冀东-辽西太古宙火成岩岩石组合和动力学意义

冀东-辽西地区是华北克拉通北部出露面积最大的太古宙变质基底区.经过岩石组合填图和综合研究,将其太古宙变质火成岩分为2.64~2.60 Ga MORB型拉斑玄武质火山岩、2.61~2.52 Ga拉斑玄武质-钙碱性变质火山岩、2.52~2.50 Ga浅变质钙碱性火山岩组合和2.54~2.50 Ga英云闪长质-奥长花岗质-花岗闪长质片麻岩、2.54~2.51 Ga闪长质-石英闪长质-英云闪长质-奥长花岗质-花岗闪长质片麻岩、2.54~2.51 Ga紫苏花岗闪长质-紫苏花岗质岩石、2.57~2.52 Ga闪长质-石英二长闪长质-花岗闪长质-二长花岗质片麻岩和2.53~2.51 Ga弱片麻状到块状二长花岗质-正长花岗质深成侵入体岩石组合.这些岩石组合从东北部的辽西阜新到西南部的遵化马兰峪地区呈现出条带状时-空分布特征.变质作用研究揭示了青龙-上营-洒河桥-马兰峪为高压麻粒岩带,记录了ITD型PTt轨迹,与NNW-NW向SSE-SE方向逆冲推覆构造相伴生;而三屯营-太平寨高温麻粒岩带,记录了IBC型PTt轨迹,与锦州-兴城-安子岭-界岭口-太平寨-三屯营伸展-底劈构造带相伴生.综合分析表明冀东-辽西太古宙晚期的构造-岩浆活动形成于热造山带型俯冲-弧后伸展到碰撞隆升的侧向增生动力学过程.      

辽北开原地区新太古代变质深成岩LA-ICP-MS 锆石U-Pb 年龄及地球化学特征

辽北开原地区新太古代变质深成岩位于华北板块北缘陆缘活动带东段,主要岩性为二长花岗质片麻岩、花岗闪长质片麻岩和英云闪长质片麻岩,其中英云闪长质片麻岩LA-ICP-MS锆石207Pb/206Pb年龄加权平均值为2489.6±9.1 Ma,为新太古代。新太古代变质深成岩属高钾钙碱性-钾玄岩,准铝-过铝质岩石系列,轻稀土元素较富集,重稀土元素相对亏损,具有下地壳或太古宙沉积岩部分熔融形成的特征。通过岩石学、岩石地球化学和构造环境及就位机制分析,结合邻区构造演化研究,认为辽北开原地区变质深成岩岩浆来自较浅的基性古陆壳局部熔融。大地构造位置可能处在洋壳与陆壳的接触带,说明新太古代清河断裂附近可能出现陆壳碰撞增生活动。闪长质-石英闪长质-花岗闪长质-二长花岗质片麻岩体现了陆壳经历长时间的增生、造陆活动,已由早期的基性陆壳向现今的硅铝质陆壳转变。     

甘肃北山勒巴泉南一带新元古代变质侵入岩的地质地球化学特征及成因探讨

在甘肃北山勒巴泉一带赋存一套变质侵入岩。岩性主要为闪长质片麻岩、石英闪长质片麻岩、英云闪长质片麻岩、花岗闪长质片麻岩及二长花岗质片麻岩。Rb-Sr全岩等时线定年获得似斑状中细粒花岗闪长质片麻岩年龄值727±50Ma,锆石Pb-Pb定年获得中细粒花岗闪长质片麻岩年龄值766±49Ma,结合其与围岩的接触关系及强变形变质特征,形成时代为南华纪中晚期。其岩石地球化学特点为:岩石A12O3CaO+Na2O+K2O,A/CNK=1.30~1.38,属过铝质类型;σ=2.08~3.78,NK/A=0.32~0.61,属钙碱性系列。在微量元素组成上,富集LREE和大离子亲石元素(LILE),而亏损HREE、高场强元素(Nb、Ta、Yb),Eu异常具弱—明显Eu负异常—弱的Eu正异常(δEu=0.24~1.20)。这些花岗岩类总体具有俯冲的构造背景,岩浆的产生可能与北山地区在新元古代末古陆壳裂解作用有关。     

