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181.
Ziminaite,Fe3+VO4, a new howardevansite-group mineral from the Bezymyannyi volcano,Kamchatka, Russia
Pekov Igor V. Siidra Oleg I. Yapaskurt Vasiliy O. Polekhovsky Yury S. Kartashov Pavel M. 《Mineralogy and Petrology》2018,112(3):371-379
Mineralogy and Petrology - The new mineral ziminaite, ideally Fe3+VO4, was found in fumarole sublimates at the Bezymyannyi volcano, Kamchatka, Russia. Ziminaite occurs as lamellar, tabular or... 相似文献
182.
Ramacciotti Carlos D. Casquet César Baldo Edgardo G. Galindo Carmen Pankhurst Robert J. Verdecchia Sebastián O. Rapela Carlos W. Fanning Mark 《International Journal of Earth Sciences》2018,107(7):2605-2625
International Journal of Earth Sciences - The Western Sierras Pampeanas (WSP) of Argentina record a protracted geological history from the Mesoproterozoic assembly of the Rodinia supercontinent to... 相似文献
183.
Microstructural and magnetic investigations (anisotropy of magnetic susceptibility, AMS) on sections across basement–cover interfaces (BCI) revealed a complex evolution in the crystalline basement rocks beneath and in the basal units of the Caledonian fold-and-thrust belt: (1) Pre-Caledonian mylonitic fabrics in basement granite relate to steep shear zones. (2) Palaeoweathering formed smectite and illite at the expense of feldspar and mica. Secondary Fe-bearing clay minerals and the intensity of the chemical weathering control the bulk susceptibility. Changing susceptibility and AMS relate to a (time) sequence from primary magnetite to secondary paramagnetic clay to pyrite and ferrimagnetic pyrrhotite. (3) Burial compaction with BCI-parallel fabrics. (4) Caledonian cleavage, overprinted by décollement zones with S–C–C′ fabrics. Décollement cataclasis overprinted pre-existing magnetic fabrics and produced horizontal magnetic lineations and subhorizontal foliations defined by the S–C–C′ fabrics. Clay mineral enrichment, together with subsequent, BCI-parallel compaction fabrics, decreased the shear strength in the basement rocks beneath the BCI. Detachments initiated at such low-strength zones and produced allochthonous units with their footwall within crystalline basement rocks, an observation of general importance for orogenic fold-and-thrust belts. 相似文献
184.
Platinum-group element (PGE) abundances in mantle rocks are generally considered to result from a late meteorite addition to the early Earth, post-dating the core separation event. As such, PGEs are key tracers for the Earth accretion history. For decades, the PGEs systematics of undepleted mantle peridotites has been used to constrain the composition of meteorite impactors involved in the late veneer material. Despite multiple evidence of considerable modifications by partial melting, harzburgites from the Sumail ophiolite (Oman) display a mean PGE composition very akin to recently refined estimates for the Primitive Upper Mantle (PUM) of the Earth. These rocks document a resetting of the PUM signature by percolating basaltic melts, which precipitated Pd-enriched Cu–Ni sulphides within a strongly Pd-depleted residual harzburgitic protolith. Such a resetting casts doubt on both the reliability of any PUM estimates and relevance of the PUM concept itself, at least for PGEs. 相似文献
185.
P. A. Fokin V. R. Demidova V. M. Yatsenko P. V. Stavinskii O. V. Lisunova 《Moscow University Geology Bulletin》2008,63(5):304-310
Sedimentologic analysis of cores from wells sunk in the Vankor petroleum field allowed refinement of the accumulation conditions producing the sandy strata of the Nizhnyaya Kheta River (Nizhnekhetsky) Formation accumulated in the coastal marine zone and of the Yakovlevo (Yakovlevsky) Formation accumulated under alluvial-deltaic conditions. Petrographic examination of the sandstones added information on the sources, transport, and accumulation conditions of the terrigenous material in the northeastern marginal part of the West Siberian sedimentation basin. 相似文献
186.
