内蒙古喀喇沁早白垩世橄辉云煌岩岩筒

探寻地幔物质上涌的通道口，是大陆岩石圈研究所感兴趣的，它将为人们提供更多的岩石圈深部信息。本文报道的是在内蒙古喀喇沁黑龙潭火山颈中发现的橄辉云煌岩，其K-Ar同位素年龄为124Ma。火山活动明显受到中生代构造活动控制。火山岩的元素地球化学特征反映岩浆来自富集地幔，在源区存在陆壳的混染作用。     

北山南部玻基纯橄岩的发现及其岩石学和地球化学特征

北山南部地区,二叠纪闪长岩岩体的西北部,发现玻基纯橄岩[Vitric Dunite;Meimechite,Меймечит;中文亦有音译为麦美奇岩]和蚀变玻基纯橄岩。①玻基纯橄岩样品呈致密块状,浅灰绿色,表面可见清楚的粒状斑晶矿物和黑色胶结物,具发丝一样的小条带。蚀变玻基纯橄岩样品呈致密块状,深黑色,局部具细小条带。显微镜下,前者主要矿物橄榄石为斑状结构;后者主要矿物橄榄石多蚀变为蛇纹石,表现为变余斑状结构,斑晶是蛇纹石化的橄榄石假像。基质均为玻璃质结构。②X射线衍射分析表明:橄榄石为镁橄榄石[forsterite,(Mg_(1.8)Fe_(0.2))(SiO_4)],蛇纹石为利蛇纹石{lizardite,(Mg,Al)_3[(Si,Fe)_2O_5](OH)_4}。③电子探针检测,磁铁矿呈细条纹状,基质矿物有绿泥石、绿帘石、黝帘石、角闪石、钛铁矿、褐铁矿、镍黄铁矿、斜长石、尖晶石、金云母等。④样品岩石化学分析,主元素氧化物的含量分别为,SiO_2为36.40%～37.29%,Al_2O_3为2.61%～4.70%,TiO_2为0.058%～0.22%,MgO为33.30%～35.36%,Fe_2O_3+FeO为10.51%～12.89%,Na_2O+K_2O为0.03%～0.14%,为超铁镁质超基性喷出岩。Mg#为83.5～86.5,δSr为1.14～4.61,Sr/Y为5.70～42.74。稀土元素∑REE为2.18～9.71,δEu为0.68～2.43,La/Yb为0.90～10.00。微量元素和稀土元素具有原始地幔的岩石化学特征。⑤原始岩浆可能经历了结晶分异过程,并可能在裂谷构造环境形成。⑥本文发现的玻基纯橄岩,类似于典型的西伯利亚麦美奇河流域和勘察加半岛的低钛"麦美奇岩"。玻基纯橄岩在该地区的发现,为该地区岩浆的形成和演化研究及铜镍矿的找矿和勘探工作,提供了重要的岩石学依据。     

纯橄岩捕虏体在闪长质岩浆中的存留时间尺度:Mg-Fe扩散剖面模拟研究

我国华北板块中-东部的中生代高镁闪长岩中含有许多超基性岩捕虏体.超基性岩与低镁的中酸性壳源岩浆之间发生反应,形成了高镁闪长岩现有的成分特征.然而,对超基性岩捕虏体在高温岩浆中的存留时间尺度的了解还很少.本文对鲁西铁铜沟和河北邯邢地区高镁闪长岩中纯橄岩捕虏体中保存的Mg-Fe扩散成分环带进行了数值模拟研究,结果表明,纯橄...     

