Epidote group minerals, including allanite, clinozoisite and epidote are common in a range of metamorphic, igneous and hydrothermal systems, and are stable across a wide range of pressure–temperature (P–T) conditions. These minerals can incorporate substantial amounts of rare earth elements (REEs) during their crystallisation, making them potential candidates for Lu–Hf geochronology to provide age constraints on various geological processes. Here we report on a first exploration into the feasibility of in situ Lu–Hf geochronology for epidote group minerals from various geological settings and compare the results with age constraints from other geochronometers. Magmatic allanite samples from pegmatites and monzogranites in the Greenland anorthosite complex, Coompana Province and Qingling Orogen provided dates consistent with magmatic events spanning from c. 2660 to 1171 Ma. In the Qingling pegmatites, a younger phase of hydrothermal allanite was dated at c. 215 Ma, consistent with the timing of regional REE mineralisation. Allanite from the Yambah Shear Zone, Strangways Metamorphic Complex, yielded Lu–Hf age of c. 430 Ma. It predates the garnet and apatite growth at c. 380 Ma, suggesting the Lu–Hf system can be preserved in allanite during prograde amphibolite-facies metamorphism. Additionally, Lu–Hf dates for hydrothermal clinozoisite and epidote are consistent with the timing of hydrothermal alteration and mineralisation in a range of settings, demonstrating the utility of the technique for mineral exploration. Despite the current lack of matrix-matched reference materials, the successful application of laser ablation Lu–Hf geochronology to epidote group minerals offers valuable geochronological insights into various geological processes that can be difficult to access through other geochronometers.

The ReOs isotope system can directly date sulphide formation, making it useful for ore deposit studies. Recent work has demonstrated that laser ablation inductively coupled tandem mass spectrometry (LA-ICP-MS/MS) can be used to effectively separate Re-187 from Os-187 during analysis by reacting Os with CH4 gas, allowing for in situ ReOs age determination of molybdenite. However, the age calculation often requires a significant interference correction of (ReCH2+)-Re-187 on (OsCH2+)-Os-187. Here, we demonstrate that N2O gas is a viable alternative reaction gas for in situ ReOs geochronology. In this new method, Os forms a tetra-oxide complex, while Re shows very low reactivity with the N2O reaction gas (similar to 0.15 %), reducing the isobaric interference correction requirement relative to the CH4 method. We compare results from both reaction gases across a range of molybdenite samples of different ages (spanning ca. 1700-300 Ma), demonstrating that the N2O method achieves greater precision and accuracy for young molybdenite samples (ca. 300 Ma) compared to CH4. In addition, we demonstrate that in situ ReOs is capable of dating high-Re pyrite (i.e., >10 ppm).

In situ Lu - Hf geochronology offers the potential for direct dating of garnet within petrographic context. However, the method requires matrix -matched standards to calibrate measured Lu/Hf ratios. In order to assess the accuracy of this calibration, as well as the reproducibility of the resulting Lu - Hf dates, two Lu-rich (up to 1 wt% Lu) garnet samples from the T & oslash; rdal pegmatite field in southern Norway were analysed over six analytical sessions. Multi -session isochron Lu - Hf dates of 930.3 +/- 1.4 Ma (MSWD = 1.0, 164 analyses) and 930.3 +/- 1.7 Ma (MSWD = 1.5; 125 analyses) were obtained, conform with previously published age constraints. The relative standard deviation of 0.1% between the analytical sessions indicates that the dates are highly reproducible. For each individual analytical session, age uncertainties of 0.3-0.6% were achieved by measuring high Lu count rates in analog detection mode. We further describe a calibration strategy that deals with Lu - Hf datasets where Lu is measured in both pulse and analog detector mode. Given the high analytical precision and reproducibility, we suggest that the T & oslash; rdal garnets are suitable reference materials for future LA-ICP-MS/MS Lu - Hf studies.

