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1.
Oxygen isotope systematics of emerald: relevance for its origin and geological significance 总被引:2,自引:0,他引:2
G. Giuliani C. France-Lanord P. Coget D. Schwarz A. Cheilletz Y. Branquet D. Giard A. Martin-Izard P. Alexandrov D. H. Piat 《Mineralium Deposita》1998,33(5):513-519
Oxygen isotopic composition of emerald from 62 occurrences and deposits in the world reveals a wide range in δ18O (SMOW) between +6.2 and +24.7‰. The δ18O-values for each deposit are restricted and can be used to determine the origin of emerald from the world's most important
producers. The δ18O-value of emerald appears to be a fingerprint of its origin, especially for gems of exceptional quality from Colombia (eastern
emerald zone, δ18O = +16.8 ± 0.1‰; western emerald zone, δ18O = +21.2 ± 0.5‰), Afghanistan (δ18O = +13.5 ± 0.1‰), Pakistan (Swat-Mingora districts, δ18O = +15.7 ± 0.1‰), Brazil (Santa Terezinha de Goiás, δ18O = +12.2 ± 0.1‰; Quadrilatero Ferrifero, δ18O = +6.9 ± 0.4‰) and Zimbabwe (Sandawana, δ18O = +7.5 ± 0.5‰). Furthermore, the 18O-composition of emerald appears to be a good marker of its geological environment because the data suggest that host-rock-buffering
of fluid δ18O is considerable during fluid-rock interaction.
Received: 29 January 1998 / Accepted: 25 March 1998 相似文献
2.
Oxygen isotope constraints on the petrogenesis of the Sybille intrusion of the Proterozoic Laramie Anorthosite Complex 总被引:2,自引:0,他引:2
The origin of monzonitic intrusions that are associated with Proterozoic massif-type anorthosite complexes is controversial.
A detailed oxygen isotope study of the Sybille intrusion, a monzonitic intrusion of the Laramie Anorthosite Complex (Wyoming),
indicates that either derivation from a basaltic magma of mantle origin with a metasedimentary component (∼20%) incorporated
early in its magmatic history, or a partial melt of lower crustal rocks is consistent with the data. The oxygen isotope compositions
of plagioclase, pyroxene and zircon from the Sybille monzosyenite, the dominant rock type in the Sybille intrusion, were analyzed
in order to establish the isotopic composition of the source of the magma. Plagioclase δ18O values range from 6.77 to 9.17‰. We interpret the higher plagioclase δ18O values (average 8.69 ± 0.30‰, n = 19) to be magmatic in origin, lower plagioclase δ18O values (average 7.51 ± 0.44‰, n = 22) to be the result of variable subsolidus alteration, and pyroxene δ18O values (average 6.34 ± 0.38‰, n = 19) to be the result of closed-system diffusional exchange during cooling. Low magnetic zircons, which have been shown
to retain magmatic oxygen isotope values despite high grade metamorphism and extensive subsolidus hydrothermal alteration,
have δ18O values (7.40 ± 0.24‰, n = 11) which are consistent with our interpretation of the plagioclase and pyroxene results. Oxygen isotope data from all
three minerals indicate that the magmatic oxygen isotope composition of the Sybille intrusion is enriched in 18O relative to the composition of average or “normal” mantle-derived magmas. This enrichment is approximately twice the oxygen
isotope enrichment that could result from closed-system fractionation, rendering a closed-system, comag- matic petrogenetic
model between the Sybille intrusion and the mantle-derived anorthositic lithologies of the Laramie Anorthosite Complex improbable.
Received: 7 April 1998 / Accepted: 19 January 1999 相似文献
3.
A comparative study on isotopic composition of precipitation in wet tropic and semi-arid stations across southern India 总被引:2,自引:0,他引:2
Isotopic composition of monthly composite precipitation samples from Kozhikode (n = 31), a wet tropic station and Hyderabad (n = 25), a semi-arid station across southern India were studied for a period of four years from 2005 to 2008. During the study
period, the Kozhikode station recorded an average rainfall of 3500 mm while the Hyderabad station showed an average rainfall
of 790 mm. The average stable isotope values in precipitation at the Kozhikode station were δ
18O = −3.52‰, d-excess = 13.72‰; δ
18O = −2.94‰, d-excess = 10.57‰; and δ
18O = −7.53‰, d-excess = 13.79‰, respectively during the pre-monsoon (March–May), monsoon (June–September) and post-monsoon
(October–February) seasons. For the Hyderabad station, the average stable isotope values were δ
18O = −5.88‰, d-excess = 2.34‰; δ
18O = −4.39‰, d-excess = 9.21‰; and δ
18O = −8.69‰, d-excess = 14.29‰, respectively for the three seasons. The precipitation at the two stations showed distinctive
isotopic signatures. The stable isotopic composition of precipitation at the Hyderabad station showed significant variations
from the global trend while the Kozhikode station almost followed the global value. These differences are mainly attributed
to the latitudinal differences of the two stations coupled with the differences in climatic conditions. 相似文献
4.
