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1.
The Bottle Lake Complex is a composite granitic batholith emplaced into Cambrian to Lower Devonian metasedimentary rocks. Both plutons (Whitney Cove and Passadumkeag River) are very coarse grained hornblende and biotite-bearing granites showing petrographic and geochemical reverse zonation. Two linear whole rock Rb/Sr isochrons on xenolith-free Whitney Cove and Passadumkeag River samples indicate ages of 379±5 m.y. and 381±4 m.y., respectively, in close agreement with published K-Ar ages for biotite from Whitney Cove of 377 m.y. and 379 m.y., and for hornblende 40Ar/39Ar determinations from Passadumkeag River which indicate an age of 378±4 m.y. The initial Sr isotopic ratio for Whitney Cove is 0.70553 and for Passadumkeag River is 0.70414. A whole-rock isochron on a suite of xenoliths from the Passadumkeag River granite indicates a whole rock Rb-Sr age of 496±14 m.y., with an initial Sr isotopic ratio of 0.70262.Two types of zircon exhibiting wide petrographic diversity are evident in variable proportions throughout the batholith. One of these types is preferentially found in a mafic xenolith and it is widely dispersed in the host granites forming discrete grains and probably as inclusions in the other type of zircon. U-Pb analyses of zircons give concordia intercept ages of 399±8 m.y. for Whitney Cove, 388±6 m.y. for Passadumkeag River, 415 m.y. for a mafic xenolith in Passadumkeag River, and 396±32 for combined Whitney Cove and Passadumkeag River granite. The zircons show a spread of up to 20 m.y. in the 207Pb/206Pb ages. Omitting the finest zircon fraction in the Passadumkeag River results in a concordia intercept age of 381±3 m.y., in better agreement with the whole-rock Rb-Sr and mineral K-Ar ages. For the Whitney Cove pluton, exclusion of the finest fraction does not bring the zircon age into agreement with the Rb-Sr data.Age estimates by the whole rock Rb-Sr, mineral K-Ar and Ar-Ar methods suggest that the crystallization age of the plutons is about 380 m.y., slightly younger than the U-Pb zircon intercept ages. A possible reason for this discrepancy is that the zircons contain inherited lead. Thus, zircon U-Pb ages might represent a mixture of newly developed zircon and older inherited zircon, whereas the Rb-Sr whole rock age (380 m.y.) reflects the time of crystallization, and the argon ages result from rapid cooling after emplacement.  相似文献   

2.
The Late Triassic Central Patagonian Batholith is a key element in paleogeographic models of West Gondwana just before to the break-up of the supercontinent. The preexisting classification of units of this batholith was mainly based on isotopic and geochemical data. Here we report the results of field mapping and petrography, backed up by three new 40Ar/39Ar biotite ages, which reveal previously unnoticed relationships of the rocks in the batholith. Based on the new information we present a reorganization of units where the batholith is primarily formed by the Gastre and the Lipetrén superunits. The Gastre Superunit is the oldest magmatic suite and is composed of I-type granites which display evidence of felsic and mafic magma interaction. It is formed by 4 second-order units: 1) equigranular hornblende–biotite granodiorites, 2) porphyritic biotite–hornblende monzogranites, 3) equigranular biotitic monzogranites and 4) hornblende quartz-diorites. Emplacement depth of the Gastre Superunit is bracketed between 6 and 11 km (1.8–3 kbar), and the maximum recorded temperatures of emplacement are comprised between 660 and 800 °C. The recalculated Rb/Sr age is 222 ± 3 Ma and the porphyritic biotite–hornblende monzogranites yielded a 40Ar/39Ar age in biotite of 213 ± 5 Ma. On the other hand, the Lipetrén Superunit is made up by fine-grained biotitic monzo- and syenogranites that postdate magma hybridization processes and intrude all the other units. The recalculated Rb/Sr age for this suite is identical to a 40Ar/39Ar age in biotite extracted from one of its monzogranites (206.4 ± 5.3 and 206 ± 4 Ma, respectively). This and the observed textural features suggest very fast cooling related to a subvolcanic emplacement. An independent unit, the “Horqueta Granodiorite”, which has previously been considered as the record of a Jurassic intrusive stage in the Central Patagonian Batholith, gave a 40Ar/39Ar age in biotite of 214 ± 2 Ma. This and the reexamination of available isotopic data allow propose that this granodiorite unit is part of the Late Paleozoic intrusives in the region. The Late Triassic Central Patagonian Batholith is overlain by 190–185 Ma volcano-sedimentary rocks, suggesting that it was exposed sometime between the latest Triassic and earliest Jurassic times, roughly coeval with a major accretionary episode in the southwestern margin of Gondwana.  相似文献   

