Scientific Drilling Research Articles

Mesozoic rifting in SW Gondwana and break-up of the Southern South Atlantic Ocean

Abstract The opening of the South Atlantic Ocean in the Early Cretaceous was only the final stage of the complex rifting process of SW Gondwana. In this contribution, we reassess the chronology of Mesozoic basin formation in southern South America and Africa and integrate it in the long-term rifting and break-up history of SW Gondwana. During the Triassic, after the Gondwanides orogeny, plate-scale instabilities produced intracontinental rifting in Africa, and retro-arc extension on the SW-margin of Gondwana. This process was followed and accentuated by the impingement of the Karoo plume in the Early Jurassic, which triggered rifting in East Africa and ultimately produced the break-up of Eastern from Western Gondwana in the Middle Jurassic. Retro-arc extension continued to affect the palaeo-Pacific margin, with emplacement of the Chon Aike magmatic province in the Patagonian retro-arc during the Early–Middle Jurassic. By the Late Jurassic, retro-arc rifting reached a point of oceanic crust accretion, with the establishment of the Rocas Verdes back-arc basin in southern Patagonia, together with the formation of the Weddell Sea further south, between the South American plate and Antarctica. The core of the Late Paleozoic Gondwanides orogen, between southern South America and Africa, was subjected to oblique rifting at this time and produced the Outeniqua and Rawson/Valdés basins. This area was the locus of extension and oceanization in the Early Cretaceous associated with a rotation of the stress field from NE–SW to east–west extension. The formation of the South Atlantic Ocean resulted from lithospheric extension and was accompanied by extensive intrusive magmatism and extrusive flood basalts identified as seaward dipping reflectors, which were emplaced diachronically from south to north, along different segments along both conjugate margins. These volcanic rocks form the South Atlantic Large Igneous Province. The chronology of the South Atlantic opening and the magmatic sources and processes associated with the formation of seaward dipping reflectors remain interpretative as they have only been studied on seismic data but are still undrilled; hence, scientific drilling will be key to unravel many of these unknowns.

Sedimentary Paleoenvironment and Organic Matter Enrichment Characteristics of Lacustrine Shahezi Shale in Songliao Basin: Insights from the Continental Scientific Drilling.

The lacustrine shale of the Shahezi Formation in the Songliao Basin has obvious organic matter enrichment characteristics and great potential for oil and gas resources. At present, the understanding of the sedimentary paleoenvironment and organic matter enrichment characteristics of the lacustrine shale of the Shahezi Formation is relatively weak. Therefore, taking the international continental scientific drilling Program (ICDP) borehole Songke-2 (SK-2) with continuous and whole Shahezi cores as the research object, combined with organic geochemistry, elemental geochemistry, and logging data, the sedimentary paleoenvironment and organic matter enrichment mechanism were studied. The results show that the organic matter of Shahezi shale is generally in the high to over mature stage. The kerogen type of organic matter is mainly II2-III. The organic matter is mainly derived from the lake basin's own algae and terrestrial higher plants. The total organic carbon (TOC) content of Shahezi shale is relatively high, and the TOC is mainly distributed between 1% and 2%. The Shahezi Formation is dominated by clay shale and siliceous shale, and experienced moderate chemical weathering during deposition. According to the analysis of organic geochemistry and elemental geochemistry data, the paleoenvironment of organic matter deposition in Shahezi shale was dominated by warm and humid climate in the early stage, and then experienced multiple cooling and arid periods. The climate type turned to semihumid-semiarid, with stable terrigenous debris input, low deposition rate, brackish water salinity and oxygen-rich-oxygen-poor water environment. The sedimentary period of Shahezi Formation is in the Cretaceous oceanic anoxic Aptian-Albian stage. During the oceanic anoxic event, the anoxic sedimentary environment and the frequent volcanic activity have an important impact on the organic matter enrichment. The oceanic anoxic event and volcanic activity are the main causes of water body hypoxia in the lake basin. The nutrients brought by volcanic activity are also one of the reasons for promoting the growth of lake basin organisms, creating good conditions for organic matter enrichment. The enrichment of organic matter in Shahezi Formation is the result of the interaction and coupling of various factors such as paleoclimate, paleoenvironment, paleoproductivity, water environment, terrestrial input, and major geological events. And, the organic matter enrichment model of Shahezi Formation shale is established.

Fracture network characterisation of the Balmuccia peridotite using drone-based photogrammetry, implications for active-seismic site survey for scientific drilling

