Geochemistry Geophysics Geosystems最新文献

The southwest region of Western Australia is one of the oldest continental regions on Earth, hosting the Archean Yilgarn Craton, bounded by the Proterozoic Albany-Fraser and Pinjarra orogens. Here we calculate shear wave splitting of the PKS and SKS teleseismic phases using new broadband arrays with unprecedented station spacing across the region. We find evidence for coherent seismic anisotropy, with the regional average delay time ($��1.05�\pm �0.39�$ s) comparable to the global average, $��\delta �$t = 1 s. Although fast polarization orientations show variation, they are not aligned with current plate motion and the expected mantle flow direction. In the South West Terrane and Albany-Fraser Orogen, fast polarization orientations match the trend of ancient structural faults. In contrast, structural faults in the Youanmi Terrane are oriented at an angle compared to the E–W and NE–SW fast polarizations. Instead, seismic anisotropy patterns show an intriguing similarity to E–W trending Precambrian (2.42 Ga) dykes that extend uninterrupted across the Yilgarn Craton. We propose that lithospheric fabrics frozen-in at the time of craton formation (2.76–2.65 Ga) generated a mechanical weakness which subsequently influenced the orientation and emplacement of the dykes. Further evidence for a similar, ancient (2.73 Ga) architectural fabric comes from recent isotope geochemistry analysis of primary ENE-trends within the Yilgarn Craton. Overall, these results point toward large-scale, fossilized lithospheric fabric within the Yilgarn Craton, preserved for over two billion years, offering a unique window into the formation and early evolution of the continent.

The Goiás Magmatic Arc (GMA) is a Neoproterozoic juvenile terrain formed through oceanic-oceanic and oceanic-continental subduction. It comprises three main segments: Mara Rosa, Anicuns-Itaberaí (GMAAI), and Arenópolis (GMAA), whose tectonic evolution and connectivity remain uncertain. Debate persists on: (a) whether these segments evolved together from the start or were juxtaposed during collision; (b) metallogenic models lack information on the lower crust and upper mantle, essential for fertility analysis; (c) why the Cretaceous Goiás Alkaline Province (GAP) outcrops exclusively in the GMAA. To address these questions, we conducted a long-period magnetotelluric survey (34 stations, 10–13,000 s) across the GMAA/GMAAI. The resulting 3D resistivity model (nRMS = 1.21) reveals distinct lithospheric structures. GMAA exhibits significant crustal thickness and resistivity variations, while GMAAI shows higher resistivity and a thicker lithosphere, which likely controlled the confinement of the GAP within the GMAA. The absence of a continuous conductor along the Moiporá-Novo Brasil shear zone suggests that these segments may be splays of the Transbrasiliano Lineament. Thus, the GMAA and GMAAI likely evolved along the same subduction front, amalgamating in the final stages of the Brasiliano orogeny. Three major conductors were identified: C1, associated with the Bom Jardim deposit (Cu); C2, linked to the Americano do Brasil deposit (Ni–Cu sulfide); and C3, related to the Caldas Novas geothermal anomaly. These findings provide new insights into the GMA's tectonic evolution and metallogenic significance, revealing deep conductive zones linked to known mineral deposits and highlighting the control exerted by lithospheric architecture in the region.

This study explores the isotopologues m/z 47 (¹³C¹⁸O¹⁶O, denoted Δ₄₇) and m/z 48 (¹²C¹⁸O₂, denoted Δ₄₈) in CO₂ derived from carbonate minerals, focusing on their temperature dependency, kinetic isotope effects, and distinct reaction pathways. By conducting experiments at four temperatures (5°C, 10°C, 15°C, and 25°C) using the enzyme carbonic anhydrase (CA) at pH 8.3, we approached isotopic equilibrium in dissolved inorganic carbon and measured Δ₄₇, Δ₄₈, and δ¹⁸O. Our results were compared with data from Devils Hole cave calcite and existing temperature calibrations, yielding regression equations correlating Δ₄₇ and Δ₄₈ with temperature: Δ_{47 I-CDES} = (2.43 ± 0.289) Δ_{48 CDES 90} − (0.006 ± 0.074); r² = 0.96; Δ_{47 I-CDES} = (0.038 ± 0.003) × 10⁶T⁻² + (0.161 ± 0.032); r² = 0.99; Δ_{48 CDES 90} = (0.015 ± 0.002) × 10⁶T⁻² + (0.076 ± 0.025); r² = 0.94. Further, calcite precipitated at varying temperatures and pHs of 8.3–11 had kinetic enrichments of Δ₄₇ and depletions of Δ₄₈ and δ¹⁸O at pH ≥ 9.5, with CA presence leading to distinct kinetic slopes and more efficient Δ₄₈ catalysis. These findings are consistent with theoretical predictions for kinetic effects from CO₂ hydration/hydroxylation. Additionally, methodological details for Δ₄₈ measurements using the Nu Perspective mass spectrometer are provided, including shot noise calculations, baseline corrections, and how nonlinearity evolves over time. We show that these instruments do not have pressure baseline effects on m/z 48, which is a result of secondary electron suppression on the m/z 48 collector. Therefore, calibration data should be unbiased by these analytical effects.

