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The Takestan area is in the western part of the Alborz magmatic arc. Magmatic rocks of the area consist of plutonic rocks (e.g. granitoids), effusive volcanic, and pyroclastic rocks. Using U-Pb zircon LA ICP-MS dating, we conclude that major parts of Takestan plutonic rocks were emplaced at 41–39 Ma (Late Eocene, Bartonian), but a small part of these rocks have ages of ~37 Ma (Late Eocene, Priabonian). The dacitic rocks have an age of ~39 Ma (Late Eocene, Bartonian) and the rhyolitic rocks are the youngest part of the magmatic rocks of the region with ages of 37–35 Ma (Late Eocene, Priabonian). Old zircons are present in all of granitoid and volcanic samples, except for a dacitic sample. They are interpreted both as earlier components in a long-lived magma chamber and inherited zircons from older continental crust. The age of magmatic rocks in the western part of the Alborz magmatic arc decreases from east to west, but the ages of the majority of them are limited to Palaeogene. The studied rocks like other Palaeogene magmatic rocks of Iran were possibly formed in a subduction related tectonic environment. Indeed, the Palaeogene magmatism of Iran is akin to geodynamic events related to Neotethyan subduction beneath Iranian micro-continent at the southern part of Eurasia. [ABSTRACT FROM AUTHOR]

The Central Africa Orogenic Belt (CAOB) and the Transaharan and Sergipano belts form a major West Gondwana suturing orogen affected by D1–D4 compressional deformation. Microstructural observations, mineral chemistry, zircon, and titanite laser ablation ICP-MS U-Pb dating, and biotite, muscovite, and K-feldspar 40Ar-39Ar age data are used to constrain the timing of rocks formation and D1–D4 events in the Yaoundé Domain of the CAOB, as well as characterize the Neoproterozoic-Cambrian transition. The Yaoundé Domain rocks were deposited on a pre-Neoproterozoic structure that was overprinted by a c. 1000–700 Ma mega arc/back-arc system and related Tonian to Ediacaran magmatism. Older U-Pb dates (1000 up to 2700 Ma) are inheritance from a pre-existing crust. The D1–D4 compressional events relate to the inversion of the c. 1000–700 Ma mega-rift system. New dates at c. 700 Ma, c. 630 Ma, c. 580–555 Ma constrain the timing of D1, D2, D3+D4, respectively. The peak of accompanying metamorphism occurred at 614 ± 4 Ma during D2. This was followed by a c. 115 Ma period of deformation-driven crustal exhumation and cooling that extended into the Cambrian. New data document short episodes of rapid denudation and cooling (up to 0.9 km/Ma and 40°C/Ma at c. 578 Ma in gneiss and up to 5 km/Ma and >125°C/Ma at c. 555 Ma in micaschist). It is proposed that the CAOB and correlative belts are parts of the orogenic hinterland formed from accretion and collision between the West African Craton and the Sahara Metacraton precursor. The correlated belts appear to represent the result of a protracted tectono-metamorphic and magmatic process that started in late Mesoproterozoic (c. 1167 Ma) and continued through the Neoproterozoic to the Cambrian (c. 500 Ma). [ABSTRACT FROM AUTHOR]

The Cape Spencer area is located 15 km southeast of Saint John, New Brunswick. Gold mineralization has been identified mainly in illitized (illite-carbonate [+ or -] quartz [+ or -] [...]

The Cape Spencer area is located 15 km southeast of Saint John in southern New Brunswick, Canada. Gold mineralization has been identified in illitized (illite-carbonate [+ or -] quartz [+ [...]

Crystal growth mechanisms are investigated using EPMA, [mu]XRF, and petrography on a euhedral andradite crystal from the Crowsnest Formation in southwestern Alberta. A micrometre scale, non-earth geographical reference system is [...]

