共查询到20条相似文献，搜索用时 46 毫秒
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F. C. Brassington 《Hydrogeology Journal》2008,16(5):1017-1018
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Tolga Oyman 《Ore Geology Reviews》2010,37(3-4):175-201
The Ayazmant Fe–Cu skarn deposit is located approximately 20 km SE of Ayval?k or 140 km N of Izmir in western Turkey. The skarn occurs at the contact between metapelites and the metabasites of the Early Triassic K?n?k Formation and the porphyritic hypabyssal intrusive rocks of the Late Oligocene Kozak Intrusive Complex. The major, trace, and rare earth-element geochemical analysis of the igneous rocks indicate that they are I-type, subalkaline, calc-alkaline, metaluminous, I-type products of a high-level magma chamber, generated in a continental arc setting. The 40Ar–39Ar isochron age obtained from biotite of hornfels is 20.3 ± 0.1 Ma, probably reflecting the age of metamorphic–bimetasomatic alteration which commenced shortly after intrusion into impure carbonates. Three stages of skarn formation and ore development are recognized: (1) Early skarn stage (Stage I) consisting mainly of garnet with grossular-rich (Gr75–79) cores and andradite-rich (Gr36–38) rims, diopside (Di94–97), scapolite and magnetite; (2) sulfide-rich skarn (Stage II), dominated by chalcopyrite with magnetite, andraditic garnet (Ad84–89), diopside (Di65–75) and actinolite; and (3) retrograde alteration (Stage III) dominated by actinolite, epidote, orthoclase, phlogopite and chlorite in which sulfides are the main ore phases. 40Ar–39Ar age data indicate that potassic alteration, synchronous or postdating magnetite–pyroxene–amphibole skarn, occurred at 20.0 ± 0.1 Ma. The high pyroxene/garnet ratio, plus the presence of scapolite in calc-silicate and associated ore paragenesis characterized by magnetite (± hematite), chalcopyrite and bornite, suggests that the bulk of the Ayazmant skarns were formed under oxidized conditions. Oxygen isotope compositions of pyroxene, magnetite and garnet of prograde skarn alteration indicate a magmatic fluid with δ18O values between 5.4 and 9.5‰. On the basis of oxygen isotope data from mineral pairs, the early stage of prograde skarn formation is characterized by pyroxene (Di94–97)-magnetite assemblage formed at an upper temperature limit of 576 °C. The lower temperature limit for magnetite precipitation is estimated below 300 °C, on the basis of magnetite–calcite pairs either as fracture-fillings or massive ore in recrystallized limestone-marble. The sulfide assemblage is dominated by chalcopyrite with subordinate molybdenite, pyrite, cubanite, bornite, pyrrhotite, galena, sphalerite and idaite. Gold–copper mineralization formed adjacent to andradite-dominated skarn which occurs in close proximity to the intrusion contacts. Native gold and electrum are most abundant in sulfides, as fine-grained inclusions; grain size with varying from 5 to 20 µm. Sulfur isotope compositions obtained from pyrrhotite, pyrite, chalcopyrite, sphalerite and galena form a narrow range between ? 4.8 and 1.6‰, suggesting the sulfur was probably mantle-derived or leached from magmatic rocks. Geochemical data from Ayazmant shows that Cu is strongly associated with Au, Bi, Te, Se, Cd, Zn, Pb, Ni and Co. The Ayazmant mineralizing system possesses all the ingredients of a skarn system either cogenetic with, or formed prior to a porphyry Cu(Au–Mo) system. The results of this study indicate that the Aegean Region of Turkey has considerable exploration potential for both porphyry-related skarns and porphyry Cu and Au mineralization. 相似文献
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A palynological analysis of a Late Jurassic–Early Cretaceous succession in the Himalayan Tethys, Gyangzê County, southern Xizang (Tibet) provides, for the first time, evidence of changing palynofloras through the Jurassic/Cretaceous (J/K) boundary. Species that are stratigraphically important and potential markers for delineating the boundary include both miospores and dinoflagellate cysts. The presence of the spores Crybelosporites sp. cf. stylosus, Foraminisporis wonthaggiensis, Jiaohepollis verus and Toroisporis welzowense and the cysts Cassiculosphaeridia delicata and Rhynchodiniopsis serrata imply that the J/K boundary is between samples 06-21-1 and 06-21-3. The occurrence of Aequitriradites spinulosus and Cicatricosisporites spp. a little below this level and of ?Dictyotosporites sp. cf. speciosus slightly above it is