Abstract The investigation of key minerals including zircon, apatite, titanite, rutile, monazite, xenotime, allanite, baddeleyite and garnet can retain critical information about petrogenetic and geodynamic processes and may be utilized to understand complex geological histories and the dynamic evolution of the continental crust. They act as small but often robust petrochronological capsules and provide information about crustal evolution, from local processes to plate tectonics and supercontinent cycles. They offer us insights into processes of magmatism, sedimentation, metamorphism and alteration, even when the original protolith is not preserved. In situ techniques have enabled a more in-depth understanding of trace element behaviour in these minerals within their textural context. This has led to more meaningful ages for many stages of geological events. New developments of analytical procedures have further allowed us to expand our petrochronological toolbox while improving precision and accuracy. Combining multiple proxies with multiple minerals has contributed to new interpretations of the crustal history of our planet.

Abstract Detrital heavy minerals have helped address geologically complex issues such as the nature and origin of the early terrestrial crust, the growth and evolution of the continental crust, and the onset of plate tectonics, together with palaeogeographic and supercontinent cycles reconstructions. With the advent of in situ analytical techniques and a more complete understanding of trace element behaviour in rock-forming and accessory minerals, we have now at our disposal a powerful suite of tools that we can apply to multiple proxies found as detrital minerals. These can be in situ dating, trace element or isotopic tracing applied to both mineral hosts and their inclusions. We opted to showcase minerals that occur as primary minerals in a wide range of rock compositions and that can provide reliable age information. Additionally, over recent decades their chemistries have been tested as proxies to understand crustal processes. These are zircon, garnet, apatite, monazite, rutile and titanite. We include an overview and provide some approaches to overcome common biases that specifically affect these minerals. This review brings together petrological, sedimentological and geochemical considerations related to the application of these detrital minerals in crustal evolution studies, highlighting their strengths, limitations and possible future developments.

Abstract The study of magmatic and metamorphic processes is challenged by geological complexities like geochemical variations, geochronological uncertainties and the presence/absence of fluids and/or melts. However, by integrating petrographic and microstructural studies with geochronology, geochemistry and phase equilibrium diagram investigations of different key mineral phases, it is possible to reconstruct insightful pressure–temperature–deformation–time histories. Using multiple geochronometers in a rock can provide a detailed temporal account of its evolution, as these geological clocks have different closure temperatures. Given the continuous improvement of existing and new in situ analytical techniques, this contribution provides an overview of frequently utilized petrochronometers such as garnet, zircon, titanite, allanite, rutile, monazite/xenotime and apatite, by describing the geological record that each mineral can retain and explaining how to retrieve this information. These key minerals were chosen as they provide reliable age information in a variety of rock types and, when coupled with their trace element (TE) composition, form powerful tools to investigate crustal processes at different scales. This review recommends best applications for each petrochronometer, highlights limitations to be aware of and discusses future perspectives. Finally, this contribution underscores the importance of integrating information retrieved by multi-petrochronometer studies to gain an in-depth understanding of complex thermal and deformation crustal processes.

Abstract Rutile is an important accessory mineral in metamorphic rocks and is used as a geothermobarometer or geochronometer. This study aims to bridge the gap between diffusion studies in simplified and complex natural systems by investigating the incorporation and mobility of Al in natural rutile and its high-pressure polymorph TiO 2 (II). Experiments were performed at 0.1 MPa to 7 GPa, 1223–1373 K, at buffered μ(Al 2 O 3 ) and with f O 2 constrained to ≤CCO, which is the equilibrium between graphite and a CO-CO 2 gas phase. Based on electron probe microanalysis, secondary ion mass spectrometry and Fourier transform infrared analyses, we suggest a complex combination of mechanisms to explain the incorporation of Al and H in natural rutile and TiO 2 (II). This includes: (1) the incorporation of Al 3+ on octahedral Ti-sites charge balanced by the formation of oxygen vacancies; and (2) the incorporation of oxygen in interstitial positions charge balanced by hydrogen interstitials. Determined Al-diffusivities in natural TiO 2 are approximately eight to nine orders of magnitude faster compared to previously published data. A possible explanation includes a significantly enhanced rate of ionic diffusion through the combined effect of hydrolytic weakening, enhanced Al-diffusion through extended defects and to a minor extent oxygen fugacity variations. Consequently, results of this study question that the inferred high closure temperatures for the Al-in-rutile geothermobarometer can be applied to all natural systems.

