A La-Icp-MS and Shrimp U/Pb Age Constraint on the Timing of Ree Mineralisation Associated With Bushveld Granites

Buick, Ian S.; Lana, Cristiano; Gregory, Courtney J.

doi:10.2113/gssajg.114.1.1

Cited by 18 publications

(7 citation statements)

References 36 publications

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“…The standard and unknown zircon grains were ablated in a small-volume (tear-drop shape) sample cell with an insert that holds one 25-mm-diameter sample mount and a 7-mm-diameter standard mount . The acquisitions consisted of a 20 s of laser warm-up and a measurement of the gas blank, followed by 40 s measurements of the U, Th and Pb signals during ablation, and a 20 s washout (e.g., Buick et al, 2011;Lana et al, 2011). The samples, the standards and the sample holders were acid-washed before being analyzed to remove possible surface Pb contamination.…”

Section: Methodsmentioning

confidence: 99%

Constraints on the Statherian evolution of the intraplate rifting in a Paleo-Mesoproterozoic paleocontinent: New stratigraphic and geochronology record from the eastern São Francisco craton

et al. 2015

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An integrated approach of stratigraphic analysis and U-Pb age dating reveals some information on the tectonosedimentary evolution of the Statherian cover of the São Francisco craton in the so-called Espinhaço basin (Atlantic shield in eastern Brazil). Here, continental sedimentation patterns, such as alluvial fan, braided-plain and lacustrine facies associations, with associated volcanic rocks are documented in two superposed basin fill-successions, which are defined as the Algodão and Sapiranga Synthems and grouped in the Botuporã Supersynthem. Both studied units consist mainly of conglomerates and cross-bedded sandstones and minor amounts of mudstones, sedimentary breccias, volcanic lava beds and volcaniclastic rocks, which were deposited in a rift basin -the Botuporã rift -during two syn-rifting phases. The Algodão Synthem represents the first rifting phase. The basal synsedimentary conglomerates of this unit were deposited mainly by subaerial debris flows, most likely along and near a rift border fault. The framework of this rock consists of only crystalline rock clasts from the basement and no fragments of volcanic rocks. Detrital zircon grains that were extracted from this facies show ages older than 2.05 Ga. The remainder of the section is dominated by fluvial sandy lithofacies with minor conglomerate lenses and sandstone-mudstone heterolithic lithofacies, which represent distal, waning-flood deposits in a lacustrine environment. The upper section also contains hummocky cross-stratified sandstone lithofacies, which are related to a storm-influenced deposition. On top of the Algodão succession, the volcanic rocks were dated at 1775 ± 7 Ma, which was interpreted as the near final age of the first rift-phase. Representing the second rift-phase, the Sapiranga Synthem shows similar sedimentation patterns to the Algodão Synthem. The Sapiranga Synthem rests directly on the volcanic rocks of the Algodão Synthem, and its basal conglomerates (which are most likely also related to a master fault) contain voluminous clasts of volcanic rocks, sandstones and crystalline rocks. The detrital zircon grains that were extracted from this facies show ages of 1741 ± 14 and 1766 Ma as well older than 2.05 Ga. The volcanic rocks on the upper succession of the Sapiranga Synthem record ages of 1740 ± 10 Ma, which finalized the Botuporã rift evolution. A preliminary geochemical study of volcanic rocks from the Botuporã Supersynthem showed that these rocks are alkaline rocks with high K 2 O/Na 2 O ratios, which belong to an ultrapotassic suite. The low concentrations of MgO wt.% suggest a felsic ultrapotassic character. The Botuporã Supersynthem is unconformably covered by a volcanosedimentary rift-succession of EoCalymmian age -the Pajeú Synthem, which represents the second rifting stage of the Espinhaço basin. Several Statherian-related volcano-sedimentary sequences and anorogenic granitoids occur dispersed in the São Francisco block, which requires a regional geologic model to explain the extensional and magmatism process during ...

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Section: Methodsmentioning

confidence: 99%

Constraints on the Statherian evolution of the intraplate rifting in a Paleo-Mesoproterozoic paleocontinent: New stratigraphic and geochronology record from the eastern São Francisco craton

et al. 2015

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“…Monazite USGS 44069 is widely used in various studies as a calibration RM, e.g., [5,15,29,30,[33][34][35][36][37][38]. Despite the above noted discrepancy, reference monazite USGS 44069 is an excellent RM for U-Th/Pb dating of monazite, because of its reliable age reproducibility [32,38].…”

Section: Usgs 44069mentioning

confidence: 99%

“…Data from the first two analytical sessions (120605, 130111) were used to (1) evaluate the effect of spot size and repetition rate on accuracy and precision of the U-Th/Pb age of the monazites and to (2) establish an analytical protocol that can be applied in different laboratories. The most commonly used analytical parameters for U-Th/Pb monazite dating such as a spot size (5, 10 and 20 µm) and repetition rate (5 and 10 Hz) were applied, e.g., [5,8,10,16,17,22,29,36,51,56]. To compare the results, the same ablation conditions were maintained by applying the same analytical setting and analyzing the same growth zone of the grains.…”