The upper Green River Formation of the eastern Uinta Basin of Utah comprises variably organic-rich mudrock deposited in a stratified, alkaline lake that fluctuated in size and in hydrology from open to evaporitic. Beds of oil shale, representing periods of deep lake, suboxic-anoxic deposition include examples with anomalously high phosphate and toxic trace-metal levels, as determined by whole rock X-ray diffraction, scanning electron microscopy (SEM), and both solution and laser-ablation (LA) inductively coupled plasma-mass spectrometry (ICP-MS). The SEM identifies an early, pre-compaction, diagenetic succession of euhedral rhombic dolomite and high-Mg-calcite, nodular pyrite, blocky low-Mg calcite, and microcrystalline carbonate fluorapatite (CFA). LA-ICP-MS indicates the CFA intervals have distinct lower and upper margins where P content rises from ~0.079 to ~3.2% across 2-3 cm of section. Enrichments of rare earth elements (REEs) and actinides (Th, U) show a complex correlation with the phosphatic margins. Light REEs average a tenfold enrichment at the outer margins with progressively heavier REEs exhibiting up to 20-fold enrichment toward the inner margin (Lu from 0.15 to 2.63 ppm). Actinide abundances also increase tenfold (U from ~5 to ~80 ppm) toward the inner margin. There is greatest similarity between Th and the Ho distributions and between U and Lu. This is a similar distribution to what elsewhere has been found in fossil bone and teeth. The microcrystalline CFA is interpreted to have precipitated (or recrystallized from a precursor phosphate) when the rate of dissolved P being generated from organic-matter breakdown exceeded P diffusion rates into the water column, allowing for P supersaturation. As the crystallites grew, diffusion of REE and actinide ions and complexes from surrounding porewaters into the concreting phosphate occurred only until pores were occluded and permeability dropped. As with fossil bone, at the outer margin of the phosphate interval, this allowed for fractionation and preferential substitution of Ca cations in the CFA lattice by light REEs of similar ionic radius. Heavier REEs and actinides of smaller ionic radius diffused further into margin of the phosphate interval. [ABSTRACT FROM AUTHOR]

Devonian and younger plutonic suites of the Appalachian orogen in Newfoundland form a curvilinear belt straddling the boundary between Ganderia and Avalonia, and exhibit a general pattern of younging to the southeast. However, many individual plutonic suites within this belt remain undated or have ages that are poorly constrained. This study reports U-Pb sensitive high-resolution ion microprobe (SHRIMP) data from zircon and 40Ar-39Ar data from hornblende, biotite, and muscovite, which collectively improve definition of post-tectonic plutonic events in southeastern Newfoundland, but at the same time raise new questions for further study. U-Pb zircon SHRIMP determinations provide valuable new geochronological information for the Deadman's Bay Granite (390 ± 4 Ma), the Gander Lake Granite (378 ± 4 Ma), the Terra Nova Granite (384 ± 4 Ma), the Old Woman stock (376 ± 4 Ma), and the easternmost unit (Tolt phase) of the composite Ackley Granite (372 ± 4 Ma). The Pass Island Granite, long considered part of this age group, gave a Silurian age of 423 ± 4 Ma and provides the first confirmation of Silurian granitoid magmatism in Avalonia of Newfoundland. The Berry Hills Granite on the Burin Peninsula, previously designated as Devonian, instead gave a Neoproterozoic age of 570 ± 6 Ma, and a similar age of 575 ± 6 Ma was obtained from granite that is intruded by the ca. 376 Ma Old Woman stock. These results indicate that regional geological context, deformation state, and (or) petrographic-geochemical data are not reliable indicators of emplacement age in this region. 40Ar-39Ar data from the Paleozoic granites provide mixed results in comparison to the U-Pb emplacement ages, and in some cases Ar systematics appear to have been disturbed by later hydrothermal alteration. In other cases, correspondence between the U-Pb and 40Ar-39Ar data sets is consistent with rapid postemplacement exhumation. Granophile-type mineralization (Mo, W, F, base metals) is present within both Ganderia and Avalonia examples, but is generally restricted to the youngest plutons, in which it is associated with high-level, near-roof, or apical settings. This age versus mineralization pattern is consistent with an interpretation in which mineralized environments within older suites have been preferentially eroded as a consequence of greater exhumation. The identification of a Silurian (ca. 423 Ma) granite in an area previously assigned to Avalonia may be important in constraining tectonic models for Ganderia-Avalonia interaction, which has generally been considered Silurian or younger. Given that many other plutonic suites in Avalonia are not well constrained by regional geology and remain undated, more work is needed to better define the extent of such magmatism and evaluate its implications for broader models of orogenic development. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present study combines textures, compositions, and in situ dating of allanite and whole-rock geochemistry from the Bagjata uranium deposit in the Singhbhum shear zone, the most important uranium-producing belt in India, to investigate the chemical evolution of rare earth element (REE) mineralization. Allanite, volu-metrically the most important sink of light rare earth elements (LREEs) in this deposit, occurs as disseminated grains, pockets, veins, and stringers in biotite schist and chlorite schist. Metasomatic addition of LREEs in the rock was associated with Ca-K-Fe ± B metasomatism, as evident from the vein mineralogy. The Allanite-bear-ing inetasomatized rocks are locally extremely enriched in REEs, reaching up to ~4.S wt percent ΣREEs. The textures and compositions of allanite demonstrate that early REE-rich allanite was replaced by later, relatively less REE bearing allanite-epidote, and this alteration followed a substitution scheme of REE+3 + (Fe+2 Mg+2) → Ca+2 + (Al, Fe+3). he presence of halite-bearing fluid inclusions in associated tourmaline, high Cl content of biotite, and other circumstantial evidence indicate that a high-salinity, Cl-rich fluid was likely responsible for initial LREE metasomatism. A later hydrothermal event altered preexisting allanite and removed REEs. The more oxidized nature of altered allanite and the presence of unidentified secondary REE minerals in association with sulfide might indicate the involvement of oxidized, sulfate-rich fluid in the alteration of allanite and the removal of REEs. Alternatively, fluoride complexing of REEs and selective removal of HREEs during this alteration arc possible. In situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating of allanite and monazite indicates that LREE metasomatism took place at -1.88 Ga. The next hydrothermal event, which altered existing allanite, removed some REEs, and perhaps was associated with U ( + HREE) addition, is dated at ~1.66 Ga. The youngest age determined from the thin rim of allanite is -1.02 Ga. These three different ages, determined from allanite, overlap with the known thermotectonic events in and around the Singhbhum shear zone. Comparison between the calculated ΣREE content of allanite-rich rock prior to allanite alteration and whole-rock ΣREE composition of the same rock suggests that the addition of a large quantity of REEs was followed by significant REE removal. Strong variations in the modal abundances of the constituent minerals and in whole-rock compositions, including REEs, indicate open-system behavior. The whole-rock REE pattern suggests that decoupling between LREEs and HREEs might be possible during superimposed alteration. Therefore, petrogenetic modeling using an REE-based discrimination diagram and REE patterns should be done with caution for rocks that underwent multiple events of hydrothermal fluid flux. [ABSTRACT FROM AUTHOR]

