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1.
Lead isotope ratios of galena from the carbonate-hosted massive sulphide deposits of Kabwe (Pb-Zn) and Tsumeb (Pb-Zn-Cu)
in Zambia and Namibia, respectively, have been measured and found to be homogeneous and characteristic of upper crustal source
rocks. Kabwe galena has average isotope ratios of 206/204Pb = 17.997 ± 0.007, 207/204Pb = 15.713 ± 0.010 and 208/204Pb = 38.410 ± 0.033. Tsumeb galena has slightly higher 206/204Pb (18.112 ± 0.035) and slightly lower 207/204Pb (15.674 ± 0.016) and 208/204Pb (38.276 ± 0.073) ratios than Kabwe galena. The isotopic differences are attributed to local differences in the age and
composition of the respective source rocks for Kabwe and Tsumeb. The homogeneity of the ore lead in the two epigenetic deposits
suggests lead sources of uniform isotopic composition or, alternatively, thorough mixing of lead derived from sources with
relatively similar isotopic compositions. Both deposits have relatively high 238U/204Pb ratios of 10.31 and 10.09 for Kabwe and Tsumeb galenas, respectively. These isotope ratios are considered to be typical
of the upper continental crust in the Damaran-Lufilian orogenic belt, as also indicated by basement rocks and Cu-Co sulphides
in stratiform Katangan metasediments which have a mean μ-value of 10.25 ± 0.12 in the Copperbelt region of Zambia and the
Democratic Republic of Congo (formerly Zaire). The 232Th/204Pb isotope ratios of 43.08 and 40.42 for Kabwe and Tsumeb suggest Th-enriched source regions with 232Th/235U (κ-values) of 4.18 and 4.01, respectively. Model isotopic ages determined for the Kabwe (680 Ma) and Tsumeb (530 Ma) deposits
indicate that the timing of the mineralisation was probably related to phases of orogenic activity associated with the Pan-African
Lufilian and Damaran orogenies, respectively. Galena from the carbonate-hosted Kipushi Cu-Pb-Zn massive sulphide deposit in
the Congo also has homogeneous lead isotope ratios, but its isotopic composition is comparable to that of the average global
lead evolution curve for conformable massive sulphide deposits. The μ (9.84) and κ (3.69) values indicate a significant mantle
component, and the isotopic age of the Kipushi deposit (456 Ma) suggests that the emplacement of the mineralisation was related
to a post-tectonic phase of igneous activity in the Lufilian belt. The isotope ratios (206/204Pb, 207/204Pb, 208/204Pb) of the three deposits are markedly different from the heterogeneous lead ratios of the Katangan Cu-Co stratiform mineralisation
of the Copperbelt as well as those of the volcanogenic Nampundwe massive pyrite deposit in the Zambezi belt which typically
define radiogenic linear trends on lead-lead plots. The host-rock dolomite of the Kabwe deposit also has homogeneous lead
isotope ratios identical to the ore galena. This observation indicates contamination of the Kabwe Dolomite Formation with
ore lead during mineralisation.
Received: 8 September 1997 / Accepted: 21 August 1998 相似文献
2.
The Habo alkaline intrusion, which is located in the south of the Sanjiang area, Yunnan Province, China, is a typical Cenozoic alkaline intrusion. There are a series of small to medium-sized Au and Pb–(Zn) deposits around this intrusion. Those deposits are spatially associated with the Habo alkaline intrusion. (1) The δ34S values of sulfides from Au deposits range from ?1.91 ‰ to 2.69 ‰, which are similar to those of Pb–(Zn) deposits (?3.82 ‰ to ?0.05 ‰) and both indicate a much greater contribution from magma. (2) The Habo alkaline intrusion has relatively homogeneous Pb isotopic compositions with 206Pb/204Pb ranging from 18.608 to 18.761, 207Pb/204Pb from 15.572 to 15.722 and 208Pb/204Pb from 38.599 to 39.110. These Pb isotope ratios are similar to those of Au deposits, whose 206Pb/204Pb range from 18.564 to 18.734, 207Pb/204Pb from 15.582 to 15.738 and 208Pb/204Pb from 38.592 to 39.319. Pb ratios in both the intrusion and Au deposits suggest that Pb mainly derived from the depth, probably represents a mixture of mantle and crust. Pb–(Zn) deposits, however, show a decentralized trait, and most of them are similar to that of the alkaline intrusion with 206Pb/204Pb ranging from 18.523 to 18.648, 207Pb/204Pb from 15.599 to 15.802, and 208Pb/204Pb from 38.659 to 39.206. (3) In the plumbotectonic diagram 207Pb/204Pb versus 206Pb/204Pb, almost all of Au and Pb–(Zn) deposits have the same projection area with the Habo alkaline intrusion, which indicates that those deposits almost share the same source with the alkaline intrusion. (4) Isotopic age of the Habo alkaline intrusion is 36–33 Ma, which is similar to that of Beiya, whose ore-related alkaline porphyries age is 38–31 Ma and molybdenite Re–Os age is 36.9 Ma. Therefore, along with S–Pb isotope traits, we suggest that the Habo Au and Pb–(Zn) deposits should be typically Ailaoshan-Red RiverCenozoicalkaline-related deposits and ore-forming ages of these deposits should be later than that of the Habo alkaline intrusion. 相似文献
3.
