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1.
The abundances and isotopic compositions of carbon, nitrogen and sulfur were measured in eleven lunar rocks. Samples were combusted sequentially at three temperatures to resolve terrestrial contamination from indigenous volatiles.Sulfur abundances in Apollo 16 highland rocks range from 73 to 1165 μg/g-whereas sulfur contents in Apollo 15 and 17 basalts range from 719 to 1455 μg/g and correlate with TiO2 content. Lunar rocks as a group have a remarkably uniform sulfur isotopic composition, which may reflect the low oxygen fugacity of the basaltic magmas. Much of the range of reported δ34Scd values (?2 to + 2.5 permil) is caused by systematic analytical discrepancies between laboratories.Lunar rocks very likely contain less than 0.1 μg/g of nitrogen. The measured spallogenic production rate, 4.1 × 10?6 μg 15N/g sample/m.y., agrees remarkably closely with previous estimates. An estimate which includes all available data is 3.7 × 10?6 μg15N/g sample/m.y.Lunar basalts may contain no indigenous lunar carbon in excess of procedural blank levels (~0.7 μg/g). Highlands rocks consistently release about 1 to 5 μg/g of carbon in excess of blank levels, but this carbon might either derive from ancient meteoritic debris or be a mineralogie product of terrestrial weathering. The average measured spallogenic 13C production rate is 4.1 × 10?6 μg13C/g sample/m.y. The 13C spallation exposure ages of rocks 15058 and 15499 are 184 and 135 m.y., respectively.  相似文献   

2.
Twenty different rocks have been analyzed for tellurium by atomic absorption. The average tellurium content of 12 igneous rocks is 82 p.p.b., with a range, 3.4 p.p.b. ≥ Te = 210 p.p.b. In ultrabasic rocks, the tellurium content is ? 10 p.p.b. Of the rocks analyzed, carbonates showed the highest Te content, 1–2 p.p.m., and the tellurium concentrations in 6 sedimentary rocks decrease in the following order: carbonates > shales > sandstones.  相似文献   

3.
The isotopic compositions of strontium in 25 basalts and relatedvolcanic rocks from both oceanic and continental localitieshave been determined. The isotopic abundance of Sr87, convenientlyexpressed as the Sr87/Sr86 ratio, was found to vary from 0?7047to 0?7101. The range of variation is outside experimental errorsand is considered to be significant. No consistent differencein the value of the Sr87/Sr86 ratio was observed for basaltsfrom continental and oceanic localities. The average Sr87/Sr86ratio for eleven oceanic basalts was found to be 0?7072?0?0003,whereas fourteen continental basalts and related volcanic rocksaveraged Sr87/Sr86=0?7082?0?0003. The errors are the standarddeviations of the mean. The average Sr87/Sr86 ratio for all25 basalts is 0?7078 with limits of variation of +0?002 and–0?003. The concentrations of rubidium and strontium in a representativenumber of the basalts were determined by isotope dilution. Fiveolivine basalts averaged Rb=17?6 p.p.m., Sr=390?55 p.p.m., Rb/Sr=0?044?0?018;whereas six tholeiitic basalts were found to contain 30?7 p.p.m.Rb, 504?167 p.p.m. Sr, Rb/Sr=0?060?0?024. On the basis of the most reliable rubidium and strontium analysesof igneous and sedimentary rocks available in the literaturethe Rb/Sr ratio of the near-surface part of the continentalcrust is estimated to be 0?25. If its average age is approximately2 billion years and its initial Sr87/Sr86 ratio was 0?704, thepresent average value would be 0?725. This estimate is compatiblewith results obtained for two composites of Palaeozoic shalewhich averaged Sr87/Sr86=0?7215?0?001. The hypothesis is advanced that there is sufficient enrichmentof Sr87 in crustal materials so that the value of the Sr87/Sr86ratio of igneous rocks at the time of crystallization can beused as a criterion for the origin of the material. The initialSr87/Sr86 ratio of an igneous rock formed by assimilation, remelting,or granitization of old crustal material enriched in rubidiumis expected to be measurably higher than that of igneous rockswhich are products of fractional crystallization of basalt magmaor were derived from undifferentiated basaltic material at depthin the crust. The initial Sr87/Sr86 ratio, time of crystallization, and possibleco-magmatic relationships of differentiated intrusive igneousrocks or series of lava flows of different compositions canbe indicated by the convergence of the whole-rock strontiumdevelopment lines. This method is illustrated by the intrusivealkaline rocks of the Monteregian hills, Quebec.  相似文献   

