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1.
Aaron J. Cavosie John W. Valley Noriko T. Kita Michael J. Spicuzza Takayuki Ushikubo Simon A. Wilde 《Contributions to Mineralogy and Petrology》2011,162(5):961-974
The oxygen isotope ratios (δ18O) of most igneous zircons range from 5 to 8‰, with 99% of published values from 1345 rocks below 10‰. Metamorphic zircons
from quartzite, metapelite, metabasite, and eclogite record δ18O values from 5 to 17‰, with 99% below 15‰. However, zircons with anomalously high δ18O, up to 23‰, have been reported in detrital suites; source rocks for these unusual zircons have not been identified. We report
data for zircons from Sri Lanka and Myanmar that constrain a metamorphic petrogenesis for anomalously high δ18O in zircon. A suite of 28 large detrital zircon megacrysts from Mogok (Myanmar) analyzed by laser fluorination yields δ18O from 9.4 to 25.5‰. The U–Pb standard, CZ3, a large detrital zircon megacryst from Sri Lanka, yields δ18O = 15.4 ± 0.1‰ (2 SE) by ion microprobe. A euhedral unzoned zircon in a thin section of Sri Lanka granulite facies calcite
marble yields δ18O = 19.4‰ by ion microprobe and confirms a metamorphic petrogenesis of zircon in marble. Small oxygen isotope fractionations
between zircon and most minerals require a high δ18O source for the high δ18O zircons. Predicted equilibrium values of Δ18O(calcite-zircon) = 2–3‰ from 800 to 600°C show that metamorphic zircon crystallizing in a high δ18O marble will have high δ18O. The high δ18O zircons (>15‰) from both Sri Lanka and Mogok overlap the values of primary marine carbonates, and marbles are known detrital
gemstone sources in both localities. The high δ18O zircons are thus metamorphic; the 15–25‰ zircon values are consistent with a marble origin in a rock-dominated system (i.e.,
low fluid(external)/rock); the lower δ18O zircon values (9–15‰) are consistent with an origin in an external fluid-dominated system, such as skarn derived from marble,
although many non-metasomatized marbles also fall in this range of δ18O. High δ18O (>15‰) and the absence of zoning can thus be used as a tracer to identify a marble source for high δ18O detrital zircons; this recognition can aid provenance studies in complex metamorphic terranes where age determinations alone
may not allow discrimination of coeval source rocks. Metamorphic zircon megacrysts have not been reported previously and appear
to be associated with high-grade marble. Identification of high δ18O zircons can also aid geochronology studies that seek to date high-grade metamorphic events due to the ability to distinguish
metamorphic from detrital zircons in marble. 相似文献
2.
Hypogene Zn carbonate ores in the Angouran deposit,NW Iran 总被引:1,自引:0,他引:1
Maria Boni H. Albert Gilg Giuseppina Balassone Jens Schneider Cameron R. Allen Farid Moore 《Mineralium Deposita》2007,42(8):799-820
The world-class Angouran nonsulfide Zn–Pb deposit is one of the major Zn producers in Iran, with resources estimated at about
18 Mt at 28% Zn, mainly in the form of the Zn carbonate smithsonite. This study aims to characterize these carbonate ores
by means of their mineralogy and geochemistry, which has also been extended to the host rocks of mineralization and other
local carbonate rock types, including the prominent travertines in the Angouran district, as well as to the local spring waters.
Petrographical, chemical, and stable isotope (O, H, C, Sr) data indicate that the genesis of the Zn carbonate ores at Angouran
is fairly distinct from that of other “classical” nonsulfide Zn deposits that formed entirely by supergene processes. Mineralization
occurred during two successive stages, with the zinc being derived from a preexisting sulfide ore body. A first, main stage
of Zn carbonates (stage I carbonate ore) is associated with both preexisting and subordinate newly formed sulfides, whereas
a second stage is characterized by supergene carbonates (Zn and minor Pb) coexisting with oxides and hydroxides (stage II
carbonate ore). The coprecipitation of smithsonite with galena, pyrite and arsenopyrite, as well as the absence of Fe- and
Mn-oxides/hydroxides and of any discernible oxidation or dissolution of the sphalerite-rich primary sulfide ore, shows that
the fluids responsible for the main, stage I carbonate ores were relatively reduced and close to neutral to slightly basic
pH with high fCO2. Smithsonite δ18OVSMOW values from stage I carbonate ore range from 18.3 to 23.6‰, while those of stage II carbonate ore show a much smaller range
between 24.3 and 24.9‰. The δ13C values are fairly constant in smithsonite of stage I carbonate ore (3.2–6.0‰) but show a considerable spread towards lower
δ13CVPDB values (4.6 to −11.2‰) in stage II carbonate ore. This suggests a hypogene formation of stage I carbonate ore at Angouran
from low-temperature hydrothermal fluids, probably mobilized during the waning stages of Tertiary–Quaternary volcanic activity
in an environment characterized by abundant travertine systems throughout the whole region. Conversely, stage II carbonate
ore is unambiguously related to supergene weathering, as evidenced by the absence of sulfides, the presence of Fe-Mn-oxides
and arsenates, and by high δ18O values found in smithsonite II. The variable, but still relatively heavy carbon isotope values of supergene smithsonite
II, suggests only a very minor contribution by organic soil carbon, as is generally the case in supergene nonsulfide deposits. 相似文献
3.
