Constraining the timing of brittle faulting is critical in understanding crustal deformation and fluid flow, but many regional-scale fault systems lack readily available techniques to provide absolute chronological information. Calcite mineralization occurs in crustal faults in many geological settings, and can be suitable for U-Pb geochronology.This application has remained under-utilized because traditional bulk dissolution techniques require uncommonly high U concentration. As U and Pb are distributed heterogeneously throughout calcite crystals, high spatial-resolution sampling techniques can target domains with high U and variable U/Pb ratios. Here we present a novel application of in situ laser ablation inductively coupled mass spectrometry (LA-ICPMS) to basaltic fault rock geochronology in the Faroe Islands, NE Atlantic margin. Faults that are kinematically linked to deformation associated with continental break-up were targeted. Acquired ages for fault events range from Mid-Eocene to Mid-Miocene, and are therefore consistently younger than the regional Early Eocene onset of ocean spreading, highlighting protracted brittle deformation within the newly-developed continental
Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. Samples of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft. We measure the mineralogy, bulk chemical and isotopic compositions of Ryugu samples. They are mainly composed of materials similar to carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group. The samples consist predominantly of minerals formed in aqueous fluid on a parent planetesimal. The primary minerals were altered by fluids at a temperature of 37 ± 10°C, 5.2 − 0.8 + 0.7 (Stat.) − 2.1 + 1.6 (Syst.) million years after formation of the first solids in the Solar System. After aqueous alteration, the Ryugu samples were likely never heated above ~100°C. The samples have a chemical composition that more closely resembles the Sun’s photosphere than other natural samples do.
Abstract. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb geochronology of carbonate minerals, calcite in particular, is rapidly gaining popularity as an absolute dating method. The high spatial resolution of LA-ICP-MS U–Pb carbonate geochronology has benefits over traditional isotope dilution methods, particularly for diagenetic and hydrothermal calcite, because uranium and lead are heterogeneously distributed on the sub-millimetre scale. At the same time, this can provide limitations to the method, as locating zones of radiogenic lead can be time-consuming and “hit or miss”. Here, we present strategies for dating carbonates with in situ techniques, through imaging and petrographic techniques to data interpretation; our examples are drawn from the dating of fracture-filling calcite, but our discussion is relevant to all carbonate applications. We review several limitations to the method, including open-system behaviour, variable initial-lead compositions, and U–daughter disequilibrium. We also discuss two approaches to data collection: traditional spot analyses guided by petrographic and elemental imaging and image-based dating that utilises LA-ICP-MS elemental and isotopic map data.
9The strength of rocks in the subsurface is critically important across the geosciences, with 10 implications for fluid flow, mineralization, seismicity, and the deep biosphere. Most studies 11of porous rock strength consider the scalar quantity of porosity, in which strength shows a 12 broadly inverse relationship with total porosity, but pore shape is not explicitly defined. Here
23The geometry and distribution of planar igneous bodies (i.e. sheet intrusions), such as dykes, 24 sills, and inclined sheets, has long been used to determine emplacement mechanics, define 25 melt source locations, and reconstruct palaeostress conditions to shed light on various 26 M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT tectonic and magmatic processes. Since the 1970's we have recognised that sheet intrusions 27do not necessarily display a continuous, planar geometry, but commonly consist of segments. 28The morphology of these segments and their connectors is controlled by, and provide insights 29 into, the behaviour of the host rock during emplacement. For example, tensile brittle 30 fracturing leads to the formation of intrusive steps or bridge structures between adjacent 31 segments. In contrast, brittle shear faulting, cataclastic and ductile flow processes, as well as 32 heat-induced viscous flow or fluidization, promotes magma finger development. Textural 33 indicators of magma flow (e.g., rock fabrics) reveal that segments are aligned parallel to the 34 initial sheet propagation direction. Recognising and mapping segment long axes thus allows 35 melt source location hypotheses, derived from sheet distribution and orientation, to be 36 robustly tested. Despite the information that can be obtained from these structural signatures 37 of sheet intrusion propagation, they are largely overlooked by the structural and 38 volcanological communities. To highlight their utility, we briefly review the formation of 39 sheet intrusion segments, discuss how they inform interpretations of magma emplacement, 40 and outline future research directions. 41 42 48 , 1951; Gautneb and Gudmundsson, 1992; Rubin, 1995; Muirhead et al., 2015). Anderson 49Mapping and analysing the emplacement of igneous sheet swarms therefore allows volcano-50 tectonic processes to be unravelled, as well as aiding in identifying magma source locations 52 Geshi, 2005). Overall, the link between intrusion geometry and contemporaneous stress field 53 conditions has underpinned and dominated research and teaching of igneous sheet 54 emplacement in the fields of structural geology and volcanology. 55Over the last 50 years, it has been recognised that most igneous sheet intrusions 56 consist of segments (e.g., Pollard et al., 1975; Delaney and Pollard, 1981; Rickwood, 1990; 57 Schofield et al., 2012a), similar to structures observed in clastic intrusions (e.g., Vétel and 58 Cartwright, 2010) and mineralized veins (e.g., Nicholson and Pollard, 1985). Most research 59 has focused on segmented dykes emplaced via tensile elastic fracturing of the host rock (e.g., 60Delaney and Pollard, 1981; Rickwood, 1990). However, several studies have demonstrated 61 that mechanisms other than tensile elastic fracturing, such as brittle shear faulting, ductile 62 flow, and granular flow host rock deformation (e.g., fluidization), can also promote 63 segmentation of sheet intrusions (e.g., Pollard et al., 1975; Hutton, 2009; Schofield et al., 64 2010;...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
334 Leonard St
Brooklyn, NY 11211
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.