Raúl O. C. Fonseca

Ruhr University Bochum | RUB · Institute of Geology, Geophysics and Mineralogy

doi: 10.7185/geochemlet.2007 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 th...

The Izu-Bonin-Mariana volcanic arc is situated at a convergent plate margin where subduction initiation triggered the formation of MORB-like forearc basalts as a result of decompression melting and near-trench spreading. International Ocean Discovery Program (IODP) Expedition 352 recovered samples within the forearc basalt stratigraphy that contain...

In terrestrial magmas titanium is predominantly tetravalent (Ti 4+), in contrast, lunar magmas are more reduced (IW-1) and hence approximately 10% of their bulk Ti content is trivalent (Ti 3+). Changes in oxidation state and coordination number are both important parameters that can serve to drive Ti stable isotope fractionation. As such, mineral-m...

https://doi.org/10.7185/geochemlet.2342 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...

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 fra...

In the last two decades, boron has gained significance as a geochemical tracer in mantle studies, particularly related to fluid-mediated processes. In our investigation, we explore how boron and its stable isotopes distribute between basaltic melt and hydrous fluid under conditions relevant to magmatic degassing in the shallow crust (1000–1250 °C,...

Base‐metal sulfur liquids (mattes) play a crucial role as metasomatic agents and carriers of highly siderophile elements (HSE) within the Earth's mantle. Prior research has predominantly focused on sulfur‐poor metallic liquids involved in core formation scenarios. We conducted high‐pressure experiments using a multi‐anvil apparatus to investigate t...

The presence of an Eocene subduction event, in addition to Jurassic and Cretaceous ones, in the Rhodopes of Greece and Bulgaria is controversial. We report the first dating of an eclogite from the Lower Allochthon of the Rhodopes. The eclogite is a mafic lens enclosed in orthogneiss of the Arda‐2 Unit at Chepelare, Central Rhodopes. It was metamorp...

Base metal sulfides (Fe-Ni-Cu-S) are ubiquitous phases in mantle and subduction-related lithologies. Sulfides in the mantle often melt incongruently, which leads to the production of a Cu-Ni-rich sulfide melt and a solid residue called monosulfide solid solution (mss). Even though peridotite-hosted sulfides, which tend to be more Ni-rich, are likel...

Normally, volatiles in silicate melts are ephemeral components that escape as gases when the melt reaches fluid saturation. When fluid saturation occurs at elevated pressure, magmatic fluids may have large amounts of oxide solute dissolved, are less volatile, and may resemble viscous gels. In Cyprus we have the rare case that solutes of a magmatic...

Base metal sulfides (Fe-Ni-Cu-S) are ubiquitous phases in mantle and subduction-related lithologies. Sulfides in the mantle often melt incongruently, which leads to the production of a Cu-Ni-rich sulfide melt and leaves a solid residue called mono-sulfide solid solution (mss). However, the persistence of crystalline sulfide phases like mss in the E...

It is not well known which chemical differentiation pathways basaltic melts will take when they are iron metal saturated. Thermodynamically, the pathway seems predictable. So long as Fe metal is a stable liquidus phase and relative oxygen fugacity (fO2) is not subject to major fluctuations, the activity of FeO (aFeOmelt) is buffered by the iron-wüs...

High- and ultrahigh-pressure rocks occur in the Austroalpine Nappes in a ~400 km long belt from the Texel Complex in the west to the Sieggraben Unit in the east. Garnet growth during pressure increase was dated using Lu-Hf chronometry. The results range between c. 100 and 90 Ma, indicating a short period of subduction. Combined with already publish...

Elements with variable valence state (i.e., redox‐sensitive) often show contrasting mineral/melt partition coefficients as a function of oxygen fugacity ( f O 2 ) in magmatic systems. This is because trace‐element incorporation into crystal lattices depends on the charge, size, and crystal‐field stabilization energy of atoms, all of which differ gr...

An electrum–quartz pebble with a weight of 10.4 g was discovered in a cliff of Saalian glaciogenic sediments on the west coast of the German North Sea island of Sylt in 2012. It has a roundish water-worn appearance and consists of intergrown electrum and milky quartz. It is the largest known electrum find in Germany, and regarding its weight it als...

Several recent papers have purported to find ultra-reduced minerals-as natural examples-within ophiolitic mantle sections, including SiC moissanite, Fe-Si alloys, various metal carbides, nitrides, and borides. All those phases were interpreted to be mantle derived. The phases are recovered from mineral concentrates and are assigned to the deep mant...

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 valence...

Evidence of immiscibility between arsenide and sulfide melts has been observed both in experimental studies and natural samples from several localities worldwide (e.g., Ronda, Spain; Beni Bousera, Morocco; Dundonald Beach South, Canada). Platinum-group elements (PGE) have shown to have a strong affinity for arsenide melts but little is known about...

The aim of this study is the development of a separation technique for geological samples, namely bismuthinites, with the goal to isolate Tl from excess amounts of Bi. This will enable an isotopic measurement of the Tl content on the ultra-trace level to identify a possible signature of Bi α-decay. The separation of Tl from other elements like e.g....