We report the oxygen isotope composition of olivine and orthopyroxene phenocrysts in lavas from the main magma types at Mt
Shasta and Medicine Lake Volcanoes: primitive high-alumina olivine tholeiite (HAOT), basaltic andesites (BA), primitive magnesian
andesites (PMA), and dacites. The most primitive HAOT (MgO > 9 wt%) from Mt. Shasta has olivine δ18O (δ18OOl) values of 5.9–6.1‰, which are about 1‰ higher than those observed in olivine from normal mantle-derived magmas. In contrast,
HAOT lavas from Medicine Lake have δ18OOl values ranging from 4.7 to 5.5‰, which are similar to or lower than values for olivine in equilibrium with mantle-derived
magmas. Other magma types from both volcanoes show intermediate δ18OOl values. The oxygen isotope composition of the most magnesian lavas cannot be explained by crustal contamination and the trace
element composition of olivine phenocrysts precludes a pyroxenitic mantle source. Therefore, the high and variable δ18OOl signature of the most magnesian samples studied (HAOT and BA) comes from the peridotitic mantle wedge itself. As HAOT magma
is generated by anhydrous adiabatic partial melting of the shallow mantle, its 1.4‰ range in δ18OOl reflects a heterogeneous composition of the shallow mantle source that has been influenced by subduction fluids and/or melts
sometime in the past. Magmas generated in the mantle wedge by flux melting due to modern subduction fluids, as exemplified
by BA and probably PMA, display more homogeneous composition with only 0.5‰ variation. The high-δ18O values observed in magnesian lavas, and principally in the HAOT, are difficult to explain by a single-stage flux-melting
process in the mantle wedge above the modern subduction zone and require a mantle source enriched in 18O. It is here explained by flow of older, pre-enriched portions of the mantle through the slab window beneath the South Cascades. 相似文献
4.
Using dual-isotope data to trace the origin and processes of dissolved sulphate: a case study in Calders stream (Llobregat basin,Spain) 总被引:1,自引:0,他引:1
Whereas most of the reported δ34S values of dissolved sulphate are positive in the Llobregat basin, Calders stream, which is a tributary of the Llobregat
River, is characterised by negative values. Stream waters, sampled monthly between 1997 and 1998, and quarterly in 1999, show
an overall increase in δ34S from −10‰ to 0‰, coupled with an increase in Na and Cl concentration. On the other hand, the oxygen isotopic composition
of dissolved sulphate, δ18O, displayed an opposite trend with a slight decrease, from +9‰ to +6‰. Detailed sampling up stream in November 2000 indicated
that, contrary to most of the surficial waters of the Llobregat basin with a δ34SSO4 mainly controlled by evaporites, in Calders stream, sulphate is derived from pyrite oxidation. The dual-isotope approach,
coupled with chemical data, allowed us to identify the contribution of 34S-rich sulphate effluents from anthropogenic sources, while mixing models, calculated between natural and anthropogenic sources,
enabled us to estimate their contribution. Sudden increases of δ34S and δ18O of dissolved sulphate in stream waters are believed to be caused by a sulphate reduction process related to oil spillage.
The long-term enrichment in δ34S, coupled with a decrease in δ18OSO4, from Jan-97 to Aug-99, is interpreted as a progressive increase in the contribution of pig manure. 相似文献
5.
