华北克拉通大青山-集宁地区古元古代变质沉积岩的锆石氧同位素组成:SHRIMP微区原位分析

在已获得锆石U-Pb年龄基础上,我们首次对孔兹岩带典型出露区大青山和集宁土贵乌拉地区古元古代变质沉积岩进行了锆石SHRIMP氧同位素研究。锆石具有复杂的内部结构和年龄分布。大青山地区古元古代早期变质沉积岩4个样品碎屑锆石的δ18O为5.52‰~7.11‰,部分重结晶锆石的δ18O为7.22‰~7.90‰,变质新生锆石的δ18O为6.37‰~8.31‰。大青山地区古元古代晚期变质沉积岩2个样品的锆石O同位素组成特征与古元古代早期的类似,另外2个样品的锆石O同位素组成与之不同,碎屑锆石、部分重结晶锆石和变质新生锆石的δ18O分别为6.26‰~10.80‰、9.00‰~11.20‰和9.66‰~11.90‰。集宁土贵乌拉地区古元古代晚期超高温变质沉积岩4个样品不存在碎屑锆石,变质锆石的δ18O变化范围为11.41‰~13.57‰。主要认识如下:1)大青山地区碎屑沉积物主要来自新太古代晚期-古元古代早期成熟度不高的TTG花岗质岩石物源区,与之相比,集宁土贵乌拉地区古元古代晚期超高温岩石的变质原岩成熟度更高;2)不同类型变质沉积岩变质新生锆石的δ18O和变质新生锆石与碎屑锆石的Δ18O存在明显区别,主要反映了岩石体系和变质流体的O同位素组成不同;3)大青山地区高角闪岩相-麻粒岩相变质沉积岩,重结晶锆石的O同位素完全重置,但U-Th-Pb体系未完全重置,集宁土贵乌拉地区超高温变质沉积岩的重结晶锆石O和U-Th-Pb同位素体系都完全重置。变质作用强度不同是主要原因。     

Timing of Proterozoic magmatism in the Sunsas belt,Bolivian Precambrian Shield,SW Amazonian Craton

We present new U-Pb zircon and monazite ages from the Sunsas belt granitic magmatism in Bolivia,SW Amazonian Craton.The geochronological results revealed four major magmatic events recorded along the Sunsas belt domains.The older igneous event formed a granitic basement coeval to the Rio Apa Terrane(1.95-1.85 Ga)in the southern domain.The second magmatic episode is represented by 1.68 Ga granites associated to the Paraguá Terrane(1.69-1.66 Ga)in the northern domain.The 1.37-1.34 Ga granites related to San Ignacio orogeny represent the third and more pervasive magmatic event,recorded throughout the Sunsas belt.Moreover,magmatic ages of～1.42 Ga revealed that the granitogenesis asso-ciated to the Santa Helena orogeny also affected the Sunsas belt,indicating that it was not restricted to the Jauru Terrane.Lastly,the 1.10-1.04 Ga youngest magmatism was developed during the Sunsas oro-geny and represents the final magmatic evolution related to Rodinia assembly.Likewise,the 1.95-1.85 and 1.68 Ga inherited zircon cores obtained in the～1.3 Ga and 1.0 Ga granite samples suggest strong par-tial melting of the Paleoproterozoic sources.The 1079±14 Ma and 1018±6 Ma monazite crystallization ages can be correlated to the collisional tectono-thermal event of the Sunsas orogeny,associated to reac-tions of medium-to high-grade metamorphism.Thus,the Sunsas belt was built by heterogeneous 1.95-1.85 Ga and 1.68 Ga crustal fragments that were reworked at 1.37-1.34 Ga and 1.10-1.04 Ga related to orogenic collages.Furthermore,the 1.01 Ga monazite age suggests that granites previously dated by zir-con can bear evidence of a younger thermal history.Therefore,the geochronological evolution of the Sunsas belt may have been more complex than previously thought.     