The presence of discontinuities (e.g. faults, fractures, veins, layering) in crystalline rocks can be challenging for seismic interpretations because the wide range of their size, orientation, and intensity, which controls the mechanical properties of the rock and elastic wave propagation, resulting in equally varying seismic responses at different scales. The geometrical characterisation of adjacent outcrop discontinuity networks allows a better understanding of the nature of the subsurface rocks and aids seismic interpretation. In this study, we characterise the discontinuity network of the Balmuccia peridotite (BP) in the Ivrea–Verbano Zone (IVZ), northwestern Italy. This geological body is the focus of the Drilling the Ivrea–Verbano zonE (DIVE), an international continental scientific drilling project, and two active seismic surveys, SEismic imaging of the Ivrea ZonE (SEIZE) and high-resolution SEIZE (Hi-SEIZE), which aim to resolve the subsurface structure of the DIVE drilling target through high-resolution seismic imaging. For fracture characterisation, we developed two drone-based digital outcrop models (DOMs) at two different resolutions (10−3–10 m and 10−1–103 m), which allowed us to quantitatively characterise the orientation, size, and intensity of the main rock discontinuities. These properties affect the seismic velocity and consequently the interpretation of the seismic data. We found that (i) the outcropping BP discontinuity network is represented by three more sets of fractures with respect to those reported in the literature; (ii) the discontinuity sizes follow a power-law distribution, indicating similarity across scales, and (iii) discontinuity intensity is not uniformly distributed along the outcrop. Our results help to explain the seismic behaviour of the BP detected by the SEIZE survey, suggesting that the low P-wave velocities observed can be related to the discontinuity network, and provide the basic topological parameters (orientation, density, distribution, and aperture) of the fracture network unique to the BP. These, in turn, can be used for interpretation of the Hi-SEIZE seismic survey and forward modelling of the seismic response.

CALDERA: a scientific drilling concept to unravel Connections Among Life, geo-Dynamics and Eruptions in a Rifting Arc caldera, Okataina Volcanic Centre, Aotearoa New Zealand

Abstract. Silicic caldera volcanoes present major volcanic and seismic hazards but also host dynamic hydrothermal and groundwater systems and a rich but largely unexplored subsurface biosphere. Many of these volcanoes are hosted in rift settings. The intricate connections and feedbacks among magmatism, rifting, hydrothermal processes, and the biosphere in these complex systems remain poorly understood, necessitating subsurface joint observations that are only enabled by scientific drilling. The CALDERA (Connections Among Life, geo-Dynamics and Eruptions in a Rifting Arc caldera) project workshop funded by the International Continental Scientific Drilling Program (ICDP) gathered multi-disciplinary international experts in January 2023 to advance planning of a scientific drilling project within one of these dynamic, rift-hosted calderas, the Okataina Volcanic Centre (OVC), Aotearoa New Zealand. The OVC's high eruption rate, frequent unrest events and earthquake swarms, location in a densely faulted rapidly extending rift, abundant groundwater–geothermal fluid circulations, and diverse surface hot spring microbiota make it an ideal location for exploring a connected geo-hydro-biosphere via scientific drilling and developing a test bed for novel volcano monitoring approaches. Drilling configurations with at least two boreholes (∼ 200 and ∼ 1000–1500 m deep) were favoured to achieve the multi-disciplinary objectives of the CALDERA project. Decadal monitoring including biosphere activity and composition has the potential to evaluate the response of the hydro-bio system to volcano-tectonic activity. In addition to the OVC caldera-scale datasets already available, site surveys will be conducted to select the best drilling locations. The CALDERA project at the OVC would provide, for the first time, an understanding of volcanic–tectonic–hydrological–biological connections in a caldera–rift system and a baseline for global comparisons with other volcanoes, rifts, and hydrothermal systems. CALDERA would serve as an unprecedented model system to understand how and how quickly the subsurface biosphere responds to geologic activities. Discoveries will improve assessment of volcanic and seismic hazards, guide the sustainable management and/or conservation of groundwater and geothermal resources and microbial ecosystems, and provide a forum for interweaving mātauranga Māori and Western knowledge systems.

NorthGreen: unlocking records from sea to land in Northeast Greenland

Abstract. The increasing anthropogenic CO2 forcing of the climate system calls for a better understanding of how polar ice sheets may respond to accelerating global warming. The sensitivity of the Greenland ice sheet to polar amplification, changes in ocean heat transport, and deteriorating perennial sea ice conditions makes the Northeast Greenland margin a pertinent location with respect to understanding the impact of climate change on ice sheet instability and associated sea level rise. Throughout the Cenozoic, ocean heat fluxes toward and along Northeast Greenland have been controlled by water mass exchanges between the Arctic and Atlantic oceans. A key element here is the current flow through oceanic gateways, notably the Fram Strait and the Greenland–Scotland Ridge. To gain a long-term (million-year) perspective of ice sheet variability in this region, it is essential to understand the broader context of ice–ocean–tectonic interactions. Coupling between the ice sheet, the subsurface, the ocean, and sea ice are readily observable today in Northeast Greenland, but geological records to illuminate long-term trends and their interplay with other parts of the global climate system are lacking. Consequently, the NorthGreen workshop was organized by the Geological Survey of Denmark and Greenland in collaboration with Aarhus (Denmark) and Stockholm (Sweden) universities in November 2022 to develop mission-specific platform (MSP) proposals for drilling the Northeast Greenland margin under the umbrella of the MagellanPlus Workshop Series Programme of the European Consortium for Ocean Research Drilling (ECORD). Seventy-one participants representing a broad scientific community discussed key scientific questions and primary targets that could be addressed through scientific drilling in Northeast Greenland. Three pre-proposals were initiated during the workshop targeting Morris Jesup Rise, the Northeast Greenland continental shelf, and Denmark Strait.

