Plate Reorganization Research Articles

Reviewing the geochemistry and petrology of the subcordilleran plutonic belt, early Jurassic magmatic arc in northern Patagonia

The Subcordilleran Plutonic Belt, formed in Early Jurassic times, is a short-lived batholith that developed during Gondwana dismembering. In our study, we analyzed both well-known and potential new localities of the belt of plutonic rocks, considering new whole-rock geochemical data as well as data from the literature. Additionally, new geochemical data from five samples and one U-Pb zircon date are presented from the diorites and granodiorites from the Cerro Catedral, at Bariloche (41°S). The obtained U-Pb age in zircon is Early Jurassic (192 ± 1.5 Ma).The granitoids of the Subcordilleran Plutonic Belt are calc-alkaline, of medium to high potassium. They exhibit similar alkali content than the granitoids of the Middle Jurassic-Cretaceous Patagonian Batholith, and lower alkalis than the volcanic and plutonic rocks of the Jurassic Chon Aike Silicic Large Igneous Province. These findings suggest that the Subcordilleran Plutonic Belt represents, in the region comprised within 39° and 45° S, an early stage of the Andean arc. Our observations indicate that while some granitoids in potential localities, such as Cerro Catedral, can now belong to the Subcordilleran Plutonic Belt, other sites, like Pilcaniyeu and Pilahue, may be associated with the plutonic facies of the Chon Aike Province.The Subcordilleran Plutonic Belt is an example of arc magmatism that developed during a period of major plate reorganization, along with the subduction of mature sea floor beneath the Gondwana margin, and the latter promoted slab roll-back processes and a subduction with extension tectonic regime.

Significant variations in the structure and composition of the crust beneath northwestern India: Imprints of magmatism

Northwestern India was affected by the Neoproterozoic Malani and Erinpura magmatism, Cretaceous rifting, and magmatism associated with the Deccan precursors. Receiver function analysis was done using 1704 RFs from 18 stations to image and decipher the imprints of the magmatic events and comprehend the crustal modifications in terms of variations in structure and composition. The H-κ grid search and neighbourhood inversion techniques are used to retrieve the crustal structure and Vp/Vs ratios (κ). The study reveals significant variations in the crustal thickness (H = 34 km to 43 km), composition (κ=1.74 to 1.92) and shear wave velocity structure across northwestern India. The terrains encompassing the Erinpura granite and the Malani igneous suite in the vicinity of the Barmer rift are characterized by a thick (H ≥ 41 km) crust with felsic to intermediate composition (κ ≤ 1.81). The crust beneath the southern part of the Marwar basin is ≈ 38–40 km thick with mafic composition (κ> 1.81). The region around the Barmer rift has a thin crust (H = 34–36 km) with intermediate to mafic composition. The region hosting the Early Cretaceous to Paleogene alkaline complexes exhibits a high Vp/Vs ratio (κ= 1.91) that may be associated with mafic cumulates emplaced by magmatic events that overprint the signatures of the Malani event. The crust is heterogeneous with low/high velocity intracrustal layers that reflect the fractionation of magma at different depths. The mafic residue, together with magmatic intrusions, results in a mafic lowermost crust with high shear velocities of 3.9–4.0 km/s beneath most stations. Overall, northwestern India is characterized by a thick crust with intermediate crustal composition and intracrustal layering resulting from large scale magmatic events linked to the Neoproterozoic reorganization of plates and younger magmatic events.

The Role of Slab Remnants in Modulating Free Subduction Dynamics: A 3‐D Spherical Numerical Study

