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1.
Whole rock and mineral stable isotope and microprobe analyses are presented from granitoids of the North Chilean Precordillera.
The Cretaceous to Tertiary plutonic rocks contain important ore deposits and frequently display compositional and textural
evidence of hydrothermal alteration even in barren rocks. Deuteric alteration includes replacement of biotite and amphibole
by chlorite and epidote, sericitization and saussuritization of feldspars, and uralitization of clinopyroxene and/or amphibole.
While whole rock compositions are not significantly affected, compositional variations in amphiboles suggest two types of
hydrothermal alteration. Hornblende with actinolitic patches and rims and tight compositional trends from hornblende to Mg-rich
actinolite indicate increasing oxygen fugacity from magmatic to hydrothermal conditions. Uralitic amphiboles exhibiting irregular
Mg-Fe distribution and variable Al content are interpreted as reflecting subsolidus hydration reactions at low temperatures.
The δD values of hydrous silicates vary from −63 to −105‰. Most δ18O values of whole rocks are in the range of 5.7 to 7.7‰ and are considered normal for igneous rocks in the Andes. These δ18O values also coincide well with the oxygen isotope composition of geochemically similar recent volcanics from the Central
Andean Volcanic Zone (δ18O = 7.0–7.4‰). Only one sample in this study (δ18O = 3.0‰) appears to be depleted by isotope exchange with light meteoric water at high temperatures. The formation of secondary
minerals in all other intrusions is mainly the product of deuteric alteration. This also holds true for the sample from El
Abra, the only pluton associated with mineralization. This indicates the dominant role of a magmatic rather than a meteoric
fluid in the alteration of the Cretaceous and Tertiary granitoids in northern Chile.
Received: 8 July 1998 / Accepted: 15 April 1999 相似文献
2.
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
3.
Summary The eastern Pyrenees host a large number of talc-chlorite mineralizations of Albian age (112–97 Ma), the largest of which
occur in the St. Barthelemy massif. There talc develops by hydrothermal replacement of dolostones, which were formed by alteration
of calcite marbles. This alteration is progressive. Unaltered calcite marbles have oxygen isotope composition of about 25‰
(V-SMOW). The δ18O values decrease down to values of 12‰ towards the contact with dolostones. This 18O depletion is accompanied by Mg enrichment, LREE fractionation and systematic shifts in the Sr isotope compositions, which
vary from 87Sr/86Sr = 0.7087–0.7092 in unaltered calcite marbles to slightly more radiogenic compositions with 87Sr/86Sr = 0.7094 near dolomitization fronts. Dolostones have δ18O values (about 9‰) lower than calcitic marbles, higher REE content and more radiogenic Sr isotope composition (87Sr/86Sr = 0.7109 to 0.7130). Hydrothermal calcites have δ18O values close to dolostones but substantially lower δ13C values, down to −6.5‰, which is indicative of the contribution of organic matter. The REE content of hydrothermal calcite
is one order of magnitude higher than that of calcitic marbles. Its highly radiogenic Sr composition with 87Sr/86Sr = 0.7091 to 0.7132 suggests that these elements were derived from silicate rocks, which experienced intense chlorite alteration
during mineralization. The chemical and isotopic compositions of the calcite marbles, the dolostones and the hydrothermal
calcites are interpreted as products of successive stages of fluid-rock interaction with increasing fluid-rock ratios. The
hydrothermal quartz, calcite, talc and chlorite are in global mutual isotopic equilibrium. This allows the calculation of
the O isotope composition of the infiltrating water at 300 °C, which is in the δ18O
= 2–4.5‰ range. Hydrogen isotope compositions of talc and chlorite indicate a δD
= 0 to −20‰. This water probably derived from seawater, with minor contribution of evolved continental water. 相似文献
4.
Hamdy A. El Desouky Philippe Muchez Adrian J. Boyce Jens Schneider Jacques L. H. Cailteux Stijn Dewaele Albrecht von Quadt 《Mineralium Deposita》2010,45(8):735-763
The sediment-hosted stratiform Cu–Co mineralization of the Luiswishi and Kamoto deposits in the Katangan Copperbelt is hosted
by the Neoproterozoic Mines Subgroup. Two main hypogene Cu–Co sulfide mineralization stages and associated gangue minerals
(dolomite and quartz) are distinguished. The first is an early diagenetic, typical stratiform mineralization with fine-grained
minerals, whereas the second is a multistage syn-orogenic stratiform to stratabound mineralization with coarse-grained minerals.