3.
Generally synmetamorphic granitic stocks intrude high-grade, Silurian-lowermost Devonian metasedimentary rocks near Augusta, Maine. Rb-Sr whole-rock isochrons (8 points each) define mutually overlapping crystallization ages of 394±8 m.y. (Togus quartz monzonite), 387±11 m.y. (Hallowell quartz monzonite), and 381±14 m.y. (Three Mile Pond biotite granodiorite), thereby providing a narrow chronologic bracket for Acadian tectonothermal activity in the area. Igneous hornblende, muscovite, and biotite display internally concordant 40Ar/39Ar age spectra with plateau dates of 350 m.y. (hornblende) and 300-265 m.y. (muscovite and biotite), with an overall southwestward younging trend. The mineral dates are similar to those recorded in adjacent portions of the regional metamorphic terrain and suggest a prolonged postmagmatic cooling which closely followed the diachronous northeast-southwest post-Acadian cooling of the country rocks. No evidence for a distinct Permian thermal overprint of older isotopic systems has been observed.  相似文献   

4.
<正>Thus far,our understanding of the emplacement of Xuebaoding granite and the occurrence and evolution of the Songpan-Garze Orogenic Belt has been complicated by differing age spectra results.Therefore,in this study,the ~(40)Ar/~(39)Ar and sensitive high resolution ion micro-probe(SHRIMP) U-Pb dating methods were both used and the results compared,particularly with respect to dating data for Pankou and Pukouling granites from Xuebaoding,to establish ages that are close to the real emplacements.The results of SHRIMP U-Pb dating for zircon showed a high amount of U,but a very low value for Th/U.The high U amount,coupled with characteristics of inclusions in zircons,indicates that Xuebaoding granites are not suitable for U-Pb dating.Therefore,muscovite in the same granite samples was selected for ~(40)Ar/~(39)Ar dating.The ~(40)Ar/~(39)Ar age spectrum obtained on bulk muscovite from Pukouling granite in the Xuebaoding,gave a plateau age of 200.1±1.2 Ma and an inverse isochron age of 200.6±1.2 Ma.The ~(40)Ar/~(39)Ar age spectrum obtained on bulk muscovite from Pankou granite in the Xuebaoding gave another plateau age of 193.4±1.1 Ma and an inverse isochron age of 193.7±1.1 Ma. The ~(40)Ar/~(36)Ar intercept of 277.0±23.4(2σ) was very close to the air ratio,indicating that no apparent excess argon contamination was present.These age dating spectra indicate that both granites were emplaced at 200.6±1.3 Ma and 193.7±1.1 Ma,respectively.Through comparison of both dating methods and their results,we can conclude that it is feasible that the muscovite in the granite bearing high U could be used for ~(40)Ar/~(39)Ar dating without extra Ar.Based on this evidence,as well as the geological characteristics of the Xuebaoding W-Sn-Be deposit and petrology of granites,it can be concluded that the material origin of the Xuebaoding W-Sn-Be deposit might partially originate from the Xuebaoding granite group emplacement at about 200 Ma.Moreover,compared with other granites and deposits distributed in various positions in the Songpan-Garze Orogenic Belt,the Xuebaoding emplacement ages further show that the main rare metal deposits and granites in peripheral regions occurred earlier than those in the inner Songpan-Garze.Therefore,~(40)Ar/~(39)Ar dating of Xuebaoding granite will lay a solid foundation for studying the occurrence and evolution of granite and rare earth element deposits in the Songpan-Garze Orogenic Belt.  相似文献   