AbstractSeismic tomography of Earth's mantle images abundant slab remnants, often located in close proximity to active subduction systems. The impact of such remnants on the dynamics of subduction remains underexplored. Here, we use simulations of multi‐material free subduction in a 3‐D spherical shell geometry to examine the interaction between visco‐plastic slabs and remnants that are positioned above, within and below the mantle transition zone. Depending on their size, negatively buoyant remnants can set up mantle flow of similar strength and length scales as that due to active subduction. As such, we find that remnants located within a few hundred km from a slab tip can locally enhance sinking by up to a factor 2. Remnant location influences trench motion: the trench advances toward a remnant positioned in the mantle wedge region, whereas remnants in the sub‐slab region enhance trench retreat. These motions aid in rotating the subducting slab and remnant toward each other, reducing the distance between them, and further enhancing the positive interaction of their mantle flow fields. In this process, the trench develops along‐strike variations in shape that are dependent on the remnant's location. Slab‐remnant interactions may explain the poor correlation between subducting plate velocities and subducting plate age found in recent plate tectonic reconstructions. Our results imply that slab‐remnant interactions affect the evolution of subducting slabs and trench geometry. Remnant‐induced downwelling may also anchor and sustain subduction systems, facilitate subduction initiation, and contribute to plate reorganization events.

Time constraint on global-scale plate reorganizations using records of continental deformation

ABSTRACT Seafloor fabric indicators are the main features used for dating global-scale plate reorganizations. However, the lack of oceanic crusts older than 200 Ma limits their application only to the Mesozoic and Cenozoic eras. Furthermore, in cases such as the mid-Cretaceous time when reversals in Earth’s magnetic field did not occur, the plate reorganization ages obtained from seafloor fabric indicators are imprecise. I propose the record of continental deformation as an alternative approach for dating these events. A compilation of cooling/deformation, migmatization, and unconformity ages recorded around the globe collectively indicates that continental deformation associated with the mid-Cretaceous plate reorganization culminated at 107 Ma. This age strongly correlates with ages obtained from other data such as palaeomagnetic poles. Considering that the deformational features similar to which are compiled in this study appear to be temporally correlated with other reorganization events, the record of globally distributed continental deformation might be used for other reorganization events whose timing is poorly constrained.

New geochemical and geochronological insights on forearc magmatism across the Sanak-Baranof belt, southern Alaska: A tale of two belts

Abstract The Sanak-Baranof belt includes a series of near-trench plutons that intrude the outboard Chugach–Prince William terrane over ~2200 km along the southern Alaskan margin. We present new petrological, geochronological, and geochemical data for comagmatic microgranitoid enclaves and granitoid rocks from the Crawfish Inlet (ca. 53–47 Ma) and Krestof Island (ca. 52 Ma) plutons on Baranof and Krestof Islands, as well as the Mount Stamy (ca. 51 Ma) and Mount Draper (ca. 54–53 Ma) plutons and associated mafic rocks that intrude the Boundary block at Nunatak Fiord near Yakutat, Alaska, USA. These data suggest that intrusion of the Sanak-Baranof belt plutons is actually a tale of two distinct belts: a western belt with crystallization ages that young systematically from west to east (63–56 Ma) and an eastern belt with crystallization ages ranging from 55 to 47 Ma, but with no clear age progression along the margin. Hf isotope analyses of magmatic zircon from the western Sanak-Baranof belt become increasingly evolved toward the east with εHft = 9.3 ± 0.7 on Sanak Island versus εHft = 5.1 ± 0.5 for the Hive Island pluton in Resurrection Bay. The Hf isotope ratios of eastern Sanak-Baranof belt rocks also vary systematically with age but in reverse, with more evolved ratios in the oldest plutons (εHft = +4.7 ± 0.7) and more primitive ratios in the youngest plutons (εHft = +13.7 ± 0.7). We propose that these findings indicate distinct modes of origin and emplacement histories for the western and eastern segments of the Sanak-Baranof belt, and that the petrogenesis of eastern Sanak-Baranof belt plutons (emplaced subsequent to 57–55 Ma) was associated with an increasing mantle component supplied to the youngest eastern Sanak-Baranof belt magmas. These plutons reveal important information about offshore plate geometries and a dynamic period of plate reorganization ca. 57–55 Ma, but a clearer picture of the tectonic setting that facilitated these Sanak-Baranof belt intrusions cannot be resolved until the magnitude and significance of lateral translation of the Chugach–Prince William terrane are better understood.

Revisiting Ediacaran to early Cambrian depositional history of western North China: did it remain passive until the mid-Paleozoic?