also significant. These results show that it is possible to locate the J/K boundary in the Himalayan Tethys near top of the Weimei Formation and the lower part of the Gyabula Formation in southern Xizang. This succession also contains various marine invertebrate fossils, including ammonites, bivalves and belemnites, and thus has considerable potential for erecting an integrated biostratigraphy around the J/K boundary in the eastern Tethyan realm. Palynofloristic correlation implies a more northerly location for the fossil locality at Gyangzê than that of northwest Australia during the latest Jurassic and earliest Cretaceous, which can be further constrained to around 43°S. 相似文献
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Yu. O. Gavrilov Yu. V. Kushcheva I. V. Latysheva A. I. Gushchin A. L. Sokolova 《Moscow University Geology Bulletin》2016,71(2):137-150
The variations in the structural, textural, mineralogical, and geochemical (isotope) features of Lower to Middle Jurassic siliciclastic sediments along the Chanty-Argun River in Mountainous Chechnya and Georgia are discussed. This profile transects areas with various types of deformed sediments, from the northern comparatively weakly deformed and altered zone, to the southern zone of intense deformation and cleavage. Southward along the profile, these alterations are accompanied by the evolution of clay mineral assemblages, as well as polytypic modifications of micas and their crystallinity index. Increasing intensity of rock alteration and cleavage leads to a change of the K–Ar system, which results in a substantially rejuvenated isotope age of the sediments with a simultaneous increase of their stratigraphic age. 相似文献
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Background
Although uniquely capable of measuring multiple redox constituents nearly simultaneously with no or minimal sample pretreatment, voltammetry is currently underutilized in characterizing redox conditions in aquatic and terrestrial systems. Investigation of undisturbed media such as pore water requires a solid-state electrode, and such electrodes can be difficult to fabricate reproducibly. An approach to determine the concentrations of electroactive constituents using indirectly calibrated electrodes has been developed, but the protocol for and accuracy of this approach??the pilot ion method??has not been documented in detail.Results
A detailed procedure for testing electrode quality is provided, and the application and limitations of the pilot ion method have been documented. To quantify Fe(II) and Mn(II), subtraction of non-linear baseline functions from voltammetric signals produced better calibration curves than did linear baselines, enabled lower detection limits and reliable deconvolution of overlapping signals, and was successfully applied to sediment pore water signals. We observed that electrode sensitivities often vary by tens of percent, and that the sensitivity declines over time. The ratio of calibration slopes of Mn(II) to Fe(II) varied by no more than 11% from one Hg/Au electrode to another and Fe(II) concentrations predicted by the Mn(II) pilot ion were, on average, 13% different from their actual values. However, concentration predictions by the pilot ion method were worse for less than 15???M Fe(II) (46% different on average). The ratio of calibration slopes of Mn(II) to S(?II) varied by almost 20% from one Hg/Au electrode to another, and S(?II) predicted concentrations were as much as 58% different from their actual values. These predictions of Fe(II) and S(?II) concentrations indicate that the accuracy of the pilot ion method depends on how independent calibration slope ratios are from the electrode used. At medium-to-high concentration for the ocean, naturally derived dissolved organic carbon did not significantly affect the baseline-corrected electrode response of Mn(II) and Fe(II), but did significantly affect the response of S(?II).Conclusions
Despite their intrinsic variability, Hg/Au electrodes fabricated by hand can be used to quantify O2, S(?II), Fe(II), and Mn(II) without calibrating every electrode for every constituent of interest. The pilot ion method can achieve accuracies to within 20% or less, provided that the underlying principle??the independence of slope ratios??is demonstrated for all voltammetric techniques used, and effects of the physicochemical properties of the system on voltammetric signals are addressed through baseline subtraction. 相似文献10.