For both stages, the main hypogene Cu–Co sulfide minerals are chalcopyrite, bornite, carrollite, and chalcocite. These minerals
are in many places replaced by supergene sulfides (e.g., digenite and covellite), especially near the surface, and are completely
oxidized in the weathered superficial zone and in surface outcrops, with malachite, heterogenite, chrysocolla, and azurite
as the main oxidation products. The hypogene sulfides of the first Cu–Co stage display δ34S values (−10.3‰ to +3.1‰ Vienna Canyon Diablo Troilite (V-CDT)), which partly overlap with the δ34S signature of framboidal pyrites (−28.7‰ to 4.2‰ V-CDT) and have ∆34SSO4-Sulfides in the range of 14.4‰ to 27.8‰. This fractionation is consistent with bacterial sulfate reduction (BSR). The hypogene sulfides
of the second Cu–Co stage display δ34S signatures that are either similar (−13.1‰ to +5.2‰ V-CDT) to the δ34S values of the sulfides of the first Cu–Co stage or comparable (+18.6‰ to +21.0‰ V-CDT) to the δ34S of Neoproterozoic seawater. This indicates that the sulfides of the second stage obtained their sulfur by both remobilization
from early diagenetic sulfides and from thermochemical sulfate reduction (TSR). The carbon (−9.9‰ to −1.4‰ Vienna Pee Dee
Belemnite (V-PDB)) and oxygen (−14.3‰ to −7.7‰ V-PDB) isotope signatures of dolomites associated with the first Cu–Co stage
are in agreement with the interpretation that these dolomites are by-products of BSR. The carbon (−8.6‰ to +0.3‰ V-PDB) and
oxygen (−24.0‰ to −10.3‰ V-PDB) isotope signatures of dolomites associated with the second Cu–Co stage are mostly similar
to the δ13C (−7.1‰ to +1.3‰ V-PDB) and δ18O (−14.5‰ to −7.2‰ V-PDB) of the host rock and of the dolomites of the first Cu–Co stage. This indicates that the dolomites
of the second Cu–Co stage precipitated from a high-temperature, host rock-buffered fluid, possibly under the influence of
TSR. The dolomites associated with the first Cu–Co stage are characterized by significantly radiogenic Sr isotope signatures
(0.70987 to 0.73576) that show a good correspondence with the Sr isotope signatures of the granitic basement rocks at an age
of ca. 816 Ma. This indicates that the mineralizing fluid of the first Cu–Co stage has most likely leached radiogenic Sr and
Cu–Co metals by interaction with the underlying basement rocks and/or with arenitic sedimentary rocks derived from such a
basement. In contrast, the Sr isotope signatures (0.70883 to 0.71215) of the dolomites associated with the second stage show
a good correspondence with the 87Sr/86Sr ratios (0.70723 to 0.70927) of poorly mineralized/barren host rocks at ca. 590 Ma. This indicates that the fluid of the
second Cu–Co stage was likely a remobilizing fluid that significantly interacted with the country rocks and possibly did not
mobilize additional metals from the basement rocks. 相似文献
5.
V. E. Strikha 《Geochemistry International》2006,44(8):791-807
Geochemical and isotopic data were used for a comparative analysis of Late Mesozoic (150–120 Ma) granitoids in various geological
structures of the upper Amur area. The granitoids are metaluminous high-potassic I-type rocks of the magnetite series. They
have variable alkalinity and consist of the monzonite-granite and granosyenite-granite associations. The monzonite-granite
association consists of calc-alkaline granitoids of normal alkalinity belonging to the Umlekan-Ogodzhinskaya volcanic-plutonic
zone and the Tynda-Bakaran Complex of the Stanovoy terrane. The rocks are characterized by negative anomalies of U, Ta, Nd,
Hf, and Ti (in patterns normalized to the primitive mantle), with Eu anomalies pronounced weakly in the granodiorites and
quartz and monzodiorites and more clearly in the granites: Eu/Eu* = 0.37–0.95, and (La/Yb)n = 7–24, Tbn/Ybn = 1.4–3.2. The granosyenite-granite association comprises of moderately alkaline rocks, which are subdivided into three groups
according to their geochemistry. The first group consists of phase-I granosyenites of the Uskalinskii Massif of the Umlekan-Ogodzhinskaya
zone with the highest concentrations of Sc, V, Cr, Co, Ni, Cu, Cs, Rb, Sr, Y, Zr, Yb, and Th; negative anomalies at Ba, Ta,
Sr, and Hf; Eu/Eu* = 0.50–0.58, (La/Yb)n = 15–16, and Tbn/Ybn = 1.8. The second group comprises of moderately alkaline granitoids of the Umlekan-Ogodzhinskaya zone and the Khaiktinskii
Complex of the Baikal-Vitim superterrane. Geochemically, the granitoids of this group are generally similar to the monzodiorite-granite
association and differ from it in having lower concentrations of REE and Y, Eu/Eu* = 6.2–1.0, (La/Yb)n = 28–63, and Tbn/Ybn = 2.1–4.5. The third group consists of granitoids of the Chubachinskii Complex of the Stanovoi terrane, which typically show
negative Cs, Rb, Th, U, Ta, Hf, and Ti anomalies; the lowest concentrations of V, Cr, Co, and Ni; and the highest contents
of Sr. The granosyenites of the first phase display clearly pronounced negative Eu anomalies (Eu/Eu* = 0.53–0.68), (La/Yb)n = 7–24, and Tbn/Ybn = 0.8–2.0. The granitoids of the second phase have (La/Yb)n = 51–84, no Eu anomalies, or very weak Eu anomalies (Eu/Eu* = 0.97–1.23). The silica-oversaturated leucogranites of the third
phase are characterized by elevated concentrations of REE, clearly pronounced Eu anomalies (Eu/Eu* = 0.48), and flat REE patterns
(Tbn/Ybn = 1.3). The diversity of the granitoids is demonstrated to have been caused largely by the composition of the Precambrian
source, which was isotopically heterogeneous. The rocks of the monzodiorite-granite association and first-group granosyenites
of the granosyenite-granite association of the Tynda-Bakaran Complex were supposedly derived from garnet-bearing biotite amphibolites.