Whether the North China Block (NCB) remained in extension from its cratonization to the mid-Paleozoic is questionable. Here, we conduct a synthesis of zircon U–Pb data of Statherian–Ordovician sandstones to provide a historical review of provenance changes in the western NCB through time. In contrast to typical NCB basement sources characterized by c. 2.7–1.8 Ga ages with spectral peaks at c. 2.5 and 1.9 Ga during much of c. 1.8–0.45 Ga, Ediacaran to Cambrian Stage 3 succussions contain abundant zircons with Meso- to Neoproterozoic ages. The exotic provenance, further verified by southeastward palaeo-flow, implies sources from the western Bainaimiao arc terrane (BAT), where basement rocks with suitable ages exist. Hence, the BAT should have evolved at the NCB margin before c. 0.56 Ga, but after rifting of the NCB (until c. 773 Ma). This event led to a craton-wide stratigraphic break during the Mesoproterozoic–Ediacaran. The presence of 521–515 Ma detrital zircons in Cambrian Stage 3 strata indicates subduction onset of the Palaeo-Asian Ocean before c. 515 Ma, coincident with the Precambrian–Cambrian boundary paraconformity. A sequence of depositional shifts triggered by the tectonic activities of the BAT unveils a complicated plate reorganization history of the northern NCB, contesting the view that the NCB remained passive from the Statherian. Supplementary material : Figures S1, S2 and Tables S1 and S2 are available at https://doi.org/10.6084/m9.figshare.c.7040743

Arc-arc amalgamation during accretionary orogenesis: Insights from mid-Paleozoic tectono-magmatic records in eastern Junggar, NW China

Abstract Arc-arc amalgamation occurs during the evolution of composite orogens at convergent plate margins and plays a critical role in controlling accretionary patterns and processes. The eastern Junggar terrane in the southern Central Asian Orogenic Belt underwent a long-lived subduction-accretion process in the Paleozoic, but whether and how the Yemaquan and Dananhu-Harlik arcs were amalgamated remain debatable. A systematic U-Pb–Hf-O isotopic study was conducted on zircons from Silurian granitic rocks in the Yemaquan arc. The U-Pb dating results suggest that these rocks were emplaced at 433–422 Ma and inherited abundant 536–435 Ma zircons representing a predominant magmatic episode in the Yemaquan arc. Their positive εHf(t) values and young Hf model ages indicate that the Yemaquan arc is dominated by juvenile basement with significant crustal growth during the Neoproterozoic to early Paleozoic. The variations in zircon Eu/Eu*, εHf(t), and δ18O values reveal that the Yemaquan arc experienced remarkable crustal thickening and remobilization at ca. 450 Ma, similar to the northern Dananhu-Harlik arc, and this was followed by extension that initiated at ca. 420 Ma. These features support the amalgamation of these two arcs occurring ca. 450–420 Ma. Integrated with regional data, we correlated this amalgamation event in the eastern Junggar terrane with the orogenic event in the Chinese Altai terrane, and we propose a middle Paleozoic tectonic evolution model in the eastern Junggar–Altai area from arc assembly to dispersal in association with a transition in accretionary mode. This scenario probably took place as a response to plate reorganization during the breakup of the northern margin of Gondwana.

Enhanced volcanic activity and long-term warmth in the middle Eocene revealed by mercury and osmium isotopes from IODP Expedition 369 Site U1514