内蒙古二道河子铅锌矿成因研究

基于矿床地质调查,并通过岩矿石地球化学和锆石U-Pb测年研究,探讨了二道河子铅锌矿床成因。该矿床赋存于中侏罗统塔木兰沟组中,受北西向断裂-裂隙构造控制,矿体多呈脉状,围岩以火山岩为主,夹有砾岩。据常量、微量、稀土元素和Pb、Sr、Nd同位素测试结果:火山熔岩中SiO2质量分数为48.01%～56.44%,岩屑晶屑凝灰岩中为69.09%～71.73%。前者稀土总量高于后者,两者稀土配分型式相似,均显弱负铕异常;而前者Pb、Zn、Cu等成矿元素的含量却远低于后者。火山岩富集Rb、U、Th等大离子亲石元素,Sr普遍亏损,相对亏损Nb、Ta以及Ti等高场强元素。火山岩ISr=0.704 925～0.706 632,εNd(t)=0.5～2.0,εSr(t)=8.5～32.8,tDM=619～730Ma。火山岩和矿石的Pb同位素组成十分接近,206Pb/204Pb=18.130～18.475,207Pb/204Pb=15.526～15.567,208 Pb/204 Pb=38.078～38.286,μ值为9.32～9.40。矿床主要围岩岩屑晶屑凝灰岩的SHRIMP锆石U-Pb年龄为(164.2±2.3)Ma,这表明火山岩为混有壳源物质的幔源岩浆形成。火山活动分为2期:早期表现为中(基)性火山喷发;晚期岩浆活动发生于中侏罗世晚期,形成酸性火山碎屑岩。成矿物质由与火山岩有关的岩浆系统提供,富集于晚期岩浆中。与成矿有关的侵入岩可能是晚期岩浆作用形成的次火山岩。矿床可能是岩浆分异的含矿热液沿火山岩中的断裂、裂隙充填交代形成,成矿时代为中侏罗世晚期—晚侏罗世。     

新疆西天山菁布拉克基性杂岩体闪长岩锆石SHRIMP定年及其地质意义

文章对新疆西天山特克斯县菁布拉克基性杂岩体中辉石闪长岩样品中的锆石进行了SHRIMP U-Pb定年研究,获得了(434.4±6.2)Ma的和谐年龄,该结果表明菁布拉克岩体的侵位时间为早志留世。结合岩石地球化学分析所揭示的形成环境信息和最新的区域地质资料,认为菁布拉克岩体的形成与早志留世到早石炭世发生的南天山洋向北与中天山板块的俯冲作用密切相关,岩浆显现出的岛弧岩浆特点可能是由于洋壳向亏损地幔的俯冲所引起的。     

聂荣微陆块花岗片麻岩锆石LA-ICP-MS U-Pb定年——新元古代基底岩石的发现及其意义

聂荣微陆块呈透镜体状夹持在班公湖-怒江板块缝合带内,其上出露有黑云母花岗片麻岩以及二长花岗片麻岩等不同类型的古老片麻岩,本文报道产出于聂荣微陆块上花岗片麻岩的锆石LA-ICP-MS U-Pb定年结果,样品锆石的岩浆震荡环带十分发育,多数锆石具有典型的岩浆结晶锆石的特征。所有测点中有16个测点的Th/U值较高,介于0.58~1.24之间,平均值为0.79,获得的²⁰⁶Pb/²³⁸U年龄基本一致,加权平均值为819.6±5.2Ma,笔者等认为该年龄代表了花岗片麻岩的原岩结晶时代为新元古代。我们在羌塘南部地区的碎屑岩中获得了同样的年龄峰值(809Ma)。此外,我们认为年龄中具有507Ma左右的信息反映了泛非事件之后另外一次强烈构造热事件的影响在该区的存在。     

Structure,Timing, and Mechanism of the Pliocene and Late Miocene Uplift Process of the Ailao Shan-Diancang Shan,SE Tibet,China