Abstract Allanite is a major host of rare earth elements (REEs) in the continental crust. In this study, reaction mechanisms behind allanite alteration are investigated through batch experiment runs on natural allanite grains in carbonate-bearing hydrothermal fluids at 200°C, with initial acidic (pH = 4) or alkaline (pH = 8) conditions and with different aqueous ligands (120 mmol kg −1 of F, Cl, P or S). Time-series experiment runs in F-doped systems at different durations between 15 and 180 days reached a steady state at 120 days. The pH efficiently controls the allanite alteration process, with initial high pH, alkaline conditions being more reactive (75% alteration compared with 25% under acidic conditions). The ligand also significantly influences the alteration process under initial acidic conditions with the P-doped system (70%) almost non-reactive for the Cl- and S-doped systems (<5%). In the alteration rim, REEs are mainly redistributed in REE-bearing phases either as carbonates (F-doped) or phosphates (P-doped). The relatively flat REE-normalized patterns of the recovered experimental fluids suggest a fractionation of light rare earth elements (LREEs) over heavy rare earth elements (HREEs) during the course of the alteration reactions. It is proposed that secondary REE mineral precipitation at the reaction front creates a local disequilibrium in the solution and a steep chemical gradient promoting allanite dissolution and thus its alterability.

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.

Abstract Monazite–xenotime thermometry is a potentially powerful technique for understanding the evolution of Earth systems. While a rich set of experimental and empirical datasets are available for monazite–xenotime equilibria, five different thermometric calibrations yield significantly different results, making this technique difficult to apply in practice. To clarify best practices for monazite–xenotime thermometry, a compilation of published compositional data for monazite and xenotime with independently determined pressure–temperature conditions is evaluated. For each existing thermometer, we examine how closely estimated temperatures match independent empirical temperatures and consider how best to calculate monazite end-members for each thermometer. Monazite–xenotime thermometry is applied to samples from the Northern Highlands Terrane of northern Scotland, which experienced amphibolite–upper greenschist facies metamorphism and penetrative deformation during the Scandian orogeny. Thermometry data in conjunction with U–Pb dating define relatively slow regional cooling across the Scandian thrust nappes. Thermometry data closely match quartz c -axis fabric-based deformation thermometry across the structurally lower nappes, suggesting that monazite and xenotime record the timing and temperature of penetrative deformation and shearing. The data suggest that ductile deformation in the hinterland nappes of the Scandian orogen in Scotland occurred as late as 415–410 Ma.

Abstract The Barberton Granite–Greenstone Belt remains a key location in the debate concerning the nature of Archean tectonic processes. Much work has focused on deciphering the tectonic significance of the c. 3.23 Ga metamorphism, as this has been correlated with lower geothermal gradient conditions potentially indicating Archean subduction. However, several studies also found evidence of an earlier, 3.45 Ga metamorphic episode, overprinted by the 3.23 Ga event. Here we apply in situ Pb–Pb dating and P–T modelling to a large (3 cm diameter) garnet crystal, allowing for the direct dating of the metamorphic conditions obtained from the garnet. The garnet core produced an isochron age of 3435 ± 45 Ma, corresponding to an increase in P and T evolution reaching peak conditions of at least 7 kbar and 700°C. Analyses obtained from the garnet rim give an isochron age of 3245 ± 41 Ma, corresponding to P–T conditions reaching 8–9 kbar and 700°C. The preservation of two moderate- to high-pressure events occurring 200 million years apart is consistent with lateral tectonic processes producing crustal thickening at 3.2 Ga and may also be a viable process for the earlier event.