Contrasting sediment flux in Val Lumnezia (Graubünden, Eastern Swiss Alps), and implications for landscape development 总被引：1，自引：0，他引：1
Marco Schwab Fritz Schlunegger Heinz Schneider Gregor Stöckli Dirk Rieke-Zapp 《Swiss Journal of Geoscience》2009,102(2):211-222
This paper presents qualitative estimates of sediment discharge from opposite valley flanks in the S–N-oriented Val Lumnezia,
eastern Swiss Alps, and relates inferred differences in sediment flux to the litho-tectonic architecture of bedrock. The valley
flank on the western side hosts the deep-seated Lumnezia landslide where an area of ca. 30 km2 has experienced slip rates of several centimetres per year, potentially resulting in high sediment discharge to the trunk
stream (i.e. the Glogn River). High slip rates have resulted in topographic changes that are detectable on aerial photographs
and measurable with geodetic tools. In contrast, a network of tributary channels dissects the valley flank on the eastern
side. There, an area of approximately 18 km2 corresponding to < 30% of the surface has experienced a change in the landscape mainly by rock avalanche and rock fall, and
the magnitudes of changes are below the calibration limit of digital photogrammetry. We thus infer lower magnitudes of sediment
discharge on the eastern tributaries than on the western valley side, where landsliding has been the predominant erosional
process. These differences are interpreted to be controlled by the dip-slope situation of bedrock on the western side that
favours down-slope slip of material.
Morphometric investigations reveal that the western valley side is characterized by a low topographic roughness because this
valley flank has not been dissected by a channel network. It appears that high sediment discharge of the Lumnezia landslide
has inhibited the establishment of a stable channel network and has largely controlled the overall evolution of the landscape.
This contrasts to the general notion that channelized processes exert the first-order control on landscape evolution and formation
of relief and needs to be considered in future studies about landscape architecture, drainage network and sediment discharge. 相似文献
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Please refer to the attachment(s) for more details 相似文献
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Franz Walter Hans-Peter Bojar Christine E. Hollerer Kurt Mereiter 《Mineralogy and Petrology》2013,107(2):189-199
Galgenbergite-(Ce) from the type locality, the railroad tunnel Galgenberg between Leoben and St. Michael, Styria, Austria, was investigated. There it occurs in small fissures of an albite-chlorite schist as very thin tabular crystals building rosette-shaped aggregates associated with siderite, ancylite-(Ce), pyrite and calcite. Electron microprobe analyses gave CaO 9.49, Ce2O3 28.95, La2O3 11.70, Nd2O3 11.86, Pr2O3 3.48, CO2 30.00, H2O 3.07, total 98.55 wt.%. CO2 and H2O calculated by stoichiometry. The empirical formula (based on Ca + REE ∑3.0) is $ \mathrm{C}{{\mathrm{a}}_{1.00 }}{{\left( {\mathrm{C}{{\mathrm{e}}_{1.04 }}\mathrm{L}{{\mathrm{a}}_{0.42 }}\mathrm{N}{{\mathrm{d}}_{0.42 }}\mathrm{P}{{\mathrm{r}}_{0.12 }}} \right)}_{2.00 }}{{\left( {\mathrm{C}{{\mathrm{O}}_3}} \right)}_4}\cdot {{\mathrm{H}}_2}\mathrm{O} $ , and the simplified formula is $ \mathrm{CaC}{{\mathrm{e}}_2}{{\left( {\mathrm{C}{{\mathrm{O}}_3}} \right)}_4}\cdot {{\mathrm{H}}_2}\mathrm{O} $ . According to X-ray single crystal diffraction galgenbergite-(Ce) is triclinic, space group $ P\overline{1},a=6.3916(5) $ , b?=?6.4005(4), c?=?12.3898(9) Å, α?=?100.884(4), β?=?96.525(4), γ?=?100.492(4)°, V?=?483.64(6) Å3, Z?