5.
The Gaik Granite is a part of the Ladakh batholith outcropping between Gaik and Kiari in NW Himalaya. This is a pink porphyritic granite rich in biotite and poor in hornblende. Rb-Sr analyses have been made on six whole-rock samples of the Gaik Granite. Though the samples are poorly enriched in radiogenic Sr, they define a reliable isochron corresponding to an age of 235±13 (2σ) m.y. and initial87Sr/86Sr ratio of 0·7081±0·0004 (2σ). Biotite, plagioclase and potash feldspar fractions separated from two of the samples have yielded a much younger mineral isochron at 30±1·5 m.y. indicating a nearly complete redistribution of Sr isotopes between mineral phases at a time much later than the primary emplacement of the granite. The present results show that at least some components of the Ladakh batholith are of Permo-Triassic age. These rocks were isotopically re-equilibrated on a mineral scale during Upper Oligocene in response to the Himalayan orogeny.  相似文献   

6.
S.S Iyer  P.J Woodford  A.F Wilson 《Lithos》1976,9(3):211-224
Rb-Sr isotopic investigation of forty rocks from three different granulite localities in the Strangways Ranges, central Australia indicated two distinct granulite metamorphisms, namely M1: 1860±80 m.y., and M2: 1470±60 m.y. and 1430±60 m.y., λ=1.39x10?11yr?1. M2 has been recorded in the felsic granulites of two of the three localities. Although the Sr isotopic systems in the felsic granulites seem to show a normal growth in a closed system during M2, the Rb-Sr systems for some calcareous and mafic granulites have not completely re-equilibrated during M2, as shown by the scatter with respect to the reference isochrons for M1 and M2. Ca-carbonate rocks display unusually low level of Sr (20–120 ppm. Sr, and high Ca/Sr ratios). Schistose zones of retrogression in the granulites, dated by K-Ar and 40Ar-39Ar methods at ≈350 m.y., yield anomalous Rb-Sr data.  相似文献   

7.
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8.
The Mount Brome complex of the Monteregian province of southern Quebec, Canada, consits of several major intrusions ranging compositionally from gabbro to syenite. The relative ages of these intrusives have been investigated with high-resolution 40Ar/39Ar analyses, including a specially designed irradiation configuration to cancel the effects of fluence gradients. Small yet distinct apparent age differences are observed. While a number of analytical and geological factors could be proposed to explain the small variations, evaluation of these suggests the age differences reflect those in emplacement times. The gabbro and nepheline diorite were emplaced within a short span 123.1 Ma ago. Generally more evolved lithologies (biotite monzodiorite, pulaskite, nordmarkite) appear to have been emplaced within a restricted interval 1.4±0.3 Ma later. Whole-rock Rb-Sr systematics do not give acceptable isochrons because of significant scatter interpreted to reflect initial 87Sr/86Sr heterogeneities resulting from crustal contamination. Considering the variations in initial ratio, the Rb-Sr data are consistent with the 40Ar/39Ar age.  相似文献   

9.
40Ar/39Ar dating was conducted on the Da Lien granite related to greisen‐skarn type polymetallic (W‐CaF2‐Cu‐Bi‐Au) mineralization in Nui Phao, northern part of Vietnam in the South China Plate. Biotite and muscovite separates from the biotite‐muscovite granite and greisenized granite indicate four plateau ages: 82.2 ± 0.4 Ma, 82.8 ± 0.3 Ma, 81.5 ± 0.3 Ma and 82.5 ± 0.4 Ma. The plateau ages were not significantly influenced by excess 40Ar in dated minerals or by loss of radiogenic 40Ar due to hydrothermal activities. The results indicate that solidification of granite related to the polymetallic mineralization occurred in the Late Cretaceous between 82.8 Ma and 81.5 Ma.  相似文献   