4.
Based on REE abundances in megacrysts and host basalts and their equilibrium conditions,it has proved that megacrysts may have been produced from the magma derived from the host rocks or of more basic composition.The REE ratios of megacrysts to host rocks may be taken as partition coefficients when both are equilibrium with each other.The crystal fractionation of megacrysts has caused the evolution of REE in the magma.It is obvious that some host basalts are the product of magma evolution after crystal fractionation.According to REE abundances in the host rocks and the partition coefficients between crystal and liquid,the history of crystal fractionation of magma can be traced.  相似文献   

5.
Rare earth abundances were determined by neutron activation in twenty Hawaiian lavas and one diabase of known chemical and mineralogical compositions. These results demonstrate a systematic relationship between the absolute or relative rare earth abundances and the petrochemistry of these rocks. Three distinct lava groups are recognized. These correspond to: (1) tholeiites, (2) alkali series, (3) nepheline-melilite basalts.Based on rare earths: a) The hawaiites and mugearite of the alkali series represent residual melts derived from alkali olivine basalts, most likely by fractional crystallization; the trachyte, however, seems to have a more complicated history. b) Fractional crystallization models linking nephelinites or alkali olivine basalts to tholeiites are possible. However, production of these three lava groups, independently, by various degrees of partial melting of the mantle is equally likely and cannot be distinguished from these fractional crystallization models. c) Daly limestone syntexis hypothesis to produce the nephelinites is unlikely.  相似文献   

6.

The Petroi Metabasalt comprises approximately 2000 m of massive and pillowed metabasalt flows, breccias, and metadolerite sills that overlie and are intercalated with Early Permian epiclastic rocks of the Nambucca Slate Belt. Both the basaltic rocks and associated sedimentary material were multiply deformed and metamorphosed to pumpellyite‐actinolite facies grade at about 255 Ma. Metamorphism and earlier sea‐floor alteration of these mafic rocks have led to hydration, carbonation and oxidation and considerable redistribution of the major elements and the more labile traces, notably Rb, Ba and Sr. However, abundances of TiO2, the high field strength trace elements, Ni, Cr and V, the light rare earths and yttrium are interpretable as being the largely unmodified magmatic abundances of mildly alkaline within‐plate basalts. This interpretation is supported by the composition of relic Ca‐rich pyroxenes in the metadolerites which fall in the fields of mildly alkaline basalts. The field relationships, age and composition of these rocks suggest either eruption on oceanic crust covered by a thick sequence of epiclastic rocks and subsequent incorporation into an accretionary subduction complex, or generation during rifting of the eastern part of the New England Fold Belt and accumulation, together with the associated sedimentary rocks, in a graben. The chemical and mineral characteristics of the igneous rocks indicate that the volcanism was not related to magmatic arc activity, and their presence demonstrates the rocks of the Nambucca Slate Belt are neither fore‐arc basin nor slope‐basin deposits.  相似文献   

7.
Carbon abundances have been determined in mantle xenoliths from alkalic basalts and kimberlites and interpreted in terms of the nature and distribution of the C-rich phases. Anhydrous Cr-diopside Group I spinel lherzolites from basalts typically contain 15–50 ppm C, and amphibole-bearing ones have only marginally higher concentrations (40–100 ppm). Carbon abundances in Al-augite Group II pyroxenites are not significantly different from those of the Group I rocks. Although most LREE-depleted lherzolite xenoliths contain less C than enriched samples, there is no clear relationship between abundances of C and the incompatible trace elements.In the suite of deformed cumulate peridotite and dunite xenoliths of the 1801 Kaupulehu flow of the Hualalai volcano, Hawaii, C abundances are clearly related to texture, modal composition, and style of deformation. The most C-rich rocks are wehrlites in which the clinopyroxenes deformed more brittly and thus possess higher fluid inclusion and crack densities than the surrounding olivines.Regardless of their lithology, all xenoliths from kimberlites (including both peridotites and eclogites) are C-rich compared to those from basalts. Most of the C in these xenoliths exists as calcite or carbonaceous matter associated with serpentine veins and was thus probably contributed by the kimberlite host. Primary carbonates are extremely rare in all xenoliths, although occasionally they have been observed as daughter products in fluid inclusions.Although most C exists as inclusions of CO2-rich vapor, condensed carbonaceous matter also appears to occur in all rocks as discrete platy grains and as a film on natural surfaces such as grain boundaries and cracks.  相似文献   

