塔里木东南缘安南坝地区约2.5Ga花岗闪长质片麻岩的发现及岩石成因

塔里木东南缘安南坝地区新发现的花岗闪长质片麻岩主要由斜长石、碱性长石、石英、角闪石、黑云母等组成。岩石SiO_2(70%)、Al_2O_3(15%)、Na_2O(3.56%～4.15%)含量较高;MgO(0.39%～0.59%)、Fe_2O_3(0.23%～0.36%)、FeO(0.76%～1.11%)含量、K_2O/Na_2O值(0.64～0.81)及Mg#值(19～27)均较低。花岗闪长质片麻岩稀土元素总量低(∑REE=28.81×10~(-6)～68.51×10~(-6)),(La/Yb)N=(46.27～98.27),轻、重稀土元素分异明显,球粒陨石标准化稀土元素配分曲线表现为右倾型,Eu(δEu=1.57～2.00)呈明显的正异常。岩石Rb、Ba、Sr等大离子亲石元素含量较高,Nb、Ta等高场强元素及Cr、Ni等相容元素含量较低。地球化学特征显示,该花岗闪长质片麻岩具有高铝型TTG和低重稀土元素系列TTG的地球化学特征。研究表明,阿克塞县安南坝地区花岗闪长质片麻岩可能是在榴辉岩相压力条件下,由加厚的玄武质下地壳部分熔融形成,源区残留相主要为石榴子石、金红石(少量)及角闪石。LA-ICP-MS锆石U-Pb上交点年龄为2555±11Ma,代表了花岗闪长质片麻岩的成岩时代,说明新太古代晚期是塔里木东南缘重要的陆壳增生期。此外,岩石中还获得了约2.44Ga、约1.96Ga的变质年龄,表明塔里木东南缘基底岩石在古元古代经历了2期构造-热事件的叠加改造。     

微波消解-电感耦合等离子体发射光谱法测定煤中磷

采用硝酸、硫酸、氢氟酸在高压密封微波消解体系中完全消解褐煤、烟煤和无烟煤样品,消解温度为180℃以上,以178.283 nm作为磷的分析谱线,电感耦合等离子体发射光谱法测定煤样中磷的含量。通过扣除背景的方法消除了基体干扰和光谱干扰,Si、Fe、Ca、Al、Mg对磷的检测无显著影响。磷浓度在0～10 mg/L范围内与等离子体发射强度呈良好的线性关系,方法检出限为0.09 mg/L,回收率为94.5%～101.2%,精密度(RSD,n=12)为1.89%～5.21%。方法用于分析标准物质,测定值与标准值一致。     

Intermediate high-pressure exhumation of the northern segment of the Sanbagawa belt, Saruta-gawa area, central Shikoku, Japan

The retrograde chemical zonal structure of amphibole in hematite-bearing basic and quartz schists from the higher grade zone in the Saruta-gawa area of the Sanbagawa belt was studied to investigate the relationships between the prograde and retrograde P–T paths of the Sanbagawa metamorphism. This amphibole coexists with chlorite, epidote, muscovite, albite, quartz and hematite, and is composed of Al-rich core and Al-poor mantle. The core is fairly homogeneous and has a barroisitic composition. In the mantle part, ^[B]Na increases with decreasing ^[4]Al towards the margins, which have winchite–magnesioriebeckite compositions. The barroisite–winchite–magnesioriebeckite composite crystal is sometimes rimmed by actinolite and/or winchite with low ^[4]Al and ^[B]Na. The Al-rich core and Al-poor mantle are regarded as prograde and retrograde products, respectively. The retrograde mantle in the Saruta-gawa area: (1) is systematically richer in ^[B]Na [0.40–1.73 per formula unit (pfu; for O=23)] than that from the same grade zone in the Asemi-gawa area (0.19–0.78 pfu), about 8 km south of the studied area; (2) tends to be ^[B]Na-poorer (less than 1.73 pfu) than prograde sodic amphibole (up to 1.93 ^[B]Na pfu) produced in the peak temperature stage from the lower grade zone in the same and other areas; and (3) extends its compositional range towards higher ^[B]Na and lower ^[4]Al than prograde-formed amphibole from the same grade zone in the same area. These zonal characteristics imply that (1) the Saruta-gawa samples experienced retrograde metamorphism under higher P/T conditions than the Asemi-gawa samples, (2) the retrograde P–T path of the Saruta-gawa area passes on the lower pressure side of the metamorphic field gradient, and (3) the Saruta-gawa samples underwent retrograde metamorphism under higher P/T conditions than the prograde metamorphism. The higher P/T conditions of the retrograde metamorphism suggests an increasing dP/dT of the geotherm during exhumation. Retrograde P–T conditions during the formation of magnesioriebeckite can be roughly estimated at 7–8 kbar, 400–450°C based on semi-quantitative phase relations of actinolite–winchite–magnesioriebeckite–barroisite series associated with chlorite, epidote, muscovite, albite, quartz and hematite.     