安康双龙桥碱性辉长杂岩中磷灰石和榍石的矿物成分研究

X射线衍射分析和化学成分研究表明,磷灰石为氟磷灰石,榍石成分中存在着的主要类质同象替代是(Fe~(3+)、Al)+(F,OH)~-=Ti~(4+)+O~(2-)。磷灰石和榍石是碱性辉长岩的REE、Ba、Zr等微量元素的主要载体;它们是在较高氧逸度的条件下结晶的。磷灰石的Sr同位素特征说明形成双龙桥碱性辉长杂岩的物质来源于上地幔。     

一维到三维密度分布函数及其可视化在大数据分析中的应用——以苦橄质玄武岩等为例

提出不同维度的密度分布函数的计算方法和可视化方案,以解决不同数量级和不同测量误差的岩石样本数据分析对比困难的问题。通过SiO_2、全碱和MgO指标的三维密度分布函数和t-分布随机邻域嵌入可视化方法对GEOROC和PETDB数据库进行发掘,发现大洋岩(oceanite)和富辉橄玄岩(ankaramite)与苦橄质玄武岩(basalt, picritic)成分相近,而铁质苦橄岩(picrite,ferro)与侵入的橄榄辉长岩和苦橄岩(picrite)成分相似。利用二维密度分布函数和可视化技术,对比分析了不同岩石在TAS图解和硅镁图上的数据分布状态和数据集中核心区域。发现总体分布上,更富镁的苦橄岩的SiO_2含量高于苦橄质玄武岩,超基性的苦橄岩(picrate)核心区域主要分布在TAS图解的B区,这与以SiO_2=45%划分基性岩和超基性岩界线的观点矛盾。     

河北省东坪金矿钾质蚀变岩中的两期锆石年代学研究及意义

河北省崇礼县东坪金矿位于水泉沟碱性杂岩体内, 金矿石包括低硫化物石英脉型和钾质蚀变岩型两种类型。本次工作我们对采自东坪金矿70号脉深部的钾质蚀变岩中的锆石进行了成因矿物学和成矿年代学研究, 结果表明, 矿脉中的锆石可以分成岩浆锆石和热液锆石两种成因类型。岩浆锆石具有自形到半自形结构,在背散射电子图像(BSE)上呈暗灰色, 在阴极发光图像(CL)上具有明显的岩浆振荡环带, 锆石U-Pb加权平均年龄为382.8±3.3 Ma。热液锆石多呈不规则状充填在岩浆锆石中, 在BSE图像上呈亮灰白色, 在CL图像上为深黑色(无阴极发光), 锆石的Th、U含量和Th/U比值较岩浆锆石明显增高, 锆石U-Pb加权平均年龄为140.3±1.4 Ma, 说明东坪金矿形成于早白垩世。140 Ma成矿年龄的发现, 为认识河北省东坪金矿的成矿时代提供了新证据, 具有重要的地质意义。     

Nanometric modulation in apatite

Brazilian gem-grade apatite (B-Ap) consists of contiguous fluorine-enriched (host-Ap) domains (∼400 nm), interspersed by isolated domains (∼200 nm) of a chlorine-enriched (guest-Ap) apatite in a long period compositional modulation. Within each of these domains a third modulation differentiating Si- and S-rich nanocrystals (5–10 nm) of ellestadite (El-Ap), a monoclinic apatite variety, developed possibly during a short term high temperature event. These unexpected miscibility gaps may be useful geothermometric tools, and could prove decisive for enhancing the properties of apatites used as heterogeneous catalysts and fuel–cell electrolytes.     

Diffusion of helium in zircon and apatite

Diffusion of helium has been characterized in natural zircon and apatite. Polished slabs of zircon and apatite, oriented either normal or parallel to c were implanted with 100 keV ³He at a dose of 5 × 10^{15 3} He/cm². Diffusion experiments on implanted zircon and apatite were run in Pt capsules in 1-atm furnaces. ³He distributions following experiments were measured with Nuclear Reaction Analysis using the reaction ³He(d,p)⁴He. For diffusion in zircon we obtain the following Arrhenius relations:

Although activation energies for diffusion normal and parallel to c are comparable, there is marked diffusional anisotropy, with diffusion parallel to c nearly 2 orders of magnitude faster than transport normal to c. These diffusivities bracket the range of values determined for He diffusion in zircon in bulk-release experiments, although the role of anisotropy could not be directly evaluated in those measurements.In apatite, the following Arrhenius relation was obtained over the temperature range of 148–449 °C for diffusion normal to c:

