中晚泥盆世期间，阿拉善地块的岩浆作用从幔源弧岩浆岩过渡到壳源高Sr低Y型花岗岩再到岩浆作用逐渐消失，反映了阿拉善地块陆缘弧从相对伸展环境向挤压弧的转变。这一岩浆作用演化记录了区域构造作用从典型洋陆俯冲到俯冲作用逐渐减弱(直至停止)或者俯冲角度(从陡俯冲向平俯冲)的转变过程；总体上，阿拉善地块早... 相似文献
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新疆白干湖地区处于东昆仑-祁漫塔格构造带与阿尔金地块的结合部位,出露的巴什尔希岩浆序列对理解该区早中志留世的构造环境有重要意义。本文在巴什尔希岩浆序列中白干湖岩体的不同部位采集了二长花岗岩(BGH-1)和正长花岗岩(BGH-4)两件样品,并进行了详细的岩相学、LA-ICP-MS锆石U-Pb年代学和地球化学研究。白干湖岩体含有白云母、石榴子石等特征矿物,其A/CNK和A/NK的分布范围分别是1.07~1.12和1.41~1.59,属于弱过铝质高钾钙碱性S型花岗岩,并具有富集LREE和LILEs、亏损HFSEs,Nb、P、Ti明显负异常的特点。锆石U-Pb定年结果显示,二长花岗岩形成于428.2±4.2 Ma,正长花岗岩形成于422.5±2.3 Ma。本文和前人的研究成果表明,巴什尔希岩浆序列具有S型花岗岩与A型花岗岩共生的特点,主要活动时代为早中志留世(433~421Ma),形成于后碰撞伸展构造体制。然而,在白干湖断裂以东至格尔木的东祁漫塔格,早中古生代岩浆活动记录了晚奥陶世一早志留世俯冲、中志留世一早泥盆世碰撞和早泥盆世晚期开始后碰撞的演化过程,其中东祁漫塔格早中志留世岩浆岩和白干湖断裂西侧的巴什尔希岩浆序列分别形成于不同的构造环境,因此二者很可能属于不同的构造体系。 相似文献
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阿拉善地块处于华北克拉通,塔里木克拉通和祁连造山带的交汇处,其南缘古生代花岗岩广泛分布。结合近年来阿拉善南缘古生代花岗岩研究成果,从锆石U-Pb年代学和地球化学等方面进行分析总结,认为阿拉善南缘早古生代花岗岩主要受控于祁连造山带的构造演化,其岩浆活动可分为两期,中奥陶世—早志留世和中志留世—早泥盆世,前者处于俯冲环境,后者为后碰撞伸展环境;晚古生代花岗岩仅零星出露于龙首山地区,岩石地球化学特征与宗乃山—沙拉扎山构造带花岗岩相似,与中亚造山带的构造演化相关。并对目前研究中存在的问题和未来研究的方向提出了建议。 相似文献
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通过内蒙古标山一带区域地质矿产调查,查明该区早志留世侵入岩由早到晚依次为花岗闪长岩、二长花岗岩和正长花岗岩。该期侵入体为钙碱性岩系,准铝质岩石,SiO_2、K_2O具正相关变化特征。三者球粒陨石标准化稀土配分曲线均具Eu负异常(δEu值分别为0.60～1.06,0.44～0.81,0.12～0.39)。原始地幔标准化蛛网图显示中等不相容元素La、Ce、Sm、Hf、Zr及强不相容元素Rb、Th、U相对富集,高场强元素Nb、Ta、P、Ti相对亏损。在花岗闪长岩、二长花岗岩、正长花岗岩中获得LA-ICP-MS锆石U-Pb同位素年龄值分别为(444±12)Ma、(441.2±1.8)Ma、(441.1±3.3)Ma,代表该期侵入体就位时代为早志留世。综合前人及本次项目研究成果可见,标山一带早志留世侵入岩就位于岛弧的构造环境。区域上早志留世古亚洲洋壳沿红柳河—月牙山—洗肠井一线向北强烈俯冲,导致本区早志留世深成岩侵位,形成石头井-化石山早古生代岩浆弧。 相似文献
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龙首山铀成矿带位于北祁连造山带与阿拉善地块的结合部位,中志留世—早泥盆世受控于祁连造山带的构造演化而处于后碰撞伸展环境,然而关于龙首山铀成矿带在后碰撞伸展环境的结束时限尚缺乏精确的年代学约束。为此本文以该成矿带青山堡中牌细粒花岗岩为研究对象,开展了岩相学、锆石U-Pb年代学和全岩主微量元素组成分析,据此探讨了岩石类型及成因、源区特征及构造环境。结果显示,中牌细粒花岗岩成岩年龄为(413.7±3.0) Ma,为早泥盆世岩浆活动的产物,形成于碰撞后伸展环境。岩石具有高Si、富碱及低CaO、MgO和P2O5的特征,A/CNK=1.01～1.04;富集轻稀土元素,重稀土元素相对亏损,具有明显的负Eu异常;相对富集Th、U、Nd、K,亏损Ba、Sr、P、Ti等元素。岩石的地球化学特征指示,中牌细粒花岗岩应属于弱过铝质高分异I型花岗岩。中牌细粒花岗岩形成于碰撞后的伸展环境,岩浆来源于下地壳,岩浆源区主要残留相为角闪石,在岩浆演化过程中经历了显著的结晶分异作用。结合前人研究成果,提出龙首山地区早古生代形成的岩浆活动按照时间可划分为晚奥陶世—早志留世(452... 相似文献
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中亚造山带早古生代的构造演化一直存在不同的认识,特别是其俯冲转为碰撞的时限.内蒙古朱日和南部的额尔登陶勒盖地区出露的早古生代岩浆岩,对于限定白乃庙岛弧的延伸方向、岛弧演化和拼贴时间具有重要意义.对额尔登地区出露的火山岩和侵入岩进行了精确的锆石SHRIMP和LA-ICP-MS U-Pb定年、锆石Lu-Hf同位素和地球化学分析以确定其时代和成因.研究获得4个岩浆岩年龄,1件英安岩年龄为434.0±4.4 Ma,2件花岗岩年龄分别为432.8±2.6 Ma和428.1±1.8 Ma,此3件样品形成于早中志留世;另有1件流纹岩年龄为411.8±1.0 Ma,形成于早泥盆世.早中志留世侵入岩为低钾、过铝质钙碱性中酸性岩石,富集Rb、Th,弱富集Zr、Hf,明显亏损Nb、Ta、P、Ti.在稀土配分曲线上,侵入岩均不存在Eu的负异常.其中2件花岗岩样品的锆石基本为正εHf（t）值（-1.19~11.51,3.32~10.28）,TDM2为684~1 493 Ma及759~1 202 Ma,主要来自新生地壳;早中志留世火山岩具有中-低钾、偏铝质-过铝质、钙碱性酸性岩石特征,富集Rb、Th,弱富集Zr、Hf,明显亏损Nb、Ta、P、Ti.在稀土配分曲线上,多数火山岩不存在Eu负异常.英安岩中的锆石具有正εHf（t）值（3.70~7.94）,TDM2为912~1 183 Ma,主要来自新生地壳;而早泥盆世流纹岩（411 Ma）存在明显的Eu负异常,其锆石具有负εHf（t）值（-14.95~-7.07）,TDM2为1.8~2.3 Ga,应为古老地壳再循环的产物,与早中志留世岩浆岩源区明显不同,可能代表构造环境的转变.综合区域地质和前人研究资料表明,早志留世英安岩和花岗岩形成于俯冲岛弧环境,白乃庙岛弧向东可延伸至本区,而早泥盆世流纹岩可能形成于后碰撞环境. 相似文献