Rapid plate reorganization may have influenced global climate during the Eocene; however, its linkage remains poorly constrained, particularly during the middle Eocene. To elucidate this tectonic–climatic relationship, here, we conducted a comprehensive analysis based on high-resolution mercury (Hg) and osmium (Os) abundance and isotope data obtained from the complete Eocene sedimentary sequence of Site U1514, drilled in the Mentelle Basin off southwest Australia. The Hg signals in this sedimentary sequence, which are characterized by significantly high enrichment and insignificant mass-independent fractionation (Δ199Hg) signal, confirm that the middle Eocene (∼45–38 Ma) was a period of persistent, increased volcanism, accompanied by intense tectonic activity. In particular, a remarkable seafloor volcanic eruption persisted for approximately 1.5 million years (∼42.0–40.5 Ma), immediately preceding the Middle Eocene Climate Optimum (MECO). Contemporaneously, the trends toward a slightly more radiogenic seawater 187Os/188Os (Osi) composition denote the prevalence of intensified continental weathering under a warm, humid climate during the middle Eocene, a phenomenon particularly evident during the MECO. Importantly, the Hg and Os records from Site U1514 reveal the occurrence of a multi-million-year warming reversal amid the long-term Eocene cooling trend, which likely contributed to significant CO2 reduction during the late Eocene. These findings significantly enhance our understanding of Eocene climate dynamics, which are fundamentally linked to intensive tectonic-driven volcanic activity and associated continental chemical weathering.

The Conrad Rise Revisited: Eocene to Miocene Volcanism and Its Implications for Magma Sources and Tectonic Development

AbstractThe Conrad Rise (CR), located midway between Antarctica and the Southwest Indian Ridge (SWIR), remains one of the least explored submarine large igneous provinces (LIPs) in the Indian Ocean to date. Relying on only seafloor paleomagnetic records, early studies hypothesized that the formation of the CR occurred during the Late Cretaceous. Here, we present new geochemical and geochronological data, including Sr‒Nd‒Pb‒Hf isotopes and 40Ar/39Ar data. Our results indicate that the uppermost part of the CR (Ob and Lena seamounts) unexpectedly formed later than previously predicted, at approximately 40 Ma in an intraplate setting. Another small seamount north of the Ob seamount formed later, at 8.5 Ma. The isotopic composition of lava from the small seamount north of the Ob seamount overlaps with that commonly defined by the Indian plume component. Overall, the isotopic variations defined by the volcanic suite from the CR could be accounted for by a three‐component mixing model involving the common component, lower continental crust, and depleted mantle endmembers. The newly obtained 40Ar/39Ar ages imply that the CR volcanism might have been triggered by major regional plate reorganizations during the middle to late Eocene and the late Miocene, inducing the release of a small upwelling rising from the African large low‐velocity province.

Mid-Cretaceous to early Eocene Neo-Tethyan subduction records in West Sulawesi, Indonesia

Situated in the heart of the Indonesian archipelago, Sulawesi records well-developed Cenozoic magmatism, yet its Cretaceous magmatic evolution remains enigmatic. Here, we report new U-Pb-Hf isotopic data of detrital zircons from West Sulawesi, Indonesia to constrain its Cretaceous to Eocene magmatic tempo. Detrital zircons aged at ca. 105−80 Ma and ca. 70−45 Ma occur as the most dominant age populations and show high positive εHf(t) values, indicating derivation from juvenile sources with limited continental crustal contamination. Our new data, combined with available results, support the existence of an Andean-type continental margin in West Sulawesi during mid-Cretaceous to early Eocene times. Importantly, the magmatic tempo of West Sulawesi is also consistent with those of southern Lhasa (Tibet) and Sumatra (Indonesia), but contrasts with those of Paleo-Pacific subduction-related arcs in SE China, SE Vietnam, East Malaysia, and NW Borneo. Therefore, we put forward that West Sulawesi may be the southeasternmost component of the Neo-Tethyan arc system that spreads over 7500 km, from southern Tibet to SE Sundaland. Such a huge arc system with concurrent magmatic flare-ups and lulls in South Asia may have played a significant role in global-scale plate reorganization.

Nature and Origin of Magnetic Lineations Within Valdivia Bank: Ocean Plateau Formation by Complex Seafloor Spreading

AbstractValdivia Bank (VB) is a Late Cretaceous oceanic plateau formed by volcanism from the Tristan‐Gough hotspot at the Mid‐Atlantic Ridge (MAR). To better understand its origin and evolution, magnetic data were used to generate a magnetic anomaly grid, which was inverted to determine crustal magnetization. The magnetization model reveals quasi‐linear polarity zones crossing the plateau and following expected MAR paleo‐locations, implying formation by seafloor spreading over ∼4 Myr during the formation of anomalies C34n‐C33r. Paleomagnetism and biostratigraphy data from International Ocean Discovery Program Expedition 391 confirm the magnetic interpretation. Anomaly C33r is split into two negative bands, likely by a westward ridge jump. One of these negative anomalies coincides with deep rift valleys, indicating their age and mechanism of formation. These findings imply that VB originated by seafloor spreading‐type volcanism during a plate reorganization, not from a vertical stack of lava flows as expected for a large volcano.

