大兴安岭新林区中生代流纹岩年代学、地球化学特征及其地质意义

大兴安岭北段新林区满克头鄂博组火山岩主要由流纹岩、英安岩及其凝灰岩组成,LA-ICP-MS锆石U-Pb年龄为154.5±0.68 Ma,时代为晚侏罗世.白音高老组火山岩主要由流纹岩及其凝灰岩组成,LA-ICP-MS锆石U-Pb年龄为121.12±0.5 Ma,时代为早白垩世.满克头鄂博组火山岩属于高钾钙碱性系列-钾玄质系列.稀土元素配分模式图呈右倾型,轻重稀土分馏明显,具有中等的Eu负异常.微量元素显示相对富集大离子亲石元素K、Rb、Ba、Sr和轻稀土元素,亏损高场强元素Nb、Ta、Ti、P等.白音高老组火山岩属于高钾钙碱性系列.稀土元素配分模式图呈右倾型,轻重稀土分馏明显,明显Eu负异常.微量元素显示相对富集大离子亲石元素K、Rb和轻稀土元素,Ba、Sr明显亏损,高场强元素Nb、Ta,Ti强烈亏损.结合地球化学特征和前人研究资料,认为新林区满克头鄂博组火山岩来源于下地壳玄武质岩浆的结晶分异作用,与蒙古-鄂霍次克洋闭合造山后的伸展环境有关.白音高老组火山岩源于下地壳斜长角闪岩的非理想熔融,与太平洋板块俯冲影响的伸展作用有关.     

大兴安岭中段白音高老组流纹岩年代学、地球化学及其地质意义

对大兴安岭中段(阿尔山—柴河地区)白音高老组流纹岩进行了年代学、地球化学详细测试,结果表明:白音高老组流纹岩LA—ICP—MS锆石U—Pb表面年龄值为124.8~135.6 Ma,加权平均年龄值为127.0±0.5 Ma,形成时代为早白垩世;岩石主体属高硅高钾弱过铝质钙碱性系列;稀土元素配分模式图呈右倾型,轻重稀土分馏明显((La/Yb)N=3.12~10.28,平均7.57),铕弱负异常(δEu=0.18~0.73,平均0.53);大离子亲石元素Rb、Th、U相对富集,Ba、Sr明显亏损,高场强元素Zr较为富集,Ti强烈亏损。根据区域对比并结合他人研究成果,认为大兴安岭中段白音高老组流纹岩形成于早白垩世板内伸展环境,与太平洋板块俯冲关系密切。     

大兴安岭中段白音高老组火山岩的形成时代及地球化学特征

大兴安岭中段柴河地区白音高老组火山岩主要由流纹岩及流纹质火山碎屑岩等一套酸性火山岩组成。锆石SHIRMP U--Pb定年结果显示白音高老组火山岩的年龄为131±1 Ma,为早白垩世。地球化学测试结果显示,白音高老组火山岩属钙碱性系列,其微量元素亏损Ba、Sr、P、Ti、U元素,相对富集Rb、Th、K、Nd、Hf等元素。稀土元素配分曲线右倾,轻重稀土分馏明显,具有明显的Eu负异常。研究表明,白音高老组火山岩来源于下地壳的部分熔融,其形成的构造背景可能为蒙古—鄂霍茨克洋闭合—碰撞造山后的伸展。     

冈底斯中段达布埃达克质含矿斑岩:增厚下地壳熔融与斑岩铜钼矿成因

冈底斯中段达布斑岩铜钼矿床发育在印度-欧亚大陆后碰撞地壳伸展环境,含矿斑岩为一套高钾钙碱性岩系,其地球化学组成与典型的埃达克岩的地球化学组成非常类似,如高w(Sr)(401×10-6～1 060×10-6)与w(Sr)/w(Y)、[w(La)/w(Yb)]N比值,亏损重稀土元素Yb与Y,无Eu异常、具正Sr异常等.在微量元素原始地幔蛛网图中,明显富集大离子亲石元素Rb、Ba、Th、Sr,亏损高场强元素Nb、Ta、P、Ti.认为达布埃达克质含矿斑岩起源于富钾增厚下地壳的部分熔融,是在中新世后碰撞构造环境中在板片断离作用下受到软流圈热源上涌影响而触发形成的.埃达克质岩浆在上升的过程中可能交代同时期形成的超钾质岩浆,使二者产生混合交换反应,一方面导致埃达克质岩浆的w(MgO)增高,一方面埃达克质岩浆萃取超钾质岩浆中的金属元素,有利于成矿.达布Cu、Mo成矿作用与高Mg#埃达克质岩关系密切,表明在冈底斯地块上寻找与高Mg#埃达克质岩有关的Cu多金属矿床是一个新的找矿思路.     