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柴达木盆地北缘之全吉地块花岗质岩体大量发育,具多期次多阶段特征。通过对全吉地块金泉山—化石沟一带古生代花岗质岩体岩石学、岩石化学特征及单颗粒锆石U-Pb同位素定年,发现该区花岗岩有4次侵入,侵入时代分别为早奥陶世(471~476Ma)、中奥陶世(459±5Ma)、早志留世(423±4Ma)和中泥盆世(366±2Ma)。岩石地球化学研究显示,该4期花岗岩均具典型的钙碱性特征,轻稀土富集、重稀土轻度亏损、Eu轻微负异常—正异常,大离子亲石元素K2O、Rb、Ba、Th等相对强烈富集,高场强元素Nb、Ta、Hf、Zr及Yb明显亏损,除第4期岩体即具I型,又具S花岗岩特征外,其它各期次均属I型花岗岩,总体显示岩体具壳源特征,为板块碰撞前消减地区花岗岩,研究推测,金泉山—化石沟一带古生代花岗质岩体第1、2组年龄为全吉地块与柴达木陆块碰撞的时代,第3组年龄反映了深俯冲地下的板块由于拆沉而折返的时代,第4组年龄为碰撞隆起后造山带伸展、滑塌的时代。 相似文献
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东昆仑祁漫塔格晚志留世——早泥盆世花岗岩:年代学、地球化学及形成环境 总被引：2，自引：0，他引：2
东昆仑祁漫塔格构造—岩浆岩带发育大量与加里东期造山有关的花岗岩,对其进行研究不仅能为祁漫塔格早古生代构造演化提供新信息,而且对探讨整个东昆仑造山带的动力学演化过程具有重要的意义。本文报道祁漫塔格东部那棱郭勒河东黑云母二长花岗岩及祁漫塔格乌兰乌珠尔钾长花岗岩的锆石U-Pb年龄和地球化学数据,并对研究区晚志留世—早泥盆世花岗岩成因及其构造意义进行探讨。本区的黑云母二长花岗岩、钾长花岗岩的LA-ICP-MS锆石U-Pb年龄分别为420.6±2.6Ma、421.2±1.9Ma。祁漫塔格晚志留世—早泥盆世花岗岩类整体属高钾钙碱性准铝—过铝质花岗岩,稀土配分曲线为轻稀土元素相对富集、重稀土元素相对平坦、中等负铕异常,微量元素表现为大离子亲石元素Rb、Th相对富集,高场强元素Nb、Sr、P、Ti亏损的特征;该时期为后碰撞构造环境,岩石成因类型以高钾钙碱性I型花岗岩为主,但同时出露同时期S型花岗岩,推测在同碰撞挤压造山作用向后碰撞区域拉伸构造体制(约420Ma)的转换时期,产生了具有A型花岗岩特征的花岗岩、高钾钙碱性I型花岗岩及过铝质花岗岩。 相似文献
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东昆仑祁漫塔格构造—岩浆岩带发育大量与加里东期造山有关的花岗岩,对其进行研究不仅能为祁漫塔格早古生代构造演化提供新信息,而且对探讨整个东昆仑造山带的动力学演化过程具有重要的意义。本文报道祁漫塔格东部那棱郭勒河东黑云母二长花岗岩及祁漫塔格乌兰乌珠尔钾长花岗岩的锆石U Pb年龄和地球化学数据,并对研究区晚志留世—早泥盆世花岗岩成因及其构造意义进行探讨。本区的黑云母二长花岗岩、钾长花岗岩的LA ICP MS锆石U Pb年龄分别为4206 ±26Ma、4212 ±19Ma。祁漫塔格晚志留世—早泥盆世花岗岩类整体属高钾钙碱性准铝—过铝质花岗岩,稀土配分曲线为轻稀土元素相对富集、重稀土元素相对平坦、中等负铕异常, 微量元素表现为大离子亲石元素Rb、Th相对富集,高场强元素Nb、Sr、P、Ti亏损的特征;该时期为后碰撞构造环境,岩石成因类型以高钾钙碱性 I 型花岗岩为主,但同时出露同时期S型花岗岩,推测在同碰撞挤压造山作用向后碰撞区域拉伸构造体制（约420Ma）的转换时期,产生了具有A型花岗岩特征的花岗岩、高钾钙碱性 I 型花岗岩及过铝质花岗岩。 相似文献
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江西乐平早二叠世地层朱相水（江西师范大学地理系，江西南昌，３３００２７）关键词地层，早二叠世，栖霞期，乐平，江西实测剖面位于江西乐平沿沟煤矿矿区东隅，３ｋｍ无甲村附近，早Ｍ叠世地层发育于象鼻山与鲤鱼山之间。剖面系笔者与乐平矿务局沿沟煤矿的姚克敏、徐光... 相似文献
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辽宁北票四合屯地区早白垩世早期鸟类集群死亡原因探析 总被引：3，自引：0，他引：3
通过大规模系统挖掘,在对四合屯7个含鸟层进行澄清的基础上,以四合屯剖面为主,黄半吉沟剖面为辅,分别在含鸟层的底板、含鸟层、含鸟层顶板,不含鸟沉积层及含鸟层底部的火山岩系统取样,进行多项相关元素分析。应用元素地球化学理论,根据其环境地球化学场特征,结合相关地质资料,重点对鸟类集群死亡原因进行了探讨。结果表明包括二氧化硫(SO2)、硫化氢(H2S)、铅(Pb)的卤化物盐(PbBr2、PbBrCl、Pb(OH)Br、(PbO)2PbBr2)及汞(Hg)蒸汽等有毒气体是导致鸟类集群死亡的主要原因;含鸟化石密集的原因是由于火山口在四合屯附近。 相似文献