Genesis of the South Zhuguang Uranium Ore Field,South China: Pb Isotopic Compositions and Mineralization Ages 总被引：1，自引：0，他引：1
U–Pb isotopic analyses indicate that ores from the South Zhuguang uranium ore field, south China, have high common (non‐radiogenic) Pb contents, with variable and relatively radiogenic initial Pb contents. The U–Pb isochron method was used to date these ores, with plots of 208Pb/204Pb and 207Pb/204Pb versus 206Pb/204Pb being used to identify sample suites with similar initial Pb isotopic ratios and to normalize variable initial Pb isotopic ratios. The resulting U–Pb isochrons indicate two substages of uranium mineralization at ~57 and 52 Ma, with a later hydrothermal reformation at ~49 Ma, which homogenized Pb isotopic compositions. Initial Pb isotopic systematics indicate that the ore‐forming fluid was characterized by high 206Pb/204Pb and 207Pb/204Pb ratios and low 208Pb/204Pb ratios, suggesting that the ore‐forming fluid was sourced from Cretaceous–Paleogene red‐bed basins, rather than from magma or the mantle, with consideration of mineralization ages. 相似文献
4.
I. V. Chernyshev A. V. Chugaev N. S. Bortnikov G. N. Gamyanin A. V. Prokopiev 《Geology of Ore Deposits》2018,60(5):398-417
The paper considers the results of high-precision Pb–Pb isotopic analysis of 120 galena samples from 27 Au and Ag deposits of the South Verkhoyansk Synclinorium (SVS) including large Nezhdaninsky deposit (628.8 t Au). The Pb isotopic composition is analyzed on a MC-ICP-MS NEPTUNE mass-spectrometer from solutions with an error of no more than ±0.02% (2σ). Four types of deposits are studied: (i) stratified vein gold–quartz deposits (type 1) hosted in metamorphosed Upper Carboniferous–Lower Permian terrigenous rocks and formed during accretion of the Okhotsk Block to the North Asian Craton synchronously with dislocation metamorphism and related granitic magmatism; (ii) vein gold–quartz (Nezhdaninsky type) deposits also hosted in Lower Permian metasedimentary rocks; (iii) Au–Bi deposits localized at the contact zones of the Late Cretaceous granitic plutons; and (iv) Sn–Ag polymetallic deposits related to granitic and subvolcanic rocks of the Okhotsk Zone of the SVS. The deposits of types 2, 3, and 4 are postaccretionary. The general range of 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios is 18.1516–18.5903 (2.4%), 15.5175–15.6155 (0.63%), and 38.3010–39.0481 (2.0%), respectively. In 206Pb/204Pb–207Pb/204Pb and 206Pb/204Pb–208Pb/204Pb diagrams, the data points of Pb isotopic compositions of all deposits occupy restricted, partly overlapping areas along a general elongated trend. The various SVS Au–Ag deposits can be classified according to the Pb isotopic composition in accordance with all three Pb ratios. Deposits of the same type show distinct Pb isotopic compositions that strongly exceed the scale of analytical error (±0.02%). The differences in Pb isotopic composition within specific deposits are low and subordinate and have little effect on variations in the Pb isotopic composition of the SVS deposits. The μ2 values (Stacey–Kramers model), which characterize the 238U/204Pb ratios of ore lead sources of the SVS deposits, widely vary from 9.7 to 9.38. The ω2 values (232Th/204Pb) are 39.82–36.61, whereas the Th/U ratios are 4.04–3.86. The content of all three radiogenic Pb isotopes and μ2 values of feldspars from SVS intrusive rocks are strongly distinct from those of galena of stratified gold–quartz and vein gold–quartz deposits and are identical to Pb of galena from Au–Bi and Sn–Ag polymetallic deposits, indicating a mostly magmatic origin for the Pb of these deposits. Detailed isotopic study of the Nezhdaninsky deposit shows different Pb isotopic composition of two consecutive mineral assemblages (gold–sulfide and Ag polymetallic): ~0.30, ~0.07, and ~0.22% for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios, respectively. These differences are interpreted as a result of involvement of at least two metal sources during the evolution of an ore-forming system: (i) host Lower Permian terrigenous rocks and (ii) a magmatic source similar in Pb isotopic composition to that of Sn–Ag polymetallic deposits. The Pb isotopic composition and μ2 and Th/U values show that lead of stratified gold–quartz deposits combines isotopic tracers of lower and upper crustal sources (Upper Carboniferous–Lower Permian terrigenous rocks), lead of which was mobilized by ore-bearing fluids. The high 208Pb/206Pb ratios and Th/U evolutionary parameter are common to all Pb isotopic composition of all studied Au–Ag deposits and SVS Cretaceous intrusive rocks and indicate that Pb sources were depleted in U relative to Th. Taking into account the structure of the region and conceptions on its evolution, we can suggest that the magma source was related to lower crustal subducted rocks of the Archean (~2.6 Ga) North Asian Craton and the Okhotsk terrane. 相似文献
5.