In contrast to these rocks, the source of the second-group granites of the granosyenite-granite association was of mixed amphibolite-metagraywacke
composition. The third-group of granitoids were melted out of Early Proterozoic crustal feldspar-rich granulites of variable
basicity, with minor amounts of Archean crustal material. The granitoids were emplaced in a collisional environment, perhaps,
during the collision of the Amur superterrane and Siberian craton. This makes it possible to consider these rocks as components
of a single continental volcanic-plutonic belt.
Original Russian Text ? V.E. Strikha, 2006, published in Geokhimiya, 2006, No. 8, pp. 855–872. 相似文献
6.
A. I. Grabezhev 《Geology of Ore Deposits》2010,52(2):138-153
The Early Devonian Gumeshevo deposit is one of the largest ore objects pertaining to the dioritic model of the porphyry copper
system paragenetically related to the low-K quartz diorite island-arc complex. The (87Sr/86Sr)t and (ɛNd)t of quartz diorite calculated for t = 390 Ma are 0.7038–0.7045 and 5.0–5.1, respectively, testifying to a large contribution of the mantle component to the composition
of this rock. The contents of typomorphic trace elements (ppm) are as follows: 30–48 REE sum, 5–10 Rb, 9–15 Y, and 1–2 Nb.
The REE pattern is devoid of Eu anomaly. Endoskarn of low-temperature and highly oxidized amphibole-epidote-garnet facies
is surrounded by the outer epidosite zone. Widespread retrograde metasomatism is expressed in replacement of exoskarn and
marble with silicate (chlorite, talc, tremolite)-magnetite-quartz-carbonate mineral assemblage. The 87Sr/86Sr ratios of epidote in endoskarn and carbonate in retrograde metasomatic rocks (0.7054–0.7058 and 0.7053–0.7065, respectively)
are intermediate between the Sr isotope ratios of quartz dioritic rocks and marble (87Sr/86Sr = 0.70784 ± 2). Isotopic parameters of the fluid equilibrated with silicates of skarn and retrograde metasomatic rocks
replacing exoskarn at 400°C are δ18O = +7.4 to +8.5‰ and δD = −49 to −61‰ (relative to SMOW). The δ13C and δ18O of carbonates in retrograde metasomatic rocks after marble are −5.3 to +0.6 (relative to PDB) and +13.0 to +20.2% (relative
to SMOW), respectively. Sulfidation completes metasomatism, nonuniformly superimposed on all metasomatic rocks and marbles
with formation of orebodies, including massive sulfide ore. The δ34S of sulfides is 0 to 2‰ (relative to CDT);87Sr/86Sr of calcite from the late calcite-pyrite assemblage replacing marble is 0.704134 ± 6. The δ13C and 87Sr/86Sr of postore veined carbonates correlate positively (r = 0.98; n = 6). The regression line extends to the marble field. Its opposite end corresponds to magmatic (in terms of Bowman, 1998b)
calcite with minimal δ13C, δ18O, and 87Sr/86Sr values (−6.9 ‰, +6.7‰, and 0.70378 ± 4, respectively). The aforementioned isotopic data show that magmatic fluid was supplied
during all stages of mineral formation and interacted with marble and other rocks, changing its Sr, C, and O isotopic compositions.
This confirms the earlier established redistribution of major elements and REE in the process of metasomatism. A contribution
of meteoric and metamorphic water is often established in quartz from postore veins. 相似文献
7.
A. M. Moghazi 《Mineralogy and Petrology》2002,75(1-2):41-67
Summary
Three distinctive metaluminous granitic suites have been identified from the Pan-African belt of the Kab Amiri area, Eastern
Desert, Egypt. These are: 1) a trondhjemite-tonalite suite, 2) a calc-alkaline granodiorite suite, and 3) an alkali leucogranite
suite. The trondhjemite-tonalite and the granodiorite suites resemble I-type granitoids whereas the alkali leucogranites display
A-type characteristics. Geochemical attributes and field aspects indicate that three independent magmas, at different tectonic
stages of the Pan-African crustal growth, are required to explain the origin of these granitoid suites. Rocks of the trondhjemite-tonalite
suite correspond to granites of the arc stage and possess a narrow range of SiO2 with low K2O, Sr, Rb, Ba, Nb and Zr. Its composition is consistent with 20–30% partial melting of a primitive low-K tholeiitic source,
similar to the early formed tholeiitic metavolcanics of the Egyptian basement. The granodiorite suite belongs to the collision
stage and displays higher K2O, Rb, Ba, and Sr. Its magma was derived by 30–40% partial melting of LILE-enriched mafic island arc crust. The presence of
abundant microdiorite enclaves in the trondhjemite-tonalite and the granodiorite suites suggests that mantle-derived mafic
magma played an important role in their petrogenesis, acting as a heat source for melting via underplating and/or intrusion.