8.
The chlorine concentration has been determined by a chemical method in 7 quartz tholeiites, 19 alkali olivine basalts, 9 basanitic alkali olivine basalts and 11 olivine nephelinites to be on average 80, 280, 720, and 400 ppm Cl respectively. If these basalts are products of decreasing degrees of partial melting of mantle rocks a regular increase of chlorine is to be expected in this sequence. The actual chlorine abundances are a function of partial losses of gases during rock consolidation and optimum stabilities of sodalite group minerals as major chlorine traps in alkalic basalts. The occurrence of sodalite and sodalite nosean solid solutions has been detected by microprobe in 7 out of 10 alkalic basalt species in grains smaller than 70 m. Quantitative analyses of 4 sodalite group minerals from the olivine nephelinites are listed. One contains the sodalite and the nosean molecule in a proportion one to one and must be formed above 1,050 °C according to the experimental results of Tomisaka and Eugster (1968) in the respective system. In the majority of the samples apatite contains less than 20% of the total chlorine of the basalts. Biotite as chlorine containing phase (about 900 ppm Cl) is rare. The proportion of chlorine which could be extracted from rock powders by boiling water is small. No general correlation between the element pairs Cl/S and Cl/K could be observed. Excluding tholeiites a tendency of a reversed correlation between chlorine and potential primary water (as indicated by the Fe2O3/FeO ratio) and between chlorine and silica can be derived.  相似文献   

9.
Despite the fact that some greenstone belts preserve the record of contemporaneous komatiitic and tholeiitic volcanism, a genetic link between the two is not widely accepted. The significance of a compositional gap seperating these magma types and differences in their respective degree of light rare earth element (LREE) enrichment, cited as evidence against a derivative relationship, are complicated by the possibility of crustal assimilation by magmas of komatiitic affinity. In the Archean La Grande Greenstone belt of northern Quebec a succession of metamorphosed tholeiitic basalts and younger, high-Mg, LREE-enriched andesites are preserved. The tholeiites are differentiated basaltic rocks whose chemical compositions appear to have been controlled by low pressure, gabbroic fractional crystallization and are similar to Type 1 MORB. Parental magmas were probably high-Mg liquids of compositions similar to komatiitic basalts which also occur in the greenstone belt. These high-Mg liquids are believed to be themselves the product of high pressure, OLIV+OPX fractional crystallization of more magnesian primary liquids of komatiitic composition. The higher La/Sm ratios of komatiitic basalts and tholeiites relative to komatiites in this belt, can be explained by small degrees of crustal assimilation. In the central part of the belt, late-stage, mafic igneous rocks have chemical compositions similar to Archean examples of contaminated volcanic rocks (e.g., Kambalda, Australia). These late-stage lavas consist of basalts and andesites with high-Mg, Ni and Cr abundances, LREE-enriched profiles and low Ti abundances. They are believed to be the products of crustal assimilation and crystallization of OPX-PLAG-CPX from high-Mg liquids of komatiitic affinity. The volcanic stratigraphy records the progressive effects of crustal contamination through time. A light sialic crust may have initially acted as a density barrier, preventing the eruption of primary high-Mg liquids and forcing fractionation at depth which produced more buoyant compositions. With subsequent thinning of the crust, the density barrier presumably failed, and primary liquids migrated directly toward the surface. Reaction of these liquids with tonalitic crust produced contaminated differentiates.  相似文献   