Geochemical mixing models were used to decipher the dominant source of freshwater (rainfall, canal discharge, or groundwater
discharge) to Biscayne Bay, an estuary in south Florida. Discrete samples of precipitation, canal water, groundwater, and
bay surface water were collected monthly for 2 years and analyzed for salinity, stable isotopes of oxygen and hydrogen, and
Sr2+/Ca2+ concentrations. These geochemical tracers were used in three separate mixing models and then combined to trace the magnitude
and timing of the freshwater inputs to the estuary. Fresh groundwater had an isotopic signature (δ
18O = −2.66‰, δD −7.60‰) similar to rainfall (δ
18O = −2.86‰, δD = −4.78‰). Canal water had a heavy isotopic signature (δ
18O = −0.46‰, δD = −2.48‰) due to evaporation. This made it possible to use stable isotopes of oxygen and hydrogen to separate canal water
from precipitation and groundwater as a source of freshwater into the bay. A second model using Sr2+/Ca2+ ratios was developed to discern fresh groundwater inputs from precipitation inputs. Groundwater had a Sr2+/Ca2+ ratio of 0.07, while precipitation had a dissimilar ratio of 0.89. When combined, these models showed a freshwater input
ratio of canal/precipitation/groundwater of 37%:53%:10% in the wet season and 40%:55%:5% in the dry season with an error of
±25%. For a bay-wide water budget that includes saltwater and freshwater mixing, fresh groundwater accounts for 1–2% of the
total fresh and saline water input. 相似文献
5.
Benita Putlitz Alan Matthews John W. Valley 《Contributions to Mineralogy and Petrology》2000,138(2):114-126
Oxygen and hydrogen stable isotope ratios of eclogite-facies metagabbros and metabasalts from the Cycladic archipelago (Greece)
document the scale and timing of fluid–rock interaction in subducted oceanic crust. Close similarities are found between the
isotopic compositions of the high-pressure rocks and their ocean-floor equivalents. High-pressure minerals in metagabbros
have low δ18O values: garnet 2.6 to 5.9‰, glaucophane 4.3 to 7.1‰; omphacite 3.5 to 6.2‰. Precursor actinolite that was formed during
the hydrothermal alteration of the oceanic crust by seawater analyses at 3.7 to 6.3‰. These compositions are in the range
of the δ18O values of unaltered igneous oceanic crust and high-temperature hydrothermally altered oceanic crust. In contrast, high-pressure
metabasalts are characterised by 18O-enriched isotopic compositions (garnet 9.2 to 11.5‰, glaucophane 10.6 to 12.5‰, omphacite 10.2 to 12.8‰), which are consistent
with the precursor basalts having undergone low-temperature alteration by seawater. D/H ratios of glaucophane and actinolite
are also consistent with alteration by seawater. Remarkably constant oxygen isotope fractionations, compatible with isotopic
equilibrium, are observed among high-pressure minerals, with Δglaucophane−garnet = 1.37 ± 0.24‰ and Δomphacite−garnet = 0.72 ± 0.24‰. For the estimated metamorphic temperature of 500 °C, these fractionations yield coefficients in the equation
Δ = A * 106/T
2 (in Kelvin) of Aglaucophane−garnet = 0.87 ± 0.15 and Aomphacite−garnet = 0.72 ± 0.24. A fractionation of Δglaucophane–actinolite = 0.94 ± 0.21‰ is measured in metagabbros, and indicates that isotopic equilibrium was established during the metamorphic
reaction in which glaucophane formed at the expense of actinolite. The preservation of the isotopic compositions of gabbroic
and basaltic oceanic crust and the equilibrium fractionations among minerals shows that high-pressure metamorphism occurred
at low water/rock ratios. The isotopic equilibrium is only observed at hand-specimen scale, at an outcrop scale isotopic compositional
differences occur among adjacent rocks. This heterogeneity reflects metre-scale compositional variations that developed during
hydrothermal alteration by seawater and were subsequently inherited by the high-pressure metamorphic rocks.
Received: 4 January 1999 / Accepted: 7 July 1999 相似文献
6.
The Géant Dormant gold mine is a sulfide-rich quartz vein gold deposit hosted by a volcano-sedimentary sequence and an associated
felsic endogenous dome and dikes. The auriferous quartz-sulfide veins were preceded by two synvolcanic gold-bearing mineralizing
events: early sulfidic seafloor-related and later disseminated pyrite in the felsic dome. This deposit differs from classical
Archean auriferous quartz vein deposits by the low carbonate and high sulfide contents of the veins and by their formation
prior to ductile penetrative deformation. The δ18O values of quartz associated with seafloor-related auriferous sulfides average 11.9 ± 0.6‰ (n = 3). The seafloor hydrothermal fluids had a δ18O value of 3.2‰ calculated at 250 °C. The oxygen isotope composition of quartz and chlorite from veins average 12.5 ± 0.3‰
(n = 20) and 5.9 ± 1.1‰ (n = 4) respectively. Assuming oxygen isotope equilibrium between quartz and chlorite, the veins formed at a temperature of
∼275 °C, which is consistent with the calculated temperature of 269 ± 10 °C from chlorite chemistry. The gold-bearing fluids
had a δ18O value of 4.7‰ calculated at 275 °C. The δ34S values of sulfides from the three gold events range from 0.6 to 2.8‰ (n = 32) and are close to magmatic values. Sulfur isotope geothermometry constrains the sulfide precipitation in the gold-bearing
veins at a temperature of ∼350 °C. The similarity of the isotope data, the calculated δ18O of the mineralizing fluids and the likely seawater fluid source suggest that the three mineralizing events are genetically
related to a volcanogenic hydrothermal system. The high value of the auriferous fluids (δ18O = 4.7‰) is attributed to a significant magmatic fluid contribution to the evolved seawater-dominated convective hydrothermal
system. The two-stage filling of veins at increasing temperature from quartz-chlorite (275 °C) to sulfides (350 °C) may reflect
the progressive maturation of volcanogenic hydrothermal systems. These results, together with field and geochemical data,
suggest that formation of gold-rich volcanogenic systems require specific conditions that comprise a magmatic fluid contribution
and gold from arc-related felsic rocks, coeval with the mineralizing events. This study shows that some auriferous quartz-vein
orebodies in Archean terranes are formed in volcanogenic rather than mesothermal systems.
