北大别洪庙榴辉岩相岩石Sm-Nd年龄:峰期变质时代

前人工作认为北大别榴辉岩在榴辉岩相变质后,经历了麻粒岩相退变质作用,因此获得的Sm-Nd矿物等时线年龄代表了麻粒岩相变质时代.本文对北大别安徽洪庙百丈岩榴辉岩相岩石(辉石石榴石岩)的研究表明,该岩石经历了三叠纪超高压变质作用,经历了角闪岩相退变质.所研究样品在峰期变质之后是否经历了麻粒岩相退变质尚不能明确界定.结合矿物氧同位素体系平衡判据,辉石石榴石岩在峰期变质时达到了Sm-Nd同位素体系的均一化和平衡,并且在后期角闪岩相退变质中该同位素体系未出现明显的扰动,因此其Sm-Nd矿物等时线年龄[(225±14)Ma和(229±13)Ma]代表了榴辉岩相变质时代.同时,样品中矿物的同位素组成表明,在俯冲板块折返和退变质过程中,岩石受到外来和内部流体的不均匀作用,造成退变的单斜辉石在同位素组成上的不均一.     

Festkontaktierte potentiometrische Elektroden für Sulfatbestimmungen in wässrigen Lösungen

Solid‐contacted Potentiometric Electrodes for Measurements of Sulfate Ions in Aqueous Solutions A solid‐contact electrode for potentiometric measurement of sulfate ions in aqueous solutions was developed and examined. The electrode is based on a PVC membrane which contains the ionophore 3‐decyl‐1,5,8‐triazacyclodecan‐2,4‐dione (DTADD). Instead of the usual inner fluid junction, a polypyrrole layer applied on the inner side of the PVC membrane was employed as inner solid contact. The performance of this electrode was compared to solid‐state sulfate‐selective electrodes with the ionophore α,α′‐bis(N′‐phenylthioureylene)‐m‐xylene (BTH) and to electrodes in the coated‐wire configuration. For the parameters sensitivity, selectivity, and long‐term stability, electrodes with the DTADD ionophore show improved properties. In the sulfate concentration range of 5·10^–5...10^–2 mol L^–1 the slope of the response is –(26.8 ± 0.5) mV/decade. The new solid contact sulfate electrodes showed a very low drift of the electrode potential within a period of 150 days when the electrode was stored in 10^–2 M Na₂SO₄. In Na2SO4 solutions of the pH range of 4...9 the electrode potentials were constant. The 95% response time was about 10 s when the sulfate concentration was changed from 10^–4 mol L^–1 to 10^–3 mol L^–1. The selectivity with DTADD ionophore relating to the nitrate ions is higher than the selectivity with BTH. Improvements are also made in comparison with sulfate‐selective electrodes described in the literature which contain other ionophores with fluid inner reference electrolytes.     

Emission and absorption of cyclotron radiation in non-equilibrium plasma

From the kinetic Klimontovich theory we derive the equation of radiative transfer for the case of homogeneous and stationary nonequilibrium plasma in a magnetic fiel. For the sake of simplicity we shall consider only the propagation of cyclotron-radiation in the direction of the magnetic field. Explicit expressions for the coefficients of absorption and spontaneous emission, valid also at the cyclotron frequency, will be obtained. In the final results the plasma is allowed to be weakly inhomogeneous in the z-direction. Application is made of the theory to the simple equilibrium case as a test yields the Rayleigh-Jeans formula of the black-body-radiation.     

On the age of the Onverwacht Group,Swaziland Sequence,South Africa

Some rocks of the Onverwacht Group, South Africa, have been analyzed for Rb and Sr concentrations and Sr isotopie composition. These rocks include volcanic rocks, layered ultramafic differentiates and cherty sediments. Whole rock data indicate that the Rb-Sr isotopie systems in many samples were open and yield no reasonable isochron relationships. However, the data of mineral separates from a basaltic komatiite define a good isochron of $\text{t = 3.50 ± 0.20}$ (2δ) b.y. with an initial Sr⁸⁷/Sr⁸⁶ ratio of $\text{0.70048 ± 5}$(2δ). The orthodox interpretation of this age is the time of the low grade metamorphism. Since the basaltic komatiite is stratigraphically lower than the Middle Marker Horizon (dated as $\text{3.36 ± 0.07}$ b.y. Hurley et al., 1972), and since it is commonly found that volcanism, sedimentary deposition, metamorphism and igneous intrusion in many Archean greenstone-granite terrain all took place in a relatively short time interval (less than 100 m.y.), it is reasonable to assume that the age of 3.50 b.y. might also represent the time of initial Onverwacht volcanism and deposition. The initial Sr⁸⁷/Sr⁸⁶ ratio obtained above is important to an understanding of the Sr isotopic composition of the Archean upper mantle. If the komatiite represents a large degree of partial melt (40–80 per cent) of the Archean upper mantle material, then the initial ratio obtained from the metamorphic komatiite should define an upper limit for the Sr isotopic composition of the upper mantle under the African crustal segment.     