Rapid Formation of the Ellice and Osbourn Basins and Ontong Java Nui Breakup Kinematics

AbstractBreakup of the proposed greater Ontong Java Nui large igneous province during the Cretaceous Normal Superchron can be constrained by the opening of the Ellice Basin (EB) separating the Ontong Java and Manihiki Plateaus and the Osbourn Basin separating the Manihiki and Hikurangi Plateaus. Dating of recovered dredged samples using plagioclase 40Ar/39Ar and zircon U/Pb geochronology methods indicates that spreading was well underway in the EB by 118 Ma with full spreading rates up to 3X faster than any observed today of 30–45 cm/yr and spreading likely continued until 112‐108 Ma. Ellice Basin samples show diverse geochemical affinities ranging from mid‐ocean ridge basalt (MORB) or Ontong Java‐like to more enriched OIB‐like. Pb and Nd isotopes from six samples contain varying influences from Pacific MORB and possibly Ontong Java. The geochemistry shows a lack of a clear mantle plume influence despite EB's close temporal and spatial relationship to Ontong Java, while some data resemble the Louisville Seamounts. This compositional diversity complements morphological differences among dredge sites and shows that both in situ MORB and younger overprinted features related to the nearby Tuvalu Seamounts were sampled. 40Ar/39Ar geochronology confirms the age of International Ocean Discovery Program Site U1365 near the Osbourn Trough (OT) to be 102.60 ± 0.26 Ma (2σ, n = 18). This age constrains the timing of a spreading reorientation event observed in the OB to coincide with a global plate reorganization event around 105 Ma and estimates the cessation of spreading at the OT to 96 Ma.

Turonian-coniacian definition of the Caribbean plate: tectonic and metamorphic record in the Median Belt, Dominican Republic

ABSTRACT Uplift and unroofing of Jurassic-Cretaceous, mantle and crust, arc- and plume-related rock units in the Median Belt of the Dominican Republic exposed basement rocks with a protracted record of tectono-thermal events delineating the evolution of the northern edge of the Caribbean plate. In this article we focus on crustal rock units in the north-eastern half of the Median Belt. First 40Ar/39Ar dating of metamorphic ferri-winchite (86.4 ± 2.5 Ma; crystallization date) and albite (82.3 ± 5.8 and 79.8 ± 1.6 Ma; cooling dates) in metabasites of boninitic photolith from the Aptian-Albian Maimón Formation in the Ozama shear zone points to a tectono-metamorphic event in the Upper Cretaceous. Beltwide, this event caused syn-metamorphic N- to NNE-directed, simple-shear dominated, mylonitic and phyllonitic deformation of the Maimón Formation at peak metamorphic conditions of 8.2 kbar and 380°C. Such conditions are consistent with subduction of a coherent portion of forearc (represented by the Maimón Formation) to depths of ~25-29 km. The tectono-metamorphic event dated here overlaps with the inception of Turonian-Coniacian SW-dipping subduction and metamorphic sole formation in a back-arc position recorded in the Moa-Baracoa ophiolite complex in neighboring Eastern Cuba. Contemporaneity between the subduction inception of forearc and back-arc portions of the Caribbean arc and the main pulse of plume activity recorded in the Caribbean Large Igneous Province (CLIP) suggests that plume activity promoted general plate instability leading to a regional-scale plate reorganization. This mantle-plume-induced plate margin reorganization was coeval with the inception of the NE-dipping subduction of the Farallón plate beneath Central America leading to the definition of the Caribbean Plate by double-verging subduction zones along its northern and southwestern margins.