=?2. The eight strongest lines in the powder X-ray diffraction pattern are [d calc in Å/(I)/hkl]: 5.052/(100)/011; 3.011/(70)/0-22; 3.006/(66)/004; 5.899/(59)/-101; 3.900/(51)/1-12; 3.125/(46)/-201; 2.526/(42)/022; 4.694/(38)/-102. The infrared absorption spectrum reveals H2O (OH-stretching mode at 3,489 cm?1, HOH bending mode at 1,607 cm?1) and indicates the presence of distinctly non-equivalent CO3-groups by double and quadruple peaks of their ν1, ν2, ν3 and ν4 modes. The crystal structure of galgenbergite-(Ce) was refined with X-ray single crystal data to R1?=?0.019 for 2,448 unique reflections (I?>?2σ(I)) and 193 parameters. The three cation sites of the structure Ca(1), Ce(2) and Ce(3) have a modest mixed site occupation by Ca and small amount of REE (Ce, La, Pr, Nd) and vice versa. The structure is based on double layers parallel to (001), which are composed of Ca(1)Ce(2)(CO3)2 single layers with an ordered chessboard like arrangement of Ca and Ce, and with a roof tile-like stacking of the CO3 groups. Perpendicular to (001) the double layers are connected to a triclinic framework structure with good cleavage parallel to (001) by a differently organized and more open part of the structure formed by Ce(3)(CO3)2(H2O). Based on the topology of the CaCe(CO3)2 single layer in galgenbergite-(Ce), structural relationships to rutherfordine, to aragonite and ancylite type minerals, and to lanthanite are outlined. 相似文献
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Marcela Stárková Karel Martínek Radek Mikuláš Nicholas Rosenau 《International Journal of Earth Sciences》2015,104(5):1277-1298
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Summary ?The Betroka sinistral shear belt is a major geotectonic unit in the Precambrian of southern Madagascar. It consists of migmatitic
paragneiss commonly interlayered with phlogopite-bearing diopsidite, phlogopite-humite-diopside-spinel marble, sillimanite-garnet
quartzite and syn-tectonic S-type leucogranite. H?gbomite occurs sporadically in the migmatitic paragneiss in patches of magnetite
with hercynite, and at the border of magnetite where it is in contact with hercynite, rare ilmenite, rutile and cordierite,
which contains a network of chlorite, pyrophyllite and rare corundum/diaspore. XMg = Mg/(Mg + Fe) decreases as follows: Crd > Bt > Chl > H?g > Hc. The textural relations suggest the following h?gbomite-participating
reactions:
Ti-bearing hercynite ↠ hercynite + h?gbomite (intergrown/exsolution lamellae)
ilmenite + cordierite ↠ hercynite + h?gbomite + rutile + chlorite/pyrophyllite
h?gbomite ↠ hercynite + ilmenite + corundum
The chemical composition of h?gbomite varies substantially from grain to grain in individual samples and from sample to sample,
this variation being highly dependent on the associated minerals. There is a weak zoning from core to rim in individual grains
intergrown with hercynite and also in grains at the margin of hercynite, but this zoning is overprinted by zones formed at
grain rims depending on the surrounding phases. In contact with hercynite, h?gbomite has FeO (total Fe as FeO) 27.1–28.5 wt.%,
and MgO 4.5–5.8 wt.%, and in contact with magnetite FeO 24.9–26.5 wt.%, and MgO 6.0–8.5 wt.% and the core contents are within
these values. TiO27.5–4.0 wt.% and Al2O362.0–59.0 wt.% show zonations with increase from core to rim. Estimated P-T conditions are 6.0 ± 1.0 kbar and 700 ± 100 °C
reached during a peak metamorphic stage of the Pan-African orogeny. However, the presence of diaspore with exsolved hercynite-magnetite
indicates extreme retrograde metamorphism in the decompressional central part of this shear belt of southern Madagascar.