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The dominant control on the (transition between) depositional settings of the Crayfish Group of the Otway Basin in Victoria, Australia has been determined. The study first involved seismic mapping of six stratigraphic units within the Early Cretaceous, continental Crayfish Group. The resulting 3D structural model was used to identify major Early Cretaceous depocentres, and to determine which Crayfish Group sediments are restricted to individual rift depocentres and which are more widespread as a result of inter-connectivity of the basin. Five structural cross-sections were then constructed across each major depocentre of the basin; these were balanced and restored, and missing section estimated, in order to test the validity of the structural interpretations. This also enabled analysis of differing extensional rates within each depocentre and the calculation of the cumulative displacement of each major bounding fault. Results show that displacement rate, growth and linkage of the faults, as well as the amount of subsidence within the depocentres, had a significant effect on the distribution and development of the major facies within the Crayfish Group. The Casterton Formation and Sawpit Shale equivalent/McEachern Sandstone were restricted to rapidly subsiding, structurally controlled depocentres in the west, while the succeeding Sawpit Sandstone equivalent was deposited within the same depocentres, across the intervening structural highs and in the eastern part of the basin where depocentres had just begun to form. The Pretty Hill Formation shows a similar distribution pattern, while the overlying fine-grained Laira Formation also drapes structural highs but is replaced in the east by coarser-grained sediments of the upper Pretty Hill Formation. Extension was locally up to 21% in the central Otway Basin but was much less in the eastern Otway Basin. 相似文献
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Ostracoda during the Early Aptian (Early Cretaceous) greenhouse period on the Isle of Wight, England
Ian P. Wilkinson 《Proceedings of the Geologists' Association. Geologists' Association》2011,122(5):809-815
The earliest Aptian marine transgression of the Lower Cretaceous across southern England resulted in the collapse of the generally freshwater Barremian environment and the initiation of marine mileux. Salinities passed from fresh-oligohaline to meso- and pliohaline, reaching fully marine conditions during the obsoletum Subzone (P. fissicostus Zone). Newly formed environmental niches were rapidly occupied by ostracod associations. In the Isle