Understanding magma genesis through analysis of melt inclusions: application of innovative micro-sampling techniques

Melt entrapped as inclusions in early-formed phenocrysts provide geochemists with an exceptional opportunity to study sample material from the earliest stages in the formation of a suite of lavas. With a foucus on olivine-hosted melt inclusions, this Ph.D. thesis has explored the potentials for obtaining Sr isotope ratios on individual olivine-hosted melt inclusions, and examined the potentials for Sr isotope studies on melt inclusions to reveal new information on the origin of CFB and OIB. A novel technique is introduced that facilitate precise and accurate Sr isotope and trace element analysis of individual melt inclusions at sub-nanogram levels - thus applicable to typical melt inclusion suites from OIB and CFB, and in general to 'problems' where precise and accurate Sr isotope and trace element information is required on sub-nanogram Sr samples. The technique developed combines off-line sampling by micro-milling, micro Sr column chemistry, Sr isotope determination by TIMS, and trace element analysis by ICPMS. Olivine-hosted melt inclusions from two suites of high (^3)He/(^4)He lavas of the North Atlantic Igneous Province are studied. These reveal that Sr isotope and trace element measurements on individual melt inclusions provide a higher resolution picture of the pre-aggregated melt compositions and the different mantle and crustal components involved in the magma genesis, which otherwise were obscured within the whole-rock data. The Sr isotope and elemental variability recorded by the olivine-hosted melt inclusions contrast the more subtle variations of the host lava suites and raises the question of whether the (^3)He/(^4)He measured in melt inclusions in olivine phenocrysts should be related to the chemistry of melt inclusions rather than the bulk lava chemistry. The study further provides strong evidence that the extreme, high (^3)He/(^4)He signature observed in magmas from the North Atlantic Igneous Province is derived from a depleted component in their source, and hence such He isotopic signature should no longer be regarded as canonical evidence for primitive, lower mantle source

Late Cretaceous (late Campanian-Maastrichtian) sea-surface temperature record of the Boreal Chalk Sea

The last 8 Myr of the Cretaceous greenhouse interval were characterized by a progressive global cooling with superimposed cool/warm fluctuations. The mechanisms responsible for these climatic fluctuations remain a source of debate that can only be resolved through multi-disciplinary studies and better time constraints. For the first time, we present a record of very high-resolution (ca. 4.5 kyr) sea-surface temperature (SST) changes from the Boreal epicontinental Chalk Sea (Stevns-1 core, Denmark), tied to an astronomical timescale of the late Campanian–Maastrichtian (74 to 66 Ma). Well-preserved bulk stable isotope trends and calcareous nannofossil palaeoecological patterns from the fully cored Stevns-1 borehole show marked changes in SSTs. These variations correlate with deep-water records of climate change from the tropical South Atlantic and Pacific oceans but differ greatly from the climate variations of the North Atlantic. We demonstrate that the onset and end of the early Maastrichtian cooling and of the large negative Campanian–Maastrichtian boundary carbon isotope excursion are coincident in the Chalk Sea. The direct link between SSTs and δ13C variations in the Chalk Sea reassesses long-term glacio-eustasy as the potential driver of carbon isotope and climatic variations in the Maastrichtian

Regulatory control of naturally occurring radioactive material (NORM) in the Nordic countries : Report from working group Nordic NAT

Radiological risks associated with naturally occurring radioactive materials (NORM) have been fully recognized in recent decades, and hence, resulted in the integration of NORM radiation protection requirements within the EU Directive 2013/59 and IAEA BSS (2014). Still, it has been internationally emphasized that NORM-related knowledge gaps and uncertainties might present issues in coping with the existing regulatory requirements during their transposition and implementation into national legislations and regulatory frameworks. Therefore, NORM is one of the main subjects in the recently formed Nordic working group on natural ionizing radiation (WG Nordic[1]Nat). NORM regulatory approaches for radiation protection control, possibilities for collaboration, scientific projects and joint research, monitoring programmes, communication issues, etc. are considered within the group, based on the defined mandate. The current report is a result of the first joint WG Nordic-Nat activity related to NORM, and it provides an overview of national legislations, regulatory approaches and practices concerning NORM across Nordic countries i.e., Denmark, Finland, Iceland, Norway and Sweden. Denmark, Finland and Sweden are member states of the European Union (EU), and hence, the Council Directive 2013/59/Euratom (EU BSS) containing NORM specific requirements has been adopted and implemented in the legislation of these countries. Although Norway and Iceland are not member states of the EU, and thus not bound by the EU BSS, legislation and regulatory approaches for NORM have also been developed in these countries according to the international standards and specific country circumstances. Both differences and similarities related to the legislation, adopted regulatory control approaches for handling of NORM in the industries, NORM waste management and disposal as well as for environmental discharge control have been seen across Nordic countries, and are presented in this report. Furthermore, a provided description of the approahes in regulatory control of NORM-processing industries, NORM waste and pollution in the Nordic countries allows an identification of the common interest for NORM specific issues. The potential topics for future WG Nordic-Nat collaboration have been identified as (a) use of dose criteria for exemption and clearance of NORM and NORM industries from notification and authorization; (b) safety and environmental assessments for radioactive NORM waste disposal and discharge; (c) regulatory control of multi[1]contaminants in NORM waste; (d) environmental monitoring in NORM processing industries and disposal sites; (e) inspections in facilities involving NORM; (f) NORM legacy sites and remediation; (g) stakeholder engagement and risk communication in NORM; (h) transboundary movement of NORM waste for disposal and NORM contaminated materials for processing, and finally, (i) potential update of Nordic flag book - publication “Naturally Occurring Radiation in the Nordic Countries (Recommendations, 2000)

