Mass-dependent titanium isotope variations in terrestrial and extra-terrestrial basalts

Titan ist ein relativ häufiges Nebenelement. Während einige Silikate größere Mengen an Titan enthalten können (Titanit, Ca-reiche Amphibole), so sind die häufigsten Ti-reichen Phasen die Ti-Oxide, wie Ilmenit und Rutil. Als in den meisten Silikatmineralen inkompatibles Element wird Ti während der fraktionierten Kristallisation eines Magmas in der Schmelze angereichert. Der stetig steigende Titangehalt in der Schmelze führt dazu, dass ab einem gewissen Ti-Gehalt Titanoxide aus der Schmelze auskristallisieren. Die niedrigere räumliche Koordination von Ti relativ zur höheren Koordination im Kristallgitter der Oxide führt zu einem bevorzugten Einbau der leichten Ti-Isotope in das Kristallgitter der Oxide. Folglich wird während der Kristallisation die zurückbleibende Schmelze stetig an schwereren Ti-Isotopen angereichet, wodurch es möglich wird, anhand von Ti-Isotopen die Entwicklung eines magmatischen Systems nachzuvollziehen. Hochpräzise Messungen von Ti-Isotopenzusammensetzungen werden mit der sogenannten Doppelspike-Methode durchgeführt. Ein Doppelspike ist eine künstlich hergestellte Lösung, in der die Häufigkeiten zweier Ti-Isotope stark erhöht sind, wohingegen die Häufigkeiten der übrigen Ti-Isotope stark verarmt sind. Sobald diese Isotopenverhältnisse in der Lösung sehr genau bekannt ist, wird sie zu einer unbekannten Probe hinzugegeben und nach chemischer Abtrennung störender Elemente und massenspektrometrischer Bestimmung der Mischung, kann daraus durch iterative Berechnungen die Ti-Isotopenzusammensetzung der unbekannten Probe relativ zu einem Referenzmaterial sehr genau und präzise bestimmt werden. Diese Monographie beschreibt die Implementierung der Ti-Doppelspike-Isotopenverdünnungsmethode in der Arbeitsgruppe Geo- und Kosmochemie der Universität zu Köln (KAPITEL 2). Neben dem Doppelspike wird zusätzlich ein weiteres Referenzmaterial, welches dem etablierten „Origins Lab“-Ti-Standard ähnelt, kalibriert. Weiterhin werden die chemischen Trennverfahren und massenspektrometrischen Protokolle entwickelt und angepasst, um die höchstmögliche Präzision der Methode an dem Neptune Plus Multi-Kollektor-Plasmaquellen-Massenspektrometer sicherzustellen. Nach der erfolgreichen Kalibrierung der Chemikalien und der Messprotokolle werden diese angewendet, um die Ti-Isotopenzusammensetzung von Mondgesteinen sowie terrestrischen Gesteinen zu bestimmen. Die in KAPITEL 3 vorgestellten Ergebnisse erweitern die vorhandenen Ti-Isotopendaten für Mondgesteine und erlauben das genauere Bestimmen der Ti-Isotopenzusammensetzung der postulierten urKREEP-Komponente, der letzten Flüssigphase vor Erstarren des lunaren Magmaozeans (angereichert an inkompatiblen Elementen wie K, den Seltenen Erden, sowie P). Zusätzlich zu den Analysen wird die Ti-Isotopenzusammensetzung der urKREEP-Komponente durch Modellrechnungen bestimmt. Diese sind im Rahmen der Unsicherheiten identisch mit den hier gemessenen Daten und vorangegangenen Arbeiten. Titan-Isotopenzusammen-setzungen der „low-Ti“ und „high-Ti“ Mare Basalte zeigen deutliche Variationen, welche wahrscheinlich durch den petrogenetischen Entstehungsprozess der Gesteine entstanden sind. Während die vermutete „low-Ti“ Mare-Basalt-Magmenquelle der mafische Mantel des Mondes ist, benötigen die „high-Ti“ Mare-Basalte für ihre Entstehung die Gegenwart einer Ti-reichen Phase in der Magmenquelle, wie Ilmenit. Damit ist die Quellregion höchstwahrscheinlich eine Mischung aus dem mafischen Mantel und den Ilmenit-reichen Kumulaten. Die beobachteten Variationen in Ti-Isotopenzusammensetzungen in „high-Ti“ Mare-Basalten sind, gekoppelt mit „High Field Strength Element (Elemente mit hoher Valenz und kleinem Ionenradius)“ Daten, auf das partielle Schmelzen eines Ilmenit-reichen Kumulats zurückzuführen. Die Ti-Isotopenvariationen innerhalb der „low-Ti“ Mare-Basalt Gruppen sind auf fraktionierte Kristallisation von Ilmenit vor der Eruption des Magmas oder das Ausbleiben dieses Prozesses zurückzuführen. Mittels Verteilungskoeffizienten sowie möglichen Zusammensetzungen der „high-Ti“ Quellregionen, welche wiederum auf verschiedenen Magmaozean-Kristallisations-modellen basieren, wird das partielle Schmelzen des mafischen Mantels (ohne Ilmenit) oder der Ilmenit-reichen Kumulate modelliert. Die berechneten Trends stimmen mit den hier gemachten Beobachtungen überein und unterstreichen, dass die Variationen in „high-Ti“ und „low-Ti“ Mare-Basalten auf das partielle Schmelzen eines Ilmenit-reichen Kumulats und fraktionierte Kristallisation von Ilmenit zurückzuführen sind. Weiterhin kann, basierend auf den Ergebnissen dieser Studie, eine Petrogenese der „high.Ti“ Mare-Basalte durch Assimilation einer Ilmenit-reichen Komponente in ein „low-Ti“ Magma ausgeschlossen werden. In Kapitel 4 wurden Proben verschiedener Subduktionszonen, sowie dazugehörige Boninite und Sedimentproben gemessen. Titan-Isotopenzusammensetzungen mit zusätzlichen Spurenelement- und High Field Strength Element-Daten zeigen, das wasserreiche Schmelzen des subduzierten Sediments keinen Einfluss auf die Ti-Isotopenzusammensetzung haben. Vielmehr liegt der Grund für die beobachteten Variationen wahrscheinlich in der An- beziehungsweise Abwesenheit von Ti-reichen Oxiden während des partiellen Schmelzens des subduzierten Materials. Weiterhin zeigen die systematisch schwereren Ti-Isotopen-zusammensetzungen der boninitischen Proben relativ zu den dazugehörigen Tholeiiten, dass das partielle Schmelzen des verarmten Mantelkeils in der Gegenwart von Cr-reichem Spinell zu Ti-Isotopenfraktionierung führt. Anders als frühere Studien deuten die Ergebnisse in dieser Arbeit auch darauf hin, dass Amphibole Ti-Isotope fraktionieren können, was bisher nicht beobachtet wurde. Diese Monographie stellt heraus, dass die Kombination von High Field Strength Element-Daten mit Ti-Isotopendaten weitreichende Einblicke in die petrogenetischen Prozesse von Mondgesteinen und terrestrischen Gesteinen erlauben. Zusätzlich deuten terrestrische Ti-Isotopenvariationen in einer Lokalität darauf hin, dass neben Ti-reichen Oxiden auch einige silikatische Minerale, genauer Amphibole, Ti-Isotope fraktionieren können. Dies unterstreicht nur noch mehr die Notwendigkeit, Ti-Isotopenfraktionierungsfaktoren für silikatische Minerale zu bestimmen