10.
Muscovites from the Blond granite (West French Massif Central) were dated by the 40Ar/39Ar single-grain method. The 40Ar/39Ar ages obtained vary from 305.5 ± 0.3 Ma to 311.3 ± 0.5 Ma, and most of the age spectra are slightly saddle-shaped. The analyzed muscovites show phengitic recrystallization under optical microscope observations, SEM images, and electron microprobe chemical analyses. It is proposed that the saddle-shaped age spectra result from a partial recrystallization, which produced three different isotopic reservoirs in the analyzed white mica single grains: domains of early muscovite, domains of neocrystallized muscovite formed by phengitic and Al-Fe substitutions, and “low-activation energy sites.”  相似文献   

11.
The Taiping-Huangshan batholith in southeast China is a polygenetic composite granitoid consisting of two parts. The northern part is known as the Taiping granodiorite, genetically designated to the Syntexis-type granitoids of southeast China[1] or I-type[4]. Based on whole-rock Rb-Sr isochron dating, its age is 22 3 m. y. with a relatively low initial Sr ratio (0.7069), suggesting that it was emplaced during the Indosinian period. The southern part, the Huangshan multi-staged granite, is genetically ascribed to the transformation type of southeast China, or S-type, which includes two bodies known as the Huangshan and Shizilin granites. Both were formed in the late Yenshanian period as indicated by their ages: 131 m.y. for the Huangshan granite and 123 m. y. for the Shizilin granite, and high initial Sr ratios (0.714 for the Huangshan granite and 0.718 for the Shizilin granite) determine using whole-rock Rb-Sr isochron dating method. The biotite in the Taiping granodiorite is Mg-biotite with a high Mg/(Mg +ΣFe + Mn +VIAl3+) ratio (> 0.42) in its octahedral layers, and has a longerc-axis (10.220–10.224 Å) and a larger unit-cell volume (499.5 Å3), as calculated from X-ray powder diffraction data But the biotites in the Huangshan and Shizilin granies occur mostly as siderophyllite, subsequently as Fe-biotite and occasionally as zoned mica consisting of siderophyllite and musco-vite. The Mg/(Mg +ΣFe + Mn +VIAl3+) ratios are low, whileVIAl3+/(Mg+ΣFe+Mn+VIAl3+) ratios high in their octahedral layers. They have a shorterc-axis (10.128–10.196A) and a small nit-cell volume (494.5 Å3 on average). Comparison of their chemical compositions and corresponding unit-cell parameters for 13 samples from the batholith indicates that thec-axis length increases with increasing Mg content with a noticea ble positive correlation between them, but decreases with increasingVAl3+ content, showing an obvious negative correlation. The changes of theb-axis lengths with the compositions of biotites are much less pronounced than that of thec-axis length.  相似文献   

12.
Rb-Sr whole rock data for gneisses and granites from the oriental Pyrénées yield cadomian ages for the basement gneisses and hercynian ages for the granites. Granites occur in two generations. An alkaline granite dated at 335±15 m.y. is syn.—or slightly post-tectonic, and a later calcalkaline granite dated at 275±12 m.y, is clearly intrusive and marks the end of hercynian tectono-metamorphism. Initial 87Sr/86Sr ratios of the granites put limits on the proportion of juvenile contribution from the mantle to their formation. Petrogenetic models are tested using Rb and Sr as tracers.  相似文献   