Geochemical Characteristics of Pb Isotope of High-Pressure Metamorphic Rocks and Foliated Granites from HP Unit of Tongbai-Dabie Orogenic Belt

Whole-rock Pb isotopic compositions of the high-pressure (HP) metamorphic rocks, consisting of two-mica albite gneisses and eclogites, and foliated granites from the HP metamorphic unit of the Tongbai-Dabie orogenic belt are firstly reported in this paper. The results show that the tip metamorphic rocks in different parts of this orogenic belt have similar Pb isotopic compositions. The twomica albite gneisses have ^206 pb/^204 Pb=17. 657 -18. 168, ^207pb/^204 Pb=15. 318-15. 573,^ 208Pb/^204ob=38.315-38. 990, and the eclogites have ^206Pb/^204 Pb=17. 599 -18. 310, ^207Pb/^204 Pb=15. 465 -15. 615,^208Pb/^204Pb=37. 968-39. 143. The HP metamorphic rocks are characterized by upper crustal Pb isotopic composition. Although the Pb isotopic composition of the HP metamorphic rocks partly overlaps that of the ultrahigh-pressure (UHP) metamorphic rocks, as a whole, the former is higher than the latter. The high radiogenic Pb isotopic composition for the HP metamorphic rocks confirms that the subducted Yangtze continental crust in the Tongbai-Dabie orogenic belt has the chemical structure of increasing radiogenic Pb isotopic composition from lower crust to upper crust. The foliated granites, intruded in the HP metamorphic rocks post the HP/UHP metamorphism, have ^206Pb/^204 Pb=17. 128- 17. 434,^207Pb/^204pb=15. 313-15. 422 and ^208Pb/^204Pb=37. 631-38. 122, which are obviously different from the Pb isotopic compositions of the HP metamorphic rocks but similar to those of the UHP metamorphic rocks and the foliated garnet-bearing granites in the UHP unit. This shows that the foliated granites from the HP and UHP units have common magma source. Combined with the foliated granites having the geochemical characteristics of A-type granites, it is suggested that the magma for the foliated granites in the UHP and HP unit would be derived from the partial melting of the retrometamorphosed UHP metamorphic rocks exhumed into middle to lower crust, and partial magmas were intruded into the HP unit.     

苏鲁地体超高压和非超高压花岗质片麻岩的判别标志——来自锆石中矿物包裹体的证据

中国大陆科学钻探工程预先导孔CCSD－PP1中存在两类不同性质的花岗质片麻岩，它们的岩相学性质，地球化学特征，锆石中的包体矿物组合和分布规律以及阴极发光图像均存在明显的判别，其中第一类花岗质片麻岩中的锆石呈完好的自形晶，不含任何超高压矿物包体，自晶体中心至边缘均具有典型的岩浆结晶生长环带，表明该类花岗质片麻岩未经历超高压变质作用，第二类花岗质征麻岩中的锆石呈半自形晶一它形晶，晶体核部保存典型的岩浆结晶生长环带，且无超高压矿物包体，具有继承性锆石的特点，而在晶体的过渡带及其与边缘的交界部位，普遍存在以柯石英粉 包体矿物，表明第二类花岗质片麻岩曾经历了超高压变质作用，且锆石在此变质过程进一步结晶生长，形成新的生长环带，该项成果对于深入探讨苏鲁超高压变质带的俯冲－折返机制及其与岩浆作用的相互关系以及对中国大陆科学钻探工程的选址和实施有着重要的科学意义。     

差应力状态对岩石熔融程度的影响--以黑云母片麻岩的动、静态熔融对比实验为例

以河北省平山县阜平群的黑云片麻岩为实验样品,有差应力条件下的动态实验,围压10MPa,温度800℃条件下,施加相当于差应力为O～25MPa,且以每5MPa为间隔进行了天然块状岩石样品的动态熔融,在相同的围压条件下,温度由800～900℃每20℃为间隔,进行了无差应力条件下天然块状岩石的静态熔融实验,并进行了对比研究。结果表明,在相同温度条件下,岩石的熔融程度随着差应力的增加明显增高,当差应力达到25MPa时,800℃条件下岩石的熔融程度与900℃静态熔融条件下岩石的熔融程度相当。实验力学分析计算表明,动态实验中构造附加压力增加了围压,差应力每增加5MPa相当于1．67MPa的增压,其与静态实验中温度升高20℃的效果一样。该实验结果对研究岩石深熔作用的深度问题有一定的参考意义。     