The Samgwang mine is located in the Cheongyang gold district (Cheonan Metallogenic Province) of the Republic of Korea. It
consists of eight massive, gold-bearing quartz veins that filled NE- and NW-striking fractures along fault zones in Precambrian
granitic gneiss of the Gyeonggi massif. Their mineralogy and paragenesis allow two separate vein-forming episodes to be recognized,
temporally separated by a major faulting event. The ore minerals occur in quartz and calcite of stage I, associated with fracturing
and healing of veins. Hydrothermal wall-rock alteration minerals of stage I include Fe-rich chlorite (Fe/(Fe+Mg) ratios 0.74-0.81),
muscovite, illite, K-feldspar, and minor arsenopyrite, pyrite, and carbonates. Sulfide minerals deposited along with electrum
during this stage include arsenopyrite, pyrite, pyrrhotite, sphalerite, marcasite, chalcopyrite, galena, argentite, pyrargyrite,
and argentian tetrahedrite. Only calcite was deposited during stage II. Fluid inclusions in quartz contain three main types
of C–O–H fluids: CO2-rich, CO2–H2O, and aqueous inclusions. Quartz veins related to early sulfides in stage I were deposited from H2O–NaCl–CO2 fluids (1,500–5,000 bar, average 3,200) with T
htotal values of 200°C to 383°C and salinities less than about 7 wt.% NaCl equiv. Late sulfide deposition was related to H2O–NaCl fluids (140–1,300 bar, average 700) with T
htotal values of 110°C to 385°C and salinities less than about 11 wt.% NaCl equiv. These fluids either evolved through immiscibility
of H2O–NaCl–CO2 fluids as a result of a decrease in fluid pressure, or through mixing with deeply circulated meteoric waters as a result
of uplift or unloading during mineralization, or both. Measured and calculated sulfur isotope compositions (δ34SH2S = 1.5 to 4.8‰) of hydrothermal fluids from the stage I quartz veins indicate that ore sulfur was derived mainly from a magmatic
source. The calculated and measured oxygen and hydrogen isotope compositions (δ18OH2O = −5.9‰ to 10.9‰, δD = −102‰ to −87‰) of the ore-forming fluids indicate that the fluids were derived from magmatic sources
and evolved by mixing with local meteoric water by limited water–rock exchange and by partly degassing in uplift zones during
mineralization. While most features of the Samgwang mine are consistent with classification as an orogenic gold deposit, isotopic
and fluid chemistry indicate that the veins were genetically related to intrusions emplaced during the Jurassic to Cretaceous
Daebo orogeny. 相似文献
6.
Isotope geochemistry of ore fluids for the Dongsheng sandstone-type uranium deposit, China 总被引:2,自引:1,他引:2
The Dongsheng sandstone-type uranium deposit is one of the large-sized sandstone-type uranium deposits discovered in the northern part of the Ordos Basin of China in recent years. Geochemical characteristics of the Dongsheng uranium deposit are significantly different from those of the typical interlayered oxidized sandstone-type uranium ore deposits in the region of Middle Asia. Fluid inclusion studies of the uranium deposit showed that the uranium ore-forming temperatures are within the range of 150–160℃. Their 3He/4He ratios are within the range of 0.02–1.00 R/Ra, about 5–40 times those of the crust. Their 40Ar/36Ar ratios vary from 584 to 1243, much higher than the values of atmospheric argon. The δ18OH2O and δD values of fluid inclusions from the uranium deposit are -3.0‰– -8.75‰ and -55.8‰– -71.3‰, respectively, reflecting the characteristics of mixed fluid of meteoric water and magmatic water. The δ18OH2O and δD values of kaolinite layer at the bottom of the uranium ore deposit are 6.1‰ and -77‰, respectively, showing the characteristics of magmatic water. The δ13CV-PDB and δ18OH2O values of calcite veins in uranium ores are -8.0‰ and 5.76‰, respectively, showing the characteristics of mantle source. Geochemical characteristics of fluid inclusions indicated that the ore-formation fluid for the Dongsheng uranium deposit was a mixed fluid of meteoric water and deep-source fluid from the crust. It was proposed that the Jurassic-Cretaceous U-rich metamorphic rocks and granites widespread in the northern uplift area of the Ordos Basin had been weathered and denudated and the ore-forming elements, mainly uranium, were transported by meteoric waters to the Dongsheng region, where uranium ores were formed. Tectonothermal events and magmatic activities in the Ordos Basin during the Mesozoic made fluids in the deep interior and oil/gas at shallow levels upwarp along the fault zone and activated fractures, filling into U-bearing clastic sandstones, thus providing necessary energy for the formation of uranium ores. 相似文献
7.
Hydrogeochemical and isotopic investigation of the Bursa-Oylat thermal waters, Turkey 总被引:1,自引:1,他引:0
Suzan Pasvano?lu 《Environmental Earth Sciences》2011,64(4):1157-1167
The Oylat spa is located 80 km southeast of Bursa and 30 km south of Ineg?l in the Marmara region. With temperature of 40°C
and discharge of 45 l/s, the Oylat main spring is the most important hot water spring of the area. Southeast of the spa the
Forest Management spring has a temperature of 39.4°C and discharge of 2 l/s. The G?z spring 2 km north of the spa, which is
used for therapy of eye disease, and cold waters of the Saadet village springs with an acidic character are the further important
water sources of the area. EC values of Main spring and Forest Management hot spring (750–780 μS/cm) are lower than those
of Saadet and G?z spring waters (2,070–1,280 μS/cm) and ionic abundances are Ca > Na + K > Mg and SO4 > HCO3 > Cl. The Oylat and Sızı springs have low Na and K contents but high Ca and HCO3 concentrations. According to AIH classification, these are Ca–SO4–HCO3 waters. Based on the results of δ18O, 2H and 3H isotope analyses, the thermal waters have a meteoric origin. The meteoric water infiltrates along fractures and faults,
gets heated, and then returns to surface through hydrothermal conduits. Oylat waters do not have high reservoir temperatures.