Origin of Late Permian Emeishan basaltic rocks from the Panxi region (SW China): Implications for the Ti-classification and spatial–compositional distribution of the Emeishan flood basalts

Basalts and a mafic dyke collected from the city of Panzhihua show characteristics of high-Ti and low-Ti Emeishan basalts respectively. The dyke yielded a SHRIMP zircon U–Pb mean age of 261 ± 5 Ma making it contemporaneous with the eruption of Emeishan basalts. The basalts have I_Sr ranging from 0.7059 to 0.7062 with εNd_(T) ranging from ?1.1 to + 0.7 whereas the dyke has I_Sr ranging from 0.7056 to 0.7064 with εNd_(T) ranging from + 0.3 to + 0.5. Trace element modeling shows that the two rock types can be generated by different degrees of partial melting from the same garnet-bearing source. Assimilation of crustal material is required in order to produce the depletion of some trace elements (e.g. Nb and Ta) of the dyke however crustal assimilation is not required to produce the basalts. Trace element modeling and isotopic data of the Emeishan basalts suggest that, in general, the high- and low-Ti basaltic rocks are likely derived from the same source and represent different degrees of partial melting with or without crustal assimilation. The location and geological relationships of the ‘high-Ti’ basalts indicate they erupted relatively early and within the central part of the ELIP, casting doubt on the previous spatial–compositional distribution of the Emeishan basalts.     

天山0．9Ga新元古代花岗岩SHRIMP锆石U-Pb年龄及其构造意义

天山造山带的中天山隆起带中广泛出露着新元古代花岗岩类岩石。获得了东天山星星峡和西天山温泉地区片麻状花岗岩中锆石的SHRIMP U-Pb年龄,分别为（942±7）Ma（2σ）和（919±6）Ma（2σ）。这些花岗岩以特有的粗粒、巨大的眼球状片麻结构为特征。主元素数据表明它们属于过铝质的二长花岗岩,具有高SiO2（≥170％）、高K2O＋Na2O（7％～≥8％）,且K2O〉Na2O。这些新元古代花岗岩类岩石具不同的REE含量,但它们有近于平行的REE分布曲线和明显的Eu负异常,同时代的星星峡混合岩具有较高的REE含量,明显富集LREE。它们的微量元素蛛网图几乎完全相同,均有明显的Nb、Sr、Ti、P负异常。基于Nd同位素组成研究,其εNd（t）在-4至-0之间,Nd模式年龄tDM为2．0～1．6Ga。由于放射成因Sr同位素组成非常高,不可能得到精确有意义的Sr同位素初始值。上述特征均表明这些新元古代花岗岩形成于大陆边缘构造环境,由古元古代地壳重熔并经历了高度的结晶分异作用而形成。综合近年来发表的关于天山各地段,诸如温泉、赛里木湖以东、拉尔敦达坂、巴仑台和星星峡等地区较为可靠的锆石U—Pb年龄数据,我们认为天山新元古代花岗岩类岩石主要形成于960-910Ma。结合塔里木盆地周边古老地块年龄的研究结果,可以推断在早新元古代时期塔里木周边和天山的古老地块可能曾组成Rodinia超大陆的一部分。     

华南陆缘晚中生代造山及其地质意义

长乐—南澳带位于华南大陆的东南缘,是揭示晚中生代古太平洋板块与欧亚大陆相互作用和华南陆缘地质演化的一条关键性构造带。该构造带的T3-J含煤地层不整合下伏于下白垩统南园组之下,或以角闪岩相包体形式赋存于晚侏罗—早白垩世片麻状花岗岩体内。这些具有透入性混合岩化特征的副变质岩包体(T3-J)与围岩(片麻状花岗岩)发生过同变形,并且被未变形的白垩纪岩体/脉侵入。这些晚三叠—早侏罗世地层的变质和变形具有朝陆内(NW)方向减弱的特征。下白垩统南园组普遍发生褶皱和绿片岩相变质,并且被未变质的上白垩统石帽山群不整合覆盖。长乐—南澳带的主要岩石单元与构造特征表明华南陆缘在晚中生代经历过两期挤压(造山)。在第一期挤压(造山)过程中,T3-J陆相地层发生褶皱和变质。随后,这些经历了变形和变质的T3-J沉积地层与中-上地壳的其他岩石在早白垩世早期发生构造折返,其间伴随着大规模同构造岩浆作用(147～135 Ma)和区域性混合岩化。在第二期挤压过程中,早白垩世南园组发生褶皱和变质。华南陆缘110～100 Ma的岩浆杂岩、100～90 Ma的A型花岗岩和90～80 Ma的双峰式火成岩可能分别与这次挤压事件及其后的地壳伸展、减薄过程有关。因此,华南晚中生代两大岩浆旋回(165～120 Ma和110～80 Ma)可能受控于同期的两大构造旋回(165～120 Ma和115～80 Ma)。每个构造旋回包括一个地壳受挤压增厚过程和一个随后发生的地壳伸展减薄过程。值得注意的是,华南沿海地区的晚中生代构造-岩浆作用与陆内同期构造-岩浆作用似乎具有可比性。