Even though platinum group elements (PGE) solubilities are measured relative to pure metals, the PGE are assumed to dissolve as oxide complexes in silicate melts. PGE-oxide phases are, however, not known in magmatic rocks; in many cases PGE are associated with discrete magmatic phases (alloys, arsenides, bismuthotellurides, antimonides and sulfides...

Geochronology of ultra-high-pressure metamorphic rocks is able to constrain the timing and rates of subduction-zone processes. Lu–Hf garnet dating has the potential to yield information about the timing of the prograde evolution of subducting rocks under increasing pressure. In combination with other methods, it thus allows constraining the complet...

We report Lu-Hf isotope ages for garnet from the Late Archean Storø Supracrustal Belt (SSB) ranging from 2697 ± 8 Ma to 2646 ± 13 Ma. These ages essentially overlap with two previously reported Re-Os isotope ages for arsenopyrite associated with Au mineralization within the SSB, which implies that both Au-forming events took place while garnet was...

The date of the Moon-forming impact places an important constraint on Earth’s origin. Lunar age estimates range from about 30 Myr to 200 Myr after Solar System formation. Central to this age debate is the greater abundance of ¹⁸²W inferred for the silicate Moon than for the bulk silicate Earth. This compositional difference has been explained as a...

The Eo-Alpine high-pressure belt in the Austroalpine nappes consists of pre-Mesozoic basement rocks overprinted by eclogite-facies metamorphism during the Late Cretaceous. Parts of this basement were already eclogitized during the Variscan orogeny. Lu–Hf geochronology allowed to identify two high-pressure events in an eclogite body in the Schobergr...

Lunar mare basalts are a product of partial melting of the lunar mantle under more reducing conditions when compared to those expected for the Earth’s upper mantle. Alongside Fe, Ti can be a major redox sensitive element in lunar magmas, and it can be enriched by up to a factor of ten in lunar basaltic glasses when compared to their terrestrial cou...

Two Fe-Ni sulfides, resembling the chemical composition of a typical mantle base metal sulfide (BMS), were synthesized and used to test micro-analytical procedures (sample digestion and chemical separation) to determine ¹⁸⁷Os/¹⁸⁸Os and highly siderophile element (HSE) mass fractions in single BMS grains. The bulk ¹⁸⁷Os/¹⁸⁸Os and HSE mass fractions...

Griffin et al. (2018) discard our lightning experiments because we did not identify ultra-high pressure (UHP) phases. Our experiments (Ballhaus et al., 2017) provide the first rational explanation of many unusual findings in the so-called UHP ophiolites and hence undermine the foundations on which the resulting speculative geotectonic scenarios are...

The Rhodopes in Bulgaria and Greece represent a nappe stack of high-grade units with polymetamorphic history. Constraining the time of metamorphism in individual subunits is essential for unraveling the controversial framework of subduction, exhumation and nappe stacking. Here we present new evidence for Late Cretaceous high-pressure metamorphism i...

The Seve Nappe Complex of the Scandinavian Caledonides is thought to be derived from the distal passive margin of Baltica which collided with Laurentia in the Scandian Phase of the Caledonian Orogeny at 430–400 Ma. Parts of the Seve Nappe Complex were affected by pre-Scandian high- and ultrahigh-pressure metamorphism, in a tectonic framework that i...

Geochemical models describing the behaviour of niobium during Earth’s growth rely on the general paradigm that niobium was delivered by Earth’s asteroidal building blocks at chondritic abundances. This paradigm is based on the observation that niobium is traditionally regarded as a refractory and strongly lithophile element, and thus stored in the...

Since ultra-high pressure (UHP) minerals have been discovered in ophiolites from Tibet and the Polar Urals, it is speculated that the mantle sections of ophiolites may originate deep within the mantle. The UHP minerals are frequently found together with ultra-reduced silicides, carbides, and nitrides. Consequently, it is argued that the deep mantle...

http://www.sciencedirect.com/science/journal/00167037/216?sdc=1

The extreme depletion of the Earth’s mantle in sulfur is commonly seen as a signature of metal segregation from Earth’s mantle to Earth’s core. However, in addition to S, the mantle contains other elements as volatile as S that are hardly depleted relative to the lithophile volatility trend although they are potentially as siderophile as sulfur. We...

We present results of high-temperature olivine-melt, pyroxene-melt and plagioclase-melt partitioning experiments aimed at investigating the redox transition of Mo in silicate systems. Data for a series of other minor and trace elements (Sc, Ba, Sr, Cr, REE, Y, HFSE, U, Th and W) were also acquired to constrain the incorporation of Mo in silicate mi...

Competing eects of crystal chemistry and silicate melt composition on trace element behavior in magmatic systems: insights from crystal/silicate melt partitioning of the REE, Abstract We present new partition coecients for the REE, HFSE, Sn, In, Ga, Ba, Pt and Rh between clinopyroxene, olivine and basaltic melt as a function of crystal chemistry an...