They are deep, circulating recharge waters from higher enhanced elevations. δ13CDIC values of the Main spring and Forest Management hot spring are −6.31 and −4.45‰, respectively, indicating that δ13C is derived from dissolution of limestones. The neutral pH thermal waters are about +18.7‰ in δ34S while the sulfate in the cold waters is about +17‰ (practically identical to the value for the neutral pH thermal waters).
However, the G?z and Saadet springs (acid sulfate waters) have much lower δ34S values (~+4‰). 相似文献
8.
A set of sheeted quartz veins cutting 380 Ma monzogranite at Sandwich Point, Nova Scotia, Canada, provide an opportunity to
address issues regarding fluid reservoirs and genesis of intrusion-related gold deposits. The quartz veins, locally with arsenopyrite
(≤5%) and elevated Au–(Bi–Sb–Cu–Zn), occur within the reduced South Mountain Batholith, which also has other zones of anomalous
gold enrichment. The host granite intruded (P = 3.5 kbars) Lower Paleozoic metaturbiditic rocks of the Meguma Supergroup, well known for orogenic vein gold mineralization.
Relevant field observations include the following: (1) the granite contains pegmatite segregations and is cut by aplitic dykes
and zones (≤1–2 m) of spaced fracture cleavage; (2) sheeted veins containing coarse, comb-textured quartz extend into a pegmatite
zone; (3) arsenopyrite-bearing greisens dominated by F-rich muscovite occur adjacent the quartz veins; and (4) vein and greisen
formation is consistent with Riedel shear geometry. Although these features suggest a magmatic origin for the vein-forming
fluids, geochemical studies indicate a more complex origin. Vein quartz contains two types of aqueous fluid inclusion assemblages
(FIA). Type 1 is a low-salinity (≤3 wt.% equivalent NaCl) with minor CO2 (≤2 mol%) and has T
h = 280–340°C. In contrast, type 2 is a high-salinity (20–25 wt.% equivalent NaCl), Ca-rich fluid with T
h = 160–200°C. Pressure-corrected fluid inclusion data reflect expulsion of a magmatic fluid near the granite solidus (650°C)
that cooled and mixed with a lower temperature (400°C), wall rock equilibrated, Ca-rich fluid. Evidence for fluid unmixing,
an important process in some intrusion-related gold deposit settings, is lacking. Stable isotopic (O, D, S) analyses for quartz,
muscovite and arsenopyrite samples from vein and greisens indicate the following: (1) δ18Oqtz = +11.7‰ to 17.8‰ and δ18Omusc = +10.7‰ to +11.2‰; (2) δDmusc = −44‰ to−54‰; and (3) δ34Saspy = +7.8‰ to +10.3‰. These data are interpreted, in conjunction with fluid inclusion data, to reflect contamination of a magmatic-derived
fluid (d18OH2O {\delta^{{{18}}}}{{\hbox{O}}_{{{{\rm{H}}_{{2}}}{\rm{O}}}}} ≤ +10‰) by an external fluid (d18OH2O {\delta^{{{18}}}}{{\hbox{O}}_{{{{\rm{H}}_{{2}}}{\rm{O}}}}} ≥ +15‰), the latter having equilibrated with the surrounding metasedimentary rocks. The δ34S data are inconsistent with a direct igneous source based on other studies for the host intrusion (d18OH2O {\delta^{{{18}}}}{{\hbox{O}}_{{{{\rm{H}}_{{2}}}{\rm{O}}}}} = +5‰) and are, instead, consistent with an external reservoir for sulphur based on δ34SH2S data for the surrounding metasedimentary rocks. Divergent fluid reservoirs are also supported by analyses of Pb isotopes
for pegmatitic K-feldspar and vein arsenopyrite. Collectively the data indicate that the vein- and greisen-forming fluids
had a complex origin and reflect both magmatic and non-magmatic reservoirs. Thus, although the geological setting suggests
a magmatic origin, the geochemical data indicate involvement of multiple reservoirs. These results suggest multiple reservoirs
for this intrusion-related gold deposit setting and caution against interpreting the genesis of intrusion-related gold deposit
mineralization in somewhat analogous settings based on a limited geochemical data set. 相似文献
9.
