EarthArXiv

Journal: EarthArXiv

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Publications1 - 9 of 9

Pre-Cordilleran mantle metasomatism preserved in alkali basalts of Isla Isabel, México
Sieger, Leonie; Peters, Bradley J.; Giuliani, Andrea; et al. (2024)
EarthArXiv
The presence of HIMU (high-238U/204Pb) signatures in ocean island basalts has long been used to argue that ancient oceanic crust has been tectonically recycled into the mantle sources of plume-derived volcanic hotspots such as St. Helena or Mangaia. However, alternative hypotheses regarding the origins of HIMU signatures have also been put forward. This paper addresses the origins of HIMU-like Pb isotopic signatures in Isla Isabel, a small (~1 km2) intraplate volcanic island located off the western coast of México, southeast of the southern tip of Baja California. The Nd-Hf isotopic signatures of Isla Isabel are nearly identical to St. Helena and Mangaia, however since there is no mantle plume underlying Isla Isabel it is unlikely that these signatures derive from recycled oceanic crust. We argue that Isla Isabel lavas were instead produced by mixing of depleted mantle-like material and continental lithospheric mantle that was metasomatized ≥600 Ma ago, an age that overlaps with the regional breakup of Rodinia. Such preservation of ancient tectonic events is remarkable, since the exposed geological record in continental México preserves a very limited record of geological events older than the Mexican Cordillera (<165 Ma). Isla Isabel therefore illustrates that the origins of HIMU-type intraplate lavas are not limited to ancient recycled oceanic crust. Rather, they can also preserve information about the evolution of the upper mantle through large-scale tectonic cycles, even when these events have been otherwise erased from the surficial rock record.
LASIF: LArge-scale Seismic Inversion Framework, an updated version
Thrastarson, Sölvi; van Herwaarden, Dirk-Philip; Krischer, Lion; et al. (2021)
EarthArXiv
Recent methodological advances and increases in computational power have made it feasible to perform full-waveform inversions (FWI) of large domains while using more sources. This trend, along with the increasing availability of seismic data has led to an explosion of the data volumes that can, and should, be used within an inversion. Similar to machine learning problems, the incorporation of more data can result in more robust and higher quality models. In this contribution, we present the new version of LASIF, an open-source LArge-scale Seismic Inversion Framework, which helps to automate many of the historically labor-intensive tasks that were bottlenecks in earlier FWI workflows and prevented the use of the larger datasets. Among other things, the framework automates data selection, data acquisition from public web services, and data processing. It also defines an inversion project structure that organizes the data and documents the progress of the inversion. The code is open-source and available on Github. Features are available through a graphical user interface (GUI), a command-line interface (CLI), and an application programming interface (API). While we will show examples for use of LASIF with the Salvus wave equation solver, the API makes it possible to use the features of LASIF for any type of wave equation solver as long as the LASIF file formats are adhered to.
Interphase misorientation as a tool to study metamorphic reactions and crystallization in geological materials
Morales, Luiz F.G. (2021)
EarthArXiv
Interphase boundaries are planar defects that separate two different minerals, which in general have different compositions and/or crystalline structures and may play an important role as a pathway for fluids in rocks and affect their physical properties. For the proper characterization of interphase boundaries, one needs to define the misorientation between adjacent grains and the orientation of the grain boundary plane, but the analysis performed here are only limited to the misorientation characterization and the trace of the interphase boundary. Although the determination of possible orientation relationships between the two adjacent phases is routinely performed by selected area electron diffraction in the transmission electron microscope, this method lacks statistical representativeness. With the advent of techniques like electron backscatter diffraction (EBSD), it is possible to calculate orientation relationships not only in single pairs of crystals, but in full thin sections, and not limited to single phases, but also between different minerals. The interphasee misorientation is calculated from two orientations of two adjacent crystals of different phases. A set of single misorientations is then used to calculate the misorientation distribution function (MDF), from where it is possible to identify a maximum, and their crystallographic interpretation. If we then know the misorientation and the unit cell parameters of the individual phases, the crystallographic relationships between them can be described with the pairs of parallel crystallographic planes and the pairs of crystallographic directions. We present examples of the use of interphase misorientation analysis on the transformation of calcite-aragonite, olivine-antigorite, magnetite-hematite, and on the study of orientation relationships between plagioclase-olivine-ilmenite in mid-ocean ridges gabbros (ODP Hole 735).
Clumped isotopes in globally distributed Holocene coccoliths reveal their habitat depth