内蒙古贺斯格乌拉牧场白音高老组火山岩U-Pb年龄及地球化学特征

白音高老组火山岩在大兴安岭地区广泛分布,本文对大兴安岭中南部贺斯格乌拉牧场白音高老组酸性火山岩进行了锆石U-Pb年代学、岩石地球化学和Sr-Nd同位素分析,探讨其岩石成因及构造背景。位于大兴安岭中南段东乌旗地区的白音高老组火山岩,主要岩性为流纹岩、流纹质凝灰岩等,LA-ICP-MS锆石U-Pb年龄分别为129. 8±0. 8 Ma、128. 2±2. 8 Ma,属早白垩世早期;从岩石地球化学特征上看,其主量元素SiO_2含量68. 76%～76. 18%、Al_2O_3含量11. 84%～13. 38%,属高钾钙碱性岩石;稀土总量较高,(La/Yb)N 6,(La/Sm)_N 3,显示为轻稀土富集型,δEu显示负铕异常(0. 4～0. 6),微量元素以富集大离子亲石元素K、Rb、Ba,贫高场强元素Nb、P、Ti为特征; Sr-Nd同位素组成上具有低I_(Sr)、高ε_(Nd)(t)和低t_(DM)的特征(I_(Sr)=0. 7039～0. 7045,ε_(Nd)(t)=2. 65～4. 39)。火山岩浆来源于下地壳基性物质的部分熔融,综合研究并结合前人资料认为,白音高老组流纹岩形成于滨太平洋板块俯冲后伸展及蒙古-鄂霍次克洋闭合后的综合效应下。     

内蒙古扎木廷火山岩年代学、地球化学与中生代构造体制转换

大兴安岭火山带晚中生代火山岩的起源、演化及形成的构造背景一直存在争议。文章对出露于扎木廷地区白音高老组火山岩进行LA-ICP-MS锆石U-Pb定年,结果显示流纹岩及粗面岩分别形成于(131.6±1.2)Ma和(126.9±1.5)Ma,与白音高老组第二段火山沉积夹层中动植物化石鉴定结果一致,表明形成于早白垩世早期。流纹岩及粗面岩属碱性系列火山岩,具高硅、富碱、低铝、贫镁、钙和高FeOT/(FeOT+MgO)比值特征;相对富集大离子亲石元素Rb、Th、U、Pb,强烈亏损高场强元素Nb、Ta、Ti、P和Ba、Sr,流纹岩具A型花岗岩特征。微量元素与稀土元素特征表明流纹岩及粗面岩均来自于地壳的熔融,二者具有相同的岩浆来源。白音高老组火山岩形成于造山后的伸展构造背景,反映了蒙古鄂霍茨克洋向南俯冲与额尔古纳—兴安陆块碰撞拼合后,大兴安岭地区开始由挤压向伸展构造体制转换,软流圈地幔上涌底侵使下地壳发生了部分熔融,导致流纹岩喷发,残留相进一步熔融继而导致大规模粗面岩喷发。     

大兴安岭北端漠河地区早古生代埃达克质岩特征及地质意义

笔者近期在大兴安岭北端漠河地区早古生代花岗岩的研究中发现了埃达克质岩,岩石类型主要为二长花岗岩及少量花岗闪长岩,岩石富K但相对略富钠（NaO/K2O＞1）,富SiO2;高Sr低Y、Yb,Sr/Y＞40;富集LREE,亏损重稀土元素,La/Yb＞20,Eu呈弱负异常或轻微正异常（δEu=0.71～1.1）.与典型的俯冲板片熔融形成的埃达克岩相比更为富硅和钾,属高钾钙碱性系列,具有低的Mg#（31.1～34.9）及不同于Ⅰ型埃达克岩的Nd、Sr同位素组成,属Ⅱ型埃达克质岩,推测形成于加厚的中基性下地壳的部分熔融.漠河早古生代埃达克岩的确认表明额尔古纳地块早古生代有过陆壳加厚过程,大陆发生过垂向的增生.同时在德尔布干成矿带中段的本区寻找与埃达克岩有关的斑岩型铜、金矿床是一个新的找矿方向.     

