Mobile-lid tectonics is a first-order feature characterizing the modern Earth, yet its origins remain enigmatic due to a scarcity of ancient terrestrial materials. Detrital zircons provide the most complete archive of Earth's early crust and preserve the only record extending beyond ~4.0 Ga. Here, we combine U XANES oxybarometry with U-Pb and trace element analysis to investigate the igneous cores and metamorphic rims of Hadean-Archean zircon from the Jack Hills, Australia. Igneous cores record consistent, moderately oxidized magma conditions (FMQ-1 to +1), challenging notions of a highly reduced early Earth and supporting models that evoke efficient mantle convection throughout the Hadean. In contrast, redox states and trace element contents show that metamorphic rims record i) high-ƒO2 and high-intermediate T/P conditions (FMQ+1.6 to +2.5; >600 °C/GPa) and ii) low-ƒO2 and generally lower T/P conditions (FMQ-0.2 to +0.5; <500 °C/GPa). While only high T/P conditions are observed in Hadean zircon rims, Archean rims (~3.35 Ga) preserve both the low and high T/P signatures, a pattern typical of large-scale plate underthrusting. These findings imply Earth's mantle had near-modern redox states by 4.15 Ga and that mobile-lid tectonics was active by the early Archean, at the latest.

Removal of mafic-ultramafic lower crust (e.g., via delamination) is fundamental to making andesitic continental crust, yet direct evidence of this process remains elusive. A unique suite of garnet clinopyroxenite and hornblendite (arclogite) xenoliths from the northern volcanic zone of the Andes, erupted to the surface in the middle Pleistocene, have bulk-rock geochemistry and osmium (Os) isotopic compositions that demonstrate their crustal affinity, yet have equilibration pressures and temperatures below the arc Mohorovičić discontinuity (∼53 km) and some as deep as within the sub-arc mantle wedge (∼105 km). Garnet websterites from the same xenolith suite, sourced from depths approaching the Wadati-Benioff zone (∼140 km), have elemental and isotopic compositions indicative of a mantle origin, likely formed as products of peridotite-liquid reactions above the subducting slab. Variability in bulk-rock 143Nd/144Nd values and garnet oxygen isotope ratios (δ18O) for these samples is attributed to minor assimilation of subducted components and/or older crustal material, but assimilation alone cannot account for the highly radiogenic Os isotopic compositions. These results provide direct petrologic evidence for modern arclogite formation and foundering in the Andean orogen, the archetypal active continental subduction system. Elevated 187Os/188Os values of Mercaderes arclogites imply that recycling of gravitationally unstable arc cumulates during continental crust formation introduces highly radiogenic Os into the convective mantle, which has implications for mass fluxes across the crust-mantle boundary as well as the sources and evolution of mantle heterogeneity as seen in orogenic peridotite massifs and in the sources of oceanic basalts.

A megacryst zircon from Brazil, referred to here as Peixe#0, was evaluated as a potential reference material for LA-ICP-MS U-Pb dating. Results from multi-method characterisation - including CA-ID-TIMS, SIMS and a long-term LA-ICP-MS data set - enabled us to assess this crystal's suitability as a reference material for routine quality control in age determinations by LA-ICP-MS. Using CA-ID-TIMS, Peixe#0 yielded mean 206Pb/238U and 207Pb/235U ratios of 0.09257 +/- 0.1% and 0.7561 +/- 0.1%, respectively (precisions expressed as 2RSD), and weighted mean 206Pb/238U age of 570.85 +/- 0.30 Ma (2s, MSWD = 0.40, n = 4). With the LA-ICP-MS compiled database (2063 individual age determinations distributed over 167 sessions spanning eight years) acquired during routine analysis at the Isotope Geology Laboratory (LAGIS) at Unicamp, Brazil, we propose a 206Pb/238U weighted mean age of 569 +/- 13 Ma (2s), which includes the long-term excess variance in the total uncertainty. Oxygen isotopes presented a homogeneous distribution (delta 18OSMOW = +5.13 +/- 0.15 parts per thousand (1s)). The trace element chemical compositions varied substantially depending on the chosen cathodoluminescence zone containing distinct features. Approximately 4 g of Peixe#0 zircon are available for distribution upon request.