Mejía, Luz María; Bernasconi, Stefano M.; Zhang, Hongrui; et al. (2023)
EarthArXiv
Reliable temperature reconstructions are necessary to improve climate reconstructions and comparisons with paleoclimate model simulations. Most existing paleotemperature proxies are based on organic and inorganic remains of marine organisms. Despite the evidence that the habitat depth of coccolithophores and other phytoplankton depend on their ability to balance light, nutrients, and grazing pressure, calibrations of proxies based on photosynthesizers often assume they live in the surface ocean. Here we present the first globally distributed dataset of core top multi-species coccolith clumped isotopes (∆47), which show a clear latitudinal thermal gradient and demonstrate coccolith ∆47 sensitivity to temperature. The application of the most recent ∆47-temperature calibration for marine biogenic carbonates yield calcification temperatures implying deep habitats for tropical coccolithophores (from ~50 to up to ~150 m), which could photosynthesize with 1-10% of surface photosynthetic active radiation (PAR) levels. Given the low upper ocean temperature gradient of well-mixed high-latitude locations and the current uncertainties of ∆47 thermometry, coccolith ∆47 cannot be used to reliably constrain a specific habitat depth in these locations. Nevertheless, they are a good indicator of paleotemperatures of the mixed layer. We also use coccolith ∆47 to derive the first regression relating core top coccolith ∆47 and sea surface temperatures (SST). Although this formulation cannot be considered a proper coccolith-specific ∆47 calibration, since it ignores coccolithophore’s potential for calcification at depth, it facilitates comparison with temperature proxies like UK37', which are regressed to SST, rather than production temperature.
How agriculture, droughts and diseases shaped the island environments of Remote Oceania over the last Millennium
Camperio, Giorgia; Ladd, S. Nemiah; Prebble, Matiu; et al. (2023)
EarthArXiv
Over the past millennium, the Pacific Islands have experienced significant transformations, caused by different waves of human settlement and climatic variability. However, the paucity of archeological records coupled with the complex climatic setting of the tropical Pacific hinders our understanding of past environmental and societal changes. In this study, we employ a multi-proxy approach on sediment cores extracted from ponds on the west coast of Espiritu Santo, Vanuatu to investigate past human-climate dynamics. Through the analysis of human-associated proxies including fecal markers, palmitone — a specific lipid biomarker for taro — and charcoal, we reconstruct changes in human presence and activities. We reconstruct past climate from leaf wax hydrogen isotopes (δ2HLW) and branched glycerol dialkyl glycerol tetraethers (brGDGTs). Changes in pollen reveal major shifts in local and regional vegetation. In our record, the period from 1000 to 1300 CE is characterized by warm/wet conditions concomitant with demographic expansion inland. Around 1400 CE, δ2HLW data indicates a drier period. The coincident decrease in palmitone, despite high charcoal and fecal marker concentrations, suggests that drier conditions might have rapidly affected taro cultivation, but not the overall population, which declined more than a century later. We hypothesize that the establishment of one of the earliest European settlements in Oceania in 1606 CE further disrupted local demographics with the introduction of diseases. This study contributes to our understanding of the intricate relationship between human activities, climatic fluctuations, and landscape modifications in Remote Oceania over the past millennium.
Microbial lipid signatures in Arctic deltaic sediments - insights into methane cycling and climate variability
Lattaud, Julie; De Jonge, Cindy; Pearson, Ann; et al. (2020)
EarthArXiv
Glycerol Dialkyl Glycerol Tetraethers (GDGTs) are ubiquitous biomolecules whose structural diversity or isotopic composition is increasingly used to reconstruct environmental changes such as air temperatures or pCO2. Isoprenoid GDGTs, in particular GDGT-0, are biosynthesized by a large range of Archaea. To assess the potential of GDGT-0 as a tracer of past methane cycle variations, three sediment cores from the Mackenzie River Delta have been studied for iGDGT and diploptene distribution and stable carbon signature. The absence of crenarchaeol, high GDGT-0 vs crenarchaeol ratio, and 13C-enriched carbon signature of GDGT-0 indicate production by acetoclastic methanogens as well as heterotrophic Archaea. The oxidation of methane seems to be dominated by bacteria as indicated by the high abundance of 13C-depleted diploptene. Branched GDGTs, thought to be produced by heterotrophic bacteria, are dominated by hexa- and penta-methylated 5- and 6-methyl compounds. The presence of 5,6-methyl isomer IIIa’’ points towards in situ production of brGDGTs, with only a minor input from soil branched GDGT brought by the Mackenzie River. Carbon isotopic compositions of brGDGTs are in agreement with heterotrophic producers, likely living during summer. The reconstructed temperatures using a global lake calibration reflect recorded summer air temperature (± 2.14 °C) during the last 60 years, and further highlight the absence of warming in summer in this region during the last 200 years. Oxygen availability and connection time to the Mackenzie River also seem to control the distribution of branched GDGT with an increase in 6-methyl and 5,6-methyl isomers with increased period of anoxia.