内蒙古色日崩地区白音高老组流纹岩岩石地球化学特征及地质意义

内蒙古西乌旗色日崩地区早白垩世白音高老组流纹岩为高硅（SiO₂=78.32%~86.80%）、富碱（K₂O+Na₂O=3.84%~7.63%）、高铝（Al₂O₃=8.59%~13.70%）,低MgO、CaO、TiO₂、MnO,稀土元素与微量元素地球化学特征显示其类似于A型花岗岩特征;低Ti/Y、Nb/Y与Ti/Zr比值,高Rb/Nb与Rb/Y比值以及Sr、Eu强烈亏损,表明白音高老组流纹岩为上地壳物质部分熔融成因,形成于早白垩世非造山板内伸展环境.     

苏鲁地体南缘超高压变质带朐山二云花岗片麻岩的地球化学特征及其构造意义

二云花岗片麻岩是组成苏鲁地体南缘超高压变质带朐山杂岩体的重要岩石类型,虽然经历了超高压变质作用,但仍保留了花岗岩的岩石学特征。常量元素和微量元素分析结果表明该片麻岩具有高w(K₂O)、低w(CaO)、高w(TFeO)/w(MgO)比值、铝饱和指数偏高的A型花岗岩的特征,岩石类型为高钾碱性过铝质A型花岗岩。稀土元素中轻稀土富集、分馏程度高、Eu强烈亏损,微量元素中Ba、P、Ti、Sc具有明显的负异常,w(Sr)/ w(Y)、w(La)/ w(Yb)和w(Rb)/ w(Sr)、w(Rb)/ w(Ba)较高,尤其是w(TiO₂)＜0.2％和w(Y)/ w(Nb)＞1.2的特征,以及在w(Rb)-w(Yb+Ta）和w(Rb)-w(Y+Nb）判别图解上样品投点位于板内环境区等,表明该片麻岩的原岩形成于板内与裂谷有关的非造山环境。锆石SHRIMP U-Pb测年结果揭示其侵位时代为新元古代中晚期((722±32）Ma）,与杂岩体中早期侵位的二长花岗片麻岩及杂岩体上覆地层中的变质火山岩同为Rodinia大陆裂解、扬子地块陆内裂谷形成过程中伴随的岩浆活动的产物。     

锡林浩特东部早白垩世白音高老组岩石地球化学特征、LA-MC-ICP-MS锆石U-Pb年龄及地质意义

锡林浩特东部白音高老组火山岩主要由石泡流纹岩、珍珠岩、碎斑熔岩、流纹质熔结凝灰岩等组成。LA-MC-ICP-MS锆石U-Pb定年显示,火山岩形成于134 Ma~139 Ma之间的早白垩世。岩石地球化学研究表明:该组火山岩具有高硅、高钾、高Fe OT/Mg O比值(4.88~19.09),贫镁、钙特征,属高钾钙-碱性岩系;稀土元素表现为稀土总量较高(∑REE=82.02~436.61)、轻重稀土分馏明显(LaN/YbN=2.23~20.74)、属轻稀土富集型(LRE/HRE=2.71~11.87)、Eu负异常显著(δEu=0.06~0.42);微量元素特征表现为大离子亲石元素(LILE)Rb、Th、U、K相对较为富集,高场强元素(HFSE)Nb、Ta相对亏损,而Ba、Sr、Zr、Ti强烈亏损,与A2型花岗岩特征相似。其岩浆来源为典型的壳源岩浆系列,是陆壳岩石部分熔融的产物,形成于造山后的张性构造环境。     

Chronological and Geochemical Characterisitics of Volcanic Rocks of the Yingcheng Formation in the Southern Songliao Basin: Constraints on the Early Cretaceous Evolution of the Songliao Basin