Titanium isotopes are used as a tracer of magmatic differentiation, crustal evolution, and sediment provenance. The Ti isotope systematics of volcanic island arc systems have been used as a model for the formation of continental crust, however, the behavior of Ti isotopes of rocks and minerals in continental arcs and plutonic differentiation sequences has not yet been closely examined. The behavior of Ti isotopes in plutonic systems may deviate from volcanic systems due to distinct mineral assemblages and differentiation histories. Consequently, island arcs may fail to capture the full spectrum of Ti isotope variability linked to the processes that generate and differentiate crust in continental arc systems. To test this hypothesis, we conducted Ti isotope measurements of five whole rocks which lie in the compositional range of 50 to 75 wt% SiO2 and their Ti-bearing minerals (titanite, biotite, hornblende, magnetite) from the geochemically well-characterized calc-alkaline Tuolumne Intrusive Complex in eastern California, USA. The whole rock samples yield delta 49Ti values that increase from +0.033 +/- 0.030 %o (95 % CI) to +0.619 +/- 0.025 %o (95 % CI). Titanite and magnetite mineral separates yield delta 49Ti values that are up to 0.37 %o lower than the whole rock, while biotite and hornblende yield delta 49Ti values that are within uncertainty of, or up to 0.25 %o higher than the whole rock. Inter-mineral Ti isotope fractionation reveals that titanite may fractionate Ti isotopes to an extent comparable with magnetite, whereas biotite and hornblende preferentially incorporate isotopically heavy Ti. The high fO2 and fH2O conditions characteristic of continental arcs can favor titanite over Fe-Ti oxides as the primary host of Ti and the fractional crystallization of the former is interpreted to be the primary driver of Ti isotope fractionation in the Tuolumne magmas. However, the petrographic relationships between titanite and other Ti-bearing phases indicates that re-equilibration of Ti among minerals in long-lived plutonic systems can lead to complex Ti isotope fractionation mechanisms. Our data shows that Ti removal and fractionation imparted by mineral crystallization for the Tuolumne system can be described with a net fractionation factor of-0.18 %o, which is congruous with calc-alkaline island arcs, despite the observation that Ti fractionation here is controlled by a different Ti phase. This investigation may provide insights into the Ti isotope systematics of ancient continental crust, where complete differentiation sequences are absent, thereby improving our ability to interpret such data.

From the Late Cretaceous to the Quaternary, the northeastern end of the Eurasian margin experienced a complicated tectono-magmatic history including the subduction of the Izanagi-Pacific ridge in the Eocene time, the opening of the Japan and Kuril basins and the associated trench migration in the Oligocene to Miocene time, the possible collision of the Eurasian plate and the North American (Okhotsk) plate around the Oligocene to Miocene time, and subduction zone magmatism in all periods. In central Hokkaido (Japan), Eocene-Miocene plutonic bodies are distributed along the north-south orientated Hidaka Magmatic Zone (HMZ). We report new zircon U-Pb ages and geochemical data from plutonic rocks in the HMZ, which reveal Miocene compositionally bimodal magmatism; the felsic magmatism present is characterized by island-arc geochemical signatures. Trace element compositions of the Miocene mafic-intermediate plutonic rocks of the HMZ appear as a mixture between typical N-MORB and island-arc compositions. Trace element profiles from HMZ plutonic rocks are similar, albeit with less pronounced arc signatures, to the Miocene volcanic rocks formed along the Paleo-Japan Trench. Together, these data suggest the coexistence and mixing of N-MORB-type primitive magma, with the parental magmas of the HMZ mafic rocks, implying petrogenesis of a different nature than typical subduction zone magmatism. The cause of the north-south orientation of the Miocene plutono-volcanic rocks from central Hokkaido to its northern extension into Russia (Sakhalin) is probably along some kind of tectonic/structural boundary. However, the inferred paleo-position of the HMZ is very close to the trench and far from the volcanic front at that time and the existence of N-MORB-type primitive magma cannot be explained by subduction magmatism. The newly proposed possible geodynamic setting in this study that can reasonably explain the distribution and geochemical signature of these rocks is the simultaneous opening of the Japan and Kuril basins at different rates. In the Japan Trench, the Pacific plate was subducted at a relatively shallow angle and the magmatic arc forcibly moved eastward due to the opening of the Japan Basin. In the Kuril Trench, the rollback corresponding to the steep subduction of the plate and the associated opening of the Kuril Trench occurred simultaneously in a short period of time. If the Paleo-Kuril Trench retreated rapidly relative to that of the Paleo-Japan Trench, a horizontal propagating tear that cuts the slab horizontally is estimated to have occurred at the bend of both trenches, together with a (vertical) slab tearing and blocky opening of the subducting oceanic plate on the Paleo-Japan Trench side. At the western margin of the Kuril Basin, the N-MORB magma and hot asthenosphere inflow induced remelting of the mantle already contaminated to various degrees at the subduction zone.