Received: 12 December 1998 / Accepted: 5 July 1999 相似文献
7.
The Marcona–Mina Justa deposit cluster, hosted by Lower Paleozoic metaclastic rocks and Middle Jurassic shallow marine andesites,
incorporates the most important known magnetite mineralization in the Andes at Marcona (1.9 Gt at 55.4% Fe and 0.12% Cu) and
one of the few major iron oxide–copper–gold (IOCG) deposits with economic Cu grades (346.6 Mt at 0.71% Cu, 3.8 g/t Ag and
0.03 g/t Au) at Mina Justa. The Middle Jurassic Marcona deposit is centred in Ica Department, Perú, and the Lower Cretaceous
Mina Justa Cu (Ag, Au) prospect is located 3–4 km to the northeast. New fluid inclusion studies, including laser ablation
time-of-flight inductively coupled plasma mass spectrometry (LA-TOF-ICPMS) analysis, integrated with sulphur, oxygen, hydrogen
and carbon isotope analyses of minerals with well-defined paragenetic relationships, clarify the nature and origin of the
hydrothermal fluid responsible for these contiguous but genetically contrasted deposits. At Marcona, early, sulphide-free
stage M-III magnetite–biotite–calcic amphibole assemblages are inferred to have crystallized from a 700–800°C Fe oxide melt
with a δ18O value from +5.2‰ to +7.7‰. Stage M-IV magnetite–phlogopite–calcic amphibole–sulphide assemblages were subsequently precipitated
from 430–600°C aqueous fluids with dominantly magmatic isotopic compositions (δ34S = +0.8‰ to +5.9‰; δ18O = +9.6‰ to +12.2‰; δD = −73‰ to −43‰; and δ13C = −3.3‰). Stages M-III and M-IV account for over 95% of the magnetite mineralization at Marcona. Subsequent non-economic,
lower temperature sulphide–calcite–amphibole assemblages (stage M-V) were deposited from fluids with similar δ34S (+1.8‰ to +5.0‰), δ18O (+10.1‰ to +12.5‰) and δ13C (−3.4‰), but higher δD values (average −8‰). Several groups of lower (<200°C, with a mode at 120°C) and higher temperature
(>200°C) fluids can be recognized in the main polymetallic (Cu, Zn, Pb) sulphide stage M-V and may record the involvement
of modified seawater. At Mina Justa, early magnetite–pyrite assemblages precipitated from a magmatic fluid (δ34S = +0.8‰ to +3.9‰; δ18O = +9.5‰ to +11.5‰) at 540–600°C, whereas ensuing chalcopyrite–bornite–digenite–chalcocite–hematite–calcite mineralization
was the product of non-magmatic, probably evaporite-sourced, brines with δ34S ≥ +29‰, δ18O = 0.1‰ and δ13C = −8.3‰. Two groups of fluids were involved in the Cu mineralization stage: (1) Ca-rich, low-temperature (approx. 140°C)
and high-salinity, plausibly a basinal brine and (2) Na (–K)-dominant with a low-temperature (approx. 140°C) and low-salinity
probably meteoric water. LA-TOF-ICPMS analyses show that fluids at the magnetite–pyrite stage were Cu-barren, but that those
associated with external fluids in later stages were enriched in Cu and Zn, suggesting such fluids could have been critical
for the economic Cu mineralization in Andean IOCG deposits. 相似文献
8.
Distinguishing magmatic from subsolidus epidote: laser probe oxygen isotope compositions 总被引:1,自引:0,他引:1
Epidote occurs in four textural varieties in the Mount Lowe intrusion of southern California: euhedra, anhedra, intergrowths
and cross-cutting veins. Of these, conspicuous elongate euhedra, which range up to 3 cm in length, meet most of the established
textural criteria for magmatic epidote. Equant anhedral grains, which are ˜5 mm in diameter, are texturally ambiguous although
rare allanite cores are suggestive of a magmatic origin. Epidote intergrowths with hornblende and biotite also meet certain
textural criteria for crystallization from a magma, notably, euhedral faces against biotite. Finally, late-stage veins of
epidote cross-cut all phases in the rock and are likely subsolidus. Oxygen isotopic compositions of these four textural varieties
of epidote determined using the laser probe indicate that the use of textural criteria alone in establishing epidote parageneses
can be misleading. Intracrystalline δ18O variations in the euhedra document both magmatic and subsolidus compositions. Oxygen isotope compositions are bimodal averaging
5.36 ± 0.13‰ (n = 11) and 4.66 ± 0.23‰ (n = 21). These data combined with plagioclase and zircon δ18O values are interpreted to indicate that magmatic oxygen isotopic compositions have been preserved where epidote δ18O is greater than 5‰. Significant portions of each euhedral crystal have been affected by subsolidus exchange and are characterized
by epidote δ18O values less than 5‰. Intracrystalline δ18O values of epidote anhedra range from 4.50 to 6.08‰ and thus also document both magmatic and subsolidus compositions. Subsolidus
exchange is volumetrically less significant in the anhedra than in the euhedra. Values of δ18O for intergrowths and late-stage cross-cutting veins of epidote average 3.81 ± 0.22‰ and document clearly subsolidus growth.