ICDP workshop on the Lake Victoria Drilling Project (LVDP): scientific drilling of the world's largest tropical lake

Abstract. Lake Victoria, which is bordered by Uganda, Tanzania, Kenya, and has a catchment that extends to Rwanda and Burundi, is home to the largest human population surrounding any lake in the world and provides critical resources across eastern Africa. Lake Victoria is also the world's largest tropical lake by surface area, but it is relatively shallow and without a major inlet, making it very sensitive to changes in climate, and especially hydroclimate. Furthermore, its size creates abundant habitats for aquatic fauna, including the iconic hyper-diverse cichlids, and serves as a major geographic barrier to terrestrial fauna across equatorial Africa. Given Lake Victoria's importance to the eastern African region, its sensitivity to climate, and its influences on terrestrial and aquatic faunal evolution and dispersal, it is vital to understand the connection between the lake and regional climate and how the lake size, shape, and depth have changed through its depositional history. This information can only be ascertained by collecting a complete archive of Lake Victoria's sedimentary record. To evaluate the Lake Victoria basin as a potential drilling target, ∼ 50 scientists from 10 countries met in Dar es Salaam, Tanzania, in July 2022 for the International Continental Scientific Drilling Program (ICDP)-sponsored Lake Victoria Drilling Project (LVDP) workshop. Discussions of the main scientific objectives for a future drilling project included (1) recovering the Pleistocene and Holocene sedimentary records of Lake Victoria that document the dynamic nature of the lake, including multiple lacustrine and paleosol sequences; (2) establishing the chronology of recovered sediments, including using extensive tephra fingerprinting and other techniques from deposits in the region; (3) reconstructing past climate, environment, lacustrine conditions, and aquatic fauna, using an integrated multi-proxy approach, combined with climate and hydrologic modeling; and (4) connecting new records with existing sedimentary snapshots and fossils exposed in deposits around the lake, tying archaeological, paleontological, sedimentological, tectonic, and volcanic findings to new drilling results. The LVDP provides an innovative way to address critical geological, paleontological, climatological, and evolutionary biological questions about Quaternary to modern landscapes and ecosystems in eastern Africa. Importantly, this project affords an excellent opportunity to help develop conservation and management strategies for regional responses to current and future changes in climate, land use, fisheries, and resiliency of at-risk communities in equatorial Africa.

Characterizing shallow fault zones by integrating profile, borehole and array measurements of seismic data and distributed acoustic sensing

AbstractWithin the framework of the Intercontinental Scientific Drilling Programme (ICDP) ‘Drilling the Eger Rift’ project, five boreholes were drilled in the Vogtland (Germany) and West Bohemia (Czech Republic) regions. Three of them will be used to install high‐frequency three‐dimensional (3D) seismic arrays. The pilot 3D array is located 1.5 km south of Landwüst (Vogtland). The borehole, with a depth of 402 m, was equipped with eight geophones and a fibre optic cable behind the casing used for distributed acoustic sensing (DAS) measurements. The borehole is surrounded by a surface array consisting of 12 seismic stations with an aperture of 400 m. During drilling, a highly fractured zone was detected between 90 m and 165 m depth and interpreted as a possible fault zone. To characterize the fault zone, two vertical seismic profiling (VSP) experiments with drop weight sources at the surface were conducted. The aim of the VSP experiments was to estimate a local 3D seismic velocity tomography including the imaging of the steep fault zone. Our 3D tomography indicates P‐wave velocities between 1500 m/s and 3000 m/s at shallow depths (0–20 m) and higher P‐wave velocities of up to 5000 m/s at greater depths. In addition, the results suggest a NW–SE striking low‐velocity zone (LVZ; characterized by = 1500–3000 m/s), which crosses the borehole at a depth of about 90–165 m. This LVZ is inferred to be a shallow non‐tectonic, steep fault zone with a dip angle of about . The depth and width of the fault zone are supported by logging data as electrical conductivity, core recovery and changes in lithology. In this study, we present an example to test and verify 3D tomography and imaging approaches of shallow non‐tectonic fault zones based on active seismic experiments using simple surface drop weights as sources and borehole chains as well as borehole DAS behind casing as sensors, complemented by seismic stand‐alone surface arrays.

Seawater contamination by coring and pore water sampling of marine sediments

Coring of sediments with minimal physical disturbance, and sampling of pore water with minimal contamination from seawater, are critical in marine geochemistry and microbiology. Yet, sediment coring generally causes smearing of sediment down along the inside of the core liner and leaves seawater and fluid mud trapped around the core. This seawater is a source of diffusive or advective exchange of solutes with the core, which affects the chemistry of retrieved pore water. The exchange depends on the time elapsed between coring and the end of pore water extraction. The degree of seawater contamination is difficult to determine and has generally been neglected in the geochemical literature. Yet, it is possible to quantify seawater contamination due to the high millimolar concentration of sulfate in seawater and low micromolar concentration in the subsurface methanic zone, where sulfate is largely depleted. Analysis of 540 sediment cores from a global database showed that sulfate concentration data beneath the sulfate-methane transition were often truncated and stated as “0” or “0,0” mM, thereby preventing an evaluation of seawater contamination. Among the 181 sediment cores for which the mM sulfate concentrations were reported with two or three decimal places, concentrations measured in methanic sediments were up to an order of magnitude higher than the estimated in situ concentrations in gravity cores and two orders of magnitude higher in cores recovered by scientific ocean drilling. A comparison between pore water extraction by Rhizon suction samplers and by high-pressure squeezers in cores from Baltic Sea Expedition 347 of the IODP (International Ocean Discovery Program) showed no systematic difference in the degree of contamination. A comparison with a perfluorocarbon (PFC) tracer injected by IODP coring into the drilling fluid showed a seawater contamination similar to that based on sulfate in the methanic zone. In IODP cores, where the true in situ sulfate concentration is generally unknown, we calculated the theoretical sulfate concentration that corresponded to equilibrium between SO42−, Ba2+ and barite (BaSO4) to show that the equilibrium sulfate concentrations in the methanic zone are much lower than the sulfate concentrations measured in pore water samples, again indicating seawater contamination. We used a time-resolved diffusion model to calculate how contaminating seawater ions penetrate from the external liner fluid into sediment cores before pore water is extracted. We conclude that nearly all published pore water samples retrieved from subsurface sediments are contaminated by seawater to some degree. We also conclude that sensitive sulfate analyses in methanic sediments constitute a unique opportunity to quantify this contamination and thereby provide a better possibility to control it.

