Mass spectrometric isotope dilution analyses of cadmium in standard rocks

Cadmium has been determined in a range of silicate rock standards using the stable isotope dilution technique incorporating solid source mass spectrometry. Our recommended values are, in general, lower than the previously reported data.     

Mass spectrometric isotope dilution analyses of tellurium in meteorites and standard rocks

A stable isotope dilution technique using solid source mass spectrometry has been used to determine the elemental abundance of Te in 25 chondrites, 3 achondrites, 1 tektite, and 12 standard rocks. Mean values for the C1, C2, and CV3 meteorites are 2.34, 1.48, and 1.03 ppm, respectively; or atomic abundances for Te (normalized to Si = 10⁶ atoms) of 4.84, 2.49, and 1.46. The atomic abundance obtained for the C1 chondrite Orgueil is significantly lower than the accepted value of 6.42. As a consequence we recommend that the ‘cosmic’ abundance of Te and Xe should be re-examined. The depletion ratio for Te in ordinary chondrites of 0.10, is about the same as that for Zn. Elemental abundances of Te in 12 standard rocks are in the ppb range.     

On the radiogenic heat production of metamorphic,igneous, and sedimentary rocks

Sedimentary rocks cover-73% of the Earth's surface and metamorphic rocks account for approximately91% of the crust by volume. Understanding the average behavior and variability of heat production for these rock types are vitally important for developing accurate models of lithospheric temperature. We analyze the heat production of ～204,000 whole rock geochemical data to quantify how heat production of these rocks varies with respect to chemistry and their evolution during metamorphism. The heat production of metaigneous and metasedimentary rocks are similar to their respective protoliths. Igneous and metaigneous samples increase in heat production with increasing SiO_2 and K_2 O, but decrease with increasing FeO, MgO and CaO. Sedimentary and metasedimentary rocks increase in heat production with increasing Al_2 O_3, FeO, TiO_2, and K_2 O but decrease with increasing CaO. For both igneous and sedimentary rocks, the heat production variations are largely correlated with processes that affect K_2 O concentration and covary with other major oxides as a consequence. Among sedimentary rocks,aluminous shales are the highest heat producing(2.9 μW~(-3)) whereas more common iron shales are lower heat producing(1.7 μW m~(-3)). Pure quartzites and carbonates are the lowest heat producing sedimentary rocks. Globally, there is little definitive evidence for a decrease in heat production with increasing metamorphic grade. However, there remains the need for high resolution studies of heat production variations within individual protoliths that vary in metamorphic grade. These results improve estimates of heat production and natural variability of rocks that will allow for more accurate temperature models of the lithosphere.     

Rb-Sr isotope systematics in metamorphic rocks,Kongsberg sector,south Norway

Rb-Sr isotope data are presented for gneisses, migmatite neosome material and granitic and gabbroic intrusive rocks from the southern part of the Kongsberg sector, south Norway. The maximum age of the crust in this area appears to be ～1.6 AE. Two metamorphic episodes at ～1.5–1.6 AE and at ～1.1–1.2 AE are recognized. Initial ⁸⁷Sr/⁸⁶Sr ratios for the granitic rocks give evidence for reworking of sialic crust and indicate that approximately 1.6 AE old crust repeatedly acted as a source for granitic magmas for a timespan of ～0.5 AE.     

溴、碘的半熔法-电感耦合等离子质谱(ICP-MS)测定

样品用碳酸钠和氧化锌混合熔剂半熔,用80℃～100℃水提取,用强酸型阳离子树脂分离溶液中的大量钠等阳离子,采用电感耦合等离子质谱直接测定溶液中的溴和碘。测定下限溴为0．15μg／g,碘为0．028μg／g。     

Estimation of joint trace length probability distribution function in igneous,sedimentary, and metamorphic rocks

To predict the behavior of structures in and on jointed rock masses, it is necessary to characterize the geomechanical properties of joints and intact rock. Among geometry properties of joints, trace length has a vital importance, because it affects rock mass strength and controls the stability of the rock structures in jointed rock masses. Since joint length has a range of values, it is useful to have an understanding of the distribution of these values in order to predict how the extreme values may be compared to the values obtained from a small sample. For this purpose, three datasets of joint systems from nine exposures of igneous, metamorphic, and sedimentary rocks are studied. Joint trace length is one of the most difficult properties to measure accurately, but it may be possible to record other geometrical properties of exposed joints accurately; thereby, support vector machine (SVM) model is used to predict the joint trace length. SVM is a novel machine learning method, which is a powerful tool used to solve the problem characterized by small sample and non-linearity with a good generalization performance. Consequently, goodness-of-fit (GOF) tests were applied on these data. According to these GOF tests, the lognormal distribution was found to be the best probability distribution function for representing a joint trace length distribution.     