Abstract Low concentrations of Na, Ca, K, Fe, Mg and Al in quartzite commonly prevent the crystallization of index metamorphic minerals, inhibiting the obtainability of thermobarometric calculations. Quartzite typically contains quartz, zircon and rutile; therefore, single-element thermometers, such as Zr-in-rutile, may be applied. We investigate changes in trace-element composition of rutile from quartzite through increasing metamorphic conditions. Studied samples derive from a quartzite package (Luminárias Nappe, Minas Gerais, Brazil) where previous thermobarometric constraints on metapelites showed an increasing metamorphic grade southwards, from high-pressure lower amphibolite facies (580°C; 0.9 GPa) to eclogite facies (630°C; 1.4 GPa). Rutile from the lower-grade facies samples show a large spread in Zr concentrations, with the highest values corresponding to temperature estimates higher than metamorphic conditions affecting those units, and thus interpreted as inherited detrital signatures. A narrower spread in Zr concentration is observed in rutile grains from the higher-grade facies, and estimated Zr-in-rutile temperatures agree with previous thermobarometric constraints. Therefore, we show that at 630°C, Zr contents in detrital rutile from quartzites re-equilibrate. The comparison between the quartzite- and metapelite-hosting rutile grains from the same area shows that the resetting of the geothermometer in the latter seems to occur at slightly lower temperatures (∼50°C lower).

Abstract In the Saxothuringian Zone, a unique assemblage of high- to ultra-high-pressure and ultra-high-temperature metamorphic units is associated with medium- to low-pressure and temperature rocks. The units were studied in a campaign with garnet and monazite petrochronology of gneisses, micaschists and phyllites, and monazite dating in granites. P–T path segments of garnet crystallization were reconstructed by geothermobarometry and interpreted in terms of the monazite stability field, EPMA Th–U–Pb monazite ages and garnet Y + HREE zonations. One can recognize (1) Cambrian plutonism (512–503 Ma) with contact metamorphism in the Münchberg Massif. Subordinate monazite populations may indicate a (2) widespread but weak Silurian (444–418 Ma) thermal event. A (3) Devonian (389–360 Ma) high-pressure metamorphism prevails in the Münchberg and Frankenberg massifs. In the ultra-high-pressure and high-pressure units of the Erzgebirge the predominant (4) Carboniferous (336–327 Ma) monazites crystallized at the decompression paths. In the Saxonian Granulite Massif, prograde–retrograde P–T paths of cordierite-garnet gneisses can be related to monazite ages from 339 to 317 Ma. A (5) local hydrothermal overprint at 313–302 Ma coincides partly with post-tectonic (345–307 Ma) granite intrusions. Such diverse monazite age pattern and P–T time paths characterize the tectono-metamorphic evolution of each crustal segment involved in the Variscan Orogeny.

Abstract The orogenic continental crust of accretionary and collisional belts worldwide is dominated by felsic and metasedimentary rocks, which show variable responses to high-grade metamorphism. Transformation of felsic rocks is commonly limited as compared to that of the enclosed mafic rocks (including eclogites sensu stricto ), which is widely attributed to availability of H 2 O–CO 2 fluids, kinetically controlled growth of high-grade assemblages, and their preferential preservation in metabasites more competent to rehydration. We report on the results of studies of the geochemical behaviour of zircon (trace-element, U–Pb, Lu–Hf and δ 18 O) in three felsic samples (two metagranitoids and one paragneiss), which are spatially (geographically and at the outcrop-scale) juxtaposed with mafic eclogites within the North Muya block (Neoproterozoic Baikalides, northern Central Asian Orogenic Belt). The data imply that metagranitoids and metasediments within the buried continental lithosphere might follow a single subduction-related P – T – t trend, whereas contrasting degrees of mineralogical and zircon transformation were governed by mineral buffer reactions in the absence of external fluids. The latter was significant only in an H 2 O-enriched protolith of metasediments. The formation of 18 O-depleted zircon recrystallization rims together with Mn enrichment of garnet rims indicate a distinct metamorphic stage without or with minor localized fluid infiltration, most likely, related to peak temperature conditions during collision.

Abstract The metamorphic conditions of the Natal Metamorphic Province (NMP) have been the focus of previous studies to assist with Rodinia reconstructions but there are limited constraints on the age of metamorphism. We use a combination of modern techniques to provide new constraints on the conditions and timing of metamorphism in the two southernmost terranes: the Mzumbe and Margate. Metamorphism reached granulite facies, 780–834°C at 3.9–7.8 kbar in the Mzumbe Terrane and 850–892°C at 5.7–6.1 kbar in the Margate Terrane. The new pressure and temperature constraints are supportive of isobaric cooling in the Margate Terrane as previously proposed. Peak metamorphism of the two terranes is shown to have occurred c. 40 myr apart, which contrasts strongly with previous assumptions of coeval metamorphism. While the age of peak metamorphism of the Margate Terrane (1032.7 ± 4.7 Ma) coincides with the tectonism and magmatism associated with the emplacement of the Oribi Gorge Suite ( c. 1050–1030 Ma), the age of metamorphism of the Mzumbe Terrane (987.4 ± 8.1 Ma) occurs c. 30–40 myr after tectonism is previously thought to have finished. We propose that models of advective cooling during transcurrent shearing can explain the metamorphic conditions and timing of the NMP.