The discoveries of oil and gas reservoirs in the volcanic rocks of the Songliao Basin(SB) have attracted the attention of many researchers. However, the lack of studies on the genesis of the volcanic rocks has led to different opinions being presented for the genesis of the SB. In order to solve this problem, this study selected the volcanic rocks of the Yingcheng Formation in the Southern Songliao Basin(SSB) as the research object, and determined the genesis and tectonic setting of the volcanic rocks by using LA-ICP-MS zircon U-Pb dating and a geochemical analysis method(major elements, trace elements, and Hf isotopes). The volcanic rocks of the Yingcheng Formation are mainly composed of rhyolites with minor dacites and pyroclastic rocks. Our new zircon U-Pb dating results show that these volcanic rocks were erupted in the Early Cretaceous(113–118 Ma). The primary zircons from the rhyolites have εHf(t) values of +4.70 to +12.46 and twostage model age(TDM2) of 876–374 Ma. The geochemical data presented in this study allow these rhyolites to be divided into I-type rhyolites and A-type rhyolites, both of which were formed by the partial melting of the crust. They have SiO2 contents of 71.62 wt.%–75.76 wt.% and Al2 O3 contentsof 10.88 wt.% to 12.92 wt.%. The rhyolites have distinctively higher REE contents than those of ordinary granites, with obvious negative Eu anomalies. The light to heavy REE fractionation is not obvious, and the LaN/YbN(average value = 9.78) is less than 10. The A-type rhyolites depleted in Ba, Sr, P, and Ti, with relatively low Nb/Ta, indicating that the rocks belong A2 subtype granites formed in an extensional environment. The adakitic dacites are characterized by high Sr contents(624 to 1,082 ppm), low Y contents(10.6 to 12.6 ppm), high Sr/Y and Sr/Yb ratios, and low Mg# values(14.77 to 36.46), indicating that they belong to "C" type adakites. The adakitic dacite with high Sr and low Yb were likely generated by partial melting of the lower crust under high pressure conditions at least 40 km depth. The I-type rhyolites with low Sr and high Yb, and the A-type rhyolites with very low Sr and high Yb, were formed in the middle and upper crust under low pressure conditions, respectively. In addition, the formation depths of the former were approximately 30 km, whereas those of the latter were less than 30 km. The geochemical characteristics reveal that the volcanic rocks of Yingcheng Formation were formed in an extensional environment which was related to the retreat of subducted Paleo-Pacific Plate. At the late Early Cretaceous Period, the upwelling of the asthenosphere mantle and the lithosphere delamination caused by the retreat of the subducted Paleo-Pacific Plate, had resulted in lithosheric extension in the eastern part of China. Subsequently, a large area of volcanic rocks had formed. The SB has also been confirmed to be a product of the tectonic stress field in that region.     

滇西丽江地区新生代富碱斑岩年代学、地球化学特征及其地质意义

滇西丽江地区新生代富碱斑岩位于滇西“三江”褶皱造山带与扬子板块西南缘结合部位,岩石类型多样,可分为碱性岩和碱性花岗岩,前者主要有正长斑岩、正长岩及粗面斑岩;后者主要包括花岗斑岩、二长花岗斑岩及石英二长斑岩。锆石LA ICP MS U Pb定年研究确定区内斑岩结晶年龄为346～371 Ma,侵位于始新世晚期。碱性岩石的SiO2含量为5454%～6770%,K2O＞Na2O,具有钾玄岩的特征;碱性花岗岩的SiO2含量为6716%～7066%,K2O＜Na2O,具有高钾钙碱性的特征。两类岩石都具有富碱(Na2O+K2O=703%～1170%)和准铝质—弱过铝质(A/CNK=064～115)的特征。富集轻稀土元素和大离子亲石元素(Sr、Ba、K、Pb等),相对亏损重稀土元素和高场强元素(Nb、Ta、Ti等),且具有高Sr、Sr/Y和La/Yb比值及低Y、Yb和镁值(Mg#＜05),表明区内斑岩兼具钾玄质岩石和埃达克质岩石的特征。综合研究认为,区内斑岩形成于印度－亚洲大陆碰撞造山的后碰撞阶段,其形成与减压熔融及幔源岩浆底侵促使增厚下地壳底部岩石发生部分熔融有关,是青藏高原东南缘构造转换带对主碰撞带造山作用过程的岩浆事件响应,进而分析确认本区具有斑岩-热液型金多金属矿床的找矿潜力,为深入认识丽江地区构造-岩浆-成矿作用提供了重要约束。     