Preliminary Characterization of Submarine Basalt Magnetic Mineralogy Using Amplitude‐Dependence of Magnetic Susceptibility

AbstractThe past ∼200 million years of Earth's geomagnetic field behavior have been recorded within oceanic basalts, many of which are only accessible via scientific ocean drilling. Obtaining the best possible paleomagnetic measurements from such valuable samples requires an a priori understanding of their magnetic mineralogies when choosing the most appropriate protocol for stepwise demagnetization experiments (either alternating field or thermal). Here, we present a quick, and non‐destructive method that utilizes the amplitude‐dependence of magnetic susceptibility to screen submarine basalts prior to choosing a demagnetization protocol, whenever conducting a pilot study or other detailed rock‐magnetic characterization is not possible. We demonstrate this method using samples acquired during International Ocean Discovery Program Expedition 391. Our approach is rooted in the observation that amplitude‐dependent magnetic susceptibility is observed in basalt samples whose dominant magnetic carrier is multidomain titanomagnetite (∼TM60–65, (Ti0.60–0.65Fe0.35–0.40)Fe2O4). Samples with low Ti contents within titanomagnetite or samples that have experienced a high degree of oxidative weathering do not display appreciable amplitude dependence. Due to their low Curie temperatures, basalts that possess amplitude‐dependence should ideally be demagnetized either using alternating fields or via finely‐spaced thermal demagnetization heating steps below 300°C. Our screening method can enhance the success rate of paleomagnetic studies of oceanic basalt samples.

Continental scientific drilling and microbiology: (extremely) low biomass in bedrock of central Sweden

Abstract. Scientific drilling expeditions offer a unique opportunity to characterize microbial communities in the subsurface that have long been isolated from the surface. With subsurface microbial biomass being low in general, biological contamination from the drilling fluid, sample processing, or molecular work is a major concern. To address this, characterization of the contaminant populations in the drilling fluid and negative extraction controls are essential for assessing and evaluating such sequencing data. Here, rock cores down to 2250 m depth, groundwater-bearing fractures, and the drilling fluid were sampled for DNA to characterize the microbial communities using a broad genomic approach. However, even after removing potential contaminant populations present in the drilling fluid, notorious contaminants were abundant and mainly affiliated with the bacterial order Burkholderiales. These contaminant microorganisms likely originated from the reagents used for isolating DNA despite stringent quality standards during the molecular work. The detection of strictly anaerobic sulfate reducers such as Candidatus Desulforudis audaxviator suggested the presence of autochthonous deep biosphere taxa in the sequenced libraries, yet these clades represented only a minor fraction of the sequence counts (< 0.1 %), hindering further ecological interpretations. The described methods and findings emphasize the importance of sequencing extraction controls and can support experimental design for future microbiological studies in conjunction with continental drilling operations.

Iron isotope systematics of the Jiajika granite-pegmatite lithium deposit, Sichuan, China

The Jiajika deposit in western Sichuan is the largest pegmatite-type lithium deposit in China, but the mechanism of rare metal element enrichment in this giant deposit remains a topic of debate. This study presents a comprehensive Fe isotope study of granites, aplites, pegmatites, metamorphic rocks, and associated mineral separates from the 3211 m long deep Jiajika scientific drilling core (JSD-1) to constrain the magmatic-hydrothermal processes in the Jiajika deposit. Aplites and pegmatites have variable δ56Fe values that range from –0.12 ± 0.02 ‰ to 0.38 ± 0.02 ‰, by contrast, two-mica granite samples show limited variation in δ56Fe compositions (0.11 ± 0.04 ‰ to 0.21 ± 0.04 ‰). The Fe isotope data of the coexisting Fe-bearing minerals can impose critical constraints on crystal fractionation. Garnet shows the lightest δ56Fe compositions (–0.19 ± 0.06 ‰ to –0.06 ± 0.02 ‰) and tourmaline has the highest δ56Fe values (0.15 ± 0.01 ‰ to 0.22 ± 0.02 ‰) among all the investigated minerals, whereas the δ56Fe values of biotite range from 0.06 ± 0.02 ‰ to 0.18 ± 0.02 ‰. According to the compositional homogeneity of minerals and the relatively consistent offsets in δ56Fe between the three Fe-bearing mineral pairs, the co-existing Fe-bearing minerals in the Jiajika granitic pegmatites are interpreted to be in Fe isotope equilibrium. Additionally, based on the differences in mineral composition and geochemistry of bulk-rock samples at different observation depths, as well as the modeling results, the significant Fe isotope variation in Jiajika deposit reflect the combined results of biotite fractionation, hydrothermal alteration (tourmalinization), and garnet accumulation during multistage magmatic-hydrothermal processes. Spodumene-bearing pegmatites located in the upper portion of the drill core exhibit enrichment in heavy Fe isotopes (0.18 ± 0.04 ‰ and 0.30 ± 0.03 ‰) which can be attributed to their higher degree of magma evolution and the most abundant magmatic fluids related to enrichment and migration of rare metals. Furthermore, we conducted a comprehensive statistical analysis on the available Fe isotope data of granitic pegmatites, providing new insights into granite-pegmatite systems and related rare-metal mineralization processes from a Fe isotope perspective.