Frictional heating causes a transient temperature rise in fault zones during earthquakes that leads to metamorphic reactions within the fault rocks. The products of these reactions provide potential evidence of earthquakes in both the outcrop and drill core. Clay minerals such as smectites are commonly found in faults. When heated, they experience a sequence of reactions with increasing temperature: dehydration, dehydroxylation, and decomposition. Clay reactions have been suggested as rock record evidence of past earthquakes, but whether these reactions are fast enough to occur over earthquake timescales (seconds-minutes) depends on unknown reaction kinetics. We conducted ramped and isothermal heating experiments up to 900°C on smectite clays using in situ X-ray diffraction (XRD) to monitor reactions as they progressed. Dehydration was variable across experiments due to sensitivity to ambient humidity and therefore accurate kinetics could not be determined for this reaction. Dehydroxylation is not measurable using XRD. The extent of decomposition was systematic with heating duration and peak temperature, enabling the quantification of reaction kinetics. We couple our empirical decomposition kinetics to a model of fault heating to determine how much clay decomposition should occur in a single earthquake. We find that a large shallow earthquake with 70 m of slip at 810 m depth (similar to the 2011 Tohoku earthquake temperature measured through fault drilling) would cause 5%–10% decomposition. Since amorphous material is unlikely to persist and accumulate over earthquake timescales, a large temperature rise during earthquakes could occur without evidence of decomposed smectite in the rock record.

Several magmatic belts are present in the Tibetan Plateau. Among these, the Qiangtang magmatic belt in North Tibet remains elusive. In particular, the petrogenesis, magma source, and tectonic implications of the ultramafic to mafic rocks in the North Qiangtang area are underinvestigated due to their sparsity and remoteness. Here we report the age and geochemistry of newly discovered mafic rocks in North Qiangtang. Zircon U-Pb analysis on gabbros revealed a crystallization age of ca. 40 Ma with inherited zircon ages of 803 Ma and 425 Ma. The geochemical characteristics of the 40 Ma zircons show that they are MORB-type gabbro with positive Sr-Nd-Hf isotopic ratios (0.0 ∼ +6.4). Geochemical data indicate that the mafic rocks originated from the asthenosphere at a depth of over 250 km. The primary magma of the gabbros experienced fractional crystallization and ancient continental contamination as it exploited trans-lithospheric faults during its upwelling process. The gabbros in the North Qiangtang have distinct geochemical and isotopic features from the intermediate-felsic rocks in the same magmatic belt, which is different from the relationship between mafic and intermediate-felsic rocks in South Tibet. We interpret that the magmatic activities in North Tibet are derived from mantle delamination processes assisted by some trans-lithospheric faults in North Tibet. Moreover, the inherited zircon ages of 802 Ma and 426 Ma support the previous interpretation that the North Qiangtang terrane is of Cathaysian affinity, different from the South Qiangtang terrane of Gondwana affinity.

The most accepted theory for the formation of the Canada Basin is that it was created during 66° rotation of Arctic Alaska around the Euler pole located near the Mackenzie Delta sometime during the Mesozoic. Gravity and magnetic anomaly data are consistent with an extinct mid-oceanic ridge (MOR) in the central basin. This extinct MOR is critical to understand the development of the Canada Basin, but it is not well mapped due to ice conditions and is buried by thick sediment. The objective of this study is to map the ridge structure and gather all the available data to establish the role of the MOR in the history of the Amerasia Basin. We acquired multichannel seismic reflection (MCS) from RV Sikuliaq in 2021 across the Canada Basin between ∼75.5°N to 77°N. We combined our MCS data with the data collected in 2007–2011 from the IB Louis S. St. Laurent to generate a basement map of the Canada Basin. On MCS profiles, we observed the rugged axial topography of the inferred fossil spreading ridge. The MCS profiles parallel to this feature reveal the unsignificant broken basement morphology, which suggests that this ridge is not surely segmented by transform faults. The basement map is consistent with the continuous linear feature we interpret as an extinct MOR. The ridge morphology and tectonic setting are similar to the ultra-slow spreading Gakkel Ridge. If so, assuming a 1–2 cm/yr spreading rate, forming a 300 km wide strip of oceanic crust in the central basin would require between 15 and 30 My.