吉林东部汪清县九三沟金矿区石英闪长玢岩U-Pb年代学和地球化学特征

九三沟金矿区石英闪长玢岩在火山盆地内呈脉状或岩株状产出,与金矿化空间上密切伴生。本文通过岩石地球化学和LA-ICP-MS锆石U-Pb年代学研究,讨论了石英闪长玢岩的成因、源区和构造背景,厘定了成岩时代。研究表明,九三沟石英闪长玢岩属于钙碱性、过铝质系列岩石,富集大离子亲石元素(Ba、Sr)、活泼的不相容元素Th、U和轻稀土元素,亏损高场强元素Ta、Nb、Ti和重稀土元素。岩石的Nb/Ta、La/Nb、Th/La比值都显示其具壳源特征,在Al_2O_3-MgO-FeO_t和R1-R2判别图解上均表现为活动大陆边缘岩浆岩特征。石英闪长玢岩LA-ICP-MS锆石U-Pb年龄为104.2±1.4 Ma,MSWD=0.17,为早白垩世晚期(燕山晚期),形成于太平洋板块斜向俯冲引起的东亚大陆走滑伸展的构造环境。而吉黑东部中生代浅成低温热液成矿作用与该期钙碱性–碱性火山岩–浅成浅成侵位活动密切相关,因此早白垩世晚期的火山机构和浅成钙碱性–碱性侵入体是吉黑东部中生代浅成低温热液的找矿目标。     

内蒙古固阳地区角闪石等矿物分离结晶形成的新太古代TTG片麻岩——来自元素地球化学和热力学模拟的证据

内蒙古固阳地区存在大量的新太古代末期(石英)闪长质-英云闪长质-奥长花岗质-花岗闪长质(DTTG)片麻岩组合。LA-ICP-MS锆石U-Pb同位素测年得到了石英闪长质片麻岩和英云闪长质片麻岩的结晶年龄分别为(2 504±11)和(2 514±7)Ma,在石英闪长质片麻岩中同时得到了约2.6 Ga的继承锆石年龄。这些石英闪长质(D)片麻岩具有相对较低的w(SiO₂)(62.08%～62.62%)和Sr/Y值(23.3～39.8),w(MgO)(2.08%～3.06%)和w(TFe₂O₃)(5.43%～6.01%)相对较高,不具有或具有弱的Eu负异常(Eu/Eu^*为0.91～0.98),轻、重稀土元素分异相对不明显((La/Yb)_N为7.59～21.60),显示岛弧钙碱性岩石的地球化学特征。结合其锆石Hf同位素组成,本文认为其形成于相对低压较浅层次古老下地壳的部分熔融,同时有幔源熔体的加入。固阳新太古代末期英云闪长质-奥长花岗质(TT)片麻岩则显示较高的w(SiO₂     

黑龙江先锋北山金矿区花岗闪长斑岩和石英闪长玢岩年代学及地质意义

先锋北山金矿区内侵入脉岩为花岗闪长斑岩和石英闪长玢岩。花岗闪长斑岩具有高硅、富碱、富钙和贫镁等特征;轻稀土元素(LREE)相对富集,重稀土元素(HREE)相对亏损,无明显铕异常;富集大离子亲石元素(LILE)Rb、Th、K,亏损高场强元素(HFSE)Nb、Ta、P、Ti等,地球化学特征显示其属于过铝质钙碱性I型花岗岩。矿区石英闪长玢岩具有富碱、富镁和贫磷等特征,轻稀土元素(LREE)相对富集,重稀土元素(HREE)相对亏损,无铕异常;富集大离子亲石元素(LILE)Rb、Th,K等,亏损高场强元素(HFSE)Nb、Ta、P、Ti等。地球化学特征显示其属于准铝质高钾钙碱性岩石。花岗闪长斑岩及石英闪长玢岩的La--ICP--MS U--Pb同位素测年结果分别为128.3±2.6 Ma和113.2±1.7 Ma,为早白垩世。结合完达山地区地质资料,认为先锋北山花岗闪长斑岩和石英闪长玢岩是古太平洋板块构造体制由挤压变为伸展背景下的产物。     