包含变质岩分类三要素的主要变质岩分类表

变质岩分类的三要素是:变质岩的物质成分(化学成分、矿物成分)、变质岩的组构(结构、构造)和变质岩的成因(变质作用类型和形成变质岩的物理化学条件).由于变质岩的化学成分、矿物成分、组构特征和形成变质岩的地质环境十分复杂,致使至今尚无以变质岩分类三要素为基础的、内容比较完善的分类方案.本文中主要变质岩的分类是以其分类三要素为基础编制的,首次将不同成因的变质岩类并列于同一表中、将鉴定变质岩的主要标志性矿物成分和组构特征列入同一分类表中.该分类对鉴定变质岩石具有可操作性和实用性,分类表中涵盖了自然界主要的变质岩石.     

Experimental hydrogen isotope studies III: Diffusion of hydrogen in hydrous minerals,and stable isotope exchange in metamorphic rocks

Diffusion parameters for hydrogen diffusion in epidote-group minerals and micas have been measured under hydrothermal conditions, or calculated from existing experimental data, for bulk hydrogen isotope exchange experiments between hydrous minerals and water. Activation energies in the range 14 to 31 kcals/g-atom H are comparable to those derived by application of kinetic theory to experimental hydrogen isotope exchange data, and to those for oxygen diffusion in minerals under hydrothermal conditions. Diffusion of hydrogen in epidote is about four orders of magnitude faster than in muscovite, and about two orders of magnitude faster than in zoisite. Hydrogen diffusion in micas is about five orders of magnitude faster than oxygen diffusion, and hydrogen transport occurs dominantly parallel to the layers rather than parallel to the c-axis as for oxygen.Rapid hydrogen transport in minerals may proceed by hydrolysis of Si-O and Al-O bonds, followed by exchange of hydrolyzed oxygens with slower-diffusing (OH) or H₂O. Water appears to be essential for stable isotope exchange between minerals in slowly cooling metamorphic rocks.Stable isotope data for regional metamorphic mineral assemblages suggests that water is usually present in small amounts during cooling of prograde regional metamorphic systems, and estimated closure temperatures for cessation of stable isotope exchange are often more comparable to those calculated from diffusion data than to likely temperatures of metamorphism.Alpine deformation of the Hercynian Monte Rose Granite (Frey et al. 1976) permitted access of water and initiated stable isotope exchange amongst coexisting minerals. The diffusional behaviour of species in relict Hercynian muscovites is consistent with available experimental diffusion data.     

Detrital,metamorphic and metasomatic tourmaline in high-pressure metasediments from Syros (Greece): intra-grain boron isotope patterns determined by secondary-ion mass spectrometry

The boron isotopic composition of zoned tourmaline in two metasediments from the island of Syros, determined by secondary-ion mass spectrometry (SIMS), reflects the sedimentary and metamorphic record of the rocks. Tourmaline from a silicate-bearing marble contains small (≤20 μm) detrital cores with highly variable δ ¹¹B values (−10.7 to +3.6‰), pointing to a heterogeneous protolith derived from multiple sources. The sedimentary B isotopic record survived the entire metamorphic cycle with peak temperatures of ∼500°C. Prograde to peak metamorphic rims are homogeneous and similar among all analysed grains (δ ¹¹B ≈ +0.9‰). The varying δ ¹¹B values of detrital cores in the siliceous marble demonstrate that in situ B isotope analysis of tourmaline by SIMS is a potentially powerful tool for provenance studies not only in sediments but also in metasediments. A meta-tuffitic blueschist bears abundant tourmaline with dravitic cores of detrital or authigenic origin (δ ¹¹B ≈ −3.3‰), and prograde to peak metamorphic overgrowth zones (−1.6‰). Fe-rich rims, formed during influx of B-bearing fluids under retrograde conditions, show strongly increasing δ ¹¹B values (up to +7.7‰) towards the margins of the grains. The δ ¹¹B values of metamorphic tourmaline from Syros, formed in mixed terrigenous–marine sediments, reflect the B signal blended from these two different sources, and was probably not altered by dehydration during subduction.     