The formation of the 8˚20’ N seamount chain, east pacific rise

Near-axis seamounts provide a unique setting to investigate three-dimensional mantle processes associated with the formation of new oceanic crust and lithosphere. Here, we investigate the characteristics and evolution of the 8˚20’N Seamount Chain, a lineament of seamounts that extends ~ 175 km west of the East Pacific Rise (EPR) axis, just north of the fracture zone of the Siqueiros Transform Fault. Shipboard gravity, magnetic, and bathymetric data acquired in 2016 are utilized to constrain models of seamount emplacement and evolution. Geophysical observations indicate that these seamounts formed during four distinct episodes of volcanism coinciding with changes in regional plate motion that are also reflected in the development of intra-transform spreading centers (ITSCs) along the Siqueiros transform fault (Fornari et al. 1989; Pockalny et al. 1997). Although volcanism is divided into distinct segments, the magnetic data indicate continuous volcanic construction over long portions of the chain. Crustal thickness variations along the chain up to 0.75 km increase eastward, inferred from gravity measurements, suggest that plate reorganization has considerably impacted melt distribution in the area surrounding the Siqueiros-EPR ridge transform intersection. This appears to have resulted in increased volcanism and the formation of the 8˚20’N Seamounts. These findings indicate that melting processes in the mantle and subsequently the formation of new oceanic crust and lithosphere are highly sensitive to tectonic stress changes in the vicinity of fast-spreading transform fault offsets.

Tectonic and climatic controls on sediment transport to the Southeast Indian Ocean during the Eocene: New insights from IODP Site U1514

The Eocene was a critical period of global plate reorganization and it also saw the Earth's climate transition from the warmhouse state to the coolhouse state. Reconstructing the Eocene sedimentary history in the climate-sensitive Southern Ocean is important for understanding paleoenvironmental changes in response to the accelerated Australia/Antarctica separation and global cooling throughout the middle and late Eocene. Here, we present the first detailed multiproxy record of a continuous sequence from International Ocean Discovery Program (IODP) Site U1514 in the Mentelle Basin off southwestern Australia. Our aim is to reconstruct the sediment provenances and paleoenvironmental evolution in response to the abovementioned climatic and tectonic changes in the mid-high southern latitudes during the Eocene. Provenance analyses based on Sr-Nd isotopes, trace elements, and clay mineral assemblages suggest that Eocene sediments at Site U1514 predominantly originated from the southwestern Australian continent and the Naturaliste Plateau. Sediment provenance variations during the middle Eocene indicate that the onset of fast separation between Australia and Antarctica at 43 Ma caused an increased supply of volcanic materials from the Naturaliste Plateau between 43 and 38 Ma. Terrigenous inputs to the Mentelle Basin during the middle Eocene were primarily controlled by paleoclimate changes rather than tectonic processes because coeval clay mineralogical changes (higher kaolinite/smectite ratio and MARkaolinite) indicate a period of stronger physical erosion and chemical weathering on the western Australian continent that resulted in increased terrigenous materials delivered to the Mentelle Basin. Our results reveal a 5 Myr-long (43–38 Ma) warming reversal in the southern mid-high latitudes, providing an exception to the generally short-lived (10–100 kyr-long) hyperthermals that interrupted the long-term global cooling throughout the middle to late Eocene. As for the late Eocene (38–37 Ma), tectonic processes related to the sudden acceleration in seafloor spreading in the Tasman Sea led to the exposure of shallower areas, resulting in rapid detritus accumulation at the study site. During the late Eocene (37–34 Ma), major sediment provenance shifted from distal source areas (e.g., the Yilgarn Craton) to relatively proximal sources (e.g., the Leeuwin Block and Perth Basin). We interpret that the regional uplift in southwestern Australia and coeval climate cooling resulted in the diversion and inactivation of large drainage systems, thus blocking the transportation of sediment from distant regions.