The data confirm that in the Mount Lowe intrusion, large euhedra of epidote are magmatic in origin, consistent with textural
evidence. The data also indicate that equant anhedra of epidote are also magmatic in origin and thus the absence of good crystal
faces does not necessarily indicate subsolidus growth. The subsolidus origin of intergrowths of epidote with euhedral faces
against biotite indicates that well developed crystal faces do not require growth from a magma. Finally, the subsolidus origin
of the vein epidote is consistent with textural evidence. The increased resolution available with laser-based oxygen isotope
measurements offers an important test for documenting whether epidote is of magmatic or subsolidus origin. Given the barometric
significance of magmatic epidote, oxygen isotope compositions can be used to aid in the interpretation of epidote-bearing
plutons.
Received: 9 April 1996 / Accepted: 3 August 1996 相似文献
9.
The sulfur isotopic composition of sulfides and barite from hydrothermal deposits at the Valu Fa Ridge back-arc spreading
center in the southern Lau Basin has been investigated. Sulfide samples from the White Church area at the northern Valu Fa
Ridge have δ34S values averaging +3.8‰ (n= 10) for bulk sphalerite-chalcopyrite mineralization and +4.8‰ for pyrite (n= 10). Barite associated with the massive sulfides exhibits an average of +20.7‰ (n= 10). Massive sulfides from the active Vai Lili hydrothermal field at the central Valu Fa Ridge have much higher δ34S ratios averaging +8.0‰ for bulk sphalerite-chalcopyrite mineralization (n= 5), +9.3‰ for pyrite samples (n= 5), and +8.0‰ and +10.9‰ for a chalcopyrite and a sphalerite separate, respectively. The isotopic composition of barite
from the Vai Lili field is similar to that of barite from the White Church area and averages +21.0‰ (n= 8). Sulfide and barite samples from the Hine Hina area at the southern Valu Fa Ridge have δ34S values that are considerably lighter than those observed for samples from the other areas and average −4.9‰ for pyrite (n= 9), −4.0 and −5.7‰ for two samples of sphalerite-chalcopyrite intergrowth, and −3.4‰ for a single chalcopyrite separate.
The total spread in the isotopic composition of sulfides from Vai Lili and Hine Hina is more than 20‰ over a distance of less
than 30 km. The δ34S values of sulfides at Hine Hina are the lowest values so far reported for volcanic-hosted polymetallic massive sulfides
from the modern seafloor. Barite from the Hine Hina field also has unusually light sulfur with δ34S values of +16.1 to +16.7‰ (n= 5). Isotopic compositions of the sulfides at Hine Hina indicate a dramatic decrease in δ34S from ordinary magmatic values and, in the absence of biogenic sulfur and/or boiling, imply a unique 34S-depleted source of probable magmatic origin. Sulfide-barite mineralization in the Hine Hina area is associated with a distinctive
alteration assemblage consisting of cristobalite, pyrophyllite, kaolinite, opal-CT, talc, pyrite, native sulfur, and alunite.
Similar styles of alteration are typically known from high-sulfidation epithermal systems on land. Alunite-bearing, advanced
argillic alteration in the Hine Hina field confirms the role of acidic, volatile-rich fluids, and a δ34S value of +10.4‰ for the sulfur in the alunite is consistent with established kinetic isotope effects which accompany the
disproportionation of magmatic SO2 into H2S and H2SO4. The Hine Hina field occurs near the propagating tip of the Valu Fa back-arc spreading center (i.e., dominated by dike injections
and seafloor eruptions) and therefore may have experienced the largest contribution of magmatic volatiles of the three fields.
The sulfur isotopic ratios of the hydrothermal precipitates and the presence of a distinctive epithermal-like argillic alteration
in the Hine Hina field suggest a direct contribution of magmatic vapor to the hydrothermal system and support the concept
that magmatic volatiles may be an important component of some volcanogenic massive sulfide-forming hydrothermal systems.
Received: 16 January 1997 / Accepted: 28 October 1997 相似文献
10.
Ian Cartwright Ian S. Buick Roland Maas 《Contributions to Mineralogy and Petrology》1997,128(4):335-351
The Jervois region of the Arunta Inlier, central Australia, contains para- and orthogneisses that underwent low-pressure
amphibolite facies metamorphism (P = 200–300 MPa, T = 520–600 °C). Marble layers cut by metre-wide quartz + garnet ± epidote veins comprise calcite, quartz, epidote, clinopyroxene,
grandite garnet, and locally wollastonite. The marbles also contain locally discordant decimetre-thick garnet and epidote
skarn layers. The mineral assemblages imply that the rocks were infiltrated by water-rich fluids (XCO2 = 0.1–0.3) at ∼600 °C. The fluids were probably derived from the quartz-garnet vein systems that represent conduits for fluids
exsolved from crystallizing pegmatites emplaced close to the metamorphic peak. At one locality, the marble has calcite (Cc)
δ18O values of 9–18‰ and garnet (Gnt) δ18O values of 10–14‰. The δ18O(Gnt) values are only poorly correlated with δ18O(Cc), and the δ18O values of some garnet cores are higher than the rims. The isotopic disequilibrium indicates that garnet grew before the
δ18O values of the rock were reset. The marbles contain ≤15% garnet and, for water-rich fluids, garnet-forming reactions are
predicted to propagate faster than O-isotopes are reset. The Sm-Nd and Pb-Pb ages of garnets imply that fluid flow occurred
at 1750–1720 Ma. There are no significant age differences between garnet cores and rims, suggesting that fluid flow was relatively
rapid. Texturally late epidote has δ18O values of 1.5–6.2‰ implying δ18O(H2O) values of 2–7‰. Waters with such low-δ18O values are probably at least partly meteoric in origin, and the epidote may be recording the late influx of meteoric water
into a cooling hydrothermal system.