Received January 15, 1999;/revised version accepted July 6, 1999 相似文献
Zusammenfassung ?H?gbomit in migmatitischem Paragneis von Vohidava in der Betroka Scherzone im südlichen Pr?kambrium von Madagaskar Die sinistrale Betroka Scherzone ist eine ausgepr?gte tektonische Einheit des Pr?kambriums in Süd Madagaskar. Sie besteht aus migmatitischem Paragneis, in dem Phlogopit-führender Diopsidit, Phlogopit-Humit-Diopsid-Spinell-Marmor, Sillimanit-Granat-Quarzit und syntektonischer S-Typ Granit eingelagert sind. Im migmatitischen Paragneis kommen sporadisch H?gbomit/Hercynit Nester im Magnetit vor und am Magnetitrand findet sich H?gbomit im Kontakt mit Hercynit und Cordierit, der mit einem Netzwerk aus Chlorit/Pyrophyllit gefüllt ist, sowie sporadisch mit Korund/Diaspor, Ilmenit und Rutil. XMg = Mg/(Mg + Fe) nimmt in folgender Reihung ab: Crd > Bt > Chl > H?g > Hc. Aus den texturellen Beziehungen werden folgende H?gbomit-partizipierende Reaktionen abgeleitet: Ti-führender Hercynit ↠ Hercynit + H?gbomit (verwachsen/Entmischungslamellen) H?gbomit ↠ Hercynit + Ilmenit + Korund Die chemische Zusammensetzung von H?gbomit variiert betr?chtlich von Korn zu Korn in einer Probe und von Probe zu Probe; wobei die Variation von den Kontaktmineralen abh?ngt. H?gbomit im Hercynit hat eine schwache Zonierung von Kern zum Rand. Im H?gbomit am Hercynitrand ist die Kern-Rand-Zonierung durch die von den Kontaktmineralen abh?ngige Randzusammensetzung überpr?gt. Im Kontakt zum Hercynit hat H?gbomit 27,1–28,5 Gew.% FeO (total Fe als FeO) und 4,5–5,8 Gew.% MgO und im Kontakt zu Magnetit 24,9–26,5 Gew.% FeO und 6,0–8,5 Gew.% MgO, die Kernzusammensetzung liegt zwischen den beiden Randwerten. TiO2nimmt vom Kern zu den R?ndern von 7,5 bis 4,0 Gew.% ab und Al2O3von 62,0 bis 59,0 Gew.%. Die P-T Bedingungen des Metamorphose-Peaks w?hrend der Pan-Afrikanischen Orogenese erreichten 6,0 ± 1,0 Kbar und 700 ± 100 °C. Die sp?te Bildung von Diaspor und die Hercynit-Magnetit-Entmischung weisen auf eine tiefgreifende retrograde Metamorphose im Dekompressions-Zentralbereich der Betroka-Scherzone im südlichen Madagaskar hin.
Received January 15, 1999;/revised version accepted July 6, 1999 相似文献
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《Proceedings of the Geologists' Association. Geologists' Association》2023,134(2):117-124
Trace fossils are described from the Eocene Bembridge Limestone Formation from the Isle of Wight and used to constrain the paleoenvironmental interpretation. The lacustrine–palustrine succession contains three limestone beds, which are separated by clay and marl. The middle and upper limestone beds reveal complex burrow systems developed at their top. Based on their characteristics, these burrow systems are assigned to the ichnotaxon Balanoglossites triadicus Mägdefrau, which is associated with the shallow superficial grooves Sulcolithos variabilis Knaust. B. triadicus is a common marine trace fossil mainly known from shallow-marine carbonate successions throughout the Phanerozoic. It is accompanied by other marine ichnotaxa such as Arachnostega gastrochaenae Bertling, Gastrochaenolites isp. aff. G. ornatus Kelly and Bromley, Spongeliomorpha iberica Saporta and Thalassinoides suevicus (Rieth). This ichnological evidence confirms the occurrence of short-term marginal-marine incursions in a predominantly lacustrine to palustrine environment. 相似文献