Whereas Sm-Nd isochron ages have conventionally been obtained using combinations of dissolved and purified whole rock and major-mineral aliquots analyzed by TIMS, the recent development of precise and accurate LA-MC-ICPMS Sm-Nd analyses of REE-enriched accessory minerals provides a potentially rapid method to date high-temperature magmatic and metamorphic crystallization events. Monazite, allanite, titanite, and apatite, which together comprise the bulk of the LREE budget of most crustal rocks, have all been successfully analyzed for Sm-Nd using LA-MC-ICPMS at spatial resolutions raging from 16 µm (monazite) to 150 µm (apatite). For these laser crater sizes, precision better than 50 ppm (2σ) can typically be achieved on 143Nd/144Nd. This technique was originally developed to combine in-situ SHRIMP U-Pb ages and Sm-Nd systematics to investigate isotopic inheritance at the grain scale. However, the technique can also be used to obtain relatively precise Sm-Nd isochron ages independent of external calibrations, matrix corrections, or time-consuming isotope dilution. By analyzing a range of (presumed) cogenetic LREE-enriched accessory minerals from the same rock to obtain a range of Sm/Nd, a sufficient number of data points can be collected in a single analytical session to define a statistically robust isochron age. In the example presented here, a fresh granite sampled from the Morila Mine, Mali, was dated at 2093 ± 6 Ma (1σ) based on an upper intercept of near-concordant SHRIMP U-Pb data for oscillatory zoned zircon. Allanite and apatite separated from the same rock were analyzed for Sm-Nd using LA-MC-ICPMS. The range of 147Sm/144Nd both between allanite (~0.07) and apatite (up to 0.16) and within each group of analyses provides a sufficient spread of Sm/Nd to calculate a reasonably precise Sm-Nd isochron age of 2097 ± 36 Ma (1σ). This demonstrated precision and accuracy combined with the ability to target accessory minerals in thin section (unknowns and standards can be mounted separately), can, therefore, be exploited as a geochronological and Sm-Nd isotope tracer tool to help guide interpretations for the origin and evolution of Proterozoic and older rocks. [ABSTRACT FROM AUTHOR]

In northern Saskatchewan, granitic pegmatites intruded Early Paleoproterozoic Wollaston Group metasedimentary rocks and interfolded granitoids that unconformably overlie Late Archean gneisses, all of which have been subjected to deformation during the protracted 1.86 to 1.77 Ga Trans-Hudson Orogeny. The U--Th ± REE--Y--Nb pegmatite intrusions and fracture-controlled U mineralization characterize the occurrences at Kulyk Lake, Eagle Lake, and Karin Lake properties in the Wollaston Domain. The pegmatites are moderately to highly evolved, ranging from mineralogically simple to complex types. These are rare-earth element class, NYF pegmatites (Nb--Y--F), and are interpreted to have formed in a late syn- to post-collisional tectonic setting. The complex-type pegmatites are hybridized, due to metasomatic interaction with the host rocks and therefore are locally crudely zoned. Saturation of U--Th ± REE--Y--Nb occurred at the margins (predominately the border and wall zones) of the hybridized pegmatites. Partial melts were generated at depth, and then coalesced as they intruded to higher structural levels during exhumation of this orogen. This agrees with U--Pb geochronology of these granitic pegmatites, which constrains them between peak- and late-metamorphic events of the Trans-Hudson Orogeny. The age constraints and relatively high-T partial melting conditions (~750 °C) conine the pegmatite melt-forming conditions to an early deformational event (1835-1805 Ma) that was overprinted by high-T retrograde metamorphism at c. 1770 Ma. Field relationships, textures and geochemical variations provide strong evidence that the U, Th, REE ± Y--Nb phases in the studied pegmatites were progressively enriched through extreme fractionation effects of which are evident throughout multiple pegmatite injections. In addition, volatiles and other luxing components further enriched U, Th, REE ± Y--Nb during complex hybridization reactions between pegmatite melt and wallrock, up to the final stages of pegmatite emplacement. [ABSTRACT FROM AUTHOR]