Received: 29 April 1996 / Accepted: 12 March 1997 相似文献
11.
George B. Perkins Zachary D. Sharp Jane Selverstone 《Contributions to Mineralogy and Petrology》2006,151(6):633-650
Spinel lherzolite and pyroxenite xenoliths from the Rio Puerco Volcanic Field, New Mexico, were analyzed for oxygen isotope ratios by laser fluorination. In lherzolites, olivine δ18O values are high (+5.5‰), whereas δ18O values for pyroxenes are low (cpx=+5.1‰; opx=+5.4‰) compared to average mantle values. Pyroxenite δ18O values (cpx=+5.0‰; opx=+5.3‰) are similar to those of the lherzolites and are also lower than typical mantle oxygen isotope compositions. Texturally and chemically primary calcite in pyroxenite xenoliths is far from isotopic equilibrium with other phases, with δ18O values of +21‰. The isotopic characteristics of the pyroxenite xenoliths are consistent with a petrogenetic origin from mixing of lherzolitic mantle with slab-derived silicate and carbonatite melts. The anomalously low δ18O in the pyroxenes reflects metasomatism by a silicate melt from subducted altered oceanic crust, and high δ18O calcite is interpreted to have crystallized from a high δ18O carbonatitic melt derived from subducted ophicarbonate. Similar isotopic signatures of metasomatism are seen throughout the Rio Puerco xenolith suite and at Kilbourne Hole in the southern Rio Grande rift. The discrete metasomatic components likely originated from the subducted Farallon slab but were not mobilized until heating associated with Rio Grande rifting occurred. Oxygen diffusion modeling requires that metasomatism leading to the isotopic disequilibrium between calcite and pyroxene in the pyroxenites occurred immediately prior to entrainment. Melt infiltration into spinel-facies mantle (xenoliths) prior to eruption was thus likely connected to garnet-facies melting that resulted in eruption of the host alkali basalt. 相似文献
12.
The potential of teleost scales as indicator tissues of recent dietary history was investigated in the estuarine fish, Notolabrus celidotus. Treatment fish were fed a 15N-enriched bivalve diet (δ15N = 108.8‰) for up to 90 days to examine integration of the dietary source signature in scale margin, regenerated scale, and
dorsal muscle tissues. Regenerated scales exhibited the greatest and most rapid enrichment in δ15N (to 53.4 ± 5.0‰) of the tissues examined. Scale margin δ15N signatures also increased significantly from 14.5‰ to 30.9 ± 6.0‰, while muscle tissue only increased by 2.8‰ after 90 days.
Dietary contribution models suggested that isotopic equilibration of dietary nitrogen would be most rapid in regenerated scales,
followed by scale marginal increments and then muscle. In conclusion, teleost scales hold considerable potential as novel,
nondestructive indicators of recent dietary history, yet currently face constraints from uncertainties in isotopic integration
mechanisms. 相似文献
13.
The 18O and 2H (HDO) compositions are summarized for sampled springs (n = 81) within the Elwha watershed (≈692 km2) on the northern Olympic Peninsula. Samples, collected during 2001–2009, of springs (n = 158), precipitation (n = 520), streams (n = 176), and firn (n = 3) assisted the determinations for meteoric composition of recharge waters. The local mean water line (LMWL) is defined
as δ2H = 8.2δ18O − 9.3 for the watershed. Recharge history is surmised from groundwater ages ranging from 5 ± 3 years (apparent 85Kr) to 9,490 ± 420 14C cal years BP. About 56% of the springs were recharged over the last 1,000 years while 13% of springs were recharged over
5,000 years ago. Spring HDO values fluctuate between −11.8 to −15.6‰ δ18O and −90.9 to −119.4‰ δ2H. Deuterium excess values predominate around 4–6‰. The HDO proxy records from springs suggest a pronounced paleoclimate shift
in air masses near 5,000 year BP on the Peninsula. 相似文献
14.