Mineralogical Controls on the Ti Isotope Composition of Subduction Zone Magmas

The positive Ti isotope versus SiO2-content correlation in igneous rocks reflects the fractional crystallization of Ti-bearing oxide minerals. However, Ti isotope variations of subduction-related igneous rocks indicate that the Ti isotope compositions of their mantle sources are heterogeneous and additional mineral phases may promote Ti isotope fractionation. We have determined the Ti isotope composition of well-characterized subduction-related basalts, andesites and boninites. Samples from the Solomon Islands, the Troodos ophiolite in Cyprus, and Cape Vogel in Papua New Guinea show small but resolvable variations that may be related to differences in their mantle sources. Specifically, the δ49Ti of boninites (+0.109‰ to +0.168‰) is slightly higher than that of tholeiites (−0.027‰ to +0.111‰) from the same localities (Troodos in Cyprus and Cape Vogel in Papua New Guinea). Modeling suggests the partial melting of progressively depleted mantle sources where residual Cr-spinel plays a greater role in controlling the Ti budget during partial melting. More pronounced variations in δ49Ti are clearly linked to the fractional crystallization of Ti-oxides: Samples from Rabaul Volcanic Complex (New Britain, Papua New Guinea) show increasing δ49Ti (up to +0.373‰) with increasing Ti/V and decreasing Dy/Yb. Fractional crystallization models suggest that oxide minerals and amphibole are needed to sufficiently increase the δ49Ti of these magmas. Our study highlights that the combination of diagnostic trace element patterns and Ti isotope compositions in subduction-related igneous rocks can be a powerful tool to constrain petrogenetic processes and to discriminate between different crystallizing mineral phases