At Sams Creek, a gold-bearing, peralkaline granite porphyry dyke, which has a 7 km strike length and is up to 60 m in thickness, intrudes camptonite lamprophyre dykes and lower greenschist facies metapelites and quartzites of the Late Ordovician Wangapeka formation. The lamprophyre dykes occur as thin (< 3 m) slivers along the contacts of the granite dyke. δ18Omagma values (+5 to +8‰, VSMOW) of the A-type granite suggest derivation from a primitive source, with an insignificant mature crustal contribution. Hydrothermal gold–sulphide mineralisation is confined to the granite and adjacent lamprophyre; metapelite country rocks have only weak hydrothermal alteration. Three stages of hydrothermal alteration have been identified in the granite: Stage I alteration (high fO2) consisting of magnetite–siderite±biotite; Stage II consisting of thin quartz–pyrite veinlets; and Stage III (low fO2) consisting of sulphides, quartz and siderite veins, and pervasive silicification. The lamprophyre is altered to an ankerite–chlorite–sericite assemblage. Stage III sulphide veins are composed of arsenopyrite + pyrite ± galena ± sphalerite ± gold ± chalcopyrite ± pyrrhotite ± rutile ± graphite. Three phases of deformation have affected the area, and the mineralised veins and the granite and lamprophyre dykes have been deformed by two phases of folding, the youngest of which is Early Cretaceous. Locally preserved early-formed fluid inclusions are either carbonic, showing two- or three-phases at room temperature (liquid CO2-CH4 + liquid H2O ± CO2 vapour) or two-phase liquid-rich aqueous inclusions, some of which contain clathrates. Salinities of the aqueous inclusions are in the range of 1.4 to 7.6 wt% NaCl equiv. Final homogenisation temperatures (Th) of the carbonic inclusions indicate minimum trapping temperatures of 320 to 355°C, which are not too different from vein formation temperatures of 340–380°C estimated from quartz–albite stable isotope thermometry. δ18O values of Stage II and III vein quartz range from +12 and +17‰ and have a bimodal distribution (+14.5 and +16‰) with Stage II vein quartz accounting for the lower values. Siderite in Stage III veins have δ18O (+12 to +16‰) and δ13C values (−5‰, relative to VPDB), unlike those from Wangapeka Formation metasediments (δ13Cbulk carbon values of −24 to −19‰) and underlying Arthur Marble marine carbonates (δ18O = +25‰ and δ13C = 0‰). Calculated δ18Owater (+8 to +11‰, at 340°C) and
(−5‰) values from vein quartz and siderite are consistent with a magmatic hydrothermal source, but a metamorphic hydrothermal origin cannot be excluded. δ34S values of sulphides range from +5 to +10‰ (relative to CDT) and also have a bimodal distribution (modes at +6 and +9‰, correlated with Stage II and Stage III mineralisation, respectively). The δ34S values of pyrite from the Arthur Marble marine carbonates (range from +3 to +13‰) and Wangapeka Formation (range from −4 to +9.5‰) indicate that they are potential sources of sulphur for sulphides in the Sams Creek veins. Another possible source of the sulphur is the lithospheric mantle which has positive values up to +14‰. Ages of the granite, lamprophyre, alteration/mineralisation, and deformation in the region are not well constrained, which makes it difficult to identify sources of mineralisation with respect to timing. Our mineralogical and stable isotope data does not exclude a metamorphic source, but we consider that the source of the mineralisation can best be explained by a magmatic hydrothermal source. Assuming that the hydrothermal fluids were sourced from crystallisation of the Sams Creek granite or an underlying magma chamber, then the Sams Creek gold deposit appears to be a hybrid between those described as reduced granite Au–Bi deposits and alkaline intrusive-hosted Au–Mo–Cu deposits. 相似文献
10.
The Janggun iron deposits, Republic of␣Korea, occur as lens-shaped magnesian skarn, magnetite and base-metal sulfide orebodies
developed in the Cambrian Janggun Limestone Formation. Mineralization stage of the deposits can be divided into two separate
events. The skarn stage (107 Ma) consists of magnetite, pyrrhotite, base-metal sulfides, carbonates and magnesian skarn minerals.
The hydrothermal stage (70 Ma) consists of base-metal sulfides, native bismuth, bismuthinite, tetrahedrite, boulangerite,
bournonite and stannite. Mineral assemblages, chemical compositions and thermodynamic considerations indicate that formation
temperatures, −log fs2 and −log fo2 values of ore fluids from the skarn stage were 433 to 345 °C, 8.1 to 9.7 bar and 29.4 to 31.6 bar, and the hydrothermal stage
was 245 to 315 °C, 10.4 to 13.2 bar and 33.6 to 35.4 bar, respectively. Thermochemical considerations indicate that the XCO2 during magnesian skarnization ranged from 0.06 to 0.09, and the activity of H+ presumably decreased when the fluids equilibrated with host dolomitic limestone which resulted in a pH change from about
6.1 to 7.8, and decreases in fo2 and fs2. The δ34S values of ore sulfides have a wide range from 3.2 to 11.6 ‰ (CDT). Calculated 34SH2
S values of ore fluids are 2.9 to 5.4 ‰ (skarn stage) and 8.7 to 13.5 ‰ (hydrothermal stage). These are interpreted to represent
an initial deep-seated, igneous source of sulfur which gave way to influence of oxidized sedimentary sulfur to hydrothermal
stage. The δ13C values of carbonates in ores range from −4.6 to −2.5 ‰ (PDB). It is likely that carbon in the ore fluids was a mixture of
deep-seated magmatic carbon and dissolved carbon of dolomitic limestone. The δ18OH2
O and δD values (SMOW) of water in the ore fluids were 14.7 to 1.8 and −85 to −73 ‰ during the skarn stage and 11.1 to −0.2
and −87 to −80 ‰ in the hydrothermal stage.