A. I. Grabezhev B. G. Pokrovskii F. P. Buslaev V. V. Zaikov G. N. Pshenichnyi 《Lithology and Mineral Resources》2000,35(1):70-75
Substantial differences in isotopic compositions of micas and pyrophyllites from metasomatites related to various stages of
the process that formed the giant Gai massive sulfide deposit have been established. The illite from the earliest and predominant
chlorite-illite-quartz metasomatite is characterized by the least δD values of −(50–85)‰ and δ18O=7–11‰. The pyrophyllite-quartz metasomatite as well as illite and pyrophyllite schists developed locally in the southern
part of the deposit that likely correspond to the site of discharge of late geothermal paleosystem, contain pyrophyllite and
illite with much higher values of δD=−(25–45)‰ and δ18O=4–9‰. Local zones of illite-paragonite schist complete the mineral formation and are characterized by the transitional δD values of −(30–55)‰ and elevated δ18O of 10–11‰. The most plausible model of isotopic evolution in the hydrothermal system, with an initial temperature of mica
formation at 250°C, assumes the mixing of transformed sea water with a magmatic (metamorphic) water at the initial stage when
the background metasomatites and massive sulfide orebodies of the northern lode have been formed. Subsequently, after the
burial of the northern lode beneath basaltic andesite flows, the repeated sea water invasions took place in the southern discharge
site of the system. As a result, the pyrophyllite-quartz metasomatite was formed; the pyrophyllite and illite schists originated
in tectonic compression zones. The interaction of this water with silicate rocks was completed by a formation of illite-paragonite
schist. In general, the substantial contribution of sea water to the formation of metasomatic halo of the deposit casts no
doubt. 相似文献
15.
The Ouenza siderite deposit is located proximal to evaporitic diapirs of Triassic age. Mineralization occurs mainly in Aptian
neritic limestones which host important iron concentrations (120–150 MT) and minor Pb, Zn, Cu, Ba and F occurrences. The iron
ore consists of iron carbonate minerals which have been oxidized partially to hematite. Fine-grained ankerite and siderite
replace limestones, whereas sparry ankerite and siderite were emplaced in veins. Limited variation in the chemical and isotopic
compositions of ankerite and siderite were observed, which indicate that they precipitated from the same fluid. Stable isotope
compositions (δ18O and δ13C) of iron carbonates and limestones allow estimation of the isotopic composition of the mineralizing fluid and precipitation
temperature: δ18O = 7.5‰ SMOW, T = 100–120 °C. Later deposition of Pb, Zn, Cu, Ba and F minerals is controlled by fractures oriented NE–SW
and SE–NW. Fluid inclusion studies of quartz yield salinities of 18–22 wt.% equivalent NaCl and homogenization temperatures
between 150 and 180 °C. These values are similar to those of Mississippi Valley type deposits which are associated with basinal
brines.
Received: 4 January 1996 / Accepted: 17 July 1996 相似文献
16.
R. Altherr U. Henes-Klaiber E. Hegner M. Satir C. Langer 《International Journal of Earth Sciences》1999,88(3):422-443
Latest Devonian to early Carboniferous plutonic rocks from the Odenwald accretionary complex reflect the transition from
a subduction to a collisional setting. For ∼362 Ma old gabbroic rocks from the northern tectonometamorphic unit I, initial
isotopic compositions (εNd=+3.4 to +3.8;87Sr/86Sr =0.7035–0.7053;δ18O=6.8–8.0‰) and chemical signatures (e.g., low Nb/Th, Nb/U, Ce/Pb, Th/U, Rb/Cs) indicate a subduction-related origin by partial
melting of a shallow depleted mantle source metasomatized by water-rich, large ion lithophile element-loaded fluids. In the
central (unit II) and southern (unit III) Odenwald, syncollisional mafic to felsic granitoids were emplaced in a transtensional
setting at approximately 340–335 Ma B.P. Unit II comprises a mafic and a felsic suite that are genetically unrelated. Both
suites are intermediate between the medium-K and high-K series and have similar initial Nd and Sr signatures (εNd=0.0 to –2.5;87Sr/86Sr=0.7044–0.7056) but different oxygen isotopic compositions (δ18O=7.3–8.7‰ in mafic vs 9.3–9.5‰ in felsic rocks). These characteristics, in conjunction with the chemical signatures, suggest
an enriched mantle source for the mafic magmas and a shallow metaluminous crustal source for the felsic magmas. Younger intrusives
of unit II have higher Sr/Y, Zr/Y, and Tb/Yb ratios suggesting magma segregation at greater depths. Mafic high-K to shoshonitic
intrusives of the southern unit III have initial isotopic compositions (εNd=–1.1 to –1.8;87Sr/86Sr =0.7054–0.7062;δ18O=7.2–7.6‰) and chemical characteristics (e.g., high Sr/Y, Zr/Y, Tb/Yb) that are strongly indicative of a deep-seated enriched
mantle source. Spatially associated felsic high-K to shoshonitic rocks of unit III may be derived by dehydration melting of
garnet-rich metaluminous crustal source rocks or may represent hybrid magmas.
Received: 7 December 1998 / Accepted: 27 April 1999 相似文献
17.
Oxygen isotope systematics of gem corundum deposits in Madagascar: relevance for their geological origin 总被引:1,自引:1,他引:1
Gaston Giuliani Anthony Fallick Michel Rakotondrazafy Daniel Ohnenstetter Alfred Andriamamonjy Théogène Ralantoarison Saholy Rakotosamizanany Marie Razanatseheno Yohann Offant Virginie Garnier Christian Dunaigre Dietmar Schwarz Alain Mercier Voahangy Ratrimo Bruno Ralison 《Mineralium Deposita》2007,42(3):251-270
The oxygen isotopic composition of gem corundum was measured from 22 deposits and occurrences in Madagascar to provide a gemstone
geological identification and characterization. Primary corundum deposits in Madagascar are hosted in magmatic (syenite and
alkali basalt) and metamorphic rocks (gneiss, cordieritite, mafic and ultramafic rocks, marble, and calc-silicate rocks).