The internal zonation and chemical evolution of Nb--Ta oxides and muscovite have been characterized in the Moose II pegmatite, Northwest Territories, Canada, to distinguish primary magmatic mineralization from that formed during late--stage metasomatic processes. In addition, muscovite associated with Nb--Ta oxides was examined in order to assess the evolution of the pegmatite melt and the nature of the late-stage fluids. Detailed mapping shows that the studied body (430 x 61 m) is a highly fractionated, irregularly zoned, spodumene--subtype rare-element pegmatite dominated by coarse-grained to megacrystic albite, K-feldspar, and spodumene, with intergranular assemblages of quartz, K-feldspar, albite, spodumene, muscovite, and minor amblygonite--montebrasite. Monomineralic core zones (quartz and amblygonite--montebrasite), aplitic albite 'pods,' and units characterized by phyllic alteration occur in the central portions of the pegmatite. Columbite--tantalite minerals occur throughout the pegmatite, excluding the quartz cores, and patterns of internal zoning include: (1) normally zoned ferrocolumbite with early Ta--Ti-rich, and later Nb--W-rich overgrowths; (2) oscillatory zoned Ti-rich ferrotantalite with Nb-rich patchy replacement; (3) reversely zoned ferrocolumbite, with Ta-rich cores and (4) complexly zoned Ti-rich ferrotantalite with abundant late Nb- and Ta-rich patches and sieve textures. The textures and chemical patterns demonstrate an evolution from columbite to tantalite, whereby the Ta/(Ta + Nb) ratio increased with progressive fractionation (0.13-0.59) but the Mn/(Mn + Fe) ratio remained nearly constant (0.15-0.31). The chemical evolution of the Nb-Ta oxides from columbite to tantalite is consistent with crystallization from a magmatic to late-stage magmatic Na-rich melt, with a sequence of crystallization progressing from those of the wall zone, to the first intermediate zone, and finally the late aplitic albite zones. Minor remobilization of Nb, and to a lesser extent Ta, was responsible for some of the replacement features found in the Nb--Ta oxides. Textural observations and trace-element analyses of fine-grained, secondary muscovite found throughout the pegmatite indicate hydrothermal metasomatism by a late F- and Nb-rich vapor-like "supercritical" fluid. [ABSTRACT FROM AUTHOR]

New field and U-Pb zircon data from the south-central Wopmay Orogen (south of 65°N) establish crystallization ages of basement and plutonic phases and bring to the forefront questions on the architecture of the orogen. The complex and extensive >3300-2575 Ma basement domain was derived from the adjacent Slave craton. Paleoproterozoic supracrustal rocks, dominated by an extensive pelitic-psammitic sequence with basal arenite, conglomerate, and carbonate, unconformably overlie this basement. Pre- to post-kinematic Paleoproterozoic plutons intrude both basement and overlying strata and crystallized at 1877, 1867-1862, and 1858-1850 Ma. The first pulse of plutonism constrains an early generation of metamorphism and deformation to younger than 1877 Ma and is corroborated by metamorphic zircon in Archean basement. The interval from 1867 to 1862 Ma brackets ductile deformation in granite and granodiorite intrusions; although corresponding structure in the metasedimentary strata is equivocal. Post-kinematic ca. 1858-1850 Ma plutons were coeval with localized high-grade metamorphism and concomitant recrystallization of Archean basement. The absence of older (>1880 Ma) phases of the Hepburn intrusive suite in south-central Wopmay Orogen demonstrates a previously unrecognized north-south plutonic dichotomy and that the historical assignment of Calderian metamorphism to ca. 1885 Ma may be too old. The designation of part of the area to a klippe of Hottah terrane is not compatible with field and zircon age data which shows that basement and the overlying strata can be tied directly to the Slave craton. The study raises questions regarding the tectonic relationship between the Hottah terrane and Slave craton. [ABSTRACT FROM AUTHOR]