13.
The Jiehe gold deposit, containing a confirmed gold reserve of 34 tonnes (t), is a Jiaojia-type (disseminated/stockwork-style) gold deposit in Jiaodong Peninsula. Orebodies are hosted in the contact zone between the Jurassic Moshan biotite granite and the Cretaceous Shangzhuang porphyritic granodiorite, and are structurally controlled by the NNE- to NE-striking Wangershan-Hedong Fault. Sulphide minerals are composed predominantly of pyrite with lesser amounts of chalcopyrite, galena, and sphalerite. Hydrothermal alteration is strictly controlled by fracture zones, in which disseminated sulfides and native gold are spatially associated with pervasive sericitic alteration. Mineralogical, textural, and field relationships indicate four stages of alteration and mineralization, including pyrite-bearing milky and massive quartz (stage 1), light-gray granular quartz–pyrite (stage 2), quartz–polysulfide (stage 3) and quartz–carbonate (stage 4) stages. Economic gold is precipitated in stages 2 and 3.The Jiehe deposit was previously considered to form during the Eocene (46.5 ± 2.3 Ma), based on Rb-Sr dating of sericite. However, 40Ar/39Ar dating of sericite in this study yields well-defined, reproducible plateau ages between 118.8 ± 0.7 Ma and 120.7 ± 0.8 Ma. These 40Ar/39Ar ages are consistent with geochronological data from other gold deposits in the region, indicating that all gold deposits in Jiaodong formed in a short-term period around 120 Ma. The giant gold mineralization event has a tight relationship with the extensional tectonic regime, and is a shallow crustal metallogenic response of paleo-Pacific slab subduction and lithospheric destruction in the eastern NCC.  相似文献   

14.
The Costelloe Murvey Granite is a chemically evolved, high heat production, leucocratic component of the 400 Ma old Galway Granite batholith and is host to hydrothermal fluorite-quartz-calcite veins. A previously reported clinopyroxene 40Ar-39Ar age of 231±4 Ma obtained from a pre-mineralization dolerite dyke is reinterpreted as dating this mineralization. The hydrothermal fluid extensively altered its granite wallrocks, leading to lower Sm and Nd and higher Rb concentrations in altered granite, disturbing both its Rb-Sr and Sm-Nd isotopic systems. The 87Sr/86Sr ratio of the hydrothermal fluid from which fluorite and calcite precipitated ranged from 0.7101 to 0.7139. These ratios are very much lower than in the Costelloe Murvey Granite at the time of mineralization, precluding the granite as a source for more than 2% of the hydrothermal Sr. The initial 143Nd/144Nd ratio varies between fluorite in different veins due to Nd derivation from local wallrocks, and between fluorite of petrographically distinct growth phases within a single hand specimen, highlighting the difficulty of Sm-Nd isochron dating of fluorite in cases where there are multiple sources of hydrothermal Nd. It is proposed that fluorite and calcite precipitated where hot, dilute fluids rising through the granite mixed with cooler, more saline fluids of basinal origin migrating through Lower Carboniferous limestone which then overlay the granite. Received: 3 August 1995 / Accepted: 11 April 1996  相似文献   

15.
The Yingchengzi gold deposit, located 10 km west of Shalan at the eastern margin of the Zhangguangcai Range, is the only high commercially valuable gold deposit in southern Heilongjiang Province, NE China. This study investigates the chronology and geodynamic mechanisms of igneous activity and metallogenesis within the Yingchengzi gold deposit. New zircon U–Pb data, fluid inclusion 40Ar/39Ar dating, whole‐rock geochemistry and Sr–Nd isotopic analysis is presented for the Yingchengzi deposit to constrain its petrogenesis and mineralization. Zircon U–Pb dating of the granite and diabase–porphyrite rocks of the igneous complex yields mean ages of 471.7 ± 5.5 and 434 ± 15 Ma respectively. All samples are high‐K calc‐alkaline or shoshonite rocks, are enriched in light rare earth elements and large ion lithophile elements, and are depleted in high field strength elements, consistent with the geochemical characteristics of arc‐type magmas. The Sr–Nd isotope characteristics indicate that the granite formed by partial melting of the lower crust, including interaction with slab‐derived fluids from an underplated basaltic magma. The primary magma of the diabase–porphyrite was likely derived from the metasomatized mantle wedge by subducted slab‐derived fluids. Both types of intrusive rocks were closely related to subduction of the ocean plate located between the Songnen–Zhangguangcai Range and Jiamusi massifs. However, fluid inclusion 40Ar/39Ar dating indicates that the Yingchengzi gold deposit formed at ~249 Ma, implying that the mineralization is unrelated to both the granite (~472 Ma) and diabase–porphyrite (~434 Ma) intrusions. Considering the tectonic evolution of the study area and adjacent regions, we propose that the Yingchengzi gold deposit was formed in a late Palaeozoic–Early Triassic continental collision regime following the closure of the Paleo‐Asian Ocean. In addition, the Yingchengzi deposit could be classified as a typical orogenic‐type gold deposit occuring in convergent plate margins in collisional orogens, and unlikely an intrusion‐related gold deposit as reported by previous studies. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