Due to the properties of sound propagation underwater, including the existence of the SOFAR channel, sounds in the ocean can propagate over large distances with little attenuation. This makes passive acoustics a relevant method for monitoring natural events such as ice calving, earthquakes, and underwater volcanic eruptions. However, the lack of automated techniques (e.g., such as beamforming for small-aperture array) for large ($��>�$50 km) hydrophone arrays makes the data analysis very time-consuming; indeed, analysts must recognize signals such as earthquake T-phases on several hydrophones, manually pick and associate their arrival times to build event catalogs. This lengthy iterative process by trial and error often leads to underutilization of the recorded data and exposes the resulting catalogs to the analyst's subjectivity. Here we propose a pipeline that fully automates the creation of event catalogs from continuous hydroacoustic data in two steps: (a) detection of events at each recording station and (b) association of detections at multiple stations to trilaterate the source. In order to evaluate this approach, we tested it on real data recorded by the Mayotte Hydrophone Network (MAHY), which monitors the activity of the new underwater volcano off Mayotte Island in the Mozambique Channel. Its seismicity and volcanic activity were analyzed with the catalogs obtained.

Persistent arc magmatism archives fluid transport and mantle partial melting in subduction zones. However, arc magmatism often exhibits different magmatic records along the strike, as seen in the Tethyan orogenic belt. During Neo-Tethys subduction under Iran, there was pulsed arc magmatism with Middle Jurassic and Eocene magmatic flare-ups. There are few Late Cretaceous magmatic records preserved in Iran. The Zagros fold-and-thrust belt of Iran and Iraq includes the deformed passive continental margin of Arabia, but sparse records of pre-collisional, forearc rocks along the suture zone and southwest of the arc are preserved on the Eurasian side of the collision zone. Through provenance analysis of the western Makran accretionary wedge in southeastern Iran, we identify a Late Cretaceous continental arc and forearc that once existed in southwest Iran but disappeared and/or displaced to the northwest in Turkey by later subduction zone tectonics. We suggest that subduction erosion and large-scale strike-slip displacement by oblique subduction are responsible for destroying the continuous Tethyan continental arc.

The High Arctic Large Igneous Province (HALIP) formed in the circum-Arctic during the Cretaceous. The timing and duration of emplacement of these mafic magmas are important for understanding the climatic and environmental effects, yet many uncertainties remain. The dating methods used vary greatly between different regions. For example, the mafic intrusions in Svalbard have mainly been dated using the ⁴⁰K/⁴⁰Ar method, which is more sensitive to overprinting at lower temperatures. This is problematic especially in the Arctic, where the Eocene Eurekan orogeny has impacted the intrusions post-emplacement. Meanwhile, in the Canadian Arctic, ²⁰⁶Pb/²³⁸U dating on zirconium minerals has been the most common method employed, which requires much higher temperatures to be reset. We present a new compilation of ages for HALIP igneous and volcanic rocks in the circum-Arctic, derived from a thorough review and reassessment of previously reported data. This compilation applies rigorous, method-specific criteria to evaluate the reliability of existing HALIP age determinations, ensuring traceability and applicability for future data sets. By establishing a robust framework for assessing age data, this approach enhances the reliability of geological interpretations of HALIP magmatism, and highlights, for example, the spatial migration of peak magmatic activity through time in the High Arctic. To improve our understanding of the temporal evolution of the HALIP, we also present a new ²⁰⁶Pb/²³⁸U baddeleyite isotopic dilution thermal ionization mass spectrometry age from Svalbard. The new weighted mean ²⁰⁶Pb/²³⁸U age from Svalbard, 123.3 ± 1.6 Ma, is based on six samples belonging to one large sill. This age is in perfect agreement with existing published ²⁰⁶Pb/²³⁸U and ⁴⁰Ar/³⁹Ar ages, and suggests magma emplacement on Svalbard between 124.7 ± 0.3 and 120.2 ± 1.9 Ma ago.

The King's Trough cuts into an area of thickened oceanic crust associated with the 45°N melting anomaly at the Mid-Atlantic Ridge. Here we present a comprehensive geochemical data set and new ⁴⁰Ar/³⁹Ar age and bathymetric data from magmatic rocks from the King's Trough and the smaller Peake and Freen Deeps to the east and from the Gnitsevich Seamounts located to the west. The samples can be roughly divided into two groups: (a) Lavas dredged from the King's Trough (45.5–37.5 Ma) and Gnitsevich Seamounts (10–11 Ma) as well as cored rocks from the thickened oceanic crust, possessing mainly alkali basaltic, geochemically enriched compositions typical for ocean island basalts and (b) Lavas from the Peake and Freen Deeps exclusively showing depleted, normal MORB signatures. It is proposed that the current 45°N anomaly represents a remnant of the early Azores plume, which has also caused the regional thickening of the oceanic crust by plume-ridge interaction. Following the jump of the plate boundary between the Eurasian and the Iberian/African plates to this region ∼37 Ma ago, the King's Trough opened from east to west as a graben structure by oblique extension, thereby cutting into the young plateau of thickened crust. The largest extension took place at its eastern end, outside of the area of plume-influenced, thickened crust with the opening of the ultra-deep Peake and Freen Deeps. The lavas obtained from these deeps have depleted geochemical signatures consistent with being derived from the regular upper mantle by decompression melting.