Sedimentary stratigraphy and provenance off Dronning Maud Land (East Antarctica) during the mid-Pleistocene transition: Implications for paleoclimate and ice dynamics

Glacial-marine sediments from the Antarctic continental margin provide a record of depositional environment, oceanographic variability and ice dynamics that is tapped with scientific ocean drilling. This study focuses on Ocean Drilling Program Core 693A-2R, a 9.7 m sediment core retrieved from near the continental margin of the Archean Grunehogna Craton in Dronning Maud Land (DML), East Antarctica. The results contribute to a better understanding of ice-shelf behavior in DML during the mid-Pleistocene transition (MPT), a well-known transition from 40-kyr to 100-kyr cycle periods. The age model, constructed based on Sr isotope stratigraphy and geomagnetic reversals, indicates that the core spans 1.20 to 0.65 Ma. The dynamic behavior of DML ice shelves with periodic iceberg calving is revealed by the glacial–interglacial variation in sedimentation patterns, with interglacials characterized by higher concentrations of ice-rafted debris (IRD) associated with enhanced paleoproductivity than glacial intervals. The responses of DML ice shelves to warm climates are represented by a prolonged interglacial period at 1.0–1.1 Ma (MIS 31–27) and significant interglacial expressions during MIS 19 and 17. The 40Ar/39Ar ages of individual ice-rafted hornblende grains are compared with the on-land geology of DML and neighboring regions to determine the provenances of IRD. Specifically, 40Ar/39Ar results record primarily late Neoproterozoic to Cambrian ages (600–400 Ma) with a predominant peak of 520–480 Ma. This Pan-African/Ross orogeny signature is very common in East Antarctica but is not found in the most proximal margin of the Grunehogna Craton, and is instead associated with the region of DML several hundred kilometers east of the deposition site. This indicates that significant discharges of icebergs occurred in the remote DML, which were then transported by the westward-flowing Antarctic Coastal Current to deposit IRD at the studied site during the MPT. This study establishes a confirmed MPT sedimentary sequence off DML, against which future MPT proxy records from the Weddell Sea embayment and other sectors in Antarctica can be compared and correlated, and provides a basis for more detailed analyses of the response of DML ice sheet to Pleistocene climate variations.

Geochemical constraints on the origin of the rare metal mineralization in granite-pegmatite, evidence from three-kilometer scientific drilling core in the Jiajika Li deposit, eastern Tibetan Plateau

Although the metallogenic mechanism of the Jiajika super-large Li deposits in the eastern Tibetan Plateau has been proposed closely linked to development of the Majingzi granite pluton, the petrogenesis and evolutionary linkages between granite–pegmatites and Li mineralization still remain controversial. Here we investigated Li-Nd isotopes together with major and trace elemental data from a 3-km scientific drillcore and surface samples (including the Li-rich/poor pegmatites, the associated two-mica granite and the metasedimentary rocks) to reveal the magmatic evolution and Li-enrichment mechanism of the Jiajika deposit. In the drillcore, the Li-poor pegmatites overall exhibit low Li isotope values (δ7Li = −1.38 ‰ to +1.98 ‰, mean of +0.34 ‰) and low Li contents (67 to 45 ppm), while the Li-rich pegmatites show slightly higher δ7Li values (+0.9 ‰ to +1.1 ‰) and high Li contents (3078 to 6012 ppm). Additionally, the Li-poor pegmatites have εNd(t) values of −17.1 – −2.5 (mean of −10.34) and low Nd concentration (<10 ppm), similar to the two-mica granite (εNd(t)avg = −11.18 and Ndavg = 7.08 ppm), whereas the schists and calc-silicate rocks in the drillcore have relatively higher εNd(t) values (−11.9 to −2.4 with a mean of −7.3) and Nd contents (>20 ppm). These data, together with consistently low Nb/Ta、Zr/Hf of the deep-drilled pegmatites and two-mica granites, suggest that the Jiajika pegmatites are not directly derived from low degrees of partial melting of the Triassic metasediments (e.g., biotite shists or calc-silicate rocks), but more likely from extreme magmatic fractional crystallization of the Majingzi two-mica granite pluton. For the surface samples, the δ7Li values of the surface Li-poor pegmatite samples (−0.61 ‰ to +2.56 ‰ with a mean of +0.36 ‰) are slightly higher than that of the Li-rich pegmatites (−0.52 ‰ to −0.27 ‰ with a mean of −0.39 ‰), and the two-mica granites samples show relatively variation in δ7Li (−1.25 ‰ to +3.33 ‰ with a mean of +0.73 ‰). The surface granites and pegmatites are characterized by high A/CNK values (>1.1) and low K/Rb values (<200), and particularly, the degree of REE tetrad effect gradually increases from granites to pegmatites. We suggest that the Majingzi two-mica granites exposed by the Jiajika gneiss dome is analogous to the deeper granitic sheet implied by the 3 km deep drilling, which both are strongly peraluminous S-type granites with a highly fractionation. Based on the degree of evolution of the Li-rich, Li-poor pegmatites and the two-mica granites and other geochemical evidence, we used a Rayleigh fractionation model to reproduce Li isotope variations in different types of rocks around the Jiajika deposit, suggesting an extreme magmatic differentiation without significant fluid exsolution as the origin for Li enrichments in pegmatites.