On the Role of Rheological Memory for Convection‐Driven Plate Reorganizations

AbstractUnderstanding the temporal variability of plate tectonics is key to unraveling how mantle convection transports heat, and one critical factor for the formation and evolution of plate boundaries is rheological “memory,” that is, the persistence of weak zones. Here, we analyze the impact of such damage memory in global, oceanic‐lithosphere‐only models of visco‐plastic mantle convection. Self‐consistently‐formed weak zones are found to be reactivated in distinct ways, and convection preferentially selects such damaged zones for new plate boundaries. Reactivation of damage zones increases the frequency of plate reorganizations, and hence reduces the dominant periods of surface heat loss. The inheritance of distributed lithospheric damage thus dominates global surface dynamics over any local boundary stabilizing effects of weakening. In nature, progressive generation of weak zones may thus counteract and perhaps overcome any effects of reduced convective vigor throughout planetary cooling, with implications for the frequency of orogeny and convective transport throughout Wilson cycles.

Hematite geochronology reveals a tectonic trigger for iron ore mineralization during Nuna breakup

Abstract Hematite and goethite deposits hosted in banded iron formations (BIFs) in the Pilbara craton (Western Australia) represent one of Earth's most significant Fe reserves; however, the timing and tectonic triggers underpinning deposit genesis remain contentious. Uncertainty in ore genesis stems from a lack of direct age measurements, which could aid in correlating periods of BIF mineralization with tectono-thermal events observed elsewhere. Archean–Paleoproterozoic BIFs in the Hamersley Province host extensive martite–microplaty hematite orebodies that formed at 2.2–2.0 Ga, based on indirect constraints. In contrast, combined hematite in situ U-Pb geochronology and (U-Th)/He thermochronology demonstrate that martite–microplaty hematite ores in the Chichester Range crystallized ca. 1.26–1.22 Ga and underwent cratonic denudation between ca. 0.57 and 0.38 Ga. Nanoscale imaging of dated hematite indicates that U-Th-Pb is lattice bound and not hosted in inclusions. New U-Pb hematite ages overlap with other mineral ages reported at the margins of the Pilbara and Yilgarn cratons (1.3–1.1 Ga), where mineral formation was driven by plate reorganization following breakup of the Nuna supercontinent. This age correlation suggests that a combination of increased orogenic (+diagenetic) and heat (+fluid) generative processes resulting from supercontinent reconfiguration was a key trigger for iron ore formation in the Pilbara craton.

Late Eocene subduction initiation of the Indian Ocean in the North Sulawesi Arc, Indonesia, induced by abrupt Australian plate acceleration

Subduction of oceanic lithosphere is the main driving force of plate tectonics on Earth, yet, how subduction began (i.e. subduction initiation; SI) remains enigmatic, due to limited SI examples. Here, we report new whole-rock geochemical and zircon U-Pb-Hf isotopic data of arc magmatism from the North Sulawesi Arc, Indonesia, to constrain the petrogenesis, magmatic tempo, and tectonic setting, as well as the timing and trigger of SI. Zircon U-Pb dating yielded crystallization ages of ~29.7–16.7 Ma for parental magmas, which are calc-alkaline I-type in nature and show typical subduction-related signatures. Geochemical data and high positive zircon ε Hf (t) values indicate magma generation by partial melting of preexisting mafic basement rocks. Our new results, together with literature data, allow the identification of an Indian SI in the Late Eocene, as evidenced by the last vanishing of BAB-type mafic basement rocks at ~37 Ma and the first appearance of calc-alkaline felsic arc magmatism at ~30 Ma in the North Sulawesi Arc, as well as ~36–32 Ma ophiolite and ~34–29 Ma metamorphic sole in the nearby East Sulawesi Ophiolite. Such a temporal duration (maximum of ~7 Ma) from SI to typical arc magmatism is identical to that (~8–7 Ma) of the Izu-Bonin-Mariana system. Given the contemporaneousness of a sudden increase (from ~4–5 to ~8–9 cm/y) in northward drifting rate of the Australian plate, we propose that Late Eocene Indian SI was probably linked to the sharp Australian plate acceleration. Such plate reorganization may have played a significant role in driving SI in Earth history. • Calc-alkaline I-type felsic rocks in the North Sulawesi Arc developed at ~30–16 Ma. • Arc magmatism formed by melting of preexisting mafic rocks during Indian subduction. • Indian SI occurred in the Late Eocene, driven by Australian plate acceleration.