Titanium isotope constraints on the mafic sources and geodynamic origins of Archean crust

The timing and formation of Earth’s first continents during the Archean are subjects of significant debate. By examining titanium isotope variations in Archean Tonalite-Trondhjemite-Granodiorite (TTG) rocks and using advanced thermodynamic modelling, we can narrow down the processes involved and emphasise the role of mafic precursor compositions. In our study of Eoarchean Isua metabasalts and Itsaq tonalites in southern West Greenland, we observed a pattern of increasing Ti isotope enrichment with higher SiO2 content, resembling the compositions found in modern subduction zone rocks. Our modelling suggests that the Ti isotope variations in TTGs can be best explained by a combination of partial melting of low TiO2 metabasalts and subsequent crystallisation of tonalitic magmas, resulting in heavier Ti isotopes. This means that Ti isotopes help us distinguish the contributions of various mafic sources and fractional crystallisation during TTG formation. In the case of Itsaq tonalites and many other Eoarchean TTGs, low TiO2 tholeiitic metabasalts with arc-like characteristics likely represent the mafic source rocks, suggesting the formation of some of Earth’s earliest continental crust within a proto-subduction zone setting

Coping and the stages of psychosis: an investigation into the coping styles in people at risk of psychosis, in people with first-episode and multiple-episode psychoses

Aim: The concept of coping is central to recent models of psychosis. The aim of the present paper is to explore whether specific coping styles relate to certain stages of the disorder. Methods: Thirty-nine clients at clinical high risk (CHR) of first-episode psychosis, 19 clients with first-episode psychosis and 52 clients with multiple-episode psychosis completed a Stress Coping Questionnaire. This questionnaire consists of 114 items defining one overall positive coping scale (with three subscales) and one negative coping scale. Analyses of variance with group as between-subject factor and coping behaviour as within-subject factor were used to identify different coping patterns. Results: On the level of subscales no group differences could be detected, but analysis of variance revealed slightly different patterns: CHR clients used significantly more negative than positive coping styles (P = 0.001), followed by patients with multiple-episode psychosis (P = 0.074). Firstepisode patients were most likely to use negative as well as positive coping (P = 0.960). Across all stages of illness, stress control was significantly preferred compared to the other positive coping styles distraction and devaluation. Again, this pattern was especially pronounced for at-risk clients and patients with multiple-episode psychosis, whereas patients with first-episode psychosis were most likely to use devaluation as well as distraction. Conclusions: The overall coping styles were similar across the different stages of psychosis. However, at-risk persons presented especially pronounced negative coping and a small range of strategies, indicating a specific need for psychosocial support in this stage of the disorder

Unravelling lunar mantle source processes via the Ti isotope composition of lunar basalts

Formation and crystallisation of the Lunar Magma Ocean (LMO) was one of the most incisive events during the early evolution of the Moon. Lunar Magma Ocean solidification concluded with the coeval formation of K-, REE- and P-rich components (KREEP) and an ilmenite-bearing cumulate (IBC) layer. Gravitational overturn of the lunar mantle generated eruptions of basaltic rocks with variable Ti contents, of which their δ49Ti variations may now reflect variable mixtures of ambient lunar mantle and the IBC. To better understand the processes generating the spectrum of lunar low-Ti and high-Ti basalts and the role of Ti-rich phases such as ilmenite, we determined the mass dependent Ti isotope composition of four KREEP-rich samples, 12 low-Ti, and eight high-Ti mare basalts by using a 47Ti-49Ti double spike. Our data reveal significant variations in δ49Ti for KREEP-rich samples (+0.117 to +0.296 %) and intra-group variations in the mare basalts (-0.030 to +0.055 % for low-Ti and +0.009 to +0.115 % for high-Ti basalts). We modelled the δ49Ti of KREEP using previously published HFSE data as well as the δ49Ti evolution during fractional crystallisation of the LMO. Both approaches yield δ49TiKREEP similar to measured values and are in excellent agreement with previous studies. The involvement of ilmenite in the petrogenesis of the lunar mare basalts is further evaluated by combining our results with element ratios of HFSE, U and Th, revealing that partial melting in an overturned lunar mantle and fractional crystallisation of ilmenite must be the main processes accounting for mass dependent Ti isotope variations in lunar basalts. Based on our results we can also exclude formation of high-Ti basalts by simple assimilation of ilmenite by ascending melts from the depleted lunar mantle. Rather, our data are in accord with melting of these basalts from a hybrid mantle source formed in the aftermath of gravitational lunar mantle overturn, which is in good agreement with previous Fe isotope data.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