内蒙古大青山北麓蓝晶石榴长英质片麻岩的发现:岩相学、地球化学和锆石SHRIMP定年

最近1:5万地质填图发现,在华北克拉通西部阴山地块西乌兰不浪地区的高级变质杂岩中,存在一套由蓝晶石榴长英质片麻岩、石墨蓝晶石榴长英质片麻岩、石墨石榴长英片麻岩和石榴蓝晶石英岩构成的岩石组合(蓝晶石榴长英质片麻岩组合).它们以构造残片形式产于由太古宙兴和岩群和紫苏石英闪长质-紫苏斜长花岗质-紫苏花岗质片麻岩(狼牙山片麻岩...     

吉林延边地区新田石英闪长岩U-Pb年代学与岩石地球化学研究

对延边地区新田石英闪长岩进行锆石U-Pb年代学、岩石地球化学分析。获得石英闪长岩LA-ICP-MS锆石U-Pb加权平均年龄为139±2 Ma,属早白垩世。岩石地球化学特征表现为过铝质高钾钙碱性;稀土元素总量较低,轻稀土元素相对富集、轻重稀土分馏较明显,较弱的负Eu异常,大离子亲石元素(Rb、Ba、Sr)与活泼的不相容元素(U、Th)富集,高场强元素(Nb、Ta、P、Zr、Hf、Ti)亏损,微量元素比值总体接近地壳平均值,反映岩浆源区为下地壳。结合地球化学特征与区域构造演化背景,认为新田地区石英闪长岩岩体形成于与太平洋板块俯冲相关的活动大陆边缘环境。早白垩世早期是区内一个较重要的俯冲阶段,中酸性岩浆侵位活动较为发育。     

北京四合堂花岗质杂岩的两种演化趋势

北京密怀隆起西部的石城片麻岩、皂树片麻岩和云蒙山北部的片麻状花岗闪长岩是太古代同源岩浆演化形成的古深成侵入体,本文称之为四合堂花岗质杂岩。该杂岩中的石城片麻岩,皂树片麻岩的闪长质、石英门长质片麻岩—英云间长质片麻—脉状的奥长花岗岩构成了英云间长岩—奥长花岗岩演化趋势,片麻岩中的石英闪长质片麻岩与花岗间长岩—二长花岗岩构成了钙碱性演化趋势。这两个演化趋势是在不同的条件下分离的矿物相不同所致。     

冀东三屯营地区片麻岩的早太古宙全岩年龄

冀东三屯营地区麻粒岩相片麻岩由三组中酸性岩石组成。三组片麻岩Pb-Pb全岩等时线年龄为。三组片麻岩也各给自出了早太古宙年龄。岩石的这一年龄,是麻粒岩相变质过程中U和Th亏损之后发生均匀化的结果,因而表明麻粒岩相的变质作用结束于3563Ma之前。岩石在3563～2500Ma期间处于角闪岩相的环境。文中还给出了全岩Rb-Sr同位素的年龄成果,为2500～2800Ma。     

Two types of Precambrian high-grade metamorphism, Inner Mongolia, China

Abstract Archaean and Proterozoic granulite facies complexes of Inner Mongolia differ in lithological association, tectonic style, mineral assemblage and metamorphic P–T path. A nearly isobaric cooling path for Archaean high-grade metamorphic rocks is suggested by reaction textures and geothermobarometry. Early Proterozoic metamorphic rocks show nearly isothermal decompression. Archaean metamorphism may have been caused by magmatic accretion, whereas early Proterozoic metamorphism suggests a major continental thickening event followed by exhumation.     

