闽北麻源群变质岩的流体包裹体研究：岩石抬升过程的p－T－t

根据闽北麻源群变质岩流体包裹体的世代关系和显微测温研究，获得了麻源群变质峰期之后抬升过程ｐ－Ｔ－ｔ轨迹，推测岩石遭受剪切变形事件的温压条件为ｐ＝８５￣１００ＭＰａ，Ｔ＝２６５￣２８５℃。本区流体演化早期以ＣＯ２为主，晚期以水溶液为主。     

Neocalamites rugosus Sze和Equisetites asperrimus Franke是同物异名

研究表明,斯行健(1956)建立的我国晚三叠世植物化石新种Neocalamites rugosus Sze和德国哈茨山脉考依波期的Equisetites asperrimus Franke是同物异名。Franke提定的种名有优先权,但属名鉴定有误。斯行健鉴定的属名正确,但其种名却是Franke名称的晚出异名。根据国际植物命名法规,两者应合并为一种,特定名为Neocalamites asperrimus(Franke),comb.nov.     

P–V–T equation of state of Ca3Al2Si3O12 grossular garnet

The thermoelastic parameters of synthetic Ca₃Al₂Si₃O₁₂ grossular garnet were examined in situ at high-pressure and high-temperature by energy dispersive X-ray diffraction, using a Kawai-type multi-anvil press apparatus coupled with synchrotron radiation. Measurements have been conducted at pressures up to 20 GPa and temperatures up to 1,650 K: this P, T range covered the entire high-P, T stability field of grossular garnet. The analysis of room temperature data yielded V _0,300 = 1,664 ± 2 ?³ and K ₀ = 166 ± 3 GPa for K^￠₀ K^{\prime}_{0} fixed to 4.0. Fitting of our P–V–T data by means of the high-temperature third order Birch–Murnaghan or the Mie–Grüneisen–Debye thermal equations of state, gives the thermoelastic parameters: (∂K _0,T /∂T) _P  = −0.019 ± 0.001 GPa K⁻¹ and α _0,T  = 2.62 ± 0.23 × 10⁻⁵ K⁻¹, or γ ₀ = 1.21 for fixed values q ₀ = 1.0 and θ ₀ = 823 (Isaak et al. Phys Chem Min19:106–120, 1992). From the comparison of fits from two different approaches, we propose to constrain the bulk modulus of grossular garnet and its pressure derivative to K _T0 = 166 GPa and K^￠_T0 K^{\prime}_{T0}  = 4.03–4.35. Present results are compared with previously determined thermoelastic properties of grossular-rich garnets.     

HTP21/c–C2/c phase transition and kinetics of Fe2+–Mg order–disorder of an Fe-poor pigeonite: implications for the cooling history of ureilites