The redox dependence of titanium isotope fractionation in synthetic Ti-rich lunar melts

Equilibria between Ti oxides and silicate melt lead to Ti isotope fractionation in terrestrial samples, with isotopically light Ti oxides and isotopically heavy coexisting melt. However, while Ti is mostly tetravalent in terrestrial samples, around 10% of the overall Ti is trivalent at fO2 relevant to lunar magmatism (~ IW-1). The different valences of Ti in lunar samples, could additionally influence Ti stable isotope fractionation during petrogenesis of lunar basalts to an unknown extent. We performed an experimental approach using gas mixing furnaces to investigate the effect of Ti oxide formation at different fO2 on Ti stable isotope fractionation during mare basalt petrogenesis. Two identical bulk compositions were equilibrated simultaneously during each experiment to guarantee comparability. One experiment was investigated with the EPMA to characterize the petrology of experimental run products, whereas the second experiment was crushed, and fabricated phases (i.e., oxides, silicates and glass) were handpicked, separated and digested. An aliquot of each sample was mixed with a Ti double-spike, before Ti was separated from matrix and interfering elements using a modified HFSE chemistry. Our study shows fO2-dependent fractionation within seven samples from air to IW-1, especially ∆49Ti-melt and ∆49Tiarmalcolite-orthopyroxene become more fractionated from oxidized to reduced conditions (− 0.092 ± 0.028-  − 0.200 ± 0.033 ‰ and  − 0.089 ± 0.027- − 0.250 ± 0.049 ‰, respectively), whereas ∆49Tiorthopyroxene-melt shows only a minor fractionation (− 0.002 ± 0.017-0.050 ± 0.025 ‰). The results of this study show that Ti isotope fractionation during mare basalt petrogenesis is expected to be redox dependent and mineral-melt fractionation as commonly determined for terrestrial fO2 may not be directly applied to a lunar setting. This is important for the evaluation of Ti isotope fractionation resulting from lunar magmatism, which takes place under more reducing conditions compared to the more oxidized terrestrial magmatism.Deutsche ForschungsgemeinschaftProjekt DEA

Unravelling lunar mantle source processes via the Ti isotope composition of lunar basalts

Formation and crystallisation of the Lunar Magma Ocean (LMO) was one of the most incisive events during the early evolution of the Moon. Lunar Magma Ocean solidification concluded with the coeval formation of K-, REE- and P-rich components (KREEP) and an ilmenite-bearing cumulate (IBC) layer. Gravitational overturn of the lunar mantle generated eruptions of basaltic rocks with variable Ti contents, of which their delta Ti-49 variations may now reflect variable mixtures of ambient lunar mantle and the IBC. To better understand the processes generating the spectrum of lunar low-Ti and high-Ti basalts and the role of Ti-rich phases such as ilmenite, we determined the mass dependent Ti isotope composition of four KREEP-rich samples, 12 low-Ti, and eight high-Ti mare basalts by using a Ti-47 Ti-49 double spike. Our data reveal significant variations in delta Ti-49 for KREEP-rich samples (+0.117 to +0.296 parts per thousand) and intra-group variations in the mare basalts (-0.030 to +0.035 parts per thousand for low-Ti and +0.009 to +0.113 parts per thousand for high-Ti basalts). We modelled the delta Ti-49 of KREEP using previously published HFSE data as well as the b 49 Ti evolution during fractional crystallisation of the LMO. Both approaches yield delta Ti-49(KREEP) similar to measured values and are in excellent agreement with previous studies. The involvement of ilmenite in the petrogenesis of the lunar mare basalts is further evaluated by combining our results with element ratios of HFSE, U and 1h, revealing that partial melting in an overturned lunar mantle and fractional crystallisation of ilmenite must be the main processes accounting for mass dependent Ti isotope variations in lunar basalts. Based on our results we can also exclude formation of high-Ti basalts by simple assimilation of ilmenite by ascending melts from the depleted lunar mantle. Rather, our data are in accord with melting of these basalts from a hybrid mantle source formed in the aftermath of gravitational lunar mantle overturn, which is in good agreement with previous Fe isotope data