Received: 5 March 1997 / Accepted: 28 August 1997 相似文献
11.
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
12.
James M. D. Day Colin G. Macpherson David Lowry D. Graham Pearson 《Contributions to Mineralogy and Petrology》2012,164(1):177-183
Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) report laser-assisted fluorination (LF) and secondary ionization mass spectrometry (SIMS) 18O/16O datasets for olivine grains from the Canary Islands of Gran Canaria, Tenerife, La Gomera, La Palma and El Hierro. As with prior studies of oxygen isotopes in Canary Island lavas (e.g. Thirlwall et al. Chem Geol 135:233–262, 1997; Day et al. Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010), these authors find variations in δ18Ool (~4.6–6.0 ‰) beyond that measured for mantle peridotite olivine (Mattey et al. Earth Planet Sci Lett 128:231–241, 1994) and interpret this variation to reflect contributions from pyroxenite-peridotite mantle sources. Furthermore, Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) speculate that δ18Ool values for La Palma olivine grains measured by LF (Day et al. Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010) may be biased to low values due to the presence of altered silicate, possibly serpentine. The range in δ18Ool values for Canary Island lavas are of importance for constraining their origin. Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) took a subset (39 SIMS analyses from 13 grains from a single El Hierro lava; EH4) of a more extensive dataset (321 SIMS analyses from 110 grains from 16 Canary Island lavas) to suggest that δ18Ool is weakly correlated (R 2 = 0.291) with the parameter used by Gurenko et al. (Earth Planet Sci Lett 277:514–524, 2009) to describe the estimated weight fraction of pyroxenite-derived melt (Xpx). With this relationship, end-member δ18O values for HIMU-peridotite (δ18O = 5.3 ± 0.3 ‰) and depleted pyroxenite (δ18O = 5.9 ± 0.3 ‰) were defined. Although the model proposed by Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) implicates similar pyroxenite-peridotite mantle sources to those proposed by Day et al. (Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010) and Day and Hilton (Earth Planet Sci Lett 305:226–234, 2011), there are significant differences in the predicted δ18O values of end member components in the two models. In particular, Day et al. (Geochim Cosmochim Acta 74:6565–6589, 2010) proposed a mantle source for La Palma lavas with low-δ18O (<5 ‰), rather than higher-δ18O (c.f. the HIMU-peridotite composition of Gurenko et al. in Contrib Mineral Petrol 162:349–363, 2011). Here we question the approach of using weakly correlated variations in δ18Ool and the Xpx parameter to define mantle source oxygen isotope compositions, and provide examples of why this approach appears flawed. We also provide reasons why the LF datasets previously published for Canary Island lavas remain robust and discuss why LF and SIMS data may provide complementary information on oxygen isotope variations in ocean island basalts (OIB), despite unresolved small-scale uncertainties associated with both techniques. 相似文献
13.
Distribution of Hydrogen and Oxygen Isotopes in Salt Lakes of the Qinghai—Xizang Plateau,China 总被引:1,自引:0,他引:1
The Qinghai-Xizang Plateau is an area where a large number of salt lakes are distributed. We have collected several hundred
samples of natural waters over the Plateau since 1976 and carried out researches on their hydrogen and oxygen isotopes. The
results indicate that theδD and δ18O values of the salt lake waters over the Plateau range from −64.1 to +12.4‰ and from −11.19 to +8.62‰, respectively.
From the different types of surfaces, ground and lake waters of various salinities it is inferred that the compositions of
H and O isotopes in the initial water of Qinghai Lake areδD=−55.0‰ and {ie336-1}; and those in the original water from the lakes in northern Xizang, areδD=−116.0‰ and {ie336-2}. Brines in the salt lakes are derived from rain water through prolonged circulation. Oilfield water
also makes some contribution to the salt lakes in the Qaidam Basin. Similar slopes of evaporation lines of water isotopes
are noticed for the Qinghai Lake area and northern Xizang. This is attributed to the evolution of the isotopes in these water
bodies in an environment of middle latitude and high elevation. 相似文献
14.
Summary
The oxygen and strontium isotope compositions of the Cambro-Ordovician granitoids cropping out in the Wilson Terrane (Granite
Harbour Intrusives–GHI) constrain the petrological evolution of the magmatism in Antarctica, related to the Ross Orogeny.
The measured δ18OWR values of these intrusives define three different compositional groups: the metaluminous rocks (MAG), with δ18OWR ranging from 6.9 (olivine gabbro) to 11.4‰ (monzogranite); the unaltered peraluminous granites (PAG), having δ18OWR values ranging from 10.6 to 13.2‰, and the foliated peraluminous leucogranites (SKG), characterised by δ18OWR values above 14‰. The analysis of equilibrium mineral assemblages indicates that the high δ18OWR values are magmatic and unaffected by low-temperature processes. A few peraluminous granites sampled in the vicinity of Cenozoic
intrusions show anomalously low δ18OWR, due to meteoric-hydrothermal alteration. The isotopic data indicate that the coeval and spatially related metaluminous mafic
and felsic intrusives forming the GHI were not comagmatic: the mafic and intermediate rocks were likely derived from lower
crustal contamination of a pristine basaltic magma; their δ18OWR values were also increased during emplacement, due to the interaction with the adjacent 18O-rich hydrous felsic magmas (mixing). Oxygen isotope data indicate that the crustal sources producing the Granite Harbour
intrusives were not homogeneous: the felsic metaluminous intrusives were produced by partial melting of fertile rock with
possible igneous origin, whereas partial melting of a metapelitic source rock is claimed for the genesis of the peraluminous
granites.