A natural Ca-poor pigeonite (Wo₆En₇₆Fs₁₈) from the ureilite meteorite sample PCA82506-3, free of exsolved augite, was studied by in situ high-temperature single-crystal X-ray diffraction. The sample, monoclinic P2₁/c, was annealed up to 1,093°C to induce a phase transition from P2₁/c to C2/c symmetry. The variation with increasing temperature of the lattice parameters and of the intensity of the b-type reflections (h + k = 2n + 1, present only in the P2₁/c phase) showed a displacive phase transition P2₁/c to C2/c at a transition temperature T _Tr = 944°C, first order in character. The Fe–Mg exchange kinetics was studied by ex situ single-crystal X-ray diffraction in a range of temperatures between the closure temperature of the Fe–Mg exchange reaction and the transition temperature. Isothermal disordering annealing experiments, using the IW buffer, were performed on three crystals at 790, 840 and 865°C. Linear regression of ln k _D versus 1/T yielded the following equation: ln k_\textD = - 3717( ±416)/T(K) + 1.290( ±0.378);    (R² = 0.988) \ln \,k_{\text{D}} = - 3717( \pm 416)/T(K) + 1.290( \pm 0.378);\quad (R^{2} = 0.988) . The closure temperature (T _c) calculated using this equation was ∼740(±30)°C. Analysis of the kinetic data carried out taking into account the e.s.d.'s of the atomic fractions used to define the Fe–Mg degree of order, performed according to Mueller’s model, allowed us to retrieve the disordering rate constants C ₀ K _dis⁺ for all three temperatures yielding the following Arrhenius relation: ln( C₀ K_\textdis ⁺ ) = ln K₀ - Q/(RT) = 20.99( ±3.74) - 26406( ±4165)/T(K);    (R² = 0.988) \ln \left( {C_{0} K_{\text{dis}}^{ + } } \right) = \ln \,K_{0} - Q/(RT) = 20.99( \pm 3.74) - 26406( \pm 4165)/T(K);\quad (R^{2} = 0.988) . An activation energy of 52.5(±4) kcal/mol for the Fe–Mg exchange process was obtained. The above relation was used to calculate the following Arrhenius relation modified as a function of X _Fe (in the range of X _Fe = 0.20–0.50): ln( C₀ K_\textdis ⁺ ) = (21.185 - 1.47X_\textFe ) - \frac(27267 - 4170X_\textFe )T(K) \ln \left( {C_{0} K_{\text{dis}}^{ + } } \right) = (21.185 - 1.47X_{\text{Fe}} ) - {\frac{{(27267 - 4170X_{\text{Fe}} )}}{T(K)}} . The cooling time constant, η = 6 × 10⁻¹ K⁻¹ year⁻¹ calculated on the PCA82506-3 sample, provided a cooling rate of the order of 1°C/min consistent with the extremely fast late cooling history of the ureilite parent body after impact excavation.     

Hydrous olivine (Mg1? y? Fe2+y)2? x ?v x ? SiO4H2 x – a new DHMS phase of variable composition observed as nanometer-sized precipitations in mantle olivine

 An olivine grain from a peridotite nodule 9206 (Udachnaya kimberlite, Siberia) was investigated by TEM methods including AEM, HRTEM, SAED and EELS techniques. A previous study of the 9206 olivine sample revealed OH absorption bands in the IR spectrum and abundant nanometer-sized OH-bearing inclusions, of hexagonal-like or lamellar shape. Inclusions, which are several hundred nm in size, consist of 10 ? phase, talc and serpentine (chrysotile and lizardite). The lamellar (LI) and hexagon-like small inclusions of several ten nm in size (SI) are the topic of the present paper. AEM investigations of the inclusions reveal Mg, Fe and Si as cations only. The Mg/Si and Fe/Si atomic ratios are lower in the inclusions than in the host olivine. The Si concentration in the olivine host and both lamellar inclusions and small inclusions is the same. A pre-peak at 528eV was observed in EEL spectra of LI and SI, which is attributed to OH⁻ or Fe³⁺. From these data it is concluded that there is a OH⁻- or Fe³⁺-bearing cation-deficient olivine-like phase present. HRTEM lattice fringe images of LI and SI exhibit modulated band-like contrasts, which are superimposed onto the olivine lattice. Diffraction patterns (Fourier-transforms) of the HREM images as well as SAED patterns show that the band-like contrasts in HRTEM images of the inclusions are caused by periodic modulations of the olivine lattice. Three kinds of superperiodicity in the olivine structure such as 2a, 3a and 3c, were observed in SAED patterns. The corresponding olivine supercells labelled here as Hy-2a, Hy-3a and Hy-3c were derived. The M1-vacancies located in the (100) and (001) octahedral layers of the olivine lattice are suggested to form ordered arrays of planar defects (PD), which cause the band-like contrasts in HRTEM patterns as well as the superperiodicity in the SAED patterns. The vacancy concentrations as well as the chemical composition of Hy-2a, Hy-3a and Hy-3c olivine supercells were calculated using crystal chemical approaches, assuming either {(OH)^< _O−V^" _Me−(OH)^< _O}^↔, or {F e ^< _Fe −H _Me ^′}^↔ or {2F e ^< _Fe −V _Me ^"}^↔ point defect associates. The calculated theoretical compositions Mg_1.615Fe⁺² _0.135v_0.25SiO₄H_0.5 (Hy-2a) and Mg_1.54Fe²⁺ _0.12v_0.33SiO₄H_0.66 (Hy-3a and Hy-3c) are in a good agreement with the AEM data on inclusions. Hy-2a, Hy-3a and Hy-3c are considered to be a hydrous olivine with the extended chemical formula (Mg_1-yFe²⁺ _y)_2−xv_xSiO₄H_2x. The crystal structure of hydrous olivine is proposed to be a modular olivine structure with Mg-vacant modules. The crystal chemical formula of hydrous olivines in terms of a modular structure can be written as [MgSiO₄H₂] · 3[Mg_1.82Fe_0.18SiO₄] for Hy-2a, [MgSiO₄H₂] · 2[Mg_1.82Fe_0.18SiO₄] for Hy-3a and Hy-3c. Hydrous olivine is suggested to be exsolved from the olivine 9206, which has been initially saturated by OH-bearing point defects. The olivine 9206 hydration as well as the following exsolution of hydrous olivine inclusions is suggested to occur at high pressure-high temperature conditions of the upper mantle. Received: 15 January 2001 / Accepted: 2 July 2001     