Stable isotope studies of metasomatic Ca-Fe-Al-Si skarns and associated metamorphic and igneous rocks,Osgood Mountains,Nevada

Garnet-pyroxene skarns were formed 90 m.y. B.P. in the Osgood Mountains at or near contacts of grandiorite with calcareous rocks of the Cambrian Preble Formation. The metasomatic replacement followed contact metamorphic recrystallization of the Preble. The sources, temperature, and variation in H₂O/CO₂ ratios of the metasomatic fluid are interpreted from 269 analyses of oxygen, carbon, hydrogen, and sulfur isotopes in whole rocks, minerals and inclusion fluids.Skarns formed in three mineralogical stages. Oxygen isotope data indicate that temperatures during the crystallization of garnet, pyroxene and wollastonite (Stage I) were least 550 ° C, and that the metasomatic fluid had an 0.035 in the massive skarns, and 0.12 in vein skarns up to 3 cm thick. Pore fluids in isotopic equilibrium with garnet in calc-silicate metamorphic rocks, on the other hand, had 0.15.The metasomatic fluids of Stage I were derived primarily from the crystallizing magma. The isotopic composition of magmatic water was ¹⁸O =+9.0, D= –30 to –45. Oxygen isotope temperatures of greater than 620 ° C were determined for the granodiorite. Isotopic and chemical equilibria between mineral surfaces and the metasomatic fluid were approached simultaneously in parts of the skarn several meters or more apart, while isotopic and chemical disequilibria (i.e. zoning) have been preserved between 20 to 40 m-thick zones in grandite garnet. More Fe-, or andradite-rich garnet crystallized in more H₂O-rich C-O-H fluids ( 0.01) than present with grossularite-rich garnet ( 0.035).Stage II was marked by the replacement of garnet and pyroxene by quartz, amphibole, plagioclase, epidote, magnetite, and calcite. Many of the replacement reactions took place over a relatively narrow range in temperature (480–550 ° C), as indicated by ¹⁸O fractionations between quartz and amphibole. Meteoric water comprised 20 to 50% of the metasomatic fluid during Stage II.Calcite was formed along with pyrite, minor pyrrhotite, and chalcopyrite during Stage III, although the crystallization of pyrite and calcite had begun earlier, during Stages I and II, respectively. Carbon and sulfur isotope compositions of calcite and pyrite indicate a magmatic source for most of the C and S in the metasomatic fluids of Stage III. By the end of Stage III, meteoric water constituted as much as 100% of the metasomatic fluid. Minerals from grandiorite and skarn do not show large depletions in ¹⁸O because the oxygen isotope composition of the metasomatic fluid was buffered by the calcareous wall rocks and the grandiorite.Meteoric water in the vicinity of the Osgood Mountains during the Late Crectaceous (¹⁸O_cale. –14.0, D = – 107) was slightly enriched in ¹⁸O and D relative to present-day meteoric water (¹⁸O = 15.9, D = – 117)     

Oxygen isotope study of metamorphic rocks from the Ouégoa district,New Caledonia

48 minerals from 18 in situ metamorphic rocks (mostly metasediments) from the Ouégoa district have been studied. Particular emphasis was placed on obtaining isotopic data for quartz, calcite and muscovite but some pyroxenes and amphiboles were also examined. Data for Ouégoa rocks show they have tended to be isotopically homogenized by metamorphism and that the effect of increasing metamorphism is to progressively deplete the rocks of heavy C and O isotopes. These results indicate that during metamorphism the rocks isotopically exchanged through the medium of a widespread oxygen-carrying fluid phase. Tentatively assigned temperatures obtained from isotopic data for quartz-calcite and quartz-muscovite pairs, using the calibration curves of Epstein and Taylor (1967), indicate lawsonite in the Ouégoa schists to be stable over a temperature range of 250 to 400° C and epidote from ca. 380° to at least 550° C. Temperatures for metamorphic zones in Ouégoa blueschists closely parallel those obtained for Type III and IV glaucophane-bearing rocks from Ward Creek, California (Taylor and Coleman, 1968). The measured tectonic thickness of lawsonite-bearing schists has been used to calculate a lithostatic pressure increment of 2 Kb and geothermal gradient of 20° C per km for the lawsonite zone. Comparison of lithostatic pressure increment with total pressure increment estimated from the stability relations of lawsonite over the temperature range 250–400° C (3.5 Kb Nitsch, 1972) suggest P _total ≠ P _lithostatic and that that the pressure of the fluid phase may have exceeded lithostatic pressure.     