Precambrian iron oxide copper-gold (IOCG) systems have commonly experienced multiple mineralising and tectonothermal events and identifying their timing and geodynamic framework is challenging. World-class IOCG deposits in the Olympic Cu-Au Province, South Australia, are dominated by hematite and formed in the upper crust, while the magnetite-dominated Cu deposits hosted in granulite facies rocks are considered to represent the deeper expression of giant IOCG system. However, the application of novel in-situ Lu-Hf apatite geochronology reveals the magnetite-hosted Cu mineralisation is significantly younger and unrelated to the well-known 1590 Ma Gawler Craton IOCG systems. Apatite Lu-Hf ages from the granulite that predates Cu mineralisation give ages of 1490 Ma. Infiltration of Cu-bearing fluids resulted in recrystallisation of apatite, LREE mobilisation and formation of secondary monazite. Lu-Hf ages for syn-mineralisation apatite give 1460 Ma, consistent with c. 1460 Ma U-Pb ages from secondary monazite. In contrast to the apatite in situ Lu-Hf ages, all apatite types produce a single U-Pb age of c. 1460 Ma, demonstrating the ability of Lu-Hf to preserve a more complete history of apatite formation than U-Pb in high- to medium-temperature rock systems. The timing of mineralisation coincides with the onset of Nuna fragmentation, representing a previously unrecognised driver for mineral system formation in southern Australia that installed Cu in crust previously dehydrated during a long history of granulite-grade tectonic events. The recognition of this Cu system in rocks generally considered unprospective shows that continental breakup can rejuvenate metallic systems in otherwise unprospective crust.

Re‐Os isotope‐dilution geochronology has been widely used to date the timing of molybdenite, pyrite and chalcopyrite formation across a variety of geological settings. However, in situ methods have been impeded by the isobaric interference of 187Re on 187Os. In situ Re‐Os geochronology using LA‐ICP‐MS/MS has been shown to be a useful technique to chemically separate Os from Re, as Os reacts with CH4 to create higher‐mass reaction products, which can then be measured with minimised interference of 187Re. However, application of the method requires matrix‐matched primary reference materials, e.g., age‐homogenous molybdenite amenable to laser ablation. Here, we characterise and present two new molybdenite mineral reference materials for in situ Re‐Os geochronology by LA‐ICP‐MS/MS, verified by ID‐TIMS Re‐Os measurements. We also present case studies from molybdenite samples with varying Re mass fractions and Re‐Os age mapping. The method provides accurate and precise age data, with excellent precision for high Re samples. The benefits of the LA‐ICP‐MS/MS approach include: (1) simple sample preparation, (2) rapid data acquisition, (3) targeting of specific textural domains including growth zones and (4) the ability to simultaneously collect trace elements used to link the timing and conditions of ore‐formation.

The development of laser ablation inductively coupled plasma quadrupole tandem mass spectrometry (LA-ICP-Q-MS/MS) opens new opportunities to rapidly date a variety of hydrothermal minerals. Here we present in situ Lu-Hf and Re-Os dates for hydrothermal apatite and molybdenite, respectively. We further report the first in situ Lu-Hf dates for bastnäsite, dolomite, and siderite, and assess their potential for constraining ore deposit geochronology. For method validation, we report isotope-dilution Lu-Hf dates for apatite reference material Bamble-1 (1102 ± 5 Ma) and calcite reference material ME-1 (1531 ± 7 Ma), enabling improved accuracy on matrix-matched calibration for LA-ICP-MS/MS Lu-Hf dating. The new methods are applied to the Vulcan Iron-Oxide Copper-Gold (IOCG) prospect in the Olympic Cu-Au Province of South Australia. Such deposits have been difficult to accurately date, given the general lack of reliable mineral geochronometers that are cogenetic with IOCG mineralisation. Hydrothermal apatite Lu-Hf dates and molybdenite Re-Os dates demonstrate that mineralisation at Vulcan largely occurred at ca. 1.6 Ga, contemporaneous with the world class Olympic Dam deposit. Our data also indicates that the Lu-Hf system in apatite is more robust than the U-Pb system for determining the timing of primary apatite formation in an IOCG system. We further demonstrate that dolomite can retain Lu-Hf growth ages over an extended time period (>1.5 billion years), providing constraints on the timing of primary ore mineral crystallisation during brecciation and IOCG mineralisation. Finally, late Neoproterozoic (ca. 589–544 Ma) and Carboniferous (ca. 334 ± 7 Ma) Lu-Hf dates were obtained for texturally late Cu-bearing carbonate veins, illustrating that the carbonate Lu-Hf method allows direct dating of Cu remobilisation events. This has important implications for mineral exploration as the remobilised Cu may have been transferred to younger deposits hosted in Neoproterozoic sedimentary basins overlaying the Olympic IOCG province.