新疆东天山白山钼矿深部岩体地球化学特征及成因意义

白山钼矿深部钻探表明矿体下部存在着矿化花岗斑岩体,所获岩芯显示其岩性主要为似斑状钾长花岗岩、黑云母斜长花岗岩和花岗斑岩.该岩体具有高Al、Na和Sr,低Mg、Y和Yb,以及高Sr/Y和La/Yb比值等特点,类似于埃达克质岩的地球化学特征,暗示来源于较深的含石榴子石的源区;岩石形成时代和地球化学构造判别图解表明,岩体形成于造山后的构造环境.因此,白山钼矿岩体可能为加厚下地壳熔融的产物.白山钼矿床的成矿作用可能与埃达克质岩浆活动有关,其成矿过程得益于高Mo丰度的地壳源区、成岩过程中提供流体和岩浆高氧逸度环境等.     

古亚洲洋俯冲板片断离与后造山伸展：贺根山缝合带火山岩年代学和地球化学证据

本文以出露于贺根山缝合带迪彦庙蛇绿混杂岩北侧的乌兰拜其白音高老组流纹岩- 粗面岩为研究对象,通过野外地质调查和岩石学、地球化学、锆石U- Pb年代学研究,探讨岩石成因类型、构造环境和古亚洲洋俯冲板片断离与后造山伸展过程。岩石地球化学研究表明, 乌兰拜其地区白音高老组流纹岩具有较高的SiO 2、Al 2O 3、K 2O和Na 2O+K 2O含量,以及较高的Ga/Al比值,相对贫CaO、MgO、Sr、Ba、Eu、Ti和P,稀土元素配分曲线为右倾海鸥式分布,负铕异常显著。该区粗面岩属于钾玄岩系列,具有高碱(Na 2O+K 2O)、高K 2O、高Al 2O 3、低TiO 2,富集Rb、Ba、U和轻稀土元素, 亏损 Nb、Ta 和 Ti,稀土元素配分曲线为右倾式分布。岩石学和岩石地球化学特征表明,乌兰拜其地区白音高老组流纹岩为迪彦庙- 白音布拉格蛇绿混杂岩带早白垩世后造山A型花岗岩浆的喷出相- A型流纹岩,其形成于后造山伸展构造环境;粗面岩为后造山型钾玄质火山岩,与洋壳俯冲作用有关,形成于俯冲板片断离- 后造山伸展构造背景。流纹岩和粗面岩锆石LA- ICP- MS U- Pb同位素测年,获得206Pb/238U加权平均年龄分别为140. 4±1. 2Ma和134. 9±1. 1Ma,表明白音高老组流纹岩- 粗面岩喷发于早白垩世,反映了贺根山缝合带早白垩世后造山A型花岗岩浆- 钾玄质岩浆作用事件。结合贺根山缝合带的壳幔电性结构特征和晚古生代蛇绿岩- 岛弧岩浆岩、中生代后造山A型岩浆岩的时空分布与演化关系,认为根山缝合带三叠纪- 早白垩世后造山伸展岩浆作用与古亚洲洋俯冲板片断离作用有关,提出了该区后造山A型花岗岩浆- 钾玄质岩浆作用的俯冲板片断离- 后造山伸展地球动力学模式。     