G. P. Zaraisky A. M. Aksyuk V. N. Devyatova O. V. Udoratina V. Yu. Chevychelov 《Petrology》2008,16(7):710-736
The concept of granitic melt fractionation as the main process in the concentration of rare elements in granites calls for
the development of a reliable method to determine the evolutionary sequences of granite series. We propose to use for this
purpose a zirconium-hafnium indicator, the Zr/Hf weight ratio in granitic rocks (Zaraisky et al., 1999, 2000). By the example
of three classic regions of rare-metal deposits, eastern Transbaikalia, central Kazakhstan, and Erzgebirge (Czech Republic
and Germany), it was empirically shown that the Zr/Hf ratio of granites decreases during the fractional crystallization of
granite magmas in the sequence granodiorite → biotite granite → leucogranite → lithium-fluorine granite. The reason is the
higher affinity of Hf compared with Zr to a granite melt. This implies that the crystallization and settling of accessory
zircon will cause the progressive enrichment of Hf relative to Zr in the residual melt. As a result, the Zr/Hf ratio decreases
regularly in the series of sequential phases of granite intrusion related to a single magma chamber from granodiorite to biotite
granite, leucogranite, and Li-F granite (from 45-30 to 10-2). Our experimental investigations supported the preferential enrichment
of haplogranite melt in Hf and zircon crystals in equilibrium with melt in Zr (T= 800°C and P = 1 kbar). The Zr/Hf indicator was tested by the example of the wellknown Kukulbei rare-metal granite complex of eastern
Transbaikalia (J3), which is unique in the degree of fractionation of initial granite melt with the formation of three phases
of granite emplacement and vein derivatives. An important feature of the complex is its “short” differentiation trend. It
was supposed that the granite magma of the first phase is parental, and the later phases forming small intrusive bodies in
large massifs of biotite granites of the first phase are sequential products of its crystallization differentiation in a magma
chamber. The biotite granites of the first phase are barren. The leucocratic granites of the second phase are accompanied
by tin-tungsten greisen deposits (e.g., Spokoininskoe), and the upper part of cupola-like stocks of Li-F amazonite granites
of the third phase host apogranite-type tantalum deposits (Orlovka, Etyka, and Achikan). In addition to three granite phases,
the Kukulbei complex includes dikes of ongonites, elvans, amazonite granites, and chamber miarolitic pegmatites. All of the
granitic rocks of the complex have similar isotopic ages of 142± 0.6 Ma. The Zr/Hf ratio decreases systematically from phase
1 (40–25), to phase 2 (20–10), and phase 3 (10–2). The ongonites, elvans, and pegmatites have similar Zr/Hf ratios (15-5),
falling between the ranges of leucocratic muscovite granites and Li-F granites. Compared with other granite series, the granitic
rocks of the Kukulbei complex show specific petrographic and geochemical features: they are strongly enriched in Rb, Li, Cs,
Be, Sn, W, Mo, Ta, Nb, Bi, and F but depleted in Mg, Ca, Fe, Ti, P, Sr, Ba, V, Co, Ni, Cr, Zr, REE, and Y. From the early
to late intrusion phases, the degree of enrichment and depletion in these element groups increases regularly. This is accompanied
by a significant decrease (from 40 to 2) in Zr/Hf, which can be used as a reliable indicator of genetic relations, degree
of fractionation, and rare-metal potential of granites. Granites with Zr/Hf values lower than 25 are promising for prospecting
for Sn, W, Mo, and Be greisen deposits, whereas the formation of Ta deposits requires Zr/Hf values lower than 10. 相似文献
187.
Vitalis C. Ozebo Fidelis O. Ogunsanwo Gboyega A. Adebayo Olusola J. Adeniran 《Central European Journal of Geosciences》2013,5(1):43-52
The Mellin transform is a mathematical tool which has been applied in many areas of Mathematics, Physics and Engineering. Its application in Geophysics is in the computation of solution of potential problems for the determination of the mass as well as the depth to the basement of some solid mineral deposits. In this study, the Mellin transform is used to determine the depth to the top (h) and the depth to the bottom (H) of the basement of a profile of an anomalous magnetic body. Ibuji, the study area is located in Ifedore Local Government area of Ondo state, Nigeria, underlain by Precambrian complex rocks and bounded by geographical co-ordinate of Easting 5°00t’00″ to 5°4t’30″ and Northing 7°24t’00″ to 7°27t’36″. The magnetic anomaly profile due to a two- dimensional body(vertical thin sheet)over magnetic spring of the study area was digitised and the values of magnetic amplitude (nT) with respect to its horizontal distance (say interval of 5 m) obtained from the digitized profile was then used in the computation of Mellin transform using Matlab programs. In order to determine the depths H and h, the amplitudes were considered at three arbitrary point (s = ¼, ½ and ¾) such that, (0 < s < 1), where s is a complex variable of real positive integer. The value obtained for H was 47.95 m, which compared favourably with the result obtained using other methods. Meanwhile, the value obtained for h has a convergence restriction, whereby, at lower values of s, there is divergence, while at higher values of s, (about 0.9), the result converges and h was obtained to be 32.56 m. The Ibuji magnetic anomaly was therefore analysed to have a depth to the bottom (H) of 47.95 m and depth to the top of 32.56 m using this mathematical tool. 相似文献
188.
189.
190.
Two populations of mantle xenoliths from the Proterozoic Premier kimberlite show an absence of potassic metasomatism common in Phanerozoic kimberlites. The Premier samples are relatively enriched in Fe and Ti, and contain Fe mica and aluminous amphibole instead of Mg-phlogopite and K-richterite. These features are consistent with a recently identified ρ wave anomaly beneath this part of the Kaapvaal craton ascribed to refertilization of the mantle. Upwelling of sublithospheric mantle to produce the Bushveld Igneous Complex is considered to be the source of silicate melt available for metasomatism. The resultant refertilized Fe-, Ti-, and Al-enriched mantle composition resembles that which is required to form Proterozoic troctolitic magmas. 相似文献