Rapid early Permian tectonic reorganization of Laurentia’s plate margins: Evidence from volcanic tuffs in the Permian Basin, USA

Early Permian arc magmatism is critical to understanding the final assembly of the supercontinent Pangea and subsequent plate reorganization. Here we report the geochronology and geochemistry of Cisuralian and Guadalupian volcanic tuffs in southwestern Laurentia and infer the magmatic sources and plate reorganization related to Laurentia-Gondwana collision. Zircon CA-ID-TIMS U-Pb dates of tuffs in the Wolfcamp B, Wolfcamp A and lower Spraberry units in the Permian Basin provide the first set of absolute ages of Cisuralian deposits in this basin. Zircon geochemistry data further show that the parent melts of these tuffs were granitic melts that formed in continental arcs. Syn-depositional zircons from the Wolfcamp B tuff beds (288.2 ± 1.7 Ma) have an average εHf value of +5.5 and TDM2 model ages between 675 and 1207 Ma, reflecting a mixture of juvenile mantle melts and Precambrian crust. The isotopic signature is consistent with Mississippian Laurentian tuffs derived from a northern Gondwana arc formed by the subduction of the Rheic oceanic plate. However, zircons from a Wolfcamp A tuff bed (287.2 ± 0.5 Ma) show an average εHf value of −4.5, much more evolved than the inferred northern Gondwana arc, but consistent with granitoids of similar or younger age in the Oaxaquia terrane. This change in εHf most likely reflects magmatism related to subduction of a paleo-Pacific oceanic plate beneath western Pangea. Our interpretation suggests a late Cisuralian plate reorganization that was caused by plate reorganization following Pangea assembly led to rapid (∼1 Myr) initiation of subduction beneath western Pangea. This study also compares tuff dates from LA-ICPMS and CA-ID-TIMS U-Pb dating and concludes that the weighted mean date of the youngest dominant KDE mode (WMYDM) is the best way to approximate LA-ICPMS dates to true depositional ages.

The submarine Azores Plateau: Evidence for a waning mantle plume?

The submarine Azores Plateau in the Central Northern Atlantic has generally been considered to represent a large igneous plateau formed some 10 Ma by widespread volcanism, however a lack of age progression amongst the younger submarine and subaerial volcanism, an irregular distribution of platform-related magmas east and west of the Mid-Atlantic Ridge, a strong tectonic stress regime, and a lack of abundant tholeiitic compositions that reflect initial, high degrees of melting is not easily explainable in the framework of a classic, long-lived mantle plume model. Here, we present new bathymetric and seismic data from the submarine Azores Plateau obtained during cruises M113/1 and M128 with the German R/V Meteor. Our new data combined with prior geochemical and petrological studies indicate that the majority of the western Azores Plateau may indeed have formed during the arrival of a short-lived mantle melting anomaly at 10 Ma. However, our new data also indicate that volcanism <2 Ma is extremely localized and along structural features that result from plate reorganisation in the vicinity of the diffuse triple junction of the Eurasian, Nubian and North American plates, and that much of the easternmost Azores Plateau is magmatically inactive. Our model implies not only that the actual flood basalt province of the Azores is only some 30% of what has been previously estimated but may not have formed from a typical large-scale, long-lived mantle plume. Instead, excess melting as evident from the anomalously shallow water depth and the presence of islands in the Azores may be the result of a volumetrically small-scale melting anomaly in the upper mantle which is in its waning stages as evident from the localised distribution of magmatic activity at <1 Ma. Our model also solves the conundrum of a potential asymmetry of the recent submarine and subaerial volcanism both east and west of the Mid-Atlantic Ridge which instead is the result of an interacting upper mantle anomaly and the complex plate tectonic domain in the vicinity of the triple junction of the Eurasian, Nubian and North American plates.