of Wight, freshwater Cypridea-rich assemblages in the lower Shepherd's Chine Member (Vectis Formation) were gradually replaced by faunas dominated by Sternbergella cornigera, Mantelliana mantelli and Theriosynoecum fittoni. Marine taxa recorded from the Atherfield Clay Formation migrated predominantly from the Paris Basin and include Asciocythere albae, Schuleridea derooi, Neocythere gottisi, N. bordeti, Cythereis geometrica, Cytheropteron stchepinskyi and Protocythere croutesensis. 相似文献
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龚大明 《沉积与特提斯地质》1989,9(6):24-31
一、绪言保山地区是滇西泥盆系和下石炭统出露的主要地区之一,以前已有不少报道。近年来,由于该地区特殊的大地构造位置,引起了国内外广大地质工作者的密切注意,因而对泥盆石炭纪地层及其古生物的研究也更加深入。保山地区的上泥盆统目前暂分为何元寨组和整合其上的大寨门组,前者底部尚属中泥盆统(龚大明等,待刊)。下石炭统下部称鱼洞组。何元寨组在其命名剖面施甸何元寨主要是一套中层灰岩和泥灰岩,厚约220m,腕足、珊瑚、层孔及苔藓动物丰富,向东北至大寨门、由 相似文献
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I. K. Kozakov V. V. Yarmolyuk V. P. Kovach E. V. Bibikova T. I. Kirnozova A. M. Kozlovskii Yu. V. Plotkina M. M. Fugzan V. I. Lebedev Ch. Erdenezhargal 《Stratigraphy and Geological Correlation》2012,20(3):231-239
Fragments of continental blocks or microcontinents are represented in the Early Caledonian orogenic area of Central Asia (or Early Caledonian superterrane); the largest of these are the Dzabkhan and Tuva-Mongolian microcontinents, with Early and Late Precambrian crystalline basements, respectively. In the linkage zone of these microcontinents, crystalline rocks of the Tarbagatai and Songino blocks that are considered as units of the Early Precambrian ensialic basement of the superterrane are also known. They are composed of strongly metamorphosed rocks formed during the Early Baikalian orogeny about 790 to 820 Ma. U-Pb zircon dating and Nd isotope studies revealed, within the northwestern Dzabkhan microcontinent, the Dzabkhan-Mandal zone of crystalline rocks associated with the Riphean crust-forming process. The age of the gneiss substrate of this zone is estimated as 1.3 to 0.86 Ga. An early episode of metamorphism is dated at about 856 ± 2 Ma. The data available so far indicate a heterogeneous structure of the Dzabkhan microcontinent basement represented by Early Precambrian and Early and Late Baikalian crystalline formations. 相似文献
18.