Received February 9, 2001; revised version accepted August 10, 2001 相似文献
15.
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
16.
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
17.
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
18.
Jade Star Lackey John W. Valley Hans J. Hinke 《Contributions to Mineralogy and Petrology》2006,151(1):20-44
Peraluminous granitoids provide critical insight as to the amount and kinds of supracrustal material recycled in the central
Sierra Nevada batholith, California. Major element concentrations indicate Sierran peraluminous granitoids are high-SiO2 (68.9–76.9) and slightly peraluminous (average molar Al2O3/(CaO + Na2O + K2O)=1.06). Both major and trace element trends mimic those of other high-silica Sierran plutons. Garnet (Grt) in the peraluminous
plutons is almandine–spessartine-rich and of magmatic origin. Low grossular contents are consistent with shallow (<4 kbar)
depths of garnet crystallization. Metasediments of the Kings Sequence commonly occur as wallrocks associated with the plutons,
including biotite schists that are highly peraluminous (A/CNK=2.25) and have high whole rock (WR) δ18O values (9.6–21.8‰, average=14.5±2.9‰, n=26). Ultramafic wallrocks of the Kings–Kaweah ophiolite have lower average δ18O (7.1±1.3‰, n=9). The δ18O(WR) of the Kings Sequence is variable from west to east. Higher δ18O values occur in the west, where quartz in schists is derived from marine chert; values decrease eastward as the proportion
of quartz from igneous and metamorphic sources increases. Peraluminous plutons have high δ18O(WR) values (9.5–13‰) consistent with supracrustal enrichment of their sources. However, relatively low initial 87Sr/86Sr values (0.705–0.708) indicate that the supracrustal component in the source of peraluminous magmas was dominantly altered
ocean crust and/or greywacke. Also, plutons lack or have very low abundances (<1% of grains) of inherited zircon (Zrc) cores.
Average δ18O(Zrc) is 7.9‰ in peraluminous plutons, a higher value than in coeval metaluminous plutons (6–7‰). Diorites associated with
peraluminous plutons also have high δ18O(Zrc), 7.4–8.3‰, which is consistent with the diorites being derived from a similar source. Magmatic garnet has variable
δ18O (6.6–10.5‰, avg.=7.9‰) due to complex contamination and crystallization histories, evidenced by multiple garnet populations
in some rocks. Comparison of δ18O(Zrc) and δ18O(Grt) commonly reveals disequilibrium, which documents evolving magma composition. Minor (5–7%) contamination by high δ18O wallrocks occurred in the middle and upper crust in some cases, although low δ18O wallrock may have been a contaminant in one case. Overall, oxygen isotope analysis of minerals having slow oxygen diffusion
and different times of crystallization (e.g., zircon and garnet), together with detailed textural analysis, can be used to
monitor assimilation in peraluminous magmas. Moreover, oxygen isotope studies are a valuable way to identify magmatic versus
xenocrystic minerals in igneous rocks.
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
19.