The Narryer Gneiss Complex of the Yilgarn Block, Western Australia: a segment of Archaean lower crust uplifted during Proterozoic orogeny

The Narryer Gneiss Complex of the Yilgarn Block is a key segment of the Western Australian Precambrian Shield. It is a regional granulite facies terrain comprised of predominantly quartzo-feldspathic gneisses derived from granitic intrusions c. 3.6–3.4 Ga old. Granulite facies metamorphism occurred c. 3.3 Ga ago, and conditions of 750–850°C and 7–10 kbar are estimated for the Mukalo Creek Area (MCA) near Errabiddy in the north. The P–T path of the MCA has been derived from metamorphic assemblages in younger rocks that intruded the gneisses during at least three subsequent events, and this path is supported by reaction coronas in the older gneisses. There is no evidence for uplift immediately following peak metamorphism of the MCA, and a period of isobaric cooling is inferred from the pressures recorded in younger rocks. Pressures and temperatures estimated from metadolerites, which intruded the older gneisses during ‘granite–greenstone’tectonism at about 2.6 Ga and during early Proterozoic thrusting show that the Errabiddy area remained in the lower crust, although it was probably reheated during the younger events. Isothermal uplift to upper crustal levels occurred at c. 1.6 Ga ago, and was followed by further deformation and patchy retrogression of high-grade assemblages. The effects of younger deformation, cooling and reheating can be discerned in the older gneisses, but as there has been no pervasive deformation or rehydration, the minerals and microstructures formed during early Archaean granulite facies metamorphism for the most part are retained. The MCA remained in the lower crust for about 1700 Ma following peak metamorphism and some event unrelated to the original metamorphism was required to exhume it. Uplift occurred during development of the Capricorn Orogen, when some 30–35 km were added to the crust beneath the Errabiddy area. The recognition of early Proterozoic thrusting, plus crustal thickening, suggests that the Capricorn Orogen is a belt of regional compression which resulted from convergence of the Yilgarn and Pilbara Cratons.     

A basaltic-ferrobasaltic granulite association,Oonagalabi gneiss complex,Central Australia: magmatic variation in an Early Proterozoic rift

Extremely fractionated basaltic to ferrobasaltic amphibolites and granulites comprise two spatially associated mafic tholeiitic suites (?deformed sills) within the Early Proterozoic Oonagalabi basement gneiss complex, Harts Range, Central Australia. The metatholeiites are characterised by high to very high FeO, TiO₂ and P₂O₅ contents, and variable depletion in CaO and Al₂O₃. Despite similar Zr/Nb ratios, the rocks from the two suites show different degrees of enrichment in LREE and other “immobile” incompatible elements. The basaltic melts which were parental to the two mafic suites were not comagmatic and the rocks cannot be related simply by fractionation of realistic assemblages of low-pressure fractionating phases. The data suggest that primary basaltic liquids for the two suites were derived by different degrees of partial melting from essentially similar undepleted mantle source regions. Clinopyroxene in the residual mantle assemblage controlled the composition of the segregating melt at lower degrees of melting. The ferrobasaltic compositions imply long residence times for the basaltic magmas in shallow-level differentiating tholeiitic sills and/or magma chambers in a mature propagating rift environment. High-grade (granulite facies) metamorphism, and subsequent restricted metasomatic reequilibration of the mafic rocks with interlayered migmatitic and quartzofeldspathic gneisses, have affected only abundances of certain highly-smobile elements (e.g. K₂O and Rb), resulting in the partial disruption of inter-element correlations. However, the geochemical data do not indicate any large-scale depletion of large ion lithophile elements (LILE) in the Oonagalabi gneiss complex.     