10.
海南岛石炭纪双峰式火山岩及其板块构造背景   总被引：4，自引：2，他引：4  
海南岛西部的石炭纪火山岩为一套大洋拉斑玄武岩-流纹斑岩的双峰式火山岩。玄武岩中的不相容元素和稀土元素的丰度和比值,以及稀土分配模式与大陆裂谷的拉斑玄武岩的地球化学特征一致,说明海南岛晚古生代裂谷作用的存在。玄武质岩浆来源于地幔深部,演化程度较低,受下地壳物质混染。流纹质岩浆不是玄武岩浆结晶分异产物,而是受裂谷区高热流影响,由陆壳部分熔融形成。  相似文献   

11.
The ∼133 Ma volcanic rocks of Sangxiu Formation are distributed in the eastern part of the central Tethyan Himalaya and belong paleogeographically to the northeastern margin of Greater India. These volcanic rocks include alkaline basalts and felsic volcanic rocks. Major and trace element abundances and whole-rock isotopic data for selected samples of these volcanic rocks are used to infer their petrogenesis. Geochemically, the Sangxiu basalts are closely similar to the Emeishan high-Ti basalts. Major and trace element data and Sr–Nd isotopic compositions suggest that the Sangxiu basalts may have been derived from an OIB-type mantle source, with discernable contributions from subcontinental lithospheric mantle (SCLM). The basaltic magmas may have formed as a result of the infiltration of plume-derived melts into the base of the lithosphere in a continental rift setting. The Sangxiu felsic volcanic rocks share most of the geochemical features of A-type granite, and have Sr–Nd isotopic compositions which differ considerably from the Sangxiu basalts, suggesting that they originated from the anatexis of ensialic continental crust. The Sangxiu volcanic rocks may be considered as the consequence of an interaction between the Kerguelen hotspot and the lithosphere of the northeastern margin of Greater India at ∼133 Ma, and may represent the initial stage of the separation of Greater India from southwestern Australia.  相似文献   

12.
分布于甘肃省榆中县兴隆山地区的兴隆山岩群为一套浅变质火山岩与浅变质碎屑岩所组成的岩石组合，其火山岩主要出露于兴隆山岩群中岩组和上岩组。兴隆山岩群火山岩岩性主要为变质玄武岩,具有低w（K2O）、w（Na2O＋K20）和w（TiO2）的特点，且w（TiO2）和w（P2O5）接近于洋中脊玄武岩的平均质量分数，为亚碱性的拉斑玄武岩系列，火山岩稀土元素总量低，轻、重稀土元素分馏不明显，稀土元素配分曲线为轻稀土元素略亏损、重稀土元素平坦型，与洋中脊玄武岩的配分曲线类似，火山岩大离子亲石元素相对富集，高场强元素和重稀土元素平坦，稀土元素、微量元素特征及构造环境判别显示兴隆山岩群的火山岩形成于中元古代秦祁昆多岛洋中部略富集的E型洋中脊的海底扩张环境。  相似文献   

13.
A radiochemical N.A.A. method was used to obtain new values on W distribution in some 125 volcanic rocks, mainly basalts and andesites, from different petrotectonic environments.These W data are below previously reported abundances. New median values in various types of rocks are suggested (ppm W). Basalts: ocean floor, 0.15; ocean islands subalkaline, 0.28; ocean islands alkaline, 0.60; island arc, 0.19: continental margin, 0.40; continental subalkaline, 0.30: continental alkaline, 1.35. Andesites: island arc, 0.23; continental margin, 1.05.Median values for all 91 basalts and all 20 andesites are 0.36 and 0.29 ppm respectively.  相似文献   

14.
Seven volcanic rocks from neovolcanic zone of Iceland were analysed for rare-earths (RE). The bulk partition coefficients are estimated from combination of the studied samples. In contrast with the mid-ocean ridge basalts which show the solid-type RE patterns, four of five arbitrarily chosen Icelandic basalts appear to have liquid-type RE patterns. The occurrence of relatively pristine lava with relative unfractionated RE abundances to chondrite is also considered to be associated with the peculiar tectonics of Iceland.  相似文献   