In contrast to zircon, apatite shows little evidence of anisotropy. He diffusivities obtained in this study fall about an order of magnitude lower than diffusivities measured through bulk release of He through step-heating, and within an order of magnitude of determinations where ion implantation was used to introduce helium and He distributions measured with elastic recoil detection.Since the diffusion of He in zircon exhibits such pronounced anisotropy, helium diffusional loss and closure cannot be modeled with simple spherical geometries and the assumption of isotropic diffusion. A finite-element code (CYLMOD) has recently been created to simulate diffusion in cylindrical geometry with differing radial and axial diffusion coefficients. We present some applications of the code in evaluating helium lost from zircon grains as a function of grain size and length to diameter ratios, and consider the effects of “shape anisotropy”, where diffusion is isotropic (as in the case of apatite) but shapes of crystal grains or fragments may depart significantly from spherical geometry.     

Modelling the formation of fission tracks in apatite minerals using molecular dynamics simulations

We introduce a simple method to simulate the “ion explosion spike” mechanism of fission track formation within the framework of classical molecular dynamics. The method is applied to six apatite compositions and the resulting tracks are compared with each other as well as with the damage produced by another mechanism—the “Displacement spike”. In contrast to experimentally observed tracks, the radii of simulated tracks are not dependent on their direction in the crystal. Since the simulations model accurately the elastic response of apatites, this suggests that the experimentally observed difference in track radii for tracks along different crystal directions is not entirely caused by anisotropy in the elasticity of apatite. We suggest that anisotropy in the interactions between the electric fields of fission fragments and the crystal ions is a major factor in the final radii of fission tracks. In fluorapatite, the simulations also reveal the formation of small clusters of fluorite-like material in the core of the fission track, a phenomenon which has yet to be confirmed experimentally.

磷灰石低温热年代学在地学中的应用

磷灰石裂变径迹(AFT)和(U-Th)/He(AHe)是目前研究地壳表层(<5 km)中构造演化与气候驱动相互作用且记录超过1 Ma热历史最有效的手段之一。AFT和AHe这两种方法对低温(40 ℃~120 ℃)敏感, 能够较精确地获得地下1~4 km处的构造-热演化信息, 可用于解决地质体定年、盆地热历史、造山带演化、热液矿床及含油气盆地中生排烃与运移时限等诸多地质问题。本文系统归纳了这两种方法的原理、定年影响因素、年龄-高程法及应用中容易混淆的概念等内容, 并以北美西部大盆地卡林型金矿床、美国阿第伦达克山脉东部马西山、塔里木盆地早古生代的热历史演化为例, 详细阐述了它们的应用过程。为有效、合理地将磷灰石低温年代学应用于地学, 在具体的应用过程须注意以下问题: 充分把握研究区的构造背景, 根据研究目的合理设计采用剖面, 综合使用多种测年方法, 以及采用合理的数据处理、分析方法解释磷灰石低温年代学年龄数据。     

江苏青龙山磷灰石中出溶体的初步研究

最近的研究证实，在大别-苏鲁超高压变质带的多硅白云母榴辉岩和超基性岩中的磷灰石矿物内普遍发育有针柱状出溶晶体，初步研究证明这些出溶晶体多为各种硫化物：如黄铁矿、黄铜矿等。本文重点研究苏鲁青龙山地区的多硅白云母榴辉岩和退变榴辉岩中磷灰石内的出溶晶体，通过扫描电镜、电子探针和X-光能谱的线扫描分析，确认这些出溶晶体是铜的硫化物，并根据无标样定量的分析结果初步推测有可能是CuS2晶体。目前已知的CuS2晶体都是在高温高压（T=700-1000℃和P=4．5-5．0GPa）条件下人工合成的。这样的温压条件与青龙山榴辉岩的超高压变质条件是吻合的。在磷灰石中能保存超高压的硫化物，可能是由于磷灰石自身的稳定性和化学惰性。因此推测在超高压变质作用中，磷灰石晶体中易于保存硫化物出溶体与石榴石和绿辉石中易于保存柯石英和金刚石的作用相类似。     