西秦岭降扎地区寒武、志留系中的金、铀矿床,是我国相当重要的碳硅泥岩型矿床。根据金矿床中岩石和矿石异常铅模式年龄、氩-氩同位素年龄和钾-氩同位素年龄等,获得了一批有益的年代学信息。金矿床的各种同位素年龄数据主要有2组:(1)242-186Ma;(2)137-47Ma.结合区域地质发展史、成矿热液脉与岩脉的穿切关系以及矿床产出的其它宏观特征等,确定金矿床的成矿时代为137-47Ma,与区域铀矿床形成的主要时代(117-55Ma)相比,二者成矿时间大体相同。 相似文献
6.
《Gondwana Research》2006,9(4):529-538
Sr, Nd and Pb isotopic compositions of the Cenozoic basalts were analyzed from Baengnyeongdo Island, Jeongok, Ganseong, and Jejudo Island of Korea. They reveal relatively enriched Sr and Nd isotopic compositions (87Sr/86Sr = 0.70330∼0.70555, 143Nd/144Nd = 0.51298∼0.51256) compared with MORB.207Pb/204Pb and 208Pb/204Pb values of all the analyzed Korean basalts lie above the Northern Hemisphere Reference Line (NHRL) defined by Hart (1984). Pb isotopic compositions of basalts from Jejudo Islands (206Pb/204Pb = 18.61∼19.12, 207Pb/204Pb = 15.54∼15.69, 208Pb/204Pb = 38.98∼39.72) are significantly more radiogenic than the rest (206Pb/204Pb = 17.72∼18.03, 207Pb/204Pb = 15.44∼15.58, 208Pb/204Pb = 37.77∼38.64). The Cenozoic Korean basalts thus can be divided into two groups based on their Sr, Nd and Pb isotopic compositions. The north group reveals mixing between DMM and EM1 while the south group displays DMM-EM2 mixing. Such a distribution is the same as Chinese Cenozoic basalts and it can be interpreted that the subcontinental lithospheric mantle under Korea represents simple lateral continuation of the South and North China Blocks. We suggest that Korean continental collision zone cross the Korean Peninsula through the region between the north and south basalt groups of Korea. 相似文献
7.
Lead isotope analyses of galena from five ore deposits and six prospects in the Aysén region of southern Chile are reported.