15.
Sulfur isotope ratios have been determined in 27 selected volcanic rocks from Iceland together with their whole rock chemistry. The 34S of analyzed basalts ranges from –2.0 to +0.4 with an average value of –0.8 Tholeiitic and alkaline rocks exhibit little difference in 34S values but the intermediate and acid rocks analyzed have higher 34S values up to +4.2 It is suggested that the overall variation in sulfur isotope composition of the basalts is caused by degassing. The small range of the 34S values and its similarity to other oceanic and continental basalts, suggest that the depleted mantle is homogeneous in its sulfur isotope composition. The 34S of the depleted mantle is estimated to be within the range for undegassed oceanic basalts, –0.5 to +1.0  相似文献   

16.
CHARACTERISTICS OF VOLCANIC ROCKS AND ITS TECTONIC SETTING IN WESTERN PART OF LAZHULONG-JINSAJIANG STRUCTURAL BELT  相似文献   

17.
Apatite has been analyzed from mare basalts, the magnesian-suite, the alkali-suite, and KREEP-rich impact-melt rocks using an electron probe microanalysis routine developed specifically for apatite. We determined that all the lunar apatite grains analyzed are predominantly fluorine rich; however, they also contain varying concentrations of chlorine and a missing structural component that, after ruling out other possibilities, we attribute to OH. Apatite grains from mare basalts are compositionally distinct from the apatite grains in the magnesian-suite, the alkali-suite, and KREEP-rich impact-melt rocks, which all had similar apatite compositions. Apatite grains in mare basalts are depleted in chlorine, and many of the analyzed grains have stoichiometry that suggests a significant OH component (i.e., >0.08 structural formula units), whereas apatite grains in the magnesian suite, alkali suite, and KREEP-rich impact melts are enriched in chlorine and do not typically have a missing structural component that could be attributed to OH− (within the detection limit of 0.08 sfu). From these data, we infer that residual liquids in the mare basalts were enriched in H2O and fluorine relative to chlorine at the time of apatite crystallization, whereas residual liquids in magnesian-suite, alkali-suite, and KREEP-rich impact melts were enriched in chlorine relative to H2O and fluorine at the time of apatite crystallization. The relative volatile abundance that we determined for the mare basalts is identical to the previously determined relative volatile abundance for the lunar picritic glasses. This result indicates that the observed relative volatile abundance signature of the picritic glass source is the same as that in the mare basalt source regions. The magnesian-suite, alkali-suite, and KREEP-rich impact-melt rocks likely reflect a volatile source with different volatile abundances than the sources of mare volcanics. Moreover, the magnesian-suite, alkali-suite, and KREEP-rich impact-melt rocks may reveal the relative volatile abundance of urKREEP, the residual melt of the magma ocean. This difference in relative magmatic volatile abundance among the lithologic groups investigated cannot be explained by degassing of a single source composition (relative to magmatic volatiles). The most reasonable explanation for the compositional disparity is a difference in the relative volatile abundances in the magmatic source regions of the Moon. Therefore, we conclude that the Moon has a heterogeneous distribution of magmatic volatiles within its interior, with a chemical divide (with respect to magmatic volatiles) existing between magmas that arise by partial melting of the lunar mantle and magmas that have seen significant contamination by a KREEP component.  相似文献   