Mass spectrometric isotope dilution analyses of palladium,silver, cadmium and tellurium in carbonaceous chondrites

The mass spectrometric isotope dilution technique was used to measure the elemental abundances of Pd, Ag, Cd and Te in Orgueil (C1), Ivuna (C1), Murray (C2) and Allende (C3) chondrites. The Pd abundance of 554 ppb for the C1 chondrites is almost identical to the recommended value of Anders and Ebihara (1982); that for Cd (712 ppb) is approximately 5% higher, whereas that for Ag (198 ppb) is approximately 10% lower than the recommended values. A smooth distribution for the abundances of the odd-A nuclides between65 ≦ A ≦ 209 have been observed except for small irregularities in the Pd-Ag-Cd and the Sm-Eu mass regions (ANDERS and Ebihara, 1982). The results from the present work have the effect of smoothing out the dip in the Pd-Ag-Cd region and indicate that there is no systematic fractionation of cosmochemical element groups in this mass region.A Te abundance of 2.25 ppm has been determined for the C1 chondrites Orgueil and Ivuna in agreement 2+with the value of Smith et al. (1977). This value is some 30% lower than the value of Krähenbühl et al. (1973) but is in good agreement with the more recent measurements from Chicago. The Krähenbühl et al. value causes ¹²⁸Te and ¹³⁰Te to lie approximately 30% above the r-process peak at A = 130 (Käppeler el al., 1982), whereas the new value fits smoothly into the general trend.     

Determination of rare-earth elements in USGS standard rocks by mixed-solvent ion exchange and mass-spectrometric isotope dilution

The development is described of a mixed-solvent ion-exchange technique for separating trace amounts of rare-earth elements from silicate rocks and minerals. A two-column method is used, bulk separation of rare earths from other elements being accomplished on the first, and separation into three groups for mass-spectrometric analysis on the second. This has been applied to the determination of nine REE (La, Ce, Nd, Sm, Eu, Gd, Dy, Er and Yb) in standard rock samples. Smooth variation of the chondrite-normalized abundance distributions and comparison with other published results indicate that the accuracy of the method, with the exception of La, is generally ± 2%.     

On the oxygen isotope distribution among mineral triplets in igneous and metamorphic rocks

A compilation of ¹⁸O analyses of minerals separated from about 400 igneous and metamorphic rocks from published investigations reveals regularity in the fractionation of ¹⁸O among associated minerals, suggesting that an approach to isotopic equilibrium may be common. However, for only a minority of terrestrial rocks are these regularities sufficiently systematic to be compatible with the actual attainment and preservation of isotopic equilibrium among three minerals. Fractionations among triplets of quartz, calcite, feldspar, muscovite, and magnetite show some correspondence to those expected on the basis of experimental calibrations; however, there are also considerable deviations. The variability of natural data is such that less than half of the rocks analyzed to date would yield concordant ¹⁸O-derived temperatures. Of the additional 52 mineral triplets studied, plagioclase-pyrox-ene-ilmenite, plagioclase-pyroxene-magnetite, plagioclase-pyroxene-olivine, quartz-amphibole-garnet, pyroxene-ilmenite-magnetite, muscovite-biotite-magnetite, and quartz-muscovite-amphibole show the most systematic oxygen isotope fractionations. For 12 other mineral triplets a defined isotope fractionation relationship may be postulated to underlie the data; however for these a close approach to isotopic equilibrium is not commonly observed. For 33 of the mineral triplets an approach to isotopic equilibrium can be noted; however, the scatter of the available data is such that a systematic influence of a factor, such as temperature, on the size of the ¹⁸O fractionation could not be detected. In the past, regularities of oxygen isotope fractionations among three minerals have been used to establish secondary isotope geothermometers. Before this can be done with any reliability, however, the effects of possible retrograde isotope exchange and spurious correlation must be accounted for.     

The oxygen isotope composition of granitoid and sedimentary rocks of the southern Snake Range,Nevada