Sublithospheric diamond ages and the supercontinent cycle.

Subduction related to the ancient supercontinent cycle is poorly constrained by mantle samples. Sublithospheric diamond crystallization records the release of melts from subducting oceanic lithosphere at 300-700 km depths1,2 and is especially suited to tracking the timing and effects of deep mantle processes on supercontinents. Here we show that four isotope systems (Rb-Sr, Sm-Nd, U-Pb and Re-Os) applied to Fe-sulfide and CaSiO3 inclusions within 13 sublithospheric diamonds from Juína (Brazil) and Kankan (Guinea) give broadly overlapping crystallization ages from around 450 to 650 million years ago. The intracratonic location of the diamond deposits on Gondwana and the ages, initial isotopic ratios, and trace element content of the inclusions indicate formation from a peri-Gondwanan subduction system. Preservation of these Neoproterozoic-Palaeozoic sublithospheric diamonds beneath Gondwana until its Cretaceous breakup, coupled with majorite geobarometry3,4, suggests that they accreted to and were retained in the lithospheric keel for more than 300 Myr during supercontinent migration. We propose that this process of lithosphere growth-with diamonds attached to the supercontinent keel by the diapiric uprise of depleted buoyant material and pieces of slab crust-could have enhanced supercontinent stability

Extreme differences in 87Sr/86Sr between Samoan lavas and the magmatic olivines they host: Evidence for highly heterogeneous 87Sr/86Sr in the magmatic plumbing system sourcing a single lava

.Investigations of mantle heterogeneity in ocean island basalts (OIB) frequently compare heavy radiogenic isotopes (i.e. 87Sr/86Sr), often measured in whole rock powders, with 3He/4He and δ18O, commonly measured in olivines. However, the 87Sr/86Sr in the olivines, which is dominated by Sr in melt inclusions, may not be in equilibrium with the 87Sr/86Sr in the whole rock. Here we present new 87Sr/86Sr measurements made on Samoan magmatic olivines, where multiple olivine crystals are aggregated for a single isotopic measurement. The olivines host abundant melt inclusions, and yielded relatively large quantities of Sr (13.0 to 100.6 ng) in 19 to 185 mg aliquots of fresh olivine, yielding high Srsample/Srblank ratios (≥ 427). These new data on olivines show that samples can exhibit significant 87Sr/86Sr disequilibrium: in one extreme sample, where the basaltic whole rock 87Sr/86Sr (0.708901) is higher than several different aliquots of aggregate magmatic olivines (0.707385 to 0.707773), the whole rock-olivine 87Sr/86Sr disequilibrium is > 1590 ppm. The 87Sr/86Sr disequilibrium observed between whole rocks and bulk olivines relates to the isotopic disequilibrium between whole rocks and the average 87Sr/86Sr of the population of melt inclusions hosted in the olivines. Therefore, a population of olivines in a Samoan lava must have crystallized from (and trapped melts of) a different 87Sr/86Sr composition than the final erupted lava hosting the olivines. A primary question is how melts with different 87Sr/86Sr can exist in the same magmatic plumbing system and contribute heterogeneous 87Sr/86Sr to a lava and the magmatic olivines it hosts. We explore potential mechanisms for generating heterogeneous melts in magma chambers. The reliance, in part, of chemical geodynamic models of the relationships between isotopic systems measured in whole rocks (87Sr/86Sr) and systems measured in olivines (3He/4He and δ18O) means that whole rock-olivine Sr-isotopic disequilibrium will be important for evaluating relationship among these key isotopic tracer systems. Moving forward, it will be important to evaluate whether whole rock-olivine Sr-isotopic disequilibrium is a pervasive issue in OIB globally