Section: Analytical Set-up and Sequencementioning

confidence: 99%

Assessment of Five Monazite Reference Materials for U-Th/Pb Dating Using Laser-Ablation ICP-MS

et al. 2019

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Monazite is a common accessory phosphate mineral that occurs under a wide range of pressure and temperature conditions in sedimentary, metamorphic and igneous rocks. Monazite contains high amounts of Th and U, rendering single monazite grains suitable for in-situ U-Th/Pb dating using laser ablation inductively-coupled mass spectrometry (LA-ICP-MS). Two key aspects of monazite dating that are critical for accurate age data with maximum precision are (i) optimized instrumental conditions to minimize analytical scatter and (ii) a well characterized reference material to ensure the accuracy of the obtained aged. Here, we analyzed five monazite reference materials (USGS 44069, 94-222, MAdel, Moacir and Thompson Mine Monazite) for their U-Th/Pb ages using LA-ICP-MS technique and applied a variety of laser spot diameters and repetition rates to find the best operational conditions to achieve accurate age data while maintaining maximum precision. We find that a spot diameter of 10 µm and a repetition rate of 10 Hz yield the most precise ages with a deviation of ±2.0% from their respective high-precision U/Pb literature age data. Ages were reproduced in three different LA-ICP-MS laboratories using these parameters. Each reference material was tested for its suitability as a matrix-matched age reference material. For this, a rotating, iterative approach was adopted in which one reference monazite was used as calibration reference material against all others, which were treated as unknowns. The results reveal that USGS 44069, 94-222, Thompson Mine Monazite and MAdel all agree with their respective calculated ages and ID-TIMS reference ages and thus are suggested as suitable calibration reference materials. Moacir, however, appears slightly older than previously suggested (up to 4%), thus, caution is advised here when using Moacir as reference material for U-Th/Pb LA-ICP-MS dating in the absence of further absolute age calibration.

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“…The general operating conditions and U-Pb protocols are described in Moreira et al (2016) and Takenaka et al (2015). Acquisition time of the gas blank was 20 seconds, followed by a 40 s of measurement of U, Th and Pb signals during ablation, and a 30 s washout (Buick et al, 2011;Moreira et al, 2016). Laser ablation were set at 30 µm spot size, fluence between 6 and 8 J/cm 2 at a 10 Hz repetition rate using He mixed with Ar as a carrier gas.…”

Section: A1 U-pb Isotope Analysesmentioning

confidence: 99%

U–Pb ages and Hf-isotope data of detrital zircons from the late Neoarchean-Paleoproterozoic Minas Basin, SE Brazil

Dopico

Lana

Moreira

et al. 2017

Precambrian Research

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Because of its world-class iron ore deposits and promising Au and U mineralizations, the late Neoarchean to Paleoproterozoic Minas Basin (Minas Supergroup, SE of Brazil) is one of the best-studied basins in South America. However, the lack of datable interlayered volcanic rocks prevented discourse over ages of the strata, the sources and the nature of its ore deposits. In this paper, we present detrital zircon U-Pb age patterns coupled with Lu-Hf data for 18 samples, representing different stages of the Minas Basin evolution (~2000 analyzed zircons). Age spectra for the main basal unit (Moeda Formation) show a classic rift-related detrital zircon pattern, characterized by multiple autochthonous sources, which in turn are much older than the age of deposition. Maximum age for the rifting event is constrained at ca 2600 Ma. Detritus accumulated at the base of the Minas Supergroup were derived from Archean source rocks and their sedimentation was marked by differential uplift of the Archean crust, shortly after the 2730-2600 Ma high-K calc-alkaline magmatism (Mamona Event). The age of the BIF deposits is younger than 2600 Ma, most likely coinciding with the great oxygenation event between 2400 and 2200 Ma and the precipitation of banded iron deposits worldwide. Detrital zircons from the topmost units of the Minas strata suggest that tectonic inversion and closure of the basin took place at ca 2120 Ma with the deposition of the synorogenic Sabará Group. Rhyacian zircon supply showing juvenile Hf signatures gives evidence of a late Rhyacian amalgamation between the Mineiro Belt and the craton. The εHf signatures support the hypothesis that the Archean crystalline crust of the craton was mostly built by crust-mantle mixing processes, with a successive decrease of εHf values in zircons crystallized after 3250 Ma and minor mantle-like additions after Paleoarchean times. Regionally, our dataset supports previous interpretations of a long-lived evolution of the southern São Francisco Craton comprising a succession of convergent island arcs, small microplate collisions, and development of Archean convergent and divergent basins that evolved between Archean and Paleoproterozoic times.

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A La-Icp-MS and Shrimp U/Pb Age Constraint on the Timing of Ree Mineralisation Associated With Bushveld Granites

Cited by 18 publications

References 36 publications

Constraints on the Statherian evolution of the intraplate rifting in a Paleo-Mesoproterozoic paleocontinent: New stratigraphic and geochronology record from the eastern São Francisco craton

Constraints on the Statherian evolution of the intraplate rifting in a Paleo-Mesoproterozoic paleocontinent: New stratigraphic and geochronology record from the eastern São Francisco craton

Assessment of Five Monazite Reference Materials for U-Th/Pb Dating Using Laser-Ablation ICP-MS

U–Pb ages and Hf-isotope data of detrital zircons from the late Neoarchean-Paleoproterozoic Minas Basin, SE Brazil

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