Most of the deposits are either low sulfidation epithermal gold–silver veins or skarn and manto deposits; the majority are
either suspected to be, or dated as, Late Jurassic to mid-Cretaceous. Galena lead isotope data for most of the deposits from
southern Chile cluster near the “orogene” within a “plumbotectonic” model framework. Average values (206Pb/204Pb=18.53, 207Pb/204Pb=15.63, and 208Pb/204Pb=38.50) are near Jurassic to Cretaceous model ages on the “orogene” curve of Zartman and Doe (1981) and the second-stage
curve of Stacey and Kramers (1975) on a 206Pb/204Pb versus 207Pb/204Pb plot. These model ages are compatible with absolute ages as currently known. The elongate trends in the general cluster
indicate mainly an orogenic model fit, suggesting variable mixing of lead from different sources, mainly model upper crust
and lesser model mantle and lower crust reservoirs. Galena lead associated with one deposit (El Faldeo) is relatively radiogenic,
and lies near a Jurassic age on the “upper crustal” curve of Zartman and Doe (1981), which is compatible with the Ar/Ar age
of the deposit. Galena lead isotope clusters define three main groups of deposits. These three groups appear to be related
to three mineralizing events, dated by K–Ar and Ar/Ar, in the Late Jurassic (group 3), and in the Early and mid-Cretaceous
(groups 1 and 2 respectively). Averages for group 1, the northern group including El Toqui and Katerfeld, are 206Pb/204Pb=18.51, 207Pb/204Pb=15.62, 208Pb/204Pb=38.48. Averages for group 2, the southern group with Fachinal and Mina Silva, are 206Pb/204Pb = 18.56, 207Pb/204Pb=15.63, 208Pb/204Pb=38.52. Averages for group 3, the southernmost group with the El Faldeo, Lago Chacabuco and Lago Cochrane prospects, are
206Pb/204Pb=18.83, 207Pb/204Pb=15.65, 208Pb/204Pb=38.63. The Cretaceous deposits (groups 1 and 2) contain orogene-type lead that becomes increasingly radiogenic southward.
Lead from the Late Jurassic deposits (group 3) appears to reflect mixing of orogene lead with highly radiogenic lead. The
observed linear array of lead in group 3 probably reflects mixing of orogene lead with highly radiogenic lead, which was likely
extracted by selective leaching of mineralizing hydrothermal solutions from the metamorphic basement.
Received: 10 July 1999 / Accepted: 15 July 2000 相似文献
8.
The Lovozero alkaline massif—an agpaitic nepheline syenite layered intrusion—is located in the central part of the Kola Peninsula, Russia, and belongs to the Kola ultramafic alkaline and carbonatitic province (KACP) of Devonian age. Associated loparite and eudialyte deposits, which contain immense resources of REE, Nb, Ta, and Zr, constitute a world class mineral district. Previous Sr, Nd, and Hf isotope investigations demonstrated that these rocks and mineral deposits were derived from a depleted mantle source. However, because the Sr, Nd, and Hf abundances in the Kola alkaline rocks are significantly elevated, their isotopic compositions were relatively insensitive to contamination by the underlying crustal rocks through which the intruding magmas passed. Pb occurring in relatively lower abundance in the KACP rocks, by contrast, would have been a more sensitive indicator of an acquired crustal component. Here, we investigate the lead isotopic signature of representative types of Lovozero rocks in order to further characterize their sources. The measured Pb isotopic composition was corrected using the determined U and Th concentrations to the age of the crystallization of the intrusion (376?±?28 Ma, based on a 206Pb/204Pb versus 238U/204Pb isochron and 373?±?9 Ma, from a 208Pb/204Pb versus 232Th/204Pb isochron). Unlike the previously investigated Sr, Nd, and Hf isotopes, the lead isotopic composition plot was well outside the FOZO field. The 206Pb/204Pb values fall within the depleted MORB field, with some rocks having lower 207Pb/204Pb but higher 208Pb/204Pb values. Together with other related carbonatites having both lower and higher 206Pb/204Pb values, the combined KACP rocks form an extended linear array defining either a?~2.5-Ga secondary isochron or a mixing line. The projection of this isotopic array toward the very unradiogenic composition of underlying 2.4–2.5-Ga basaltic rocks of the Matachewan superplume and associated Archean granulite facies country rock provides strong evidence that this old lower crust was the contaminant responsible for the deviation of the Lovozero rocks from a presumed original FOZO lead isotopic composition. Evaluating the presence of such a lower crustal component in the Lovozero rock samples suggests a 5–10% contamination by such rocks. Contamination by upper crustal rock is limited to only a negligible amount. 相似文献
9.
铜山岭铅锌多金属矿床位于扬子地块湘南-桂东北坳陷与华夏地块粤北坳陷的拼贴部位,是中国南岭多金属成矿区代表性矿床之一。为确定矿床成矿时代,挑选铜山岭铅锌多金属矿床中含矿矽卡岩的石榴子石进行Sm-Nd同位素定年,获得的等时线年龄为173±3Ma,指示成矿作用发生于燕山早期。对金属硫化物矿物进行了Pb同位素分析,其~(206)Pb/~(204)Pb、~(207)Pb/~(204)Pb、~(208)Pb/~(204)Pb平均值分别为18.602、15.701、38.729,表明成矿物质来源于相对富集铀铅、略微亏损钍铅的上地壳源区。从(~(207)Pb/~(204)Pb)i-(~(206)Pb/~(204)Pb)i铅同位素演化模式图可知,寄主花岗闪长岩是铜山岭铅锌多金属矿床的重要物质来源,且成矿物质中可能含有寄存在花岗闪长岩中的地幔组分。 相似文献
10.