黔东南Oryctocephalus indicus的分布及其意义

本文通过对黔东南两条新测剖面的整理、已有剖面的进一步挖掘和已有剖面的资料的整理,厘定出几个寒武系第三统底界附近有代表意义的三叶虫属种在这些剖面中产出层位。经过对比研究,认为Oryctocephalus indicus在黔东南分布广泛,个体清晰,层位稳定并延伸较长,可以作为很好的标准化石。     

秦岭商丹带沙沟糜棱岩带的显微构造及其(p)-T-t演化路径的再认识

对沙沟糜棱岩带的78个样品进行了显微构造与组构分析。石英以动态重结晶Ⅱ型条带为主,其C-轴组构型式为极密Ⅰ型,同时可见Ⅲ型石英条带残存。长石均显脆性碎裂变形,仅钾长石略具韧性变形。糜棱岩面理普遍绕过石榴石斑晶分布。存在多次后期脆性变形构造。这些显微构造与组构特征表明,该带糜棱岩化阶段处于中─高绿片岩相条件、并大致发生在晚白垩世以后。糜棱岩化阶段之前该带可能存在一个角闪岩相左行韧性剪切变形阶段。糜棱岩化阶段之后,该带直接进入脆性变形阶段。据此,笔者对前人有关沙沟糜棱岩带(p)-T-t演化路径提出修正意见。     

云南保山地区中-晚三叠世Budurovignathus及Pseudofurnishius牙形类动物群的发现及意义

Budurovignathus和Pseudofurnishius牙形类动物群是世界上具有重要地层研究价值且比较稀有的牙形类动物群,迄止目前,在滇西保山地区发现:Budurovignathus hungaricus(Kozur et Vigh)、B.mungoensis(Diebel)、B.aff.mungoensis(Diebel)or B.baoshanensis sp.nov.、B.diebeli(Kozur et Mostler)、Pseudofurnishius socioensis(Gullo et Kozur),P.murcianus(Van Den Boogaard)和Pseudofurnishius sp.A等重要的属种,本次发现,为云南保山地区中—晚三叠世地层提供有力的生物年代约束,拓展了三叠世牙形石生物带,同时也丰富了中国这两个牙形类动物群的资料。     

Beltanelloides podolicus 在中国上震旦统首次发现

Beltanelloidespodolicus可谓球形藻群体化石之最大者,压扁圆盘体直径3-30mm,呈炭质膜保存。与其一起出现的化石还有许多高级藻类和动物化石。它们的发现为扬子地台上震旦统与东欧地台文德期地层的对比又添一证据。     