New constraints on the shear wave velocity structure of the Ivrea geophysical body from seismic ambient noise tomography (Ivrea-Verbano Zone, Alps)

SUMMARY We performed seismic ambient noise tomography to investigate the shallow crustal structure around the Ivrea geophysical body (IGB) in the Ivrea-Verbano Zone (IVZ). We achieved higher resolution with respect to previous tomographic works covering the Western Alps, by processing seismic data collected by both permanent and temporary seismic networks (61 broad-band seismic stations in total). This included IvreaArray, a temporary, passive seismic experiment designed to investigate the IVZ crustal structure. Starting from continuous seismic ambient noise recordings, we measured and inverted the dispersion of the group velocity of surface Rayleigh waves (fundamental mode) in the period range 4–25 s. We obtained a new, 3-D vS model of the IVZ crust via the stochastic neighbourhood algorithm (NA), with the highest resolution between 3 to 40 km depth. The fast and shallow shear wave velocity anomaly associated with the IGB presents velocities of 3.6 km s−1 directly at the surface, in remarkable agreement with the location of the exposed lower-to-middle crustal and mantle outcrops. This suggests a continuity between the surface geological observations and the subsurface geophysical anomalies. The fast IGB structure reaches vS of 4 km s−1 at 20–25 km depth, at the boundary between the European and Adriatic tectonic plates, and in correspondence with the earlier identified Moho jump in the same area. The interpretation of a very shallow reaching IGB is further supported by the comparison of our new results with recent geophysical investigations, based on receiver functions and gravity anomaly data. By combining the new geophysical constraints and the geological observations at the surface, we provide a new structural interpretation of the IGB, which features lower crustal and mantle rocks at upper crustal depths. The comparison of the obtained vS values with the physical properties from laboratory analysis of local rock samples suggests that the bulk of the IGB consists of a combination of mantle peridotite, ultramafic and lower crustal rocks, bound in a heterogeneous structure. These new findings, based on vS tomography, corroborate the recent interpretation for which the Balmuccia peridotite outcrops are continuously linked to the IGB structure beneath. The new outcomes contribute to a multidisciplinary framework for the interpretation of the forthcoming results of the scientific drilling project DIVE. DIVE aims at probing the lower continental crust and its transition to the mantle, with two ongoing and one future boreholes (down to 4 km depth) in the IVZ area, providing new, complementary information on rock structure and composition across scales. In this framework, we constrain the upper crustal IGB geometries and lithology based on new evidence for vS, connecting prior crustal knowledge to recent active seismic investigations.

Dear NSF: Scientific Ocean Drilling Is Necessary for Climate Studies, Natural Hazards Research, and Inspiring Future Scientists

AbstractThis letter, written by two early career researchers, highlights their urgent concerns regarding the future of scientific ocean drilling (SciOD) research following the retirement of the JOIDES Resolution (JR) at the end of the 2024 fiscal year. In the letter, addressed to the director of NSF‐OCE and to key leaders in determining U.S. scientific priorities, we outline the importance of scientific ocean drilling, both historically and for future scientific advances. We urge the NSF to make immediate, concrete commitments to fund, develop, and construct a new riserless drilling vessel dedicated to SciOD. We also highlight the importance of supporting existing and future SciOD researchers and infrastructure, including the urgent need to create programs designed to support early career researchers in our field. The letter has been signed by nearly three hundred scientists, more than two hundred of which are U.S.‐based researchers and more than half of which are early career researchers.