Brian L. Gulson 《Mineralium Deposita》1975,10(4):277-286
Lead isotopic composition and uranium and lead concentrations have been determined for galena, sphalerite, pyrite and acetic acid soluble material from the McArthur area in order to test the hypothesis of a dual sulphur source suggested by the sulphur isotope data of Smith and Croxford (Sulphur isotope ratios in the McArthur lead-zinc-silver deposit, Nature Phys. Sci. 245, 10–12 (1973)). Galena, sphalerite and the acetic acid washes from the McArthur deposit have uniform isotopic ratios (206Pb/204Pb, 16.07–16.15; 207Pb/204Pb, 15.37–15.47; 208Pb/204Pb, 35.57–35.89) consistent with other conformable ore deposits, whereas the ratios for pyrite are variable and quite radiogenic (206Pb/204Pb, 16.24–16.49; 207Pb/204Pb, 15.42–15.58; 208Pb/204Pb, 35.82–36.98). Acid washes where dolomite is a major dissolved phase are also radiogenic. The lead in the pyrite appears to have been derived from at least two sources: the less radiogenic lead coming from an exhalative source as for galena and sphalerite and the more radiogenic lead probably being leached from the country rocks. It is proposed that analysis of pyrite for isotopic composition and concentration of lead could be used as an indicator for similar types of deposits in this area. 相似文献
11.
Rasoul Esmaeili Mohammad Ebrahimi Ji’En Zhang Zhiyong Zhang Yasser Abd El-Rahman 《International Geology Review》2020,62(13-14):1677-1697
ABSTRACT The Makran complex in southeast Iran provides a spectacular subduction-related accretionary complex to understand the mechanism of oceanic accretion and the evolution of subduction zones. In this paper, we present new major and trace element data as well as isotopic compositions of mafic volcanic blocks from the Makran ophiolitic mélange complex (OMC). Our aim is to assess the genesis of these rocks and discuss their implications on the evolution of Neotethys Ocean. These volcanic blocks are composed mainly of basalts with minor trachytes. The Makran lavas are occasionally interlayered with tuff layers. Zircons from these tuffs give U-Pb ages of 95 Ma, which is well in accordance with the reposted microfossil data for the interlayered pelagic limestones with pillow lavas. Makran basalts can be geochemically subdivided into four groups; normal to transitional MORB, enriched-MORB, Plume-type MORB and alkaline (-OIB-like) basalts. The OIB-like pillow lavas are represented by high values of Th/Tb (6.3–7.4) which are higher than other basalts (group 1 = 0.3–0.8; groups 2 = 0.7–1.6; group 3 = 1.58–1.36).143Nd/144Nd(t) ratios for basalts ranges from 0.51247 to 0.51292, whereas 87Sr/86Sr(t) isotopic composition of the OMC lavas varies from 0.704433 to 0.709466. The Pb isotopic composition of the lavas are quite high, ranging from 15.49–15.66 for 207Pb/204Pb(t), 18.09–19.12 for 206Pb/204Pb(t) and 37.80–39.23 for 208Pb/204Pb(t). The chemistry of these rocks suggests that they were formed most likely in an oceanic setting with clear plume-ridge interaction. These rocks can form from partial melting of a highly heterogeneous mantle source, which is extensively metasomatized with deep mantle OIB-type components. We suggest these rocks have been generated in an oceanic ridge with plume-ridge interaction, similar to the Iceland-Reykjanes Ridge, before being fragmented and accreted into the Makran accretionary complex. 相似文献
12.