In both domains the circulation of fluids, especially along shear zones for metamorphic deposits, provoked in situ transformation
of the corundum host rocks with the formation of metasomatites such as phlogopite, sakenite, and corundumite. Secondary deposits
(placers) are the most important economically and are contained in detrital basins and karsts. The oxygen isotopic ratios
(18O/16O) of ruby and sapphire from primary deposits are a good indicator of their geological origin and reveal a wide range of δ18O (Vienna Standard Mean Ocean Water) between 1.3 and 15.6‰. Metamorphic rubies are defined by two groups of δ18O values in the range of 1.7 to 2.9‰ (cordieritite) and 3.8 to 6.1‰ (amphibolite). “Magmatic” rubies from pyroxenitic xenoliths
contained in the alkali basalt of Soamiakatra have δ18O values ranging between 1.3 and 4.7‰. Sapphires are classified into two main groups with δ18O in the range of 4.7 to 9.0‰ (pyroxenite and feldspathic gneiss) and 10.7 to 15.6‰ (skarn in marble from Andranondambo).
The δ18O values for gem corundum from secondary deposits have a wide spread between −0.3 and 16.5‰. The ruby and sapphire found in
placers linked to alkali basalt environments in the northern and central regions of Madagascar have consistent δ18O values between 3.5 and 6.9‰. Ruby from the placers of Vatomandry and Andilamena has δ18O values of 5.9‰, and between 0.5 and 4.0‰, respectively. The placers of the Ilakaka area are characterized by a huge variety
of colored sapphires and rubies, with δ18O values between −0.3 and 16.5‰, and their origin is debated. A comparison with oxygen isotope data obtained on gem corundum
from Eastern Africa, India, and Sri Lanka is presented. Giant placer deposits from Sri Lanka, Madagascar, and Tanzania have
a large variety of colored sapphires and rubies with a large variation in δ18O due to mingling of corundum of different origin: mafic and ultramafic rocks for ruby, desilicated pegmatites for blue sapphire,
syenite for yellow, green, and blue sapphire, and skarn in marbles for blue sapphire. 相似文献
18.
The Eastern Iberian Central System has abundant ore showings hosted by a wide variety of hydrothermal rocks; they include
Sn-W, Fe and Zn-(W) calcic and magnesian skarns, shear zone- and episyenite-hosted Cu-Zn-Sn-W orebodies, Cu-W-Sn greisens
and W-(Sn), base metal and fluorite-barite veins. Systematic dating and fluid inclusion studies show that they can be grouped
into several hydrothermal episodes related with the waning Variscan orogeny. The first event was at about 295 Ma followed
by younger pulses associated with Early Alpine rifting and extension and dated near 277, 150 and 100 to 20 Ma, respectively
(events II–IV). The δ18O-δD and δ34S studies of hydrothermal rocks have elucidated the hydrological evolution of these systems. The event I fluids are of mixed
origin. They are metamorphic fluids (H2O-CO2-CH4-NaCl; δ18O=4.7 to 9.3‰; δD ab.−34‰) related to W-(Sn) veins and modified meteoric waters in the deep magnesian Sn-W skarns (H2O-NaCl, 4.5–6.4 wt% NaCl eq.; δ18O=7.3–7.8‰; δD=−77 to −74‰) and epizonal shallow calcic Zn-(W) and Fe skarns (H2O-NaCl, <8 wt% NaCl eq.; δ18O=−0.4 to 3.4‰; δD=−75 to −58‰). They were probably formed by local hydrothermal cells that were spatially and temporally
related to the youngest Variscan granites, the metals precipitating by fluid unmixing and fluid-rock reactions. The minor
influence of magmatic fluids confirms that the intrusion of these granites was essentially water-undersaturated, as most of
the hydrothermal fluids were external to the igneous rocks. The fluids involved in the younger hydrothermal systems (events
II–III) are very similar. The waters involved in the formation of episyenites, chlorite-rich greisens, retrograde skarns and
phyllic and chlorite-rich alterations in the shear zones show no major chemical or isotopic differences. Interaction of the
hydrothermal fluids with the host rocks was the main mechanism of ore formation. The composition (H2O-NaCl fluids with original salinities below 6.2 wt% NaCl eq.) and the δ18O (−4.6 to 6.3‰) and δD (−51 to −40‰) values are consistent with a meteoric origin, with a δ18O-shift caused by the interaction with the, mostly igneous, host rocks. These fluids circulated within regional-scale convective
cells and were then channelled along major crustal discontinuities. In these shear zones the more easily altered minerals
such as feldspars, actinolite and chlorite had their δ18O signatures overprinted by low temperature younger events while the quartz inherited the original signature. In the shallower
portions of the hydrothermal systems, basement-cover fluorite-barite-base metal veins formed by mixing of these deep fluids
with downwards percolating brines. These brines are also interpreted as of meteoric origin (δ18O< ≈ −4‰; δD=−65 to −36‰) that leached the solutes (salinity >14 wt% NaCl eq.) from evaporites hosted in the post-Variscan
sequence. The δD values are very similar to most of those recorded by Kelly and Rye in Panasqueira and confirm that the Upper
Paleozoic meteoric waters in central Iberia had very negative δD values (≤−52‰) whereas those of Early Mesozoic age ranged
between −65 and −36‰.