On the anoxic Archean Earth, prior to the onset of oxidative weathering, electron acceptors were relatively scarce, perhaps limiting microbial productivity. An important metabolite may have been sulfate produced during the photolysis of volcanogenic SO2 gas. Multiple sulfur isotope data can be used to track this sulfur source, and indeed this record indicates SO2 photolysis dating back to at least 3.7 Ga, that is, as far back as proposed evidence of life on Earth. However, measurements of multiple sulfur isotopes in some key strata from that time can be challenging due to low sulfur concentrations. Some studies have overcome this challenge with NanoSIMS or optimized gas-source mass spectrometry techniques, but those instruments are not readily accessible. Here, we applied an aqua regia leaching protocol to extract small amounts of sulfur from whole rocks for analyses of multiple sulfur isotopes by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Measurements of standards and replicates demonstrate good precision and accuracy. We applied this technique to meta-sedimentary rocks with putative biosignatures from the Eoarchean Isua Supracrustal Belt (ISB, >3.7 Ga) and found positive ∆33S (1.40-1.80‰) in four meta-turbidites and negative ∆33S (-0.80‰ and -0.66‰) in two meta-carbonates. Two meta-basalts do not display significant mass-independent fractionation (MIF, -0.01‰ and 0.16‰). In situ Re-Os dating on a molybdenite vein hosted in the meta-turbidites identifies an early ca. 3.7 Ga hydrothermal phase, and in situ Rb-Sr dating of micas in the meta-carbonates suggests metamorphism affected the rocks at ca. 2.2 and 1.7 Ga. We discuss alteration mechanisms and conclude that there is most likely a primary MIF-bearing phase in these meta-sediments. Our new method is therefore a useful addition to the geochemical toolbox, and it confirms that organisms at that time, if present, may indeed have been fed by volcanic nutrients.

Sedimentary rocks can provide important insights regarding the evolution of Earth's surface environments through deep time. Such sequences are pervasive through the geological record and currently cover >70% of the planet's surface. They are also a key repository for energy and mineral resources. However, absolute chronology of sedimentary rocks can be difficult to constrain using conventional methods due to their typically low abundances of radiogenic elements. Establishing chronology is particularly challenging for Precambrian sedimentary rocks, where the lack of a diverse fossil record makes biostratigraphic correlations ambiguous. In this study, we use shale and carbonate samples from the Proterozoic greater McArthur Basin in northern Australia as a case study to demonstrate two emerging in-situ laser-based methods that have the potential to quickly and accurately resolve the minimum depositional age of a sedimentary package. The first method provides a tool to constrain the formation of authigenic clay minerals in shales using in-situ laser ablation RbSr geochronology. The second method demonstrates an approach for dating carbonate sedimentation using UPb geochronology via a laser isotopic mapping approach. Laser rasters are compiled into isotopic maps, and this spatial and geochemical information is used to target representative subdomains within the sample. Detrital or altered regions can be avoided by monitoring chemical signatures and pixels, and to the most authigenic domains are then subdivided that give the best spread of data on an isochron. Both approaches provide the key advantage of preserving, and through the mapping approach further resolving, sample petrographic context, which together with complementary geochemical data can be triaged to yield a more appropriate age and interpretation.