Assessment of geochemical anomalies for gold exploration using lead isotopes in west Hainan, China 总被引：1，自引：0，他引：1
Huang Bin 《Journal of Geochemical Exploration》1995,55(1-3)
Lead isotopic ratios and Pb contents have been measured along typical profiles across orebodies of the Baoban and Tuwaishan gold deposits on Hainan Island, China. These deposits are hosted by the middle to upper Proterozoic Baoban Group, which is composed of migmatite and extends for about 51 km on the hanging-wall side of the Gezhen Fault. The deposits have a common initial Pb isotopic ratio of 206Pb/204Pb = 18.683, but show distinctive variations within each deposit.The Pb isotopic ratios are more homogeneous in the orebodies and altered auriferous rocks than in the migmatite wall rocks. The richest orebody in the study area is known as the V1 orebody of the Baoban deposit; it has the lowest and most homogeneous 206Pb/204Pb ratio. This feature suggests that in this migmatitic area, it is possible to distinguish ores from barren wall rocks, and rich ore shoots from non-commercial mineralization, by their distinctive Pb isotopic ratios.A lower initial Pb isotopic ratio (206Pb/204Pb= 18.538) was measured in two other deposits, Beiniu and Erjia, which occur in the same migmatite and are controlled by the same fault as the Baoban and Tuwaishan deposits. Therefore, two metallogenic phases may have taken place, one at 85 Ma and the other at 170 Ma; these ages can be calculated using the Pb growth model of Cumming and Richards.The feasibility of evaluating geochemical anomalies through their Pb isotopic signatures was investigated by comparing the Pb isotopic ratios of B horizon soils from significant and non-significant anomalies with those obtained from the ores and alteration zone rocks. The results show that the Pb isotopic ratios in significant anomalies are consistent with those of the ores, whereas the signatures of non-significant anomalies are heterogeneous and rather different from those of the ores.Six unexplored anomalies have been evaluated using this criteria; five of them were found to be non-significant. One anomaly, however, presents the same signature as the Beiniu deposit, suggesting that it may be related to undiscovered ore close to the Gezhen Fault. Plans have been made to drill this target. 相似文献
13.
Hikaru Iwamori Hitomi Nakamura Masaki Yoshida Takashi Nakagawa Kenta Ueki Atsushi Nakao Tatsuji Nishizawa Satoru Haraguchi 《Comptes Rendus Geoscience》2019,351(2-3):209-220
Recent statistical analyses on the isotopic compositions of oceanic, arc, and continental basalts have revealed that the Earth's mantle is broadly divided into eastern and western hemispheres. The present study aimed to characterize the isotopically defined east–west geochemical hemispheres using trace-element concentrations. Basalt data with Rb, Sr, Nd, Sm, Pb, Th, and U in addition to the isotopic ratios 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb were selected mostly from the GEOROC and PetDB databases. A total of 4787 samples were used to investigate the global geochemical variations. The results show that the wide trace-element variations are broadly explained by the melting of melt-metasomatized and fluid-metasomatized mantle sources. The larger amount of the fluid component derived from subducted plates in the eastern hemisphere than that in the western hemisphere is inferred from the basalts. These characteristics support the hypothesis that focused subduction towards the supercontinent created the mantle geochemical hemispheres. 相似文献
14.
Marek Slobodník Katarzyna Jacher-Śliwczyńska Matthew C. Taylor Jens Schneider Zdeněk Dolníček 《International Journal of Earth Sciences》2008,97(1):1-18
A regional isotopic study of Pb and S in hydrothermal galenas and U–Pb and S in potential source rocks was carried out for part of Moravia, Czech Republic. Two major generations of veins, (syn-) Variscan and post-Variscan, are defined based on the Pb-isotope system together with structural constraints (local structures and regional trends). The Pb-isotopic compositions of galena plot in two distinct populations with outliers in 206Pb/204Pb–207Pb/204Pb space. Galena from veins hosted in greywackes provides a cluster with the lowest Pb–Pb ratios: 206Pb/204Pb = 18.15–18.27, 207Pb/204Pb = 15.59–15.61, 208Pb/204Pb = 38.11–38.23. Those hosted in both limestones and greywackes provide the second cluster: 206Pb/204Pb = 18.37–18.44, 207Pb/204Pb = 15.60–15.63, 208Pb/204Pb = 38.14–38.32. These clusters suggest model Pb ages as Early Carboniferous and Triassic–Jurassic, the latter associated with MVT-like deposits. Two samples from veins hosted in Proterozoic rocks lie outside the two clusters: in metagranitoid (206Pb/204Pb = 18.55, 207Pb/204Pb = 15.64, 208Pb/204Pb = 38.29) and in orthogneiss (206Pb/204Pb = 18.79, 207Pb/204Pb = 15.73, 208Pb/204Pb = 38.54). The results from these two samples suggest an interaction of mineralizing fluids with the radiogenic Pb-rich source (basement?). The values of δ34S suggest the Paleozoic host rocks (mostly ?6.7 to +5.2‰ CDT) as the source of S for hydrothermal sulfides (mostly ?4.8 to +2.5‰ CDT). U–Pb data and Pb isotope evolutionary curves indicate that Late Devonian and Early Carboniferous sediments, especially siliciclastics, are the general dominant contributor of Pb for galena mineralization developed in sedimentary rocks. Plumbotectonic mixing occurred, it is deduced, only between the lower and the upper crust (the latter involving Proterozoic basement containing heterogeneous radiogenic Pb), without any significant input from the mantle. It is concluded that in the Moravo–Silesian and Rhenohercynian zones (including proximal districts in Poland) lead and sulfur have been mobilized from the adjacent rocks during multiple hydrothermal events in processes that are remarkably comparable in timing, geochemistry of fluids and nature of sources. 相似文献
15.