Wetter climate favouring early Lapita horticulture in Remote Oceania
Camperio, Giorgia; Ladd, Nemiah; Prebble, Matiu; et al. (2023)
EarthArXiv
The islands of Remote Oceania were among the last places on Earth colonised by humans. Lapita seafarers carrying with them an extensive root-tuber-tree crop complex and domestic animals, rapidly transformed nearly all of these previously unoccupied islands. However, the timing of initial Lapita settlements and the early introduction of horticulture remain a matter of debate as significant changes in climate coincided with human oceanic explorations in the mid-late Holocene. Here we show that fossil biomarkers preserved in sedimentary archives located near Teouma, the earliest dated Lapita cemetery in Remote Oceania, trace human presence and horticultural practices while providing the climatic context for the initial settlement. Using fossil faecal molecules, the hydrogen isotopic composition of leaf waxes, and palmitone, a molecular marker for the staple crop taro (Colocasia esculenta Schott), we identified signatures of human activity spanning the period of occupation recorded at the Teouma site. The temporal precision provided by our high-resolution radiocarbon chronology refines the settlement timing with a first unequivocal human trace appearing at 2739-2879 BP. The presence of taro in the initial settlement period attests to the early introduction and likely rapid expansion of horticulture by the first settlers. Lower leaf wax hydrogen isotope ratios starting approximately 2900 years ago further reveal that the initial settlement coincided with a transition to a wetter period, possibly driven by shifts of the South Pacific Convergence Zone. Our findings provide evidence of early horticulture in Remote Oceania and reveal the climatic context that favoured first human settlements in the islands.
Large-scale rotational extension triggered basin formation in interior East Antarctica
Armadillo, Egidio; Rizzello, Daniele; Balbi, Pietro; et al. (2025)
EarthArXiv
Recent sub-ice topography investigations have imaged with greatly improved detail a set of enigmatic low-elevation V-shaped basins hidden beneath a very large sector of the East Antarctic Ice Sheet. Here we show that these basins form a semi-continental sized fan shaped physiographic unit which radiates from a pin point near the South Pole and name it the East Antarctic Fan-shaped Basin Province. By jointly interpreting sub-ice topography and geophysical data, we demonstrate that the fan-like landscape originated from a distributed intraplate rotational extension before Gondwana breakup which had three continental-scale consequences. i) Laterally, to the west, it caused compression and the consequent uplift of the Gamburtsev Mountains. ii) To the east, the northernmost Transantarctic Mountains segment was rotated clockwise of ~20° overriding the West Antarctic Rift System’s hot lithosphere, causing segmentation of the mountain chain into three blocks and their differential uplift due to thermal buoyancy. iii) To the North, the transcurrent edge of the fan formed the lithospheric weakness that controlled the break-up of Gondwana by driving the propagation of Antarctica/Australia separation and shaping the resulting semi-circular passive continental margins. These processes have substantially influenced the present-day East Antarctica sub-ice landscape and the evolution of the overlying ice-sheet.
Inversionson: Fully Automated Seismic Waveform Inversions
Thrastarson, Sölvi; van Herwaarden, Dirk-Philip; Fichtner, Andreas (2021)
EarthArXiv
We present Inversionson, a Python package that fully automates modern full-waveform inversions (FWI). It supports traditional FWI, which uses the same set of events and a single simulation mesh in each iteration, as well as more advanced workflows that exploit the use of dynamic mini-batches and wavefield-adapted meshes. These recently introduced advancements can be time-consuming and challenging to implement, but offer major benefits, such as much lower compute cost in favourable cases and the ability to use much larger datasets, while having built-in optimal experimental design. Inversionson, in essence, acts as a control center that steers the functions of several other packages, making them communicate and work together to perform seismic inversions. This enables scaling of full-waveform inversion problems well on the most powerful High Performance Computing (HPC) clusters, while requiring no user input during run time. Widespread adoption of real data full-waveform inversion workflows to image regional to global 3-D Earth structure has so far been limited to a handful of research groups, with most researchers focusing on 2-D synthetic problems. This probably mainly stems from the challenging implementation, as well as a lack of computational and human resources. Inversionson is built on top of various tools and mitigates each of these challenges, by exploiting the widely used waveform solver package Salvus, supporting efficient modern workflows, and by fully automating the time-consuming steps. With this contribution, we hope that we can make FWI a more interesting option for a much larger group of researchers, thereby accelerating progress in the field.

Publications1 - 9 of 9

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