Six diverse intrusive igneous types are exposed as discrete outcrops within an area of 900 km² in the southern Snake Range, White Pine County, Nevada. The previously recognized variety among these igneous types is reflected in the wide range of ¹⁸O values (–1.1 to 13.4 permil) found in these rocks. This range of ¹⁸O values probably results from differences in source material and post-crystallization history of the different intrusive types.The Jurassic intrusive of the Snake Creek-Williams Canyon area represents the chemical equivalent of a large part of a differentiation sequence, with the entire range of composition (63–76 percent SiO₂) exposed over a horizontal distance of about five km. The rather regular increase of ¹⁸O values from the most mafic to the most felsic parts of this pluton, together with ¹⁸O values determined for constituent minerals recovered from five of the samples, supports a fractional crystallization model. The high ¹⁸O values found (10.2–12.2 permil) indicate that the magma likely was derived from or assimilated sedimentary materials.Nine samples of the Cretaceous two-mica granite of the Pole Canyon-Can Young Canyon area have ¹⁸O values in the range 10.6–12.1 permil. These high ¹⁸O values, an initial⁸⁷Sr/⁸⁶Sr ratio of 0.7165, and the presence of muscovite along with an accessory mineral suite limited to monazite, apatite, zircon, and an allanite-like mineral, characterize this intrusive mass as an S-type granite. It probably formed through anatexis of late Precambrian pelitic rocks.The granitoid rock exposed in the Young Canyon-Kious Basin area is Tertiary (32 m.y.). Most of this intrusive has been cataclastically deformed as a result of late (18 m.y.) movement on the overlying Snake Range decollement. The undeformed portion of this intrusive has ¹⁸O values of 8.7–10.0 permil. However, the deformed portion of this intrusive has ¹⁸O values as low as –1.1 permil, apparently resulting from isotopic exchange between this rock and ground water at the time of cataclasis.Although the igneous types exposed in the southern Snake Range differ petrologically and range in age from Jurassic to Tertiary, most have relatively high ¹⁸O values compared with other granitoid rocks of the Basin-Range Province.     

北疆阿尔泰南缘泥盆系浅变质碎屑沉积岩地球化学特征及其形成环境

对于北疆阿尔泰地区泥盆纪所处的大地构造环境,目前仍旧存在不同观点.前人基于阿尔泰南缘泥盆纪火山岩地球化学研究,分别提出了活动大陆边缘和被动大陆边缘裂谷等不同构造观点.阿尔泰造山带南缘的泥盆纪浅变质碎屑沉积岩地球化学研究表明,该套浅变质碎屑沉积岩原岩主要为泥质或砂质沉积岩.尽管不同岩性样品主量元素含量不同,但其化学蚀变指数(CIA)小于75,成分变异指数(ICY)接近或小于1.0,斜长石蚀变指数(PIA)平均70,说明其源区物质比较新鲜,成熟度相对较低,化学风化作用较弱.同样,不同岩性样品微量元素含量差别较大,但表生过程中不活泼的微量元素比值却比较一致,轻稀土(LREE)中度富集(LaN/YbN=2.88～9.90),重稀土(HREE)比较平坦,并伴有明显的Eu负异常(Eu/Eu*=0.45～0.89).绝大多数样品具有高的La/Sc(1～3)、La/Y(0.5～1)和Ti/Zr(10～35),以及较低的Sc/Cr(0.1～0.3)比值,类似于大陆岛弧相关环境碎屑沉积物.在La-Th-Sc和Th-Sc-Zr/10构造环境判别图解中,除一千枚岩样品外,其他所有样品均落入大陆岛弧区.以上地球化学特征明显不同于大洋岛弧和被动陆缘沉积物,说明该套浅变质碎屑沉积岩可能沉积于活动大陆边缘的大陆岛弧相关环境,为认识阿尔泰造山带泥盆纪岛弧增生构造演化过程提供了一个重要证据.     

Oxygen isotope study of metamorphic and granitic rocks of the Yanai district in the Ryoke belt,Japan

¹⁸O/¹⁶O ratios have been obtained for 134 whole-rocks and minerals from metamorphic and granitic rocks of the Yanai district in the Ryoke belt, Southwest Japan. The ¹⁸O/¹⁶O ratios of pelitic rocks of the marginal metamorphic zone decrease progressively with increasing metamorphic grade. In the gneiss-granite complex (zone of migmatite [1]), the most characteristic feature of the rocks is that oxygen isotopic homogenization proceeds on both local and regional scales in parallel with “granitization” or chemical homogenization. Granitic rocks of various origin are fairly uniform in isotopic composition with δ ¹⁸O of quartz of 12 to 14‰ (SMOW) and δ ¹⁸O of biotite of 7 to 9‰ and are about 3 to 4‰ enriched in ¹⁸O compared to other Cretaceous granites of non-metamorphic terranes in Japan. The high ¹⁸O/¹⁶O ratios of granitic rocks of this district were discussed in relation to the ¹⁸O-depletion in metasediments. Oxygen isotopic fractionations among coexisting minerals from various rock-types of the gneiss-granite complex indicate that these minerals were formed under near isotopic equilibrium at a temperature of about 600 to 700° C. Some abnormal fractionations of quartz-biotite pairs also were obtained for rocks which had undergone a progressive ¹⁸O-depletion or ¹⁸O-enrichment. This is due to high resistivity of quartz and contrastive susceptibility of biotite to isotopic exchange during metamorphism and “granitization”.