The A-type leucogranites are post-collision highly fractionated granites. They exhibit low Al2O3, MgO, CaO, TiO2, Sr, and Ba and high Rb, Nb, Y. The wide chemical variations within this suite are consistent with its evolution by fractional
crystallization of plagioclase, K-feldspar, amphibole, Fe–Ti oxides, and apatite from a mafic magma. The parent magma was
originated in the upper mantle due to crustal attenuation associated with extension in the late stage of the Pan-African crustal
evolution.
Received September 13, 2000; revised version accepted May 4, 2001 相似文献
8.
P. B. Tomascak Eirik J. Krogstad Richard J. Walker 《Contributions to Mineralogy and Petrology》1996,125(1):45-59
Neodymium and lead isotope and elemental data are presented for the Sebago batholith (293±2 Ma), the largest exposed granite
in New England. The batholith is lithologically homogeneous, yet internally heterogeneous with respect to rare earth elements
(REE) and Nd isotopic composition. Two-mica granites in the southern/central portion of the batholith (group 1) are characterized
by REE patterns with uniform shapes [CeN/YbN (chondrite normalized) = 9.4–19 and Eu/Eu* (Eu anomaly) = 0.27–0.42] and ɛ
Nd(t) = −3.1 to −2.1. Peripheral two-mica granites (group 2), spatially associated with stromatic and schlieric migmatites,
have a wider range of total REE contents and patterns with variable shapes (CeN/YbN = 6.1–67, Eu/Eu* = 0.20–0.46) and ɛ
Nd(t) = −5.6 to −2.8. The heterogeneous REE character of the group 2 granites records the effects of magmatic differentiation
that involved monazite. Coarse-grained leucogranites and aplites have kinked REE patterns and low total REE, but have Nd isotope
systematics similar to group 2 granites with ɛ
Nd(t) = −5.5 to −4.7. Rare biotite granites have steep REE patterns (CeN/YbN = 51–61, Eu/Eu* = 0.32–0.84) and ɛ
Nd(t) = −4.6 to −3.8. The two-mica granites have a restricted range in initial Pb isotopic composition (206Pb/204Pb = 18.41–18.75; 207Pb/204Pb = 15.60–15.68; 208Pb/204Pb = 38.21–38.55), requiring and old, high U/Pb (but not Th/U) source component. The Nd isotope data are consistent with magma
derivation from two sources: Avalon-like crust (ɛ
Nd>−3), and Central Maine Belt metasedimentary rocks (ɛ
Nd<−4), without material input from the mantle. The variations in isotope systematics and REE patterns are inconsistent with
models of disequilibrium melting which involved monazite.
Received: 8 December 1995 / Accepted: 29 April 1996 相似文献
9.
The Khawr Fakkan block of the Semail ophiolite (United Arab Emirates) exhibits a suite of 10–100 m scale metaluminous to
peraluminous granitic intrusions, ranging from cordierite-andalusite-biotite monzogranites to garnet-tourmaline leucogranites,
which intrude mantle sequence harzburgites and lower crustal sequence cumulate gabbros. Structural constraints suggest that
the subduction of continental sedimentary material beneath the hot proto-ophiolite in an intra-oceanic arc environment led
to granulite facies metamorphism at the subduction front and the generation of granitic melts which were emplaced up to the
level of the ophiolite Moho. Compositions indicate the analysed granitoids were largely minimum melts that crystallised at
variable a
H2O and pressures of 3 to 5 kbar. The LILE (Sr, Rb and Ba) covariation modelling suggests that the granitoids formed largely
by the dehydration melting of muscovite rich metasediments. Initial 87Sr/86Sr ratios of analysed dykes vary between 0.710 and 0.706 at initial ɛNd values of between −6.3 and −0.5. Cogenetic units of a composite sill from Ra's Dadnah yield a Sm-Nd isochron age of 98.8 ± 9.5 Ma
(MSWD = 1.18). Geochemical and isotopic characteristics of the analysed granitic intrusions indicate that the subducted continental
material was derived from oceanic trench fill (Haybi complex) sediments, preserved as greenschist (Asimah area) to granulite
facies (Bani Hamid area) ophiolitic metamorphic sole terranes. The Sr-Nd isotope systematics suggest that hybrid granitic
melts were derived from pre-magmatic mixing of two contrasting subduction zone sources.
Received: 17 December 1998 / Accepted: 19 July 1999 相似文献
10.
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
11.