18.
Sixty-five million year old continental flood basalts crop out on Qeqertarssuaq Island and the Nuussuaq Peninsula in West Greenland, and they include ～1,000 m of picritic lavas and discrete 10- to 50-m-thick members of highly contaminated basalts. On Qeqertarssuaq, the lavas are allocated to the Vaîgat and Maligât Formations of which the former includes the Naujánguit member, which consists of picrites with 7–29 wt% MgO, 80–1,400 ppm Ni, 5.7–9.4 ppb Pt and 4.2–12.9 ppb Pd. The Naujánguit member contains two horizons of contaminated basalts, the Asûk and Kûgánguaq, which have elevated SiO2 (52–58 wt%) and low to moderate MgO (7.5–12.8 wt%). These lavas are broadly characterized by low Cu and Ni abundances (average, 40 ppm Ni and 45 ppm Cu) and very low Pt (0.16–0.63 ppb) and Pd (0.13–0.68 ppb) abundances, and in the case of the Asûk, they contain shale xenoliths and droplets of native iron and troilite. The contaminated basalts from Nuussuaq, the B0 to B4 members, are also usually Ni-, Cu-, and platinum-group elements (PGE)-depleted. The geochemical signatures (especially the ratios of incompatible trace elements such as Th/Nb) of all of the contaminated basalts from Qeqertarssuaq and some of those from Nuussuaq record what appears to be a chemical contribution from deltaic shales that lie immediately below the lavas. This suggests that the contamination of the magmas occurred during the migration of the magmas through plumbing systems developed in sedimentary rocks, and hence, at a high crustal level. Nickel, Cu, and PGE depletion together with geochemical signatures produced by crustal contamination are also a feature of Siberian Trap basalts from the Noril’sk region. These basalts belong to the 0- to 500-m thick, ～5,000- to 10,000-km3 Nadezhdinsky Formation, which is centered in the Noril’sk Region. A major difference between Siberia and West Greenland is that PGE depletion in the Nadezhdinsky Formation samples with the lowest Cu and Ni contents is much more severe than that of the West Greenland contaminated basalts. Moreover, the volumes of the contaminated and metal-depleted volcanic rocks in West Greenland pale is significant when compared to the Nadezhdinsky Formation; local centers rarely contain more than 15 thin flows with a combined thickness of <50 m and more typically 10–20 m, so the volume of the eruptive portions of each system is probably two orders of magnitude smaller than the Nadezhdinsky edifice. The West Greenland centres are juxtaposed along fault zones that appear to be linked to the subsidence of the Tertiary delta, and so emplacement along N–S structures appears to be a principal control on the distribution of lavas and feeder intrusions. This leads us to suggest that the Greenland system is small and segregation of sulphide took place at high levels in the crust, whereas at Noril’sk, the saturation event took place at depth with subsequent emplacement of sulphide-bearing magmas into high levels of the crust. As a consequence, it may be unreasonable to expect that the West Greenland flood basalts experienced mineralizing processes on the scale of the Noril’sk system.  相似文献   

19.
High-alumina basalts from seven High-Andean stratovolcanoes (37 °30′S to 41 °S) have major and trace element (including rare earth elements, REE) that are consistent with derivation by partial melting (typically 10–15%) of garnet-free peridotite followed by fractional crystallization of olivine and pyroxene. High-alumina basalts from two stratovolconoes require significantly lower degrees of melting (<5%) or melting of an incompatible, element-enriched source. However, a poorly understood feature of all of these basalts-and calc-alkaline rocks in general-is the mechanism for causing their low TiO2 and heavy REE content relative to oceanic basalts. Further north in Chile (33 °–34 °S and 21 °–22 °S) amphibole-bearing andesites have REE abundances consistent with derivation from a garnet-bearing source such as incompatible, element-rich eclogite (e.g., Franciscan eclogites) or garnet peridotite. The marked petrological and geochemical changes along strike of the Andes are probably related to the varying nature of the subduction process; e.g., dips of the downgoing slab varying from 10 to 30 °.  相似文献   

20.
An elongate belt of mid-Cretaceous, compositionally banded gneisses and granulites is exposed in Cucamonga terrane, in the southeastern foothills of the San Gabriel Mountains of southern California. Banded gneisses include mafic granulites of two geochemical types: type 1 rocks are similar to high Al arc basalts and andesites but have higher HFSE (high-field-strength-element) abundances and extremely variable LILE (largeion-lithophile-element) abundances, while type 2 rocks are relatively low in Al and similar to alkali rich MOR (midocean-ridge) or intraplate basalts. Intercalated with mafic granulites are paragneisses which include felsic granulites, aluminous gneisses, marble, and calc-silicate gneisses. Type 1 mafic granulites and calcic trondhjemitic pegmatites also oceur as cross-cutting, synmetamorphic dikes or small plutons. Small-scale heterogeneity of deep continental crust is indicated by the lithologic and isotopic diversity of intercalated ortho-and paragneisses exposed in Cucamonga terrane. Geochemical and isotopic data indicate that K, Rb, and U depletion and Sm/Nd fractionation were associated with biotite +/- muscovite dehydration reactions in type 1 mafic granulites and aluminous gneisses during high-grade metamorphism. Field relations and model initial isotopic ratios imply a wide range of protolith ages, ranging from Early Proterozoic to Phanerozoic.  相似文献   

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