Received: 9 June 1999 / Accepted: 19 January 2000 相似文献
19.
Multiple origins of zircons in jadeitite 总被引:1,自引:1,他引:0
Bin Fu John W. Valley Noriko T. Kita Michael J. Spicuzza Chad Paton Tatsuki Tsujimori Michael Bröcker George E. Harlow 《Contributions to Mineralogy and Petrology》2010,159(6):769-780
Jadeitites form from hydrothermal fluids during high pressure metamorphism in subduction environments; however, the origin
of zircons in jadeitite is uncertain. We report ion microprobe analyses of δ18O and Ti in zircons, and bulk δ18O data for the jadeitite whole-rock from four terranes: Osayama serpentinite mélange, Japan; Syros mélange, Greece; the Motagua
Fault zone, Guatemala; and the Franciscan Complex, California. In the Osayama jadeitite, two texturally contrasting groups
of zircons are identified by cathodoluminescence and are distinct in δ18O: featureless or weakly zoned zircons with δ18O = 3.8 ± 0.6‰ (2 SD, VSMOW), and zircons with oscillatory or patchy zoning with higher δ18O = 5.0 ± 0.4‰. Zircons in phengite jadeitite from Guatemala and a jadeitite block from Syros have similar δ18O values to the latter from Osayama: Guatemala zircons are 4.8 ± 0.7‰, and the Syros zircons are 5.2 ± 0.5‰ in jadeitite and
5.2 ± 0.4‰ in associated omphacitite, glaucophanite and chlorite-actinolite rinds. The δ18O values for most zircons above fall within the range measured by ion microprobe in igneous zircons from oxide gabbros and
plagiogranites in modern ocean crust (5.3 ± 0.8‰) and measured in bulk by laser fluorination of zircons in equilibrium with
primitive magma compositions or the mantle (5.3 ± 0.6‰). Titanium concentrations in these zircons vary between 1 and 19 ppm,
within the range for igneous zircons worldwide. Values of δ18O (whole-rock) ≅ δ18O (jadeite) and vary from 6.3 to 10.1‰ in jadeitites in all four areas. 相似文献
20.
Mark E. Brandriss Richard J. Nevle Dennis K. Bird James R. O’Neil 《Contributions to Mineralogy and Petrology》1995,121(1):74-86
Hydrogen and oxygen isotope analyses have been made of hydrous minerals in gabbros and basaltic xenoliths from the Eocene
Kap Edvard Holm intrusive complex of East Greenland. The analyzed samples are of three types: (1) primary igneous hornblendes
and phlogopites that crystallized from partial melts of hydrothermally altered basaltic xenoliths, (2) primary igneous hornblendes
that formed during late–magmatic recrystallization of layered gabbroic cumulates, and (3) secondary actinolite, epidote and
chlorite that formed during subsolidus alteration of both xenoliths and gabbros. Secondary actinolite has a δ18O value of −5.8‰ and a δD value of −158‰. These low values reflect subsolidus alteration by low–δ18O, low–δD hydrothermal fluids of meteoric origin. The δD value is lower than the −146 to −112‰ values previously reported
for amphiboles from other early Tertiary meteoric–hydrothermal systems in East Greenland and Scotland, indicating that the
meteoric waters at Kap Edvard Holm were isotopically lighter than typical early Tertiary meteoric waters in the North Atlantic
region. This probably reflects local climatic variations caused by formation of a major topographic dome at about the time
of plutonism and hydrothermal activity. The calculated isotopic composition of the meteoric water is δD=−110 ± 10‰, δ18O ≈−15‰. Igneous hornblendes and phlogopites from pegmatitic pods in hornfelsed basaltic xenoliths have δ18O values between −6.0 and −3.8‰ and δD values between −155 and −140‰. These are both much lower than typical values of fresh
basalts. The oxygen isotope fractionations between pegmatitic hornblendes and surrounding hornfelsic minerals are close to
equilibrium fractionations for magmatic temperatures, indicating that the pegmatites crystallized from low–δ18O partial melts of xenoliths that had been hydrothermally altered and depleted in 18O prior to stoping. The pegmatitic minerals may have crystallized with low primary δD values inherited from the altered country
rocks, but these values were probably overprinted extensively by subsolidus isotopic exchange with low–δD meteoric–hydrothermal
fluids. This exchange was facilitated by rapid self–diffusion of hydrogen through the crystal structures. Primary igneous
hornblendes from the plutonic rocks have δ18O values between +2.0 and +3.2‰ and δD values between −166 and −146‰. The 18O fractionations between hornblendes and coexisting augites are close to equilibrium fractionations for magmatic temperatures,
indicating that the hornblendes crystallized directly from the magma and subsequently underwent little or no oxygen exchange.
The hornblendes may have crystallized with low primary δD values, due to contamination of the magma with altered xenolithic
material, but the final δD values were probably controlled largely by subsolidus isotopic exchange. This inference is based
partly on the observation that coexisting plagioclase has been extensively depleted in 18O via a mineral–fluid exchange reaction that is much slower than the hydrogen exchange reaction in hornblende. It is concluded
that all hydrous minerals in the study area, whether igneous or secondary, have δD values that reflect extensive subsolidus
isotopic equilibration with meteoric–hydrothermal fluids.
Received: 22 March 1994 / Accepted: 26 January 1995 相似文献