有孔虫Pseudorbitoides属地理分布新知及其西藏新种

Pseudorbitoides是Dilly(1973),Gorsel(1978)等作者所划分的晚白垩世加勒比区有孔虫动物群的主要成员。在西藏南部所发现的Pseudorbitoides yini(sp.nov)及印度标本Pseudorbitoides ariyalurensis(Rao)分类位置的确定,使该属的地理分布范围大为扩大,也使对上述作者的晚白垩世全球大有孔虫动物地理区的划分进行修改更为必要。     

花岗岩三级分类刍议

花岗岩的性质主要受源区组成与源岩性质的制约,本文根据花岗岩与源区源岩平衡理论,提出花岗岩的三级分类方案。首先按照花岗岩的全球分布分为大洋系列花岗岩(OSG)和大陆系列花岗岩(CSG)两大类。其次,OSG系列按照构造环境分为3类：大洋中脊花岗岩(MORG)、洋岛花岗岩(OIG)、岛弧花岗岩(IAG);CSG则按照变质相不同分为5类：与榴辉岩相平衡的花岗岩,与麻粒岩相平衡的花岗岩,与低温角闪岩相平衡的花岗岩,与高温角闪岩相平衡的花岗岩和与低压高温角闪岩相平衡的花岗岩。再次,OSG按照构造环境进一步细分;CSG再按源岩地球化学性质分为钠质与钾质两个亚类。这一系统分类方案,不仅解决了花岗岩分类理论问题,还提出了从花岗岩时空分布反演变质岩源区特征问题,开辟了花岗岩与变质岩结合的新思路。     

黑龙江依兰地区蓝片岩的变质演化P-T-t轨迹

黑龙江省依兰地区出露了一套经高压变质形成的蓝片岩、云母片岩、长英质糜棱岩和少量超基性岩及大理岩并经历了强变形作用改造,一直被认为是佳木斯地块与其西侧松嫩地块碰撞拼贴所形成的缝合带产物。本次研究,通过岩相学与矿物化学分析,根据矿物组合的不同,识别出研究区内三种不同类型的蓝片岩;并获得了绿帘蓝闪石片岩(T=350~550℃,P=10~14kbar)、蓝闪霓辉石片岩(T=350~550℃,P=10~14kbar)和石榴石冻蓝闪石片岩(T=500~540℃,P=10~12kbar)的峰期变质温压条件。结合前人发表的地质年代学数据,建立了变质演化P-T-t轨迹。其中,绿帘蓝闪石片岩具"发卡式"变质演化P-T-t轨迹;而蓝闪霓辉石片岩与石榴石冻蓝闪石片岩具顺时针的演化轨迹。我们推测其成因可能为不同类型的蓝片岩形成于不同的俯冲阶段,由动力学机制的变化所造成。该研究成果为进一步探索佳木斯地块与松嫩地块碰撞拼贴的构造演化过程提供重要的依据。     

山东归来庄金矿区g(Au/Ag)的空间信息统计学特征

空间信息统计学是一门集数学、空间信息科学及计算机技术于一体,在时空域内对区域化变量的随机性与结构性进行定量研究的技术。以山东归来庄金矿床为例,对其g(AuAg)异常进行空间信息统计学研究。利用指示克立格法研究g(AuAg)的空间变异结构特征,建立空间结构模型。在对结构模型和估计方案进行交叉验证后,对g(AuAg)的空间分布进行估计。根据g(AuAg)的空间分布规律,探讨其与Au空间分布的关系,并对今后该区的找金工作提出建议。     