Abstract The Central Indian Tectonic Zone (CITZ) comprises northern and southern Indian cratonic blocks and is a tectonic window that is suitable for investigating the Proterozoic crustal evolution because of the presence of a wide variety of lithologies. Geochemical and geochronological data on mafic granulites by previous workers do not ascertain the possibility of mafic protoliths and their coeval link to other CITZ units. Thus, determining the precise timing of the formation of mafic granulites may indicate a connection between metamorphism and fragmentation of the Columbian supercontinent. This study presents zircon U–Pb ages, Nd isotopes and the geochemistry of mafic granulites to evaluate their genesis and timing of metamorphism. The results show the tholeiitic affinity and primary magmatic differentiation of the parental melt. Depletion of Nb, P, Zr and Ti and positive enrichment of Ba, U and Pb indicate the derivation of mafic granulites from a variably enriched subcontinental lithospheric mantle (SCLM) source. The zircon U–Pb ages (1564 ± 8 to 1598 ± 9 Ma) are interpreted as a period of granulite-facies metamorphism. The T DM (depleted-mantle) model ages (2.9–3.4 Ga) of mafic granulites indicate the timing of mafic protolith extraction. The mineral isochron age c. 1.0 Ga indicates that these rocks underwent some events during an early Neoproterozoic period. Protolith of mafic granulites could be related to the evolution of melts derived from metasomatized SCLM through fractional crystallization processes.

Abstract The Rodinia supercontinent broke apart during the Neoproterozoic. Rodinia break-up is associated with widespread intraplate magmatism on many cratons, including the c. 720–719 Ma Franklin large igneous province (LIP) of Laurentia. Coeval magmatism has also been identified recently in Siberia and South China. This extensive magmatism terminates ∼1 myr before the onset of the Sturtian Snowball Earth. However, LIP-scale magmatism and global glaciation are probably related. U–Pb isotope dilution–thermal ionization mass spectrometry (ID-TIMS) baddeleyite dating herein identifies remnants of a new c. 724–712 Ma LIP on the eastern Kalahari Craton in southern Africa and East Antarctica: the combined Mutare–Fingeren Dyke Swarm. This dyke swarm occurs in northeastern Zimbabwe (Mutare Dyke Swarm) and western Dronning Maud Land (Fingeren Dyke Swarm). It has incompatible element-enriched mid-ocean ridge basalt-like geochemistry, suggesting an asthenospheric mantle source for the LIP. The Mutare–Fingeren LIP probably formed during rifting. This rifting would have occurred almost ∼100 myr earlier than previous estimates in eastern Kalahari. The placement of Kalahari against southeastern Laurentia in Rodinia is also questioned. Proposed alternatives, invoking linking terranes between Kalahari and southwestern Laurentia or close to northwestern Laurentia, also present challenges with no discernible resolution. Nevertheless, LIP-scale magmatism being responsible for the Sturtian Snowball Earth significantly increases.

Abstract An U–Pb isotopic investigation combined with rare earth element data for titanites, zircons and coexisting accessories has been undertaken to gain insight into the formation of the Archean peralkaline granites of the northeastern Fennoscandian Shield and to test the stability of titanite during metamorphic and hydrothermal processes. The obtained set of isotope data shows that whereas more stable zircon retains a memory of the major episodes of granite evolution, the coexisting titanite provides additional information on crystallization, subsequent growth, cooling and alteration of the plutonic complexes. In addition to titanites formed at the magmatic stages of c. 2710 and c. 2650 Ma, the peralkaline granites contain titanite populations which have undergone major resetting at c. 1870 Ma during the burial metamorphism related to the Svecofennian orogeny and the 1760 Ma hydrothermal alteration near contemporaneous with regional metamorphism of c. 1780 Ma. The peralkaline granites which contain c. 2710 Ma titanites also include inherited titanite grains of an age of 2795 Ma. These data support the concept that the titanite can remain a closed system to Pb diffusion at temperatures of peralkaline granite melt (<800°C) as long as the crystals escape magmatic or metamorphic recrystallization.