16.
Potassium-Ar and Rb-Sr dating of minerals was fundamental in early efforts to date magmatic and metamorphic processes and paved the way for geochronology to become an important discipline within the earth sciences. Although K-Ar and, in particular, 40Ar/39Ar dating of micas is still widely applied, Rb-Sr dating of micas has declined in use, even though numerous studies demonstrated that tri-octahedral mica yields geologically realistic, and more reliable and reproducible Rb-Sr ages than the K-Ar or 40Ar/39Ar system. Moreover, a reduction of uncertainties typically reported for Rb-Sr ages (ca. 1%) can now be achieved by application of multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) rubidium isotope dilution measurements (<0.3%). Replicate Rb-Sr biotite ages from the Oslo rift, Norway, yield an external reproducibility of ±0.3% (n=4) and an analytical error of ±0.8 Ma for individual ages that vary between 276.9 and 275.5 Ma. Conventional thermal ionisation mass spectrometry (TIMS) Rb analysis on the same mineral separates yields ages between 276.1 and 271.7 Ma, three times the spread compared to Rb MC-ICPMS data. Biotite and phlogopite from the central Nagssugtoqidian orogen, West Greenland, yield 40Ar/39Ar plateau ages (ca. 1700 Ma) with a spread of ±150 Ma, while Rb-Sr ages on either biotite or phlogopite separates have a much narrower range of ±10 Ma. This comparison of Rb-Sr and 40Ar/39Ar ages demonstrates the robustness of the Rb-Sr system in tri-octahedral micas and cautions against the sole use of 40Ar/39Ar tri-octahedral mica ages to date geological events. Analytical errors of 16 Ma for these Rb-Sr mica ages determined by TIMS are reduced to <±5 Ma when the Rb concentration is determined by MC-ICPMS. All the TIMS and MC-ICPMS data from the Nagssugtoqidian orogen agree within assigned analytical uncertainties. However, high precision Rb-Sr dating by MC-ICPMS can resolve geological information obscured by TIMS age determinations. TIMS data for seven phlogopite samples form an isochron age of 1645±6 Ma, and thus, no differentiation in age between the different samples can be made. In contrast, MC-ICPMS Rb measurements on the same samples reveal two distinct populations with ages of 1633±3 or 1652±5 Ma.Combining the mica Rb-Sr geochronological data with the well-constrained thermal history of this ancient orogen, we estimate the closure temperature of the Rb-Sr system in 1-2 mm slowly cooled phlogopite crystals, occurring in a matrix of calcite and plagioclase to be ∼435 °C, and at least 50 °C above that of biotite.  相似文献   

17.
江西冷水坑矿区构造-岩浆活动的年代学约束   总被引：6，自引：3，他引：3  
江西省冷水坑矿区火成岩-构造演化一直缺少系统的年代学制约.作者运用LA-ICP-MS锆石U-Pb和40Ar/39Ar测年技术,对冷水坑矿区两套火山岩地层(打鼓顶组和鹅湖岭组)、含矿花岗斑岩和主推覆断层F2进行了年代学测试,结果表明,打鼓顶组流纹质含角砾熔结凝灰岩形成于160.8±1.9Ma,鹅湖岭组合角砾熔结凝灰岩则具有间歇性和多期喷发特点,其最初活动时间为159Ma,而主体形成于146.6±2.2Ma;矿区含矿花岗斑岩与打鼓顶组、鹅湖岭组几乎同期形成,年龄介于163.6 ±2.1Ma～154.3±3.0Ma之间;研究区构造活动起始时间不晚于加里东期,推覆断层F2中保留有40Ar/39Ar年龄为398.5±2.6Ma的构造活动痕迹,中生代重新复活,导致震旦系叠覆于鹅湖岭组之上,年龄晚于146.6Ma,可能对含矿斑岩体起破坏作用.  相似文献   