The North Volcanic Zone of the Andes is the result of an overall uniform subduction of the Nazca Plate beneath the South American Plate in Ecuador and Colombia; however, age, composition, and thickness of the continental crust and the distance between the trench and arc, among other components of this subduction system, vary significantly along this segment of the Andes (Stern, 2004). Those changes are most likely responsible for differences in the geochemical characteristics of volcanic products in different parts of the Colombian arc as discussed in Monsalve (2020). Although several works related to the isotopic geochemistry of the volcanic products have been carried out in Ecuador (Bryan et al., 2006; Chiaradia et al., 2009, references therein), there are few records of the same type of data for Colombia and those available focus on the SW part of the arc (Marín-Cerón, 2007). This study seeks to fill the gap and use this new data to elucidate processes of magma generation and differentiation currently occurring under the northern Andes. Whole rock major elements, trace elements, and 176Hf/177Hf analyses from main volcanic centers along the Colombian arc are used to track lithospheric and crustal processes of mixing, assimilation, and fractional crystallization as well as the main source materials and contributions in magma generation in the subduction zone. From a broader view, this new data helps to discuss regional comparisons of the geochemical expressions in the Andean arcs caused by different tectono-magmatic processes. Bryant, J.A., Yogodzinski, G.M., Hall, M.L., Lewicki, J.L. & Bailey, D.G. (2006). Geochemical constraints on the origin of volcanic rocks from the Andean Northern Volcanic Zone, Ecuador. Journal of Petrology, 47(6): 1147–1175.Chiaradia, M., Müntener, O., Beate, B., & Fontignie, D. (2009). Adakite-like volcanism of Ecuador: lower crust magmatic evolution and recycling. Contributions to Mineralogy and Petrology, 158, 563-588.Marín–Cerón, M.I. (2007). Major, trace element and multi–isotopic systematics of SW Colombian volcanic arc, northern Andes: Implication for the stability of carbonate–rich sediment at subduction zone and the genesis of andesite magma. Doctoral thesis, Okayama University, 140 p. Okayama, Japan.Monsalve–Bustamante, M.L. (2020). The volcanic front in Colombia: Segmentation and recent and historical activity. In: Gómez, J. & Pinilla–Pachon, A.O. (editors), The Geology of Colombia, 97–159.Stern, C.R. (2004). Active Andean volcanism: its geologic and tectonic setting. Revista geológica de Chile, 31(2), 161-206.

The Amazonian Craton is host to one of Earth's largest Proterozoic silicic large igneous provinces (SLIPs), the Orocaima SLIP (ca. 1.98 Ga). Nevertheless, the mechanism(s) responsible for this large-flux felsic magmatic event and its relationships with regional tectonics and/or mantle processes remain debated. New geochronologic and geochemical results from multiple mafic dike swarms in the Amazonian Craton, namely the Guaniamo, Rio Aro, El Manteco-Supamo, and Goboy swarms, reveal a close temporal, spatial, and geochemical association with the Orocaima SLIP. The radiating arrangement of these swarms spanning 90 degrees of arc, their strongly tholeiitic geochemical affinity, and their short-lived emplacement ca. 1.98 Ga including in regions far from any inferred subducting plate margins all strongly suggest: (1) an intraplate, plume-related origin, and (2) a radiating arrangement defining a plume center located at similar to 2.5 degrees N, 61.2 degrees W, near the SW margin of proto-Amazonia at the time and coinciding with the location of the Takutu graben. Discovery of this previously unrecognized radiating swarm array, herein grouped within a proposed Yanomami large igneous province, and its close spatial and temporal association with the Orocaima SLIP suggests a plume-triggered origin for SLIP development, thus arguing against accretionary models for the origin of the Orocaima silicic magmatic belt.

AbstractSingle crystal paleointensity (SCP) reveals that the Moon lacked a long-lived core dynamo, though mysteries remain. An episodic dynamo, seemingly recorded by some Apollo basalts, is temporally and energetically problematic. We evaluate this enigma through study of ~3.7 billion-year-old (Ga) Apollo basalts 70035 and 75035. Whole rock analyses show unrealistically high nominal magnetizations, whereas SCP indicate null fields, illustrating that the former do not record an episodic dynamo. However, deep crustal magnetic anomalies might record an early lunar dynamo. SCP studies of 3.97 Ga Apollo breccia 61016 and 4.36 Ga ferroan anorthosite 60025 also yield null values, constraining any core dynamo to the Moon’s first 140 million years. These findings suggest that traces of Earth’s Hadean atmosphere, transferred to the Moon lacking a magnetosphere, could be trapped in the buried lunar regolith, presenting an exceptional target for future exploration.