胶东早白垩世中-酸性脉岩造岩矿物微区地球化学特征研究

胶东地区广泛发育早白垩世中-酸性脉岩群,但是其成因演化及成岩地质背景至今仍存在诸多争论。本文利用电子探针(EMPA)与激光剥蚀电感藕合等离子质谱(LA-ICP-MS)技术分析了胶东早白垩世石英闪长脉岩与闪长脉岩中主要造岩矿物(斜长石和黑云母)的主、微量元素组成;并结合岩石地球化学特征,对两者的岩浆源区和岩浆演化进行了研究探讨。石英闪长脉岩与闪长脉岩中黑云母低于检测线的Ca O含量与斜长石主量元素之间良好的线性关系指示两者为未受到后期变质作用影响的原生矿物,进一步说明胶东中生代石英闪长脉岩与闪长脉岩岩浆形成后,在上涌成岩过程中未受到变质作用的影响。石英闪长脉岩中壳源黑云母矿物成分基本一致的,以及斜长石正环带中核边部线性变化的An值与Fe、Mg、Sr、Ba等不相容元素特征指示石英闪长脉岩源于华北克拉通东部古老的加厚下地壳部分熔融作用,并在岩浆演化早期和晚期有一定幔源镁铁质岩浆混入,整个岩浆演化过程并未受到大气、俯冲、变质流体混入或构造作用的影响。闪长脉岩中黑云母矿物较大的Fe2+/(Fe2++Mg)比值范围,Al含量与结晶压力高度正相关以及斜长石中不相容元素特征指示本次研究中胶东闪长脉岩源自俯冲的板片来源的流体或沉积物混入所形成富集岩石圈地幔源区。胶东早白垩世石英闪长脉岩与闪长脉岩形成的大地构造动力学背景为古太平洋板俯冲-回撤引起热-机械侵蚀,进而导致岩石圈地幔减薄。在此情况下软流圈地幔上涌加热导致胶东富集岩石圈地幔部分熔融形成地幔熔体。这些幔源熔体经历分离结晶形成早白垩世闪长脉岩。此外,幔源镁铁质岩浆持续加热导致加厚下地壳部分熔融,形成了石英闪长脉岩。     

桐柏秦岭岩群的两类变质作用

本文重点对河南桐柏地区的秦岭岩群进行了观察与研究,根据野外地质、岩相关系及同位素测年资料,提出该区秦岭岩群具有明显不同的两类变质作用,一是较早期的高温麻粒岩相变质作用,以包体或长透镜群、甚至巨型条块状局限于中部郭庄组的花岗质片麻岩之中。根据伟晶岩、片麻岩及麻粒岩锆石年龄的综合限定,该变质作用的时间可能为~498Ma,多数人主张的445~430Ma的麻粒岩相变质年龄实际上是早期锆石被后期岩浆或变质事件引起的同位素体系重启年龄。另一种是相对晚期的角闪岩相变质作用,变质程度以角闪岩相为主,局部达高角闪岩相,没有任何早期高温或高压变质的残留迹象,形成秦岭岩群中主导类型的变质作用。同样,采用伟晶岩及有关片麻岩和麻粒岩中锆石测年限定,角闪岩相变质时间可能为~472Ma。高温麻粒岩的产出具有其特殊机制,大量的花岗质岩浆侵位过程中把地壳深部的高温麻粒岩裹挟上升至浅部层次,随后一起遭受区域上的角闪岩相变质作用。     

内蒙古大青山地区早前寒武纪再造岩系及再造作用

在内蒙古大青山地区存在再造太古宙基底，它经历了太古宙麻粒岩相变质作用和早元古宙角闪岩相－麻粒岩相的再造作用，再造太古宙基底岩石即为再造岩系，它是一套混合岩化变晶糜棱岩。再造岩系中混合岩化作用与再造作用同时，亦受韧性剪切变形变质作用控制。     

Major and trace element patterns established during retrogressive metamorphism of granulite-facies gneisses,NW Scotland