Megacrystic sapphires are frequently associated with alkaline basalts, most notably in Asia and Australia, although basalt is not generally normative in corundum. Most of these sapphire occurrences are located in alluvial or eluvial deposits, making it difficult to study the enigmatic relationship between the sapphires and their host rocks. Here, w...

Although Earth’s continental crust is thought to derive from melting of the Earth’s mantle, how the crust has formed and the timing of its formation are not well understood. The main difficulty in understanding how the crust was extracted from the Earth’s mantle is that most isotope systems recorded in mantle rocks have been disturbed by crustal re...

The behavior of Pt, Pd, Ni and Cu in Se-sulfide system and the role of Se in platinum-group elements (PGE) fractionation have been experimentally investigated at temperatures between 1050 and 700 ºC in evacuated silica tubes. At 1050ºC, Se partially partitions into a vapor phase. At 980 ºC, monosulfide solid solution (mss) and sulfide melt are the...

We report detailed petrographic investigations along with 187Os/188Os data in Base Metal Sulfide (BMS) on four cratonic mantle xenoliths from Somerset Island (Rae Craton, Canada). The results shed light on the processes affecting the Re-Os systematics and provide time constraints on the formation and evolution of the cratonic lithospheric mantle be...

Sulfides are among the most important petrogenetic agents in magmatic systems. They are ubiquitous in most upper-mantle rock types, common as inclusions in diamonds and they host significant amounts of geochemically and economically important chalcophile (‘sulfur-loving’) elements, such as Cu, Ni, Pb, In, Au and the platinum-group elements. Despite...

The Troodos igneous complex (Cyprus) is a ca. 90 Ma old, well preserved supra-subduction zone ophiolite. Troodos is unique in that it shows evidence of fluid-saturation throughout the complex, from its base (i.e. podiform chromitites) to its uppermost units - the upper pillow lavas (UPL). However, it is unclear what the source of dissolved water in...

Highly siderophile element (HSE) concentration and ¹⁸⁷Os/¹⁸⁸Os isotopic heterogeneity has been observed on various scales in the Earth’s mantle. Interaction of residual mantle peridotite with infiltrating melts has been suggested to overprint primary bulk rock HSE signatures originating from partial melting, contributing to the heterogeneity seen i...

The metamorphic series of the Pohorje Mountains represents a part of the Eastern Alpine realm that was subjected to ultrahigh-pressure conditions during the Cretaceous Eo-Alpine orogenic cycle. The Slovenska Bistrica Ultramafic Complex located in the south-eastern Pohorje Mountains is an 8 km wide serpentinite body that contains lenses of garnet-be...

A specific feature of some basaltic lunar rocks is that their TiO2 contents can reach concentrations as high as 16 wt.%. The high-field strength elements (HFSE) group, which includes Ti, may provide valuable information of the processes that occurred in the lunar mantle to generate high-Ti mare basalts. To assess the effect of such high TiO2 concen...

The Siebengebirge Volcanic Field (SVF) in western Germany is part of the Cenozoic Central European Volcanic Province. Amongst these volcanic fields, the relatively small SVF comprises the entire range from silica-undersaturated mafic lavas to both silica-undersaturated and silica-saturated differentiated lavas. Owing to this circumstance, the SVF r...

The Etirol-Levaz Slice in the Penninic Alps (Valtournenche, Italy) is a piece of eclogite-facies continental basement sandwiched between two oceanic units, the blueschist-facies Combin Zone in the hanging wall and the eclogite-facies Zermatt-Saas Zone in the footwall. It has been interpreted as an extensional allochthon from the continental margin...

When continents collide, continental crust of the lower plate may be subducted to mantle depth and return to the surface to form eclogite facies metamorphic terranes, as typified by the Western Gneiss Complex of the Scandinavian Caledonides. Proterozoic basement of the Lofoten Islands, located northeast and along strike of the Western Gneiss Comple...

When melts reach H2O saturation before they are emplaced at the Earth’s surface, they exsolve a hydrous fluid phase. At elevated pressure and high temperature, a hydrous fluid is not pure H2O but can contain some quantities of silicate and metal oxide solute, notably if fluid saturation occurs at high pressure. Chemically and physically, fluid-satu...

The peridotite xenoliths of the Letlhakane kimberlite (Botswana), which intrude the Proterozoic Magondi Belt on the western margin of the Zimbabwe craton, represent highly depleted melting residues. These residues suffered subsequent variable metasomatic overprinting, evidenced by cryptic trace element enrichments in the spinel peridotites to modal...

Even though the platinum-group element (PGE) concentrations in magmatic ores and basaltic rocks are at the low ppm to low ppb level, the noble metals Os, Ir, Ru, Rh, and Pt commonly form discrete mineral phases, many at liquidus temperature. The most common platinum-group minerals (PGM) are PGE alloys, sulfides, arsenides, sulfarsenides, and tellur...