The George Fisher and Hilton Zn-Pb-Ag deposits are located approximately 20 km north of Mount Isa. Although previous workers have noted the existence of a dolerite dyke at the Hilton Zn-Pb-Ag deposit (Valenta, 1994b; Valenta, 1994a), a dolerite dyke at the George Fisher Zn-Pb-Ag deposit has not been previously documented. Progressive underground expansion at the George Fisher mine has resulted in the discovery of a dolerite dyke in the southernmost portion of the deposit. The temporal and petrological relationship between the dolerite dykes and the adjacent Zn-Pb-Ag mineralisation at the George Fisher and Hilton Zn-Pb-Ag deposits has not been considered by previous studies, and has significant implications for the currently accepted syn-diagenetic metallogenic model. In assay data, the dolerite dykes correspond with a large spike in TiO2 and V values. In drill core, the dolerite dykes occur as a light grey to grey-brown coloured rock that is commonly overprinted along its margins by Zn-Pb-Ag mineralisation. In-situ U-Pb geochronology performed on igneous apatite produce a lower intercept age of 1611 & PLUSMN; 21 Ma (MSWD = 0.93) and 1619 & PLUSMN; 22 Ma (MSWD = 0.53) for the dolerite dykes at the George Fisher and Hilton deposits, respectively. This age is consistent with dyke intrusion during the earliest phases of deformation during the (1620-1500 Ma) Isan Orogeny. The dolerite dykes have experienced multiple stages of post-emplacement hydrothermal alteration/veining, which have paragenetic equivalents in the adjacent Zn-Pb-Ag orebodies. The hydrothermal stages include: (1) Quartz & PLUSMN; albite & PLUSMN;K-feldspar alteration/veining; (2) Dolomite alteration/veining; (3) Biotite-chlorite-sulphide alteration; (4) Paragenetically late calcite, dolomite and/or sulphide veining. Monazite from a quartz & PLUSMN; albite & PLUSMN;K-feldspar vein in the Hilton dyke produces a lower intercept age of 1513 & PLUSMN; 16 Ma (MSWD = 1.1), constraining the maximum age of alteration within the dolerite dykes. To assess the timing of alteration in the adjacent George Fisher Zn-Pb-Ag deposit, in-situ Lu-Hf geochronology was performed on pre-mineralisation calcite from a section of stratabound Zn-Pb-Ag mineralisation, and a paragenetically late cross-cutting sphalerite-calcite vein. Calcite from the pre-mineralisation alteration assemblage produces a Lu-Hf age of 1501 & PLUSMN; 32 Ma (MSWD = 1.04), which is interpreted to constrain the maximum age of stratabound Zn-Pb-Ag mineralisation. Calcite from the late cross-cutting vein produced a Lu-Hf age of 1289 & PLUSMN; 26 Ma (MSWD = 1.00), which is interpreted to constrain the age of postmineralisation faulting throughout the deposit. The evidence presented in this study indicates that the dolerite dykes intruded during the early Isan Orogeny at ca. 1620 Ma, and experienced subsequent hydrothermal alteration during D3 of the Isan Orogeny coeval with Zn-Pb-Ag mineralisation.

Mafic rocks are the most common type of igneous rocks on Earth, however, constraining the crystallization age of mafic rocks can be challenging. Apatite is a common accessory phase in mafic rocks and is amenable to dating using the U-Pb system. However, the U-Pb system in apatite has a relatively low closure temperature (-350 degrees- 550 degrees C) and is therefore prone to resetting by later thermal and metasomatic events. Here, a recently developed Lu-Hf dating method using laser ablation reaction-cell mass spectrometry is applied to apatite from mafic rocks. The Lu-Hf system in apatite has a higher closure temperature (-650 degrees -750 degrees C) compared to U-Pb, increasing the chances of obtaining primary crystallization ages. Furthermore, the laser-ablation method allows rapid data collection compared to traditional solution-based Lu-Hf dating techniques. Four study areas were selected to compare the Lu-Hf vs U-Pb systematics of apatite in mafic igneous rocks: the Paleoproterozoic Sudbury Igneous Complex (Canada), the Neoproterozoic Borborema Province (NE Brazil), the Paleoproterozoic Fennoscandian Shield (Finland), the Archean Yilgarn Craton and adjacent Mesoproterozoic Albany Fraser Orogen (Western Australia). For all analyzed samples that have apatite trace element compositions typical of an undisturbed primary mafic igneous lithology, the Lu-Hf system retains primary igneous apatite crystallization ages, whereas the U-Pb system in the same grains often records isotopic disturbance or a cooling age. In few cases, the Lu-Hf system has also been disturbed in response to recrystallization, however, such disturbance is readily detected with trace element data. Hence, this study demonstrates the potential of laser ablation apatite Lu-Hf dating to obtain primary crystallization ages for otherwise difficult to date mafic rocks.