A detailed study of geochemical changes associated with the retrogressive metamorphism of granulite-facies gneisses of the Lewisian Complex of NW Scotland has been made, using nearly 250 gneisses analysed for 24 major, minor and trace elements. The gneiss samples have been divided into 3 groups: (1) granulite facies, (2) granulite facies retrogressed to amphibolite facies but remaining undeformed, and (3) retrogressed (amphibolite-facies) gneisses deformed in shear zones. Element distributions within these groups have been examined using correlation coefficients, and have been compared and tested for significance using Student's t and Fisher z statistics. It is shown that the process of retrogression involved considerable large-scale chemical equilibration. Major-element pairs show marked increases in correlation during retrogression, reflecting considerable reordering of elements into one or other of the main amphibolite-facies minerals: hornblende, plagioclase and (minor) biotite. These correlations are enhanced, but otherwise unchanged, in the deformed gneisses. The retrogressed gneisses have a much more constant Fe/Mg ratio and a more uniform plagioclase composition, while there is a strong correlation between Fe³⁺ and Fe²⁺ throughout the area studied. Trace elements, by contrast, mostly show a significant loss of correlation during retrogression, although Cr and Ni are exceptions. Retrogression occurred as a result of widespread introduction of hydrous fluids up vertical structures in the gneiss complex during the Early Proterozoic. These fluids allowed considerable metasomatic redistribution of elements within the complex as the whole-rock compositions adjusted to the new mineralogy. Throughout the North Atlantic Archaean Craton there is a close association between retrogression of high-grade gneisses and basic magmatism in the form of dyke swarms. It is suggested that the two may be connected, and that the fluids causing retrogression are mantle-derived.     

Crustal contamination as an indicator of the extent of early Archaean continental crust: Pb isotopic evidence from the late Archaean gneisses of West Greenland

Ph isotopic analyses are reported for 119 samples of late Archaean (ca. 3000-2800 Myr) calc alkaline orthogneisses and associated anorthosites from southern West Greenland. Over most of the area. $\text{Pb}\text{Pb}$ whole rock isotope systematics indicate derivation of the magmatic precursors of the gneisses and anorthosites from a source region with a typically mantle-type $\text{U}\text{Pb}$ ratio (μ₁ value of 7.5) at. or shortly before, ca. 3000-2800 Myr ago. In contrast, in the Godthaabsfjord region, late Archaean Nûk gneisses and associated anorthosites were emplaced into or through early Archaean (ca. 3700 Myr) Amîtsoq gneisses, and crystallised with variable proportions of two isotopically distinct types of Pb which commenced their respective crustal developments at ca. 3000-2800 Myr and at ca. 3700 Myr ago. Isotopic and other geochemical constraints demonstrate that Nûk gneisses and their temporal equivalents were not produced by reworking or melting of Amîtsoq gneisses. Mixing of early and late Archaean Pb results from contamination of the magmatic precursors of Nûk gneisses and anorthosites (characterised by mantle-type Pb at time of emplacement) with ancient, unradiogenic Pb derived from ca. 3700 Myr-old Amîtsoq-type continental crust invaded by the Nûk magmas. The contaminant is considered to be a trace-element enriched fluid phase released from dehydrating older continental crust during progressive burial and heating by emplacement of calc alkaline magmas in the late Archaean ‘accretion differentiation superevent’. This was followed by mixing of the released fluids with younger Nûk magmas.Pb isotopic compositions of late Archaean gneisses and anorthosites outside the Godthaabsfjord region provide no evidence for the presence of early Archaean Amîtsoq-type continental crust in southern West Greenland in areas more than a few tens of km outside the known outcrop of Amîtsoq gneisses. We suggest that early Archaean crust does not exist at depth in late Archaean areas with undisturbed Pb-isotope systematics, either in Greenland or elsewhere in the North Atlantic craton.Pb-isotope evidence for crust magma interaction, involving selective extraction of certain trace elements by a fluid phase from wall rock and subsequent mixing between magma and contaminant fluid, provides a powerful tool for detection, sub-surface ‘mapping’, and geochronological and geochemical characterisation of deep, ancient continental crust.