U-Pb Zircon Age,Geochemical, and Sr-Nd-Pb Isotopic Constraints on the Age and Origin of Mafic Dykes from Eastern Shandong Province,Eastern China 总被引：1，自引：0，他引：1
LIU Shen HU Ruizhong FENG Caixi GAO Shan FENG Guangying LAI Shaocong QI Youqiang Ian M. COULSON YANG Yuhong YANG Chaogui and TANG Liang 《《地质学报》英文版》2013,87(4):1045-1057
U-Pb zircon age, geochemical, and Sr-Nd-Pb isotopic data of mafic dykes from eastern Shandong Province, eastern China is reported herein. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon analyses of two samples from the investigated mafic dykes yield consistent ages ranging from 121.9 Ma ± 0.47 Ma to 122.9 Ma ± 0.61 Ma. The mafic dykes are characterized by high (87Sr/86Sr) i ranging from 0.7087 to 0.7089, low εNd(t) values ranging from -16.9 to -17.8, 206Pb/204Pb = 17.15 to 17.17, 207Pb/204Pb = 15.45 to 15.47, and 208Pb/204Pb = 37.59 to 37.68. Results from the current study suggest that the mafic dykes are derived from partial melting of ancient lithospheric mantle that was variably hybridized by melts derived from foundered lower crustal eclogite. The mafic dykes may have been generated through subsequent insignificant crystal fractionation and very minor crustal contamination during magma ascent. Combined with previous studies, the current findings provide new evidence that the intense lithospheric thinning beneath the eastern Shandong Province of eastern China occurred at ~120 Ma, and that this condition was caused by the removal of the lower lithosphere (mantle and lower crust). 相似文献
16.
It has long been debated that the Dabie orogenic belt belongs to the North China or Yangtze craton. In recent years, eastern
China has been suggested, based on the Pb isotopic compositions of Phanerozoic ore and Mesozoic granitoid K-feldspar (revealing
the crust Pb) in combination with Meso-Cenozoic basalts (revealing the mantle Pb), being divided into the North China and
Yangtze Pb isotopic provinces, where the crust and mantle of the Yangtze craton are characterized by more radiogenic Pb. In
this sense, previous researchers suggested that the pro-EW-trending Dabie crogenic belt with less radiogenic Pb in the crust
was part of the North China craton. In this paper, however, the Late Cretaceous basalts in the central and southern parts
of the Dabie orogenic belt are characterized by some more radiogenic Pb (206Pb/204Pb=17.936−18.349,207Pb/204Pb=15.500−15.688,208Pb/204Pb=38.399−38.775) and a unique U-Th-Pb trace element system similar to those of the Yangtze craton, showing that the Mesozoic
mantle is of the Yangtze type. In addition, the decoupled Pb isotopic compositions between crust and mantle were considerably
derived from their rheological inhomogeneity, implying a complicated evolution of the Dabie orogenic belt.
The study was funded by the National Natural Science Foundation of China (No. 49794043) and the Open Laboratory of Constitution,
Interaction and Dynamics of the Crust-Mantle System, China. 相似文献
17.
Charles R. Bacon Hajime Kurasawa Maryse H. Delevaux Ronald W. Kistler Bruce R. Doe 《Contributions to Mineralogy and Petrology》1984,85(4):366-375
The isotopic compositions of Pb and Sr in Pleistocene basalt, high-silica rhyolite, and andesitic inclusions in rhyolite of the Coso volcanic field indicate that these rocks were derived from different levels of compositionally zoned magmatic systems. The 2 earliest rhyolites probably were tapped from short-lived silicic reservoirs, in contrast to the other 36 rhyolite domes and lava flows which the isotopic data suggest may have been leaked from the top of a single, long-lived magmatic system. Most Coso basalts show isotopic, geochemical, and mineralogic evidence of interaction with crustal rocks, but one analyzed flow has isotopic ratios that may represent mantle values (87Sr/86Sr=0.7036,206Pb/204Pb=19.05,207Pb/204Pb=15.62,208Pb/204Pb= 38.63). The (initial) isotopic composition of typical rhyolite (87Sr/86Sr=0.7053,206Pb/204Pb=19.29,207Pb/204Pb= 15.68,208Pb/204Pb=39.00) is representative of the middle or upper crust. Andesitic inclusions in the rhyolites are evidently samples of hybrid magmas from the silicic/mafic interface in vertically zoned magma reservoirs. Silicic end-member compositions inferred for these mixed magmas, however, are not those of erupted rhyolite but reflect the zonation within the silicic part of the magma reservoir. The compositional contrast at the interface between mafic and silicic parts of these systems apparently was greater for the earlier, smaller reservoirs. 相似文献
18.