大兴安岭北段新林战备村地区早白垩世火成岩年代学、地球化学及大地构造意义

大兴安岭北段新林战备村地区广泛发育晚中生代火山岩及花岗岩体。LA-ICP-MS锆石U-Pb测得战备村花岗岩体侵位年龄为121.0±0.8 Ma,其周围出露的白音高老组流纹岩喷发年龄为136.9±1.3 Ma,二者均形成于早白垩世。地球化学特征上,二者均属于过铝质高钾钙碱性-钾玄质系列,高SiO_2,富K_2O、Na_2O,低Mg、Ti,微量元素富集大离子亲石元素Rb、K、Ba及LREE,亏损高场强元素Nb、Ta、Ti及HREE,轻重稀土明显分异((La/Yb)_N=11~23.2),具中等-弱的Eu负异常(δEu=0.35~0.82),二者具同源岩浆演化的特征。结合前人研究结果,新林战备村地区早白垩世火成岩形成于后造山或碰撞后的构造环境,代表了伸展的大地构造背景,这些火成岩产出可能与蒙古—鄂霍茨克洋中侏罗世至早白垩世闭合造山后的伸展作用有关。     

Discovery of two stages of the Early Paleozoic adakitic intrusive rocks in the Kunlun River area,East Kunlun: Implications for collisional orogenic processesSCIEI北大核心CSCD

早古生代志留纪-泥盆纪是东昆仑原特提斯洋闭合和碰撞造山过程发生的重要时期。在该阶段出现有榴辉岩和大量A型花岗岩、镁铁-超镁铁质岩,并产出有夏日哈木镍矿、白干湖钨锡矿等一批重要的矿产资源。然而,东昆仑早古生代详细碰撞造山的深部过程、榴辉岩的折返机制等问题还没有得到合理的解释。在东昆仑造山带昆仑河地区新发现的早古生代埃达克质侵入岩可能为上述问题的解决提供了重要依据。LA-ICP-MS锆石U-Pb测年结果表明昆仑河地区存在晚奥陶世(446Ma)和晚志留世(427～425Ma)两期埃达克质侵入岩。晚奥陶世埃达克质侵入岩为花岗闪长岩,SiO₂(67.55%～68.21%)和Al₂O₃(14.59%～15.89%)含量较高,富Na₂O(4.91%～5.15%)、贫K₂O(1.54%～1.64%),亏损重稀土,Y含量是7.76×10^-6～8.61×10^-6,Yb含量是0.67×10^-6～0.93×10^-6...     

Post-collisional adakitic volcanism in the eastern part of the Sakarya Zone, Turkey: evidence for slab and crustal melting

New geochemical and isotopic data for post-collisional Early Eocene and Late Miocene adakitic rocks from the eastern part of the Sakarya Zone, Turkey, indicate that slab and lower crustal melting, respectively, played key roles in the petrogenesis of these rocks. The Early Eocene Yoncal?k dacite (54.4 Ma) exhibits high Sr/Y and La/Yb ratios, low Y and HREE concentrations, moderate Mg# (44–65), and relatively high εNd and low ISr values, similar to adakites formed by slab melting associated with subduction. Geochemical composition of the Yoncal?k dacite cannot be explained by simple crystal fractionation and/or crustal contamination of andesitic parent magma, but is consistent with the participation of different proportions of melts derived from subducted basalt and sediments. Sr/Y correlates horizontally with Rb/Y, and Pb/Nd correlates vertically with Nd isotopic composition, indicating that Sr and Pb budgets are strongly controlled by melt addition from the subducting slab, whereas positive correlations between Th/Nd and Pb/Nd, and Rb/Y and Nb/Y point to some contribution of sediment melt. In addition to low concentrations of heavy rare earth elements (~2–3 times chondrite), a systematic decrease in their concentrations and Nb/Ta ratios with increasing SiO₂ contents suggests that slab partial melting occurred in the garnet stability field and that these elements were mobilized by fluid flux. These geochemical and isotopic signatures are best explained by slab breakoff and fusion shortly after the initiation of collision. Although the Late Micone Tavda?? rhyolite (8.75 Ma) has some geochemical features identical to adakites, such as high Sr/Y and La/Yb ratios, low Y and HREE concentrations, other requirements, such as sodic andesite and/or dacite with relatively high MgO and Mg# (>50), relatively high Ni and Cr, low K₂O/Na₂O (<0.4), high Sr (>400 ppm), for slab-derived adakites are not provided. It is sodic in composition and shows no traces of fractionation from dacitic parent magma. Low Nd and high Sr isotope ratios suggest derivation by partial fusion of calc-alkaline, juvenile crust with high Sr/Y and La/Yb ratios.