阿尔金淡水泉早古生代泥质高压麻粒岩及其P-T演化轨迹

南阿尔金构造带淡水泉一带出露的含石榴石蓝晶石黑云母片麻岩是一套典型的泥质高压麻粒岩,其峰期特征矿物组合为石榴子石+蓝晶石+钾长石+金红石+石英.根据矿物内部一致性热力学数据和Thermocalc 3.23程序计算,确定其峰期变质温压条件为T>850℃和P>11kbar.结合岩相学研究和P-T视剖面图计算,可识别出该岩石经历了4个阶段的变质演化,构成了一个早期快速等温降压,后期近等压降温的顺时针型的退变质P-T演化轨迹,为与陆壳俯冲碰撞有关的高压变质事件的产物.该岩石锆石阴极发光图像显示其内部具有明显的核.边结构,核部为残留的原岩碎屑锆石,边部则表现为面状或扇状生长的变质锆石的特征.微区原位LA-ICP-MS微量元素分析表明,核部测点的重稀土含量较高,对应Th/U接近于0.4,具有岩浆锆石的特征;边部测点的重稀土相对亏损,重稀土配分曲线平坦,对应Th/U比值均小于0.1,显示与石榴子石平衡共生的变质锆石特征.LA-ICP-MS微区定年获得其变质年龄为486±5Ma,该年龄值与阿尔金江尕勒萨依和英格利萨依两地超高压变质岩石的变质年龄相近,进一步证明沿阿尔金构造带南缘断续存在一条早古生代的高压-超高压变质岩带.另外,本次研究在获得该泥质高压麻粒岩峰期变质时代的同时,还获得该岩石原岩的形成时代上限值约为719Ma,从而限定阿尔金构造带南缘阿尔金群的形成时代可能不属古元古代,而应属新元古代.     

新疆震旦纪痕迹化石Planolites,Chondrites的发现及其意义

新疆震旦纪痕迹化石的存在及其形态特征,反映那里最早的水平潜穴,在震旦纪冰期前即已存在,但痕迹细小,且相互交切,绝不分叉。之后始出现分叉现象,并向枝形潜穴方向演变。     

蚌埠隆起区石榴辉石岩变质PT轨迹及年代学研究

蚌埠隆起位于华北克拉通东部陆块的胶-辽-吉造山带的最南缘,由于侧重点和关注度的差异,对于该地区的变质演化过程的探究一直较为缺乏,制约了人们对该隆起形成过程的理解。为此,本文通过对该隆起的石榴辉石岩及其退变的黑云斜长片麻岩详细的野外观测、岩相学分析、热力学评价和年代学的研究,较为充分地探讨了该隆起的形成机制。研究显示这两类岩石记录了5个变质阶段：阶段-Ⅰ的平均温压为：T=672±17 ℃和P=1.05±0.02 GPa;阶段-Ⅱ的平均温压为：T=805±30 ℃和 P=1.21±0.04 GPa;阶段-Ⅲ的平均温压为：T=615±13 ℃和 P=0.93±0.02 GPa; 阶段-Ⅳ的平均温压为：T=632±6 ℃和P=0.50±0.01 GPa;阶段-Ⅴ的温压为推测值：T=400 ℃～450 ℃和P=0.2～0.4 GPa。其中阶段-Ⅰ～阶段-Ⅲ表象为角闪岩相→麻粒岩相→角闪岩相的过程,显示了一个近等压的可能的快速升温和降温的过程。而阶段-Ⅲ～阶段-Ⅳ表现为一个近于等温降压的快速过程,直至阶段-Ⅴ表现为可能的缓慢降温降压过程。结合背景资料和前人年龄数据,以及本次对退变黑云斜长片麻岩的锆石U-Pb定年（1 885±16 Ma）研究,推测该全过程可能反映的是两期变质事件。其中,早期的变质以阶段-Ⅰ、阶段-Ⅱ和阶段-Ⅲ为代表,揭示了大约在2.5 Ga时期,蚌埠隆起经历了大规模岩浆上侵及紧密相伴的高温麻粒岩相变质事件;而晚期变质以阶-Ⅲ→阶段-Ⅳ等温降压为代表,可能反映的是大约1.9 Ga时期,胶-辽-吉造山带的形成过程。     