Unravelling the genetic relationship between pegmatites and granites in the Jiajika Li-Be polymetallic district, Songpan-Ganze Orogenic Belt, Southwestern China: Insights from monazite U-Pb geochronology and trace element geochemistry

The Jiajika Li-Be Polymetallic District is located in the Songpan-Ganze Orogenic Belt, Southwestern China. The Li-Be mineralization is genetically, temporally, and spatially, related to pegmatites in the Jiajika District. Hundreds of pegmatite dikes were emplaced surrounding the adjacent Majingzi granite pluton. Drill core samples from the 3,200 m deep Jiajika Scientific Drilling project (JSD-1) were acquired to determine the vertical extent and the petrogenesis and metallogeny of the granites, and the pegmatites, respectively, and to obtain a better understanding of their genetic relationship. The vertical zonation of the pegmatites from shallow to deep is as follows: shallow albite pegmatites; albite-microcline pegmatites; microcline pegmatites; and deeper more albite pegmatite. Spodumene occurs mainly in the shallow albite pegmatites (55–105 m depth), and disseminated beryl, columbite-tantalite, and cassiterite, mainly occur in pegmatites at depths less than 700 m. Eight samples were selected for monazite U-Pb geochronology and trace element geochemistry analyses from pegmatites and granites at different depths. LA-ICPMS monazite U-Pb geochronology for the pegmatites indicates two episodes of magmatic activity; one at 211–205 Ma (2σ, 523–2,494 m depth) and another at 193–192 Ma (2σ, 3,170–3,211 m depth). The crystallization age of the older pegmatites is in good agreement with the monazite U-Pb geochronology of the adjacent Majingzi granite (208–205 Ma, 2σ, 1,265–2,568 m depth) within analytical uncertainty, indicating their close temporal relationship. The younger albite pegmatite (193–192 Ma) is associated with the columbite-tantalite Nb-Ta rare-metal mineralization. Compared to those in the deep pegmatites (excluding the younger albite pegmatite in 3,170–3,211 m depth), and the adjacent granites, monazites in the shallow pegmatites and the adjacent granites are relatively enriched in Li, Th, and U, indicating the continuous evolution of a felsic magmatic system; with the residual melt more enriched in various incompatible rare-metal elements. Hence, the monazite U-Pb geochronology and trace element geochemistry indicate that a highly evolved felsic magma plays an important role in the petrogenesis of the Jiajika Li-Be pegmatites.

Early Cretaceous sedimentary records of the early-stage continental rifting in the Songliao Basin, NE China

Well SK-2, a continental scientific drilling well in the Xujiaweizi fault depression of the Songliao Basin, has drilled through ca 2359 m of the Early Cretaceous Shahezi Formation. Herein, we focus on the sequence groups SSI and SSII in the lower part of the Shahezi Formation (interval 4357.38–5695.02 m) from well SK-2. There are fourteen different lithofacies and seven lithofacies associations. Syn-eruptive pyroclastic deposits and their proportions in successions indicate that SSI varies from dominantly pyroclastic fill to dominantly weathering-derived clastic fill, reflecting the development of volcanism in the early syn-rift stage. SSII exhibits another, similar evolutionary cycle. Whole-rock geochemistry of rocks from the Shahezi Formation reveals that the source rocks are felsic, andesite, and sedimentary rocks from the upper crust, and that the intermediate-acid rocks are originated from partial melting crustal materials and are hybridized with input from the mantle. In the seismic profile that intersects well SK-2, the thinning direction switches back and forth during the formation of the Shahezi Formation’s four sequence groups; that is, there is turnover superimposition in vertical stratigraphic subsidence, demonstrating strike-slipping during deposition of the Shahezi Formation.The major rift stage, especially during the deposition of the lower part of the Shahezi Formation, involved strike-slipping dominated extension. This conclusion is supported by the presence of abundant dark mudstone and coarse clastic progradation in the transgressive stage, as well as by the periodicity of volcanism combined with stratigraphic turnover superimposition.

Geochemistry and origins of hydrogen-containing natural gases in deep Songliao Basin, China: Insights from continental scientific drilling

The different reservoirs in deep Songliao Basin have non-homogeneous lithologies and include multiple layers with a high content of hydrogen gas. The gas composition and stable isotope characteristics vary significantly, but the origin analysis of different gas types has previously been weak. Based on the geochemical parameters of gas samples from different depths and the analysis of geological settings, this research covers the diverse origins of natural gas in different strata. The gas components are mainly methane with a small amount of C2+, and non-hydrocarbon gases, including nitrogen (N2), hydrogen (H2), carbon dioxide (CO2), and helium (He). At greater depth, the carbon isotope of methane becomes heavier, and the hydrogen isotope points to a lacustrine sedimentary environment. With increasing depth, the origins of N2 and CO2 change gradually from a mixture of organic and inorganic to inorganic. The origins of hydrogen gas are complex and include organic sources, water radiolysis, water-rock (Fe2+-containing minerals) reactions, and mantle-derived. The shales of Denglouku and Shahezi Formations, as source rocks, provide the premise for generation and occurrence of organic gas. Furthermore, the deep faults and fluid activities in Basement Formation control the generation and migration of mantle-derived gas. The discovery of a high content of H2 in study area not only reveals the organic and inorganic association of natural-gas generation, but also provides a scientific basis for the exploration of deep hydrogen-rich gas.