In situ radioelemental (K, U and Th) analysis and heat production estimates have been made at 59 sites in the Kerala Khondalite
Block (KKB) of the Southern Granulite Province (SGP) of India. Together with the in situ analyses on granulites and gneisses
previously reported from 28 sites, and heat production estimated from the published geochemical analyses on granites and syenites
of the KKB, the new data set allows good characterization of heat production for the major granulite facies rocks and granitoids
of the KKB. Garnet biotite gneisses are characterized by high levels of Th and U, with mean values of 60 and 3 ppm, respectively.
Khondalites, leptynites and charnockites have slightly lower levels of Th (23, 20 and 22 ppm, respectively) and U (2.9, 2.4
and 0.9 ppm, respectively). The mean K, U, Th abundances for the granites, leucogranites and granitic gneisses ranges from
3.9 to 4.3%, 2.6 to 4.3 ppm, 22 to 50 ppm respectively, and for the syenites 4.8%, 2 ppm and 5.7 ppm. Mean radiogenic heat
production values for garnet–biotite gneiss, khondalite, leptynite and charnockite are 5.5, 2.7, 2.4 and 2.2 μW m−3, respectively. For the granites, leucogranites, granitic gneisses and syenites it is 2.6, 3.4, 4.6 and 1.4 μW m−3, respectively. Heat production of granulite facies rocks, which are the most abundant rocks in KKB, correlate well with Th,
but less with U, suggesting that variation is caused by Th and U bearing accessory minerals such as monazite and zircon. The
high heat production of the KKB granulites are in contrast to the low heat production of the Late Archaean granulites of the
Northern Block (NB) of the SGP which are highly depleted in radioelements and also the granulites of Madurai Block (MB) that
have higher radioelemental abundances than in the granulites of the NB. The high heat production of the KKB granulites could
be due to the nature of protoliths and/or metasomatism associated with Neoproteroic- to- Pan African alkaline magmatic activity
represented by alkali granite and syenite–carbonatite emplacements and emplacement of pegmatites. 相似文献
12.
Summary New oxygen isotope data for metaluminous granites from the basement-dominated part of the Damara orogen (Namibia) range from
9.1 to 11.9‰. These data, together with previously published Sr, Nd and Pb isotope data indicate that these granites and associated
peraluminous granites originated from felsic meta-igneous basement sources. New and unusually low oxygen isotope data for
metaluminous granodiorites extend now the range of δ18O values from ca. 12 to 6‰ for this rock type. These low oxygen isotope values approach the values observed in mafic quartz
diorites for which a model of derivation from depleted mafic lower crust has been established. In view of the higher Pb isotope
ratios but lower oxygen isotope values of the granodiorites relative to the mafic quartz diorites, it is concluded that the
granodiorites represent partial melts of an undepleted but strongly altered mafic lower crust. Most of the peraluminous and
metaluminous granites and the metaluminous granodiorites have identical U–Pb monazite, allanite and zircon ages of ca. 510–500 Ma
implying partial melting of distinct basement rocks of Archaean to Proterozoic age at the peak of regional high-grade metamorphism. 相似文献
13.
Early carbonate cements in the Yanchang Formation sandstones are composed mainly of calcite with relatively heavier carbon isotope (their δ^18O values range from -0.3‰- -0.1‰) and lighter oxygen isotope (their δ^18O values range from -22.1‰- -19.5‰). Generally, they are closely related to the direct precipitation of oversaturated calcium carbonate from alkaline lake water. This kind of cementation plays an important role in enhancing the anti-compaction ability of sandstones, preserving intragranular volume and providing the mass basis for later disso- lution caused by acidic fluid flow to produce secondary porosity. Ferriferous calcites are characterized by relatively light carbon isotope with δ^13C values ranging from -8.02‰ to -3.23‰, and lighter oxygen isotope with δ^18O values ranging from -22.9‰ to -19.7‰, which is obviously related to the decarboxylation of organic matter during the late period of early diagenesis to the early period of late diagenesis. As the mid-late diagenetic products, ferriferous cal- cites in the study area are considered as the characteristic authigenic minerals for indicating large-scaled hydrocarbon influx and migration within the clastic reservoir. The late ankerite is relatively heavy in carbon isotope with δ^13C values ranging from -1.92‰ to -0.84‰, and shows a wide range of variations in oxygen isotopic composition, with δ^18O values ranging from -20.5‰ to -12.6‰. They are believed to have nothing to do with decarboxylation, but the previously formed marine carbonate rock fragments may serve as the chief carbon source for their precipitation, and the alkaline diagenetic environment at the mid-late stage would promote this process. 相似文献
14.