Recent advances in laser ablation reaction-cell mass spectrometry have opened the possibility for rapid and efficient Lu-Hf age dating of a variety of minerals. Of particular interest is the important metamor-phic mineral, garnet, which is traditionally dated using solution-based Lu-Hf or Sm-Nd methods that are time consuming and often lack micron scale spatial resolution. In this study, we analyse garnets from samples from the 'Moine Supergroup' Scotland with the novel laser ablation inductively coupled quadru-pole tandem mass spectrometry (LA-ICP-Q-MS/MS) Lu-Hf dating method, aiming to reveal terrane scale geochronological information in polymetamorphic rocks. We demonstrate that laser ablation Lu-Hf dat -ing of garnet can accurately reveal the timing of different metamorphic events within single multi-growth garnets with precision typically as low as-1.5% (2r, including systematic uncertainties). Garnets analysed from our samples produced dates including 957 +/- 33 Ma, corresponding to the Renlandian Orogeny, 808 +/- 14 Ma, corresponding to the Knoydartian Orogeny, and 471 +/- 8 Ma, corre-sponding to the Caledonian Orogeny; all events which have previously been recorded from this rock suite. Furthermore, laser ablation Lu-Hf dating of garnet can provide insight into micron-scale processes such as Lu diffusion and garnet recrystallization. We recommend a series of sequential protocols, from sample selection through to laser ablation analysis, which should be used to maximize the likelihood of producing well constrained garnet Lu-Hf dates.(c) 2023 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Abstract Recent developments in laser-ablation Lu–Hf dating have opened a new opportunity to rapidly obtain apatite ages that are potentially more robust to isotopic resetting compared to traditional U–Pb dating. However, the robustness of the apatite Lu–Hf system has not been systematically examined. To address this knowledge gap, we conducted four case studies to determine the resistivity of the apatite Lu–Hf system compared to the zircon and apatite U–Pb system. In all cases, the apatite U–Pb system records a secondary (metamorphic or metasomatic) overprint. The apatite Lu–Hf system, however, preserves primary crystallization ages in unfoliated granitoids at temperatures of at least c. 660°C. Above c. 730°C, the Lu–Hf system records isotopic resetting by volume diffusion. Hence, in our observations for apatites of ‘typical’ grain sizes in granitoids ( c. 0.01–0.03 mm 2 ), the closure temperature of the Lu–Hf system is between c. 660 and c. 730°C, consistent with theoretical calculations. In foliated granites, the Lu–Hf system records the timing of recrystallization, while the apatite U–Pb system tends to record younger cooling ages. We also present apatite Lu–Hf dates for lower crustal xenoliths erupted with young alkali basalts, demonstrating that the Lu–Hf system can retain a memory of primary ages when exposed to magmatic temperatures for a relatively short duration. Hence, the apatite Lu–Hf system is a new insightful addition to traditional zircon (or monazite) U–Pb dating, particularly when zircons/monazites are absent or difficult to interpret due to inheritance or when U and Pb isotopes display open system behaviour. The laser-ablation-based Lu–Hf method allows campaign-style studies to be conducted at a similar rate to U–Pb studies, opening new opportunities for magmatic and metamorphic studies.