18.
Four slate samples from subduction complex rocks exposed on the south coast of New South Wales, south of Batemans Bay, were analysed by K–Ar and 40Ar/39Ar step‐heating methods. One sample contains relatively abundant detrital muscovite flakes that are locally oblique to the regional cleavage in the rock, whereas the remaining samples appear to contain sparse detrital muscovite. Separates of detrital muscovite yielded plateau ages of 505 ± 3 Ma and 513 ± 3 Ma indicating that inheritance has not been eliminated by metamorphism and recrystallisation. Step‐heating analyses of whole‐rock chips from all four slate samples produced discordant apparent age spectra with ‘saddle shapes’ following young apparent ages at the lowest temperature increments. Elevated apparent ages associated with the highest temperature steps are attributed to the presence of variable quantities of detrital muscovite (<1–5%). Two whole‐rock slate samples yielded similar 40Ar/39Ar integrated ages of ca 455 Ma, which are some 15–30 million years older than K–Ar ages for the same samples. These discrepancies suggest that the slates have also been affected by recoil loss/redistribution of 39Ar, leading to anomalously old 40Ar/39Ar ages. Two other samples, from slaty tectonic mélange and intensely cleaved slate, yielded average 40Ar/39Ar integrated ages of ca 424 Ma, which are closer to associated mean K–Ar ages of 423 ± 4 Ma and 409 ± 16 Ma, respectively. Taking into account the potential influences of recoil loss/redistribution of 39Ar and inheritance, the results from the latter samples suggest a maximum age of ca 440 Ma for deformation/metamorphism. The current results indicate that recoil and inheritance problems may also have affected whole‐rock 40Ar/39Ar data reported from other regions of the Lachlan Fold Belt. Therefore, until these effects are adequately quantified, models for the evolution of the Lachlan Fold Belt, that are based on such whole‐rock 40Ar/39Ar data, should be treated with caution.  相似文献   

19.
南岭成矿带加里东期大花岗岩基的钨锡成矿潜力是近年来地质学家关注的热点。本文以湖南省彭公庙岩体为研究对象,精确厘定了产于彭公庙岩体内部的石牛仙钨矿的形成时代,同时厘定了彭公庙岩体中粗粒黑云母花岗闪长岩形成时代,分析了其地球化学特征,并与典型的成钨锡矿花岗岩进行对比,以此评估其钨锡成矿潜力。黑云母花岗闪长岩LA-ICP-MS锆石和独居石U-Pb年龄分别为436.1±2.5 Ma(MSWD=1.9,n=19)和436.8±2.8 Ma(MSWD=2.7,n=20),指示其侵位于早志留世。石牛仙钨矿床白云母39Ar/40Ar同位素坪年龄为150.2±1.2 Ma(MSWD=0.42),成矿时代与彭公庙成岩时代明显不同。彭公庙岩体分异程度不高,成矿元素W和Sn含量低,主要来源于上地壳贫粘土的变质砂岩,与南岭典型的成钨、成锡花岗岩分异程度高、成矿元素含量高、来源于富粘土的上地壳物质部分熔融区别明显,说明其成矿潜力有限。最后,在综合前人研究成果的基础之上,指出应综合地球物理、地球化学、构造蚀变信息等资料,重点评价彭公庙岩体内部及周缘晚期晚侏罗世花岗岩岩脉或...  相似文献   

20.
铜陵地区中酸性侵入岩年代学研究   总被引：67，自引：4，他引：67  
本文选择了铜陵地区主要岩石类型的代表性岩体中黑云母为测定对象，准确地测定了侵入岩的４０Ａｒ／３９Ａｒ同位素年龄。测定结果表明，区内侵入岩的年龄均小于１４０Ｍａ，属燕山晚期的产物，后期热事件为成矿时代，晚于岩浆侵入时代，在此基础上，分析了ＫＡｒ法、ＲｂＳｒ法同位素年龄产生偏差的原因  相似文献   

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