T. Oberthür T. G. Blenkinsop U. F. Hein M. Höppner A. Höhndorf T. W. Weiser 《Mineralium Deposita》2000,35(2-3):138-156
In the Mazowe area some 40 km NW of Harare in Zimbabwe, gold mineralization is hosted in a variety of lithologies of the
Archean Harare-Bindura-Shamva greenstone belt, in structures related to the late Archean regional D2/3 event. Conspicuous
mineralzogical differences exist between the mines; the mainly granodiorite-hosted workings at Mazowe mine are on pyrite-rich
reefs, mines of the Bernheim group have metabasalt host rocks and are characterized by arsenopyrite-rich ores, and Stori's
Golden Shaft and Alice mine, both in metabasalts, work sulfide-poor quartz veins. In contrast to the mineralogical diversity,
near-identical fluid inventories were found at the different mines. Both H2O-CO2-CH4 fluids of low salinity, and highly saline fluids are present and are regarded to indicate fluid mixing during the formation
of the deposits. Notably, these fluid compositions in the Mazowe gold field markedly contrast to ore fluids “typical” of Archean
mesothermal gold deposits on other cratons. Stable isotope compositions of quartz from the various deposits (δ18O=10.8 to 13.2‰ SMOW), calcite (δ18O=9.5 to 11.9‰ SMOW and δ13C=−3.2 to −8.0‰ PDB), inclusion water (δD=−28 to −40‰ SMOW) and sulfides (δ34S=1.3 to 3.2‰ CDT) are uniform within the range typical for Archean lode gold deposits worldwide. The fluid and stable isotope
compositions support the statement that the mineralization in the Mazowe gold field formed from relatively reduced fluids
with a “metamorphic” signature during a single event of gold mineralization. Microthermometric data further indicate that
the deposits formed in the PT range of 1.65–2.3 kbar and 250–380 °C. Ages obtained by using the Sm/Nd and Rb/Sr isotope systems on scheelites are 2604 ± 84 Ma
for the mineralization at Stori's Golden Shaft mine, and 2.40 ± 0.20 Ga for Mazowe mine. The Archean age at Stori's is regarded
as close to the true age of gold mineralization in the area, whereas the Proterozoic age at Mazowe mine probably reflects
later resetting.
Received: 30 September 1998 / Accepted: 17 August 1999 相似文献
15.
Fluid inclusion and stable isotope (O, H, C, and S) constraints on the genesis of the Serrinha gold deposit, Gurupi Belt, northern Brazil 总被引:1,自引:0,他引:1
Evandro L. Klein Chris Harris Christophe Renac André Giret Candido A. V. Moura Kazuo Fuzikawa 《Mineralium Deposita》2006,41(2):160-178
The Serrinha gold deposit of the Gurupi Belt, northern Brazil, belongs to the class of orogenic gold deposits. The deposit is hosted in highly strained graphitic schist belonging to a Paleoproterozoic (∼2,160 Ma) metavolcano-sedimentary sequence. The ore-zones are up to 11 m thick, parallel to the regional NW–SE schistosity, and characterized by quartz-carbonate-sulfide veinlets and minor disseminations. Textural and structural data indicate that mineralization was syn- to late-tectonic and postmetamorphic. Fluid inclusion studies identified early CO2 (CH4-N2) and CO2 (CH4-N2)-H2O-NaCl inclusions that show highly variable phase ratios, CO2 homogenization, and total homogenization temperatures both to liquid and vapor, interpreted as the product of fluid immiscibility under fluctuating pressure conditions, more or less associated with postentrapment modifications. The ore-bearing fluid typically has 18–33mol% of CO2, up to 4mol% of N2, and less than 2mol% of CH4 and displays moderate to high densities with salinity around 4.5wt% NaCl equiv. Mineralization occurred around 310 to 335°C and 1.3 to 3.0 kbar, based on fluid inclusion homogenization temperatures and oxygen isotope thermometry with estimated oxygen fugacity indicating relatively reduced conditions. Stable isotope data on quartz, carbonate, and fluid inclusions suggest that veins formed from fluids with δ18OH2O and δDH2O (310–335°C) values of +6.2 to +8.4‰ and −19 to −80‰, respectively, which might be metamorphic and/or magmatic and/or mantle-derived. The carbon isotope composition (δ13C) varies from −14.2 to −15.7‰ in carbonates; it is −17.6‰ in fluid inclusion CO2 and −23.6‰ in graphite from the host rock. The δ34S values of pyrite are −2.6 to −7.9‰. The strongly to moderately negative carbon isotope composition of the carbonates and inclusion fluid CO2 reflects variable contribution of organic carbon to an originally heavier fluid (magmatic, metamorphic, or mantle-derived) at the site of deposition and sulfur isotopes indicate some oxidation of the originally reduced fluid. The deposition of gold is interpreted to have occurred mainly in response to phase separation and fluid-rock interactions such as CO2 removal and desulfidation reactions that provoked variations in the fluid pH and redox conditions. 相似文献
16.