磷灰石中磁黄铁矿出溶结构的发现

中国东部苏鲁地区(江苏赣榆)出露大理岩-榴辉岩块体,其菱镁矿大理岩中保存的白云石分解结构表明地壳物质俯冲深度达到-200公里。在与该大理岩共生的榴辉岩中,我们发现了磷灰石的磁黄铁矿出溶结构。磷灰石是该榴辉岩的主要副矿物,其自形程度较高,与石榴石共生。样品中几乎所有磷灰石均发育出溶结构,至少存在两组相互垂直的出溶棒,它们各自严格沿同一个方向分布。出溶棒形状规则,宽度相近(<1μm),但长度变化大(5-50μm)。利用高分辨能谱仪测定其能谱,结果表明,出溶棒主要由Fe和S两种元素组成,但不能准确地确定其Fe/S比值。我们把这种出溶棒初步确定为磁黄铁矿(Fe1-xS)。磷灰石由于含大量稀土元素和挥发性组分如OH、F、Cl等以及我们所观察到的S,它的深循环因此可能对地球的水、硫以及其它挥发性组分的全球平衡具有重要影响。本文报道的磷灰石中磁黄铁矿出溶结构为深入探讨这个基本科学问题提供了一个新的突破口。     

苏鲁榴辉岩中磷灰石的矿物学和微量元素地球化学

磷灰石是榴辉岩中最常见的副矿物之一,见证了高压-超高压变质岩从原岩形成、俯冲和折返所伴随的物理化学过程。为进一步揭示苏鲁超高压榴辉岩经历的物理和化学过程,我们对取自中国大陆科学钻探工程（CCSD）主孔岩心和苏北地表露头榴辉岩中的磷灰石进行了详细的岩相学分析和LA-ICP-MS原位微量元素分析。分析结果表明,在苏鲁榴辉岩中,磷灰石绝大多数是在超高压变质作用阶段重结晶生长的。未受退变质影响的磷灰石富含LREE和Sr元素,退变质作用促使磷灰石中活动性较强的LREE和Sr明显降低而HREE含量略微升高,并产生负Eu异常。磷灰石边部HREE的升高可能与折返过程中的升温作用和石榴子石分解有关,Eu负异常的产生可能还与退变质过程中发生了氧逸度f^O2的降低有关;结合前人对磷灰石中“出溶”现象的研究,提出榴辉岩磷灰石中的独居石“出溶体”很可能是磷灰石与富含NaCl和硅酸盐的退变质流体发生交代反应所致,磷灰石中硫化物“出溶体”的形成除了氧逸度降低的原因外,可能也与折返过程中发生的短期升温作用有关。超高压变质岩从进变质-峰期→早期退变质→角闪岩相退变质阶段,变质流体可能经历了氧化→还原→氧化状态的复杂变化。     

花岗岩类岩石成因的磷灰石微区地球化学和同位素示踪

花岗岩类岩石是大陆地壳最重要的组成部分,通常伴生金属矿产,其成因研究可用来探索大陆地壳的形成、演化及动力学机制,并指导矿产资源的勘探。花岗岩类岩石是由岩浆经过结晶分异、地壳混染和岩浆混合等复杂演化过程形成的,且其母岩浆通常来源于不同的岩浆源区。如何准确示踪岩浆源区性质和精细刻画岩浆演化、岩石成岩过程是花岗岩成因研究的关键。磷灰石作为花岗岩类岩石中常见的副矿物,其结晶历史时间长——贯穿整个岩浆演化阶段,且富含F、Cl等挥发分和Sr、REE等微量元素,其化学特征和同位素组成在示踪花岗岩岩浆源区和成岩过程方面有独特的优势。随着微区分析技术的发展,磷灰石的微区地球化学成分记录了寄主岩浆的成分及其变化过程,可从微观角度揭示花岗岩的成因。本文结合前人研究成果及作者近年来的相关工作,系统综述磷灰石微区地球化学研究的进展,探讨如何在岩相学观察的基础上利用磷灰石的结晶过程、微区成分环带和微区同位素组成示踪岩浆源区、岩浆演化和成岩过程,以期为探索花岗岩精细成岩过程提供有效示踪方法。