Laser ablation Lu-Hf dating using reaction-cell massspectrometry [1] has recently been demonstrated on garnet [2,3] , apatite [4,5] and calcite [6] and allows to rapidly obtain primary age constraints on the timing of igneous, metamorphic and hydrothermal processes.Here, we present new method developments and applications, including the first ever Lu-Hf dates for (hydrothermal) fluorite, dolomite and epidote (at ~1-2% 2σ uncertainty for Proterozoic samples, <3% 2σ uncertainty for Palaeozoic samples).Our results illustrate great potential of the in situ method to rapidly age constrain mineralizing fluid flow events, including remobilization of metals from basement towards strata-bound deposits.In addition, we have systematically investigated the Lu-Hf systematics of apatite, confirming theoretical calculations of a closure temperature of ~660 -730 °C for volume diffusion in typical apatite grain sizes (~0.01 -0.03 mm 2 ).The U-Pb dates are all systematically younger than the Lu-Hf dates, suggesting Lu-Hf dating is a superior method to obtain primary apatite crystallization ages.However, in strongly foliated rocks, the Lu-Hf system dates the timing of apatite recrystallization.Finally, we present long-term multi-session Lu-Hf results for new Lu-rich (up to 1 wt%) garnet reference material candidates, sourced from the Norwegian Tørdal pegmatites.For these garnets, isochron and weighted mean age uncertainties can be as low as 0.3% (2σ), but analysis needs to be conducted in analogue detector mode.We will discuss strategies for P/A corrections when analysing standards and samples in different detector modes within the same analytical session.

Detrital geochronology employing the widely-used zircon U-Pb proxy is biased toward igneous events and metamorphic anatexis; additionally, zircon is highly refractory and frequently polycyclic. Garnet, a rock-forming and thus commonly occurring mineral, is predominantly metamorphic and much less refractory. Here, we report in situ U-Pb and Lu-Hf ages from detrital garnet hosted in ancient and modern sediments of the European Alps. Both geochronometers are biased toward the most recent garnet-crystallizing metamorphic event in the source area, with fewer inherited ages. This likely reflects efficient removal of inherited garnet during diagenesis and metamorphism, and is in contrast to detrital zircon, apatite, and rutile U-Pb data, which largely record pre-Alpine ages. Neither the U-Pb nor Lu-Hf system in garnet exhibits a relationship between age recovery and composition. However, the Lu-Hf system in garnet yields significantly better age recovery than the U-Pb system. Estimated initial 238U/206Pbc values at the time of crystallization are near unity, suggesting that garnet does not significantly partition U from Pb during crystallization, at least for the generally almandine-rich garnets analyzed in this study. Hence, Lu-Hf geochronology of detrital garnet offers an effective method to detect and date the most recent phase of mid-grade metamorphism in sub-anatectic source areas, in which detrital zircon U-Pb analysis may be of less utility. Mountain ranges are characterized by rapid changes in their constituent rocks as these undergo metamorphism to adjust to increasing pressure and temperature during tectonic burial. These metamorphic processes drive mineral crystallization. Once cooled, each mineral acts as a geochemical reservoir isolated from the surrounding environment. Therefore, if a mineral has incorporated a radioactive isotope during crystallization, it can be dated to constrain the timings and rates of metamorphism. As erosion ultimately converts crystalline bedrock to sediment, the geological histories of these processes are preserved in the sediment shed during erosion. Consequently, these histories can be read from sedimentary rocks in adjacent sedimentary basins. Minerals traditionally used to study the sources of these sediments, such as zircons, largely grow from molten rock rather than during metamorphism, and are tough enough to be recycled through multiple tectonic events. The mineral garnet more commonly grows under metamorphic conditions and is thus more effective at directly recording the most recent phases of significant mountain building. Here, we present uranium-lead and lutetium-hafnium ages of garnet in modern and ancient sediment from the Alps. We show that garnet preferentially records Alpine events and is thus suitable for provenance studies targeting the most recent mountain building event. Detrital garnet U-Pb and Lu-Hf ages preferentially record the most recent metamorphic event in the source areaBoth systems are less refractory than alternative detrital U-Pb geochronometersAge recovery for Lu-Hf in garnet is considerably better than for U-Pb

Figure S2. Interactive 3D version of Fig.2 from main text, using the same symbology. To open, unzip folder and launch the .xhtml file in any internet browser. Use scroll wheel to zoom, left-click and drag to rotate.Table S1. Analytical parameters for garnet U-Pb and Lu-Hf analysis.Table S2. Isotopic and trace-element data.Table S3. Raman data.