The uplift of the Ailao Shan-Diancang Shan(ASDS) along the Ailao Shan-Red River(ASRR) shear zone is an important geological event in the southeastern margin of Qinghai-Tibet Plateau tectonic domain in the Late Cenozoic,and it preserves important information on the structures,exhumational history and tectonic evolution of the ASRR shear zone.The uplift structural mode and uplift timing of the ASDS is currently an important scientific topic for understanding the ASDS formation and late stage movements and evolution of the ASRR shear zone.The formation of the ASDS has been widely considered to be the consequence of the strike-slip movements of the ASRR shear zone.However,the shaping of geomorphic units is generally direct results of the latest tectonic activities.In this study,we investigated the timing and uplift structural mechanism of the ASDS and provided the following lines of supportive evidence.Firstly,the primary tectonic foliation of the ASDS shows significant characteristic variations,with steeply dipping tectonic foliation developed on the east side of the ASDS and the relatively horizontal foliation on the west side.Secondly,from northeast to southwest direction,the deformation and metamorphism gradually weakened and this zone can be further divided into three different metamorphic degree belts.Thirdly,the contact relationship between the ASDS and the Chuxiong basin-Erhai lake is a normal fault contact which can be found on the east side of the ASDS.40Ar/39 Argeochronology suggests that the Diancang Shan had experienced a fast cooling event during 3–4 Ma.The apatite fission track testing method gives the age of 6.6–10.7 Ma in the Diancang Shan and 4.6–8.4 Ma in the Ailao Shan,respectively.Therefore the uplift of the ASDS can be explained by tilted block mode in which the east side was uplifted much higher than the west side,and it is not main reason of the shearing movements of the ASRR shear zone.The most recent uplift stages of the ASDS happened in the Pliocene(3–4 Ma) and Late Miocene(6–10 Ma).     

西藏班公湖-怒江缝合带中段碰撞后A型花岗岩的时代及其对洋盆闭合时间的约束

近年来地质调查在班公湖-怒江缝合带中段发现了一批A型花岗岩,岩体呈面积不大(＜1 km2)的岩株产出,岩性上分为钾长花岗岩和花岗闪长斑岩两种,侵入白垩系地层中.岩石化学上这些A型花岗岩相对富硅,SiO2含量在68.62％～75.36％之间,全碱含量(K2O+Na2O=8.03％ ～ 9.37％)和全铁含量(FeO(T)...     

辽宁青城子铅锌多金属矿田晚三叠世岩浆岩年代学、地球化学及地质意义

辽宁青城子铅锌矿田产出在辽东裂谷凹陷带,是中国北方重要的铅锌金银多金属矿田。研究表明,矿区内发育的以双顶沟黑云母二长花岗岩和新岭花岗岩为代表的晚三叠世花岗质岩浆事件,应与本区的矿化作用密切相关。LA-ICPMS锆石U-Pb定年结果显示双顶沟岩体侵位时间为224.2±1.2Ma。双顶沟岩体岩石化学组成呈现 SiO₂ 69.07%~71.31%,K₂O 3.53%~5.22%, Na₂O 3.87%~4.14%,属于钙碱性岩石系列。Al₂O₃为12.46%~14.48%,A/CNK<1,具有准铝质特征。微量元素数据显示稀土总量较高,轻重稀土元素之间强烈分馏, , Eu负异常不明显(δEu=0.68~0.97)。富集大离子亲石元素Rb、Th、K、Pb等,而亏损高场强元素Nb、Ta、P、Ti等。具有高Sr,Ba含量,低的Y,Yb含量特征,属于具有类似埃达克质亲和性的I型花岗岩,具有高Nb/Ta(18.4~21.2),上述岩石地球化学特征,表明其岩浆源区残留固相矿物组合中包含可观的石榴子石和金红石,可能起源于加厚下地壳的部分熔融,并可能存在与幔源基性岩浆混合作用。推测扬子和华北板块深俯冲过程中板片断离可能是诱发与成矿有关岩浆的地球动力学原因。     

黑龙江虎林岩体的锆石U——Pb 年龄及地质意义

通过虎林石青山采石场角闪花岗闪长岩的锆石U-Pb LA-ICPMS 年龄测定,确定了虎林岩体形成于118 Ma 的早白垩世晚期。根据该岩体的岩石学和地球化学特征及区域构造演化研究资料,认为虎林岩体的形成与太平洋板块的俯冲作用有关。     

激光探针质谱及单颗粒矿物^40Ar／^39Ar法年龄的测定

将掺钕的钇铝榴石（Ｎｄ：ＹＡＧ）激光器与高精密ＭＭ１２００质谱计、电子倍增器联网，应用连续激光质谱对单颗粒矿物、光片样品进行微区４０Ａｒ／３９Ａｒ测年、坪年龄和等时线年龄研究。在光片上测定南极乔治王岛北海岸玄武岩等时线年龄（５２．３８±１．０５）Ｍａ和贵州绿豆岩年龄（２３９．１６±１４．１３）Ｍａ，两者与实际地质背景吻合。对两个中生代和太古代单颗粒黑云母进行连续激光质谱阶段升温４０Ａｒ／３９Ａｒ坪年龄谱测定，获得与常规法相一致的坪年龄谱