赞皇变基性岩中锆石的U-Pb定年及其地质意义

赞皇变质杂岩区位于阜平杂岩南部,地处华北克拉通中部造山带的中段,和中部带北段杂岩一样,是洞悉华北克拉通前寒武纪基底构造演化历史的一个重要窗口.研究区变基性岩可分为斜长角闪岩和角闪斜长片麻岩两种,二者均以似层状方式产于黑云斜长片麻岩或长英质片麻岩中,斜长角闪岩亦可呈透镜状,二者后期与围岩一起共同经历了高角闪岩相变质作用....     

东喜马拉雅构造结南迦巴瓦岩群花岗质片麻岩的初步研究

野外地质填图和研究发现,东喜马拉雅构造结高喜马拉雅结晶岩系中有古老的花岗岩侵入,并在鲁霞地区圈定了9个花岗质侵入体。古老的花岗质岩石主要侵位于南迦巴瓦岩群直白岩组中,与南迦巴瓦岩群一起经历了麻粒岩相变质作用而形成花岗质片麻岩套。岩石类型有花岗闪长质片麻岩、黑云母花岗质片麻岩、闪长质片麻岩等。岩石化学研究表明这些花岗片麻岩套具“S”型特征,可能有深部幔源物质的加入。花岗岩形成深度在2～5km之间．侵位时代为552～525Ma,为新元古代晚期,属泛非期陆内演化阶段的产物。高喜马拉雅地区在元古宙末期形成了结晶基底。     

Chronology of Early to Mid-Pleistocene sediments in the northern North Sea: New evidence from amino acid and strontium isotope analyses

Sediments deposited during glacial-interglacial cycles through the Early to Mid-Pleistocene in the North Sea are chronologically poorly constrained. To contribute to the chronology of these units, amino acid racemization (AAR) and strontium (Sr) isotope analyses have been performed on samples from four shallow borings and one oil well along a transect in the northern North Sea. D/L Asp (aspartic acid) values obtained through reverse-phase liquid chromatography in the benthic foraminiferal species Elphidium excavatum is focused on because of consistent results and a good stratigraphic distribution of this benthic species. For the Early Pleistocene, an age model for the well 16/1–8, from the central part of the northern North Sea based on Sr ages allows for dating of the prograding wedges filling the pre-Quaternary central basin. A regional calibration curve for the racemization of Asp in Elphidium excavatum is developed using published ages of radiocarbon-dated samples and samples associated with the previously identified Bruhnes/Matuyama (B/M) paleomagnetic boundary and a Sr age from this study. Based on all the available geochronological evidence, samples were assigned to marine oxygen isotope stages (MIS) with uncertainties on the order of 10–70 ka.Sr ages suggest a hiatus of <2 million years (Ma) possibly due to non-deposition or low sedimentation between the Utsira Formation (Pliocene) and the Early Pleistocene. An increase in sedimentation rates around 1.5 ± 0.07 Ma (∼MIS 51) may partly be due to sediment supply from rivers from the south-east and partly due to the extension of ice sheet around 1.36 ± 0.07 Ma from the Norwegian coast to the central North Sea. A possible basin-wide glaciation occurred around 1.1 Ma (∼ MIS 32) (upper regional unconformity/top of unit Q4 in this study), resulting in erosion and regional unconformity. Two interglacials in the Norwegian Channel have been dated: the Radøy Interglacial to 1.07 ± 0.01 Ma (possibly MIS 31, the ‘super interglacial’), and the Norwegian Trench Interglacial to 0.50 ± 0.02 Ma (possibly MIS 13). A massive till unit identified at the same stratigraphic level in all shallow borings may partly represent an extensive MIS 12 glaciation. This study shows that the combined use of amino acid racemization data and Sr isotope chronology can refine the chronological ambiguities of Quaternary North Sea sediments related partly to the impact of glacial processes.     

滇西云龙漕涧地区高压片麻岩的发现及厘定

笔者在滇西云龙县漕涧新发现了一套以黑云斜长片麻岩为主的变泥质岩石,其呈构造透镜体状产出,出露面积极小,中高级变质矿物发育,与围岩特征明显不同.岩相学研究表明,片麻岩保留有明显的俯冲-折返的矿物学记录,矿物世代具顺时针变质演化特征,其中还残存有蓝晶石+铝直闪石的共生矿物组合,对应的变质压力达1.0 GPa以上.通过GBP...