Workshop on drilling the Nicaraguan lakes: bridging continents and oceans (NICA-BRIDGE)

Abstract. An international, multidisciplinary research group is proposing the “NICA-BRIDGE” drilling project, within the framework of the International Continental Scientific Drilling Program (ICDP). The project goal is to conduct scientific drilling in Lake Nicaragua and Lake Managua (Nicaragua, Central America) to obtain long lacustrine sediment records to (a) extend the neotropical paleoclimate record back to the Pliocene, making it one of the longest continental tropical climate archives in the world, and to (b) provide geological data on the long-term complex interplay among tectonics, volcanism, sea-level dynamics, climate change, and biosphere. The lakes are the two largest in Central America, and they are located in a trench-parallel half graben that hosts the volcanic front, which developed during or prior to the Pliocene, as a consequence of subduction-related tectonic activity. The lakes are uniquely suited for multidisciplinary scientific investigation as their long, continuous sediment records (several Myr) will facilitate the study of (1) terrestrial and marine basin development at the southern Central American margin, (2) alternating lacustrine and marine environments in response to tectonic and climatic changes, (3) the longest record of tropical climate proxies, (4) the evolution of (and transition between) the Miocene to Pliocene/Pleistocene and Pleistocene to present volcanic arcs, which were separated by slab rollback, (5) the significance of the lakes as hot spots for endemism, and (6) the Great American Biotic Interchange at this strategic location, i.e., the N–S and reverse migration of fauna after the land bridge between the Americas was established. The planned ICDP project offers an opportunity to explore these topics through continent-based seismological, volcanological, paleoclimatological, paleoecological, and paleoenvironmental studies, combined with an International Ocean Discovery Program (IODP) drill project to explore its oceanic continuation. In preparation of this drilling project, an ICDP workshop was held in Montelimar, Nicaragua, on 2–5 March 2020 to develop drilling strategies and refine scientific questions, objectives, and hypotheses. The workshop was organized and hosted by the principal investigators and the Instituto Nicaragüense de Estudios Territoriales (INETER), with funding from the ICDP. Forty-five researchers from 12 countries participated in the workshop, including representatives from ICDP. During the workshop, previous research data on the study lakes, including new recent surveys, were reviewed, and a three-phase strategy for the proposed research was developed. The aim of Phase 0 is to complement the pre-site surveys where we identified the need for further data. In Phase I, with ICDP support, we will obtain sediment cores ∼ 100 m long, which will allow us to investigate many of the scientific questions. Based on the data from those drill cores, coring locations will be identified for a future Phase II, which we envisage as a combined ICDP/IODP project to collect deep drill cores in the lakes and the offshore Sandino Basin in order to extend Phase I results to much deeper time. The Sandino Basin is the oceanic continuation of the depression in which the studied lakes are located, and complementary marine drilling will improve the understanding of the evolution of this complex margin.

Deep-time Arctic climate archives: high-resolution coring of Svalbard's sedimentary record – SVALCLIME, a workshop report

Abstract. ​​​​​​​We held the MagellanPlus workshop SVALCLIME “Deep-time Arctic climate archives: high-resolution coring of Svalbard's sedimentary record”, from 18 to 21 October​​​​​​​ 2022 in Longyearbyen, to discuss scientific drilling of the unique high-resolution climate archives of Neoproterozoic to Paleogene age present in the sedimentary record of Svalbard. Svalbard is globally unique in that it facilitates scientific coring across multiple stratigraphic intervals within a relatively small area. The polar location of Svalbard for some of the Mesozoic and the entire Cenozoic makes sites in Svalbard highly complementary to the more easily accessible mid-latitude sites, allowing for investigation of the polar amplification effect over geological time. The workshop focused on how understanding the geological history of Svalbard can improve our ability to predict future environmental changes, especially at higher latitudes. This topic is highly relevant for the ICDP 2020–2030 Science Plan Theme 4 “Environmental Change” and Theme 1 “Geodynamic Processes”. We concluded that systematic coring of selected Paleozoic, Mesozoic, and Paleogene age sediments in the Arctic should provide important new constraints on deep-time climate change events and the evolution of Earth's hydrosphere–atmosphere–biosphere system. We developed a scientific plan to address three main objectives through scientific onshore drilling on Svalbard: a. Investigate the coevolution of life and repeated icehouse–greenhouse climate transitions, likely forced by orbital variations, by coring Neoproterozoic and Paleozoic glacial and interglacial intervals in the Cryogenian (“Snowball/Slushball Earth”) and late Carboniferous to early Permian time periods.b. Assess the impact of Mesozoic Large Igneous Province emplacement on rapid climate change and mass extinctions, including the end-Permian mass extinction, the end-Triassic mass extinction, the Jenkyns Event (Toarcian Oceanic Anoxic Event), the Jurassic Volgian Carbon Isotopic Excursion and the Cretaceous Weissert Event and Oceanic Anoxic Event 1a.c. Examine the early Eocene hothouse and subsequent transition to a coolhouse world in the Oligocene by coring Paleogene sediments, including records of the Paleocene–Eocene Thermal Maximum, the Eocene Thermal Maximum 2, and the Eocene–Oligocene transition. The SVALCLIME science team created plans for a 3-year drilling programme using two platforms: (1) a lightweight coring system for holes of ∼ 100 m length (4–6 sites) and (2) a larger platform that can drill deep holes of up to ∼ 2 km (1–2 sites). In situ wireline log data and fluid samples will be collected in the holes, and core description and sampling will take place at The University Centre in Svalbard (UNIS) in Longyearbyen. The results from the proposed scientific drilling will be integrated with existing industry and scientific boreholes to establish an almost continuous succession of geological environmental data spanning the Phanerozoic. The results will significantly advance our understanding of how the interplay of internal and external Earth processes are linked with global climate change dynamics, the evolution of life, and mass extinctions.