The paper reports new isotope-geochemical data on Late Paleocene-Early Eocene basalts from the central part of the Kolyuchin-Mechigmen graben, eastern Chukotka Peninsula. The distribution of the major and trace elements and trace-element ratios indicates that the basalts were formed in a marginal-continental rift setting. The peculiar feature of the basalts is a combination of depleted within-plate and suprasubduction geochemical signatures, which make the volcanic rocks from Mt. Otdel’naya different from rocks of suprasubduction volcanic belts and from tholeiites and alkaline lavas of continental rifts and oceanic islands. Extremely high 87Sr/86Sr ratios in the studied basalts as compared to those of similar volcanic rocks from extension zones are probably related to the involvement of carbonate material in the magma generation zone. 相似文献
19.
The Early Paleoproterozoic Burakovsky complex contains Europe’s largest layered mafic-ultramafic pluton and giant Avdeevo gabbronorite dike. The pluton consists of two independent bodies of different age (the Aganozero and Shalozero-Burakovsky bodies), each having its own internal structure and contacting each other in their apical parts. Both bodies have a similar rock sequence including five differentiated zones (from bottom upward, based on the predominant cumulus assemblages): ultrabasic, pyroxenite, gabbronorite, pigeonite gabbronorite, and magnetite gabbronorite-diorite. Being generally similar to each other owing to a common differentiation trend of similar melts, these bodies differ notably in the character of their cumulus stratigraphy and, to a lesser extent, in mineral and geochemical composition. The pluton is distinguished by the presence of marker horizons—singular interlayers of high-temperature mafic cumulates emplaced in the sequence of lower-temperature gabbroid. Their origin is believed to have been associated with the influxes of fresh magma portions into the crystallizing magma chambers. Based on petrological, geochemical, and mineralogical data, the Aganozero and Shalozero-Burakovsky bodies, as well as additional intrusive phases, were derived from the compositionally similar but not identical melts of siliceous high-Mg (boninite like) series. The Avdeevo dike (2436 ± 46 Ma at ?Nd(T) = ?1.5) extends along the southeastern contact of the Shalozero-Burakovsky body and was formed almost simultaneously with it. The dike is made up of pigeonite gabbronorites, which are almost identical to the rocks of the Pigeonite gabbronorite zone of the Burakovsky pluton in geochemistry and mineral composition. It was concluded that the Burakovsky Complex was a long-lived igneous center, whose origin was related to the activity of an Early Paleoproterozoic mantle superplume. 相似文献
20.
下第三系名山组广泛分布于雅安地区，地层出露良好。本文简要介绍雅安国光山背斜东西两翼新测的地层剖面，将名山组（包括芦山组）划分成４段（砂岩粉砂岩段、粉砂岩泥岩泥灰岩段、泥岩粉砂岩段、泥岩段），并将芦山组归于名山组上部（Ⅳ段），从而取消该名称，综述了岩石组合特征、沉积环境，进行了生物地层和年代地层划分。 相似文献