C. O'Reilly G. R. T. Jenkin M. Feely D. H. M. Alderton A. E. Fallick 《Contributions to Mineralogy and Petrology》1997,129(2-3):120-142
Fluid inclusions in granite quartz and three generations of veins indicate that three fluids have affected the Caledonian
Galway Granite. These fluids were examined by petrography, microthermometry, chlorite thermometry, fluid chemistry and stable
isotope studies. The earliest fluid was a H2O-CO2-NaCl fluid of moderate salinity (4–10 wt% NaCl eq.) that deposited late-magmatic molybdenite mineralised quartz veins (V1) and formed the earliest secondary inclusions in granite quartz. This fluid is more abundant in the west of the batholith,
corresponding to a decrease in emplacement depth. Within veins, and to the east, this fluid was trapped homogeneously, but
in granite quartz in the west it unmixed at 305–390 °C and 0.7–1.8 kbar. Homogeneous quartz δ18O across the batholith (9.5 ± 0.4‰n = 12) suggests V1 precipitation at high temperatures (perhaps 600 °C) and pressures (1–3 kbar) from magmatic fluids. Microthermometric data
for V1 indicate lower temperatures, suggesting inclusion volumes re-equilibrated during cooling. The second fluid was a H2O-NaCl-KCl, low-moderate salinity (0–10 wt% NaCl eq.), moderate temperature (270–340 °C), high δD (−18 ± 2‰), low δ18O (0.5–2.0‰) fluid of meteoric origin. This fluid penetrated the batholith via quartz veins (V2) which infill faults active during post-consolidation uplift of the batholith. It forms the most common inclusion type in
granite quartz throughout the batholith and is responsible for widespread retrograde alteration involving chloritization of
biotite and hornblende, sericitization and saussuritization of plagioclase, and reddening of K-feldspar. The salinity was
generated by fluid-rock interactions within the granite. Within granite quartz this fluid was trapped at 0.5–2.3 kbar, having
become overpressured. This fluid probably infiltrated the Granite in a meteoric-convection system during cooling after intrusion,
but a later age cannot be ruled out. The final fluid to enter the Granite and its host rocks was a H2O-NaCl-CaCl2-KCl fluid with variable salinity (8–28 wt% NaCl eq.), temperature (125–205 °C), δD (−17 to −45‰), δ18O (−3 to + 1.2‰), δ13CCO2 (−19 to 0‰) and δ34Ssulphate (13–23‰) that deposited veins containing quartz, fluorite, calcite, barite, galena, chalcopyrite sphalerite and pyrite (V3). Correlations of salinity, temperature, δD and δ18O are interpreted as the result of mixing of two fluid end-members, one a high-δD (−17 to −8‰), moderate-δ18O (1.2–2.5‰), high-δ13CCO2 (> −4‰), low-δ34Ssulphate (13‰), high-temperature (205–230 °C), moderate-salinity (8–12 wt% NaCl eq.) fluid, the other a low-δD (−61 to −45‰), low-δ18O (−5.4 to −3‰), low-δ13C (<−10‰), high-δ34Ssulphate (20–23‰) low-temperature (80–125 °C), high-salinity (21–28 wt% NaCl eq.) fluid. Geochronological evidence suggests V3 veins are late Triassic; the high-δD end-member is interpreted as a contemporaneous surface fluid, probably mixed meteoric
water and evaporated seawater and/or dissolved evaporites, whereas the low-δD end-member is interpreted as a basinal brine
derived from the adjacent Carboniferous sequence. This study demonstrates that the Galway Granite was a locus for repeated
fluid events for a variety of reasons; from expulsion of magmatic fluids during the final stages of crystallisation, through
a meteoric convection system, probably driven by waning magmatic heat, to much later mineralisation, concentrated in its vicinity
due to thermal, tectonic and compositional properties of granite batholiths which encourage mineralisation long after magmatic
heat has abated.
Received: 3 April 1996 / Accepted: 5 May 1997 相似文献
17.
Bulk δ
34Srock values, sulfur contents, and magnetic susceptibility were determined for 12 gold-related granitoid intrusions in southwestern
New Brunswick, the Canadian Appalachians. The sulfur isotope compositions of sulfide minerals in some of the granitoid samples
were also analyzed. This new dataset was used to characterize two distinctive groups of granitoids: (1) a Late Devonian granitic
series (GS) and (2) a Late Silurian to Early Devonian granodioritic to monzogranitic series (GMS). The GS rocks have a large
range in δ
34S values of −7.1‰ to +13‰ with an average of 2.2 ± 5.0‰ (1σ), low bulk-S contents (33 to 7,710 ppm) and low magnetic susceptibility
values (<10−4 SI), consistent with reduced ilmenite-series granites. The GMS rocks have a relatively narrower variation in δ
34S values of −4.4‰ to +7.3‰ with an average 1.2 ± 2.9‰ but with larger ranges in bulk-S contents (45 to 11,100 ppm) and high
magnetic susceptibility values (>10−3 SI), indicative of oxidized magnetite-series granites. The exceptions for the GMS rocks are the Lake George granodiorite
and Tower Hill granite that display reduced characteristics, which may have resulted from interaction of the magmas forming
these intrusions with graphite- or organic carbon-bearing sedimentary rocks. The bulk δ
34S values and S contents of the GMS rocks are interpreted in terms of selective assimilation–fractional crystallization (SAFC)
processes. Degassing processes may account for the δ
34S values and S contents of some GS rocks. The characteristics of our sulfur isotope and abundance data suggest that mineralizing
components S and Au in intrusion-related gold systems are dominantly derived from magmatic sources, although minor contaminants
derived from country rocks are evident. In addition, the molar sulfate to sulfide ratio in a granitic rock sample can be calculated
from the δ
34Srock value of the whole-rock sample and the δ
34Ssulfide (or δ
34Ssulfate) value of sulfide and/or sulfate mineral in the sample on the basis of S-isotope fractionation and mass balance under the
condition of magmatic equilibrium. This may be used to predict the speciation of sulfur in granitic rocks, which can be a
potential exploration tool for intrusion-related gold systems. 相似文献
18.