北大别饶拔寨石榴辉石岩P-T-t轨迹及其构造意义

P-T-t轨迹作为变质岩的重要研究方法之一，对揭示岩石的构造演化过程具有重要意义。北大别饶拔寨镁铁-超镁铁岩形成的构造环境和就位过程长期以来尚存争议。本文通过岩相学观察、矿物化学研究和温压计计算，揭示出饶拔寨石榴辉石岩经历了四个变质演化阶段：1）超高压变质阶段（M1）：主要根据石榴子石中金红石的出溶，单斜辉石中石英的出溶和磷灰石中不透明矿物的出溶，结合前人研究，认为饶拔寨石榴辉石岩经历过超高压变质阶段（≥2.5GPa）；2）高压麻粒岩相阶段（M2）：矿物组合为石榴子石（变斑晶）和单斜辉石（基质）+斜长石（基质），记录的温压条件为T=648~700℃，P=1.47~1.94GPa；3）中压麻粒岩相阶段（M3）：以石榴子石外围发育的主要由斜方辉石+斜长石组成的内圈"白眼圈"为特征，形成的温压条件为T=781~796℃，P=0.92~0.98GPa；4）角闪岩相阶段（M4）：以石榴子石变斑晶周围发育的外圈"白眼圈"为特征，其矿物组合为角闪石+斜长石的后成合晶，形成的温压条件为T=663~685℃，P=0.50~0.58GPa。石榴辉石岩的锆石SIMS U-Pb定年得到了3组不同的交点年龄，分别为208.1~202.1Ma、227.6Ma和817.7Ma。根据锆石包裹体中角闪石+斜长石的组合，推断208.1~202.1Ma代表了角闪岩相变质年龄的下限，227.6Ma则是高压麻粒岩相的下限年龄，而新元古代年龄（817.7Ma）与区域上的变质岩原岩年龄一致，可能代表了其原岩年龄。结合前人研究，饶拔寨石榴辉石岩记录了顺时针的P-T-t轨迹，揭示了板片俯冲（超高压变质）-碰撞-折返（降压升温过程，~227Ma）-抬升（降压降温过程，208~202Ma）的完整过程。     

黑龙江依兰地区黑硬绿泥石片岩岩石学与P-T条件研究

依兰地区黑龙江杂岩中黑硬绿泥石片岩矿物组合为黑硬绿泥+绿泥石+多硅白云母+钠长石+透闪石+钾长石±黑云母.岩石矿物学研究表明黑硬绿泥石片岩形成于250～400℃,6～9kbar的变质条件下.黄褐色黑硬绿泥石呈束状、放射状集合体.黑硬绿泥石片岩形成于佳木斯地块向西与松嫩地块俯冲拼贴过程中蓝片岩变质作用的后期,压力稍有降低而温度略有升高的变质变形环境,是蓝片岩向绿片岩转变的蓝闪绿片岩相变质条件下的产物.     

金原篦羽叶Ctenis kaneharai Yokoyama最完整叶部化石的发现

概要报道产于辽西北票市常河营乡长垅地沟村东山中侏罗统海房沟组中一种大型苏铁类叶部化石——金原篦羽叶Ctenis kaneharai Yokoyama.这种化石最早被报道于辽宁东部凤城县赛马集碾子沟中侏罗统大堡组,后来在日本和英国也被发现.但是,以往发表的该种所有材料都是些植物叶部断片标本,对它的全貌并不了解.在本文中报道的该种标本,不仅数量多而且保存得特别完整.可以说,这是迄今在我国辽西中侏罗世燕辽植物群中大型苏铁类保存最完整叶部化石的又一次重要发现.它为正确了解我国燕辽植物群的性质,苏铁类的整体形态特征和古气候状况分析,提供了更为可靠的化石依据.     

云南武定下奥陶统Cruziana遗迹化石群落及其地层和地理分布

本世纪三十年代初,我国古生物学家尹赞勋先生曾详细研究采自滇东和川西南的一些 Cruziana 遗迹化石(尹赞勋,1933)。他首次在我国介绍了二叶石(Bilobites)这一名称同遗迹属名 Cruziana 的关系;讨论了三叶虫可能是 Cruziana 的遗迹动物;并系统描述了上述 Cruziana A,B,C 三种类型。这篇著作对研究我国三叶虫遗迹化石开创了方向,奠定了基础。