Zell E. Peterman Bruce R. Doe Harold J. Prostka 《Contributions to Mineralogy and Petrology》1970,27(2):121-130
The Absaroka volcanic field is comprised of predominant andesitic volcaniclastic rocks and less abundant potassium-rich mafic lavas (shoshonites and absarokites). Strontium and lead isotopic variations preclude a simple derivation from an isotopically uniform source: Sr87/Sr86, 0.7042 to 0.7090; Pb206/Pb204, 16.31 to 17.30; Pb208/Pb204, 36.82 to 37.64. We postulate that these rocks were derived from a lower crust or upper mantle which underwent a preferential loss of uranium relative to lead approximately 2800±200 m.y. ago. Variations in lead and strontium isotopic compositions are thought to reflect small inhomogeneities in U/Pb and Rb/Sr ratios in the source.Publication authorized by the Director, U.S. Geological Survey. 相似文献
19.
Pb and Sr systematics of ultrapotassic and basaltic rocks from the central Sierra Nevada,California 总被引：1，自引：0，他引：1
Gerald K. Van Kooten 《Contributions to Mineralogy and Petrology》1981,76(4):378-385
This study presents Sr and Pb isotopic ratios and Rb, Sr, U, Th, and Pb concentrations of an ultrapotassic basaltic suite and related rocks from the central Sierra Nevada, California. The ultrapotassic suite yields a narrow range of Sr and Pb isotopic compositions (87Sr/86Sr=0.70597–0.70653; 206Pb/ 204Pb=18.862–19.018; 207Pb/204Pb=15.640–15.686; 208Pb/ 204Pb=38.833–38.950). Associated basalts containing ultramafic nodules have less radiogenic Sr (87Sr/86=0.70430–0.70521) and generally higher Rb/Sr ratios than the ultrapotassic suite. Leucitites from Deep Springs Valley, California, contain high 87Sr/86Sr (71141–0.71240) and low 206Pb/204Pb (17.169–17.234) ratios, reflecting contamination by crustal granulite.The isotopic relationships support an origin of the ultrapotassic basaltic suite by partial melting of an enriched upper mantle source. Dehydration of a gently inclined oceanic slab beneath the Sierra Nevada may have provided Ba, K, Rb, Sr, and H2O, which migrated into the overlying upper mantle lithosphere. The end of subduction 10 m.y. ago allowed increased asthenospheric heat flow into the upper mantle lithosphere. The increased heat flow enhanced fluid movement in the upper mantle and contributed towards isotopic homogenization of the upper mantle source areas. Continued heating of the enriched upper mantle caused partial melting and subsequent eruption of the ultrapotassic lavas. 相似文献
20.
Lead isotopic compositions, and lead and uranium concentrations have been determined for samples from the Tongan islands of Late, Fonualei, Hunga-Ha'apai and Eua and for the Kermadec islands of Raoul, Macauley, Esperance and Napier. The Kermadec samples form a linear array in a Pb206/Pb204 vs Pb207/Pb204 plot which if interpreted in terms of a two stage mantle model indicates a mantle fractionation of Pb from U at about 1.2×109 yr. The Tongan volcanics, except Eua, have a very narrow range of isotopic compositions, only slightly exceeding the experimental error limits. This is interpreted to be the result of efficient mixing of the mantle in response to rapid extension behind the Tongan arc. The rate of extension appears to determine whether convection mixing can occur, since the sub-Kermadec mantle which experienced slower extension is not well mixed isotopically. The isotopic compositions show no evidence for a component in the magma derived from sediments dragged down the Benioff zone. The pre-Eocene Eua volcanics have lead which is substantially more radiogenic than the younger Tongan volcanics and are interpreted as a sample of the mantle before convective mixing occurred. 相似文献