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
19.
Boron recycling in the continental crust of the central Andes from the Palaeozoic to Mesozoic, NW Argentina 总被引:4,自引:2,他引:2
Simone Kasemann Jörg Erzinger Gerhard Franz 《Contributions to Mineralogy and Petrology》2000,140(3):328-343
Whole-rock chemical composition and 11B/10B isotope ratios in tourmaline was investigated to study the geochemical recycling of boron during the evolution of the Andean
basement from the Palaeozoic to Mesozoic. In the basement (Cambrian to Ordovician high-grade paragneisses, migmatites and
orthogneisses, the Eocambrian Puncoviscana Formation, and Paleozoic-Mesozoic granitoid igneous rocks) whole-rock B contents
are generally below 100 ppm, but B contents of ˜1 wt% are found in cogenetic aplite and pegmatite dikes and in tourmaline–quartz
rocks. In the metasedimentary rocks, no systematic variation in B content because of metamorphic grade and no correlation
of B with other incompatible elements are apparent. Tourmalines from the high-grade metamorphic basement yield δ11B values ranging from −11.2 to −6.8‰ and isotope fractionation during migmatisation was small. Metamorphic tourmalines from
the Puncoviscana Formation have δ11B values between −6.3 and −5.8‰. The calculated (corrected for fractionation) δ11B values of −6 to −2‰ for the sedimentary protolith of the metamorphic basement indicate a continental B source with subordinate
marine input. Tourmalines from Palaeozoic and Mesozoic granitoids display an identical range of δ11B values from −12 to −5.3‰ and indicate a similarly homogeneous B source throughout time. Tourmalines from pegmatites and
tourmaline–quartz rocks record the average δ11B values of the parental granitic magma. We assume that B in the Palaeozoic and Mesozoic granitoids is derived from the local
metamorphic basement supporting the hypothesis that recycling of the lower Palaeozoic crust is the dominant process in granitic
magma formation from Palaeozoic to Mesozoic.
Received: 15 December 1999 / Accepted: 11 July 2000 相似文献
20.
M. Zhai A. B. Kampunzu M. P. Modisi Z. Bagai 《International Journal of Earth Sciences》2006,95(3):355-369
The Francistown plutonic rocks at the south-western margin of the Zimbabwe craton consist of three igneous suites: Sanukitoid, Tonalite–Trondhjemite–Granite (TTG) suites and High-K granites. The TTG suite is subdivided into High Aluminum-TTG (HA-TTG) and Low Aluminum-TTG (LA-TTG) sub-suites. Their Rb–Sr isotope systems were partially homogenized by post-crystallization thermo–tectonic events, in which hydrothermal solutions and migmatization played an important role. Therefore, the Rb–Sr isochron age of 2427±54 Ma can only be regarded as a lower limit to the Francistown plutonic rock age. The large errors in the Sm–Nd isochron dates of Francistown granitoids indicate that these dates are not really constrained. In this study we compared the rock types of Francistown and adjacent areas, adopting the precise U, Th–Pb single zircon SHRIMP ages from the Vumba area as references. For TTG and Sanukitoid suites, the age we adopted is ca. 2.7 Ga, which is close to their depleted-mantle Sm–Nd model ages (T
DM). For High-K granites, the age adopted is ca. 2.65 Ga, which is also close to their Sm–Nd isochron age. The highest ε
Nd
t
values of Sanukitoids and TTG are +2.1 and +2.3, respectively. The positive ε
Nd
t
values and trace element geochemistry support partial melting of a depleted mantle and young oceanic crust for the genesis of Sanukitoid and the TTG suites respectively. The lowest ε
Nd
t
values of Sanukitoids and TTGs are −1.0 and −1.1, respectively, indicating contamination by continental crust, up to 10 and 14%, respectively. The ε
Nd
t
values of TTG decrease with decreasing Al2O3 and Sr contents and increasing Eu negative anomalies (Eu*–Eu), suggesting that the TTG magmas underwent a coupled fractionation crystallization and crustal contamination, and that the LA-TTG was the product of the fractionation and contamination of the HA-TTG sub-suite. In contrast, negative ε
Nd
t
values for the High-K granites (from −0.4 to −3.5) indicate the involvement of LA-TTG and some materials from an old continental crust in their genesis. The products of partial melting of both oceanic and continental crusts at the south-western margin of the Zimbabwe craton occurred within a short time interval (from 2.7 to 2.65 Ga ago) suggesting that the Francistown plutonic rocks were formed in a active continental margin environment, where a young ocean plate (Limpopo oceanic plate) subducted underneath an old continental plate (Zimbabwe craton). 相似文献