     

Cerium and Ytrium in apatite as records of magmatic processes: Insight into fractional crystallization,magma mingling and fluid saturation

Apatite is a versatile mineral crystallizing at different stages of silicic magma evolution. Its composition may record that of magma, but could also be affected by interaction with fluids. The focus of this study is the well-recognized magma mingling process that was previously detected using plagioclase composition and in this study complementary record is sought in apatite. The apatite was analysed in two dioritic enclaves (primitive and hybrid) and host quartz monzonite, which is an igneous rock emplaced at ca. 340 Ma in mylonitized Góry Sowie gneisses (NE Bohemian Massif). The apatite was analysed in-situ by microprobe that allowed for chemical characterization of different apatite populations in quartz monzonite and analyses of thin acicular apatite in the enclaves. Apatite population in the quartz monzonite was chemically distinct from that in both enclave types and characterized by higher Y and lower Ce contents, such values are usually typical for peraluminous magmas. As such, the apatite transfer from felsic to mafic magma should be well recorded in apatite composition, which was not the case. Monzonite apatite composition was not commonly observed in the hybrid enclave despite massive plagioclase transfer and only rare resorbed cores with low Ce and Y contents were present. However, such low Ce and Y cores crystalized at the latest stage of apatite crystallization in the quartz monzonite, whereas the plagioclase transfer was an early episode. Therefore, we conclude that apatite transfer was limited during mingling and the apatite composition in the quartz monzonite is best explained by an early Cl-Ce-rich fluid removal and then fractional crystallization, while apatite in the primitive enclave is affected only by fractional crystallization. Altogether, Ce and Y composition of apatite is a valuable tool to record diverse magmatic processes such as fluid removal and precipitation from fluid in addition to fractionation of different REE phases and should be further explored.     

Denudation history and landscape evolution of the northern East-Brazilian continental margin from apatite fission-track thermochronology

We reconstruct the history of denudation and landscape evolution of the northern East- Brazilian continental margin using apatite fission-track thermochronology and thermal history modeling. This part of the Brazilian Atlantic margin is morphologically characterized by inland and coastal plateaus surrounding a wide low-lying inland region, the Sertaneja Depression. The apatite fission track ages and mean track lengths vary from 39 ± 4 to 350 ± 57 Ma and from 10.0 ± 0.3 to 14.2 ± 0.2 μm, respectively, implying a protracted history of spatially variable denudation since the Permian at relatively low rates (<50 m My⁻¹). The Sertaneja Depression and inland plateaus record Permian-Early Jurassic (300–180 Ma) denudation that precedes rifting of the margin by > 60 Myrs. In contrast, the coastal regions record up to 2.5 km of Late Jurassic-Early Cretaceous (150–120 Ma) denudation, coeval with rifting of the margin. The samples from elevated coastal regions, the Borborema Plateau and the Mantiqueira Range, record cooling from temperatures above 120 °C since the Late Cretaceous extending to the Cenozoic. We interpret this denudation as related to post-rift uplift of these parts of the margin, possibly resulting from compressional stresses transmitted from the Andes and/or magmatism at that time. Several samples from these areas also record accelerated Neogene (<30 Ma) cooling, which may record landscape response to a change from a tropical to a more erosive semi-arid climate during this time. The inferred denudation history is consistent with the offshore sedimentary record, but not with evolutionary scenarios inferred from the recognition of “planation surfaces” on the margin. The denudation history of the northeastern Brazilian margin implies a control of pre-, syn- and post-rift tectonic and climatic events on landscape evolution.