Abstract Continental arcs are key sites of granitic magmatism, yet details of the origins of these magmas, including the role and contribution of mafic magma, the timing and location of initial zircon formation and how zircon isotopic signatures relate to granite formation, remain as challenges. Here we use U–Pb dating, trace elements and Hf isotopic systematics of zircon in mafic microgranular enclaves (MMEs), from the convergent plate margin Satkatbong diorite (SKD) in Korea to understand lower arc magmatism and zircon production. The host granitic body and MMEs display similar major element evolutionary trends and similar ranges of Sr, Nd and Hf isotopes, implying a cognatic relationship. Zircons show a large variability in ε Hf ( t ) ( c. 6 units) and age (>30 Ma). We propose that the SKD and MMEs originated from the same, long-lasting, lower crustal mush reservoir, enabling long and variable residence times for zircons. Prolonged zircon ages, combined with the Hf isotope variability within a single pluton (SKD and its MME), indicate that not all zircons were instantaneously crystallized in a rapidly cooling shallow magma chamber but were continuously formed in a long-lasting hot source. A low-melt-fraction mush type reservoir in a deep crustal hot zone provides a viable model for the source setting. Continuous replenishment of mafic magmas acts as the main re-activator of the reservoir, and provide a critical role in spawning zircons that record a long age span, because (1) the magma adds Zr into the reservoir, enabling it to reach zircon saturation and (2) the generated zircon grains are transported upward as antecrysts by flow inside of the reservoir. This means that antecrysts with different ages may mix with each other in the ascending magma body. The significance of this model is that a conclusive time of intrusion cannot be constrained by such zircon ages, as these antecrysts constitute inherited grains.

Abstract Different mineral clocks in granite can provide age information reflecting various aspects of rock formation, including cooling or post-emplacement fluid–rock interaction. However, the dating tool chosen can yield inconclusive age information due to differences in closure temperatures and susceptibility to fluid alteration among chronometers. This has led to an inferred superiority of U–Pb in zircon over U–Pb in monazite or Rb–Sr in mica. Here, we investigate age systematics using Rb–Sr biotite grains, U–Pb in monazite and zircon in a Devonian granite from Australia. Single-grain laser ablation ICP-MS/MS biotite analyses are combined with zircon–monazite U–Pb ages and trace element systematics. Textural and trace element evidence combined with age systematics reveals a Rb–Sr closure age of c. 360–330 Ma relative to a putative 364 Ma emplacement age, suggesting hydrothermal alteration of the granite. Trace element systematics and magnetic susceptibility in biotite grains reflect their partial chemical reset and fluid overprint in the granite. However, similar systematics are also observed for zircon and monazite. Our multiple chronometer dating approach, studied with modern laser-ablation methods, highlights the need for detailed investigation of isotope and trace element systematics in single grains and that individual ages should be used cautiously when dating altered granitoids.

Abstract Sumatra is located at the western end of the Sunda Arc, which resulted from the subduction of the Indo-Australian Plate beneath the Eurasian Plate. In this study, we report detailed zircon U–Pb and Hf isotope data for Cenozoic igneous rocks from the entire island of Sumatra to better constrain the temporal and spatial distribution of arc magmatism. The new dataset, combined with literature information, identifies the following two magmatic stages: (1) Paleocene to Early Eocene (66–48 Ma) and (2) Early Miocene to Recent (23–0 Ma), with a 25 myr-long period of magmatic quiescence in between. The magmatic zircons show predominantly positive and high ε Hf ( t ) values, ranging from +19.4 to +7.1 in western Sumatra, +17.1 to +1.6 in central Sumatra and +18.0 to +7.0 in eastern Sumatra, indicating an isotopically juvenile magma source in the mantle wedge along the western Sunda Arc. We explain the negative and low ε Hf ( t ) values (+0.5 to −13.1) of young samples around the supervolcano Toba as evidence for the subduction of sediment. We argue for a change in the subduction processes, where the first magmatic stage ceased owing to the termination of the Neo-Tethyan subduction and the following stage corresponded to the modern Sunda subduction.