Stable and radiogenic isotope composition of stratiform Cu–Co–Zn mineralization and associated sedimentary rocks within the Boléo district of the Miocene Santa Rosalía basin, Baja California Sur, constrains the evolution of seawater and hydrothermal fluids and the mechanisms responsible for sulfide and oxide deposition. Stable isotope geochemistry of limestone and evaporite units indicates a strong paleogeographic influence on the chemistry of the water column. Near-shore limestone at the base of the Boléo Formation is characterized by modified marine carbon (δ
13CPDB=−6.0 to +4.4‰) and oxygen (δ
18OSMOW=+19.5 to +26.2‰) isotope composition due to the influx of 13C- and 18O-depleted fluvial water. Sulfate sulfur isotope composition (δ
34SCDT=+17.21 to +22.3‰ and δ
18OSMOW=+10.7 to +13.1‰) for basal evaporite and claystone facies are similar to Miocene seawater. Strontium isotopes are less radiogenic than expected for Miocene seawater due to interaction with volcanic rocks. Low S/C ratios, high Mn contents and sedimentological evidence indicate the basin water column was oxidizing. The oxygenated basin restricted sulfide precipitation to within the sedimentary pile by replacement of early diagenetic framboidal pyrite and pore-space filling by Cu–Co–Zn sulfides to produce disseminated sulfides. Quartz–Mn oxide oxygen isotope geothermometry constrains mineralization temperature between 18 and 118°C. Sulfur isotopes indicate the following sources of sulfide: (1) bacterial sulfate reduction within the sedimentary pile produced negative δ
34S values (<−20‰) in framboidal pyrite; and (2) bacterial sulfate reduction at high temperature (80–118°C) within the sedimentary pile during the infiltration of the metal-bearing brines produced Cu–Co–Zn sulfides with negative, but close to 0‰, δ
34S values. Isotope modeling of fluid-rock reaction and fluid mixing indicates: (1) sedimentary and marine carbonates (δ
13C=−11.6 to −3.2‰ and δ
18O=+19.0 to +21.8‰) precipitated from basin seawater/pore water that variably mixed with isotopically depleted meteoric waters; and (2) hydrothermal calcite (δ
13C=−7.9 to +4.3‰ and δ
18O=+22.1 to +25.8‰) formed by dissolution and replacement of authigenic marine calcite by downward-infiltrating metalliferous brine and brine-sediment exchange, that prior to reaction with calcite, had mixed with isotopically depleted pore water. The downward infiltration of metalliferous brine is inferred from lateral and stratigraphic metal distributions and from the concentration of Cu sulfides along the upper contact of pyrite-bearing laminae. The co-existence and textural relationships among framboidal pyrite, base metal sulfides, carbonate and Mn–Fe oxides (including magnetite) within mineralized units are consistent with carbonate replacement and high-temperature bacterial reduction within the sedimentary pile occurring simultaneously below a seawater column under predominantly oxygenated conditions. 相似文献
20.
Jean Vallance Lluís Fontboté Massimo Chiaradia Agnès Markowski Susanne Schmidt Torsten Vennemann 《Mineralium Deposita》2009,44(4):389-413
The Jurassic (approximately 145 Ma) Nambija oxidized gold skarns are hosted by the Triassic volcanosedimentary Piuntza unit
in the sub-Andean zone of southeastern Ecuador. The skarns consist dominantly of granditic garnet (Ad20–98) with subordinate pyroxene (Di46–92Hd17–42Jo0–19) and epidote and are spatially associated with porphyritic quartz-diorite to granodiorite intrusions. Endoskarn is developed
at the intrusion margins and grades inwards into a potassic alteration zone. Exoskarn has an outer K- and Na-enriched zone
in the volcanosedimentary unit. Gold mineralization is associated with the weakly developed retrograde alteration of the exoskarn
and occurs mainly in sulfide-poor vugs and milky quartz veins and veinlets in association with hematite. Fluid inclusion data
for the main part of the prograde stage indicate the coexistence of high-temperature (500°C to >600°C), high-salinity (up
to 65 wt.% eq. NaCl), and moderate- to low-salinity aqueous-carbonic fluids interpreted to have been trapped at pressures
around 100–120 MPa, corresponding to about 4-km depth. Lower-temperature (510–300°C) and moderate- to low-salinity (23–2 wt.%
eq. NaCl) aqueous fluids are recorded in garnet and epidote of the end of the prograde stage. The microthermometric data (Th
from 513°C to 318°C and salinity from 1.0 to 23 wt.% eq. NaCl) and δ18O values between 6.2‰ and 11.5‰ for gold-bearing milky quartz from the retrograde stage suggest that the ore-forming fluid
was dominantly magmatic. Pressures during the early retrograde stage were in the range of 50–100 MPa, in line with the evidence
for CO2 effervescence and probable local boiling. The dominance of magmatic low-saline to moderately saline oxidizing fluids during
the retrograde stage is consistent with the depth of the skarn system, which could have delayed the ingression of external
fluids until relatively low temperatures were reached. The resulting low water-to-rock ratios explain the weak retrograde
alteration and the compositional variability of chlorite, essentially controlled by host rock compositions. Gold was precipitated
at this stage as a result of cooling and pH increase related to CO2 effervescence, which both result in destabilization of gold-bearing chloride complexes. Significant ingression of external
fluids took place after gold deposition only, as recorded by δ18O values of 0.4‰ to 6.2‰ for fluids depositing quartz (below 350°C) in sulfide-rich barren veins. Low-temperature (<300°C)
meteoric fluids (δ18Owater between −10.0‰ and −2.0‰) are responsible for the precipitation of late comb quartz and calcite in cavities and veins and
indicate mixing with cooler fluids of higher salinities (about 100°C and 25 wt.% eq. NaCl). The latter are similar to low-temperature
fluids (202–74.5°C) with δ18O values of −0.5‰ to 3.1‰ and salinities in the range of 21.1 to 17.3 wt.% eq. CaCl2, trapped in calcite of late veins and interpreted as basinal brines. Nambija represents a deep equivalent of the oxidized
gold skarn class, the presence of CO2 in the fluids being partly a consequence of the relatively deep setting at about 4-km depth. As in other Au-bearing skarn
deposits, not only the prograde stage but also the gold-precipitating retrograde stage is dominated by fluids of magmatic
origin. 相似文献