Geological atlas of western and central Europe

Metasedimentary rocks generally contain carbonaceous material (CM) deriving from the evolution of organic matter originally present in the host sedimentary rock. During metamorphic processes, this organic matter is progressively transformed into graphite s.s. and the degree of organisation of CM is known as a reliable indicator of metamorphic grade. In this study, the degree of organisation of CM was systematically characterised by Raman microspectroscopy across several Mesozoic and Cenozoic reference metamorphic belts. This degree of organisation, including within-sample heterogeneity, was quantified by the relative area of the defect band (R2 ratio). The results from the Schistes Lustres (Western Alps) and Sanbagawa (Japan) cross-sections show that (1) even through simple visual inspection, changes in the CM Raman spectrum appear sensitive to variations of metamorphic grade, (2) there is an excellent agreement between the R2 values calculated for the two sections when considering samples with an equivalent metamorphic grade, and (3) the evolution of the R2 ratio with metamorphic grade is controlled by temperature (T). Along the Tinos cross-section (Greece), which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks, the R2 ratio is nearly constant. Consequently, the degree of organisation of CM is not affected by the retrogression and records peak metamorphic conditions. More generally, analysis of 54 samples representative of high-temperature, low-pressure to high-pressure, low-temperature metamorphic gradients shows that there is a linear correlation between the R2 ratio and the peak temperature [T(°C) = −445 R2 + 641], whatever the metamorphic gradient and, probably, the organic precursor. The Raman spectrum of CM can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism. Temperature can be estimated to ± 50 °C in the range 330–650 °C. A few technical indications are given for optimal application.

Raman spectra of carbonaceous material in metasediments: a new geothermometer

Fluid inclusions in hydrothermal ore deposits

On the characterization of disordered and heterogeneous carbonaceous materials by Raman spectroscopy.

Raman spectroscopy for fluid inclusion analysis

This paper focuses on the similarities and differences between metamorphic graphite (formed in situ from organic matter) and fluid-deposited graphite. We discuss the formation of fluid-deposited graphite in terms of the source of carbon, the characteristics of the C-bearing fluids (the C-O-H system), the mechanisms of carbon mobilization, and the mechanisms of carbon precipitation. New and existing analytical data are compiled on the physical and chemical characteristics of fluid-deposited graphite obtained by the following techniques: optical microscopy, differential thermal analysis, thermogravimetry, X-ray diffraction, Raman spectroscopy, and stable isotope mass spectrometry. Our discussions focus on major, that is, volumetrically significant, worldwide concentrations of graphite.

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Natural fluid-deposited graphite: Mineralogical characteristics and mechanisms of formation

Production of lightweight aggregates from mining and industrial wastes.

Washing aggregate sludge from a gravel pit, fly ash of the Aliaga thermal power plant (Teruel, Spain) and used motor oil from cars have been physically, chemically and mineralogically characterized. They were mixed, milled and formed into pellets, pre-heated for 5 min and sintered in a rotary kiln at 1150 °C, 1175 °C, 1200 °C and 1225 °C for 10 min and 15 min at each temperature. The effect of raw material characteristics, heating temperatures and dwell times on loss on ignition (LOI), bloating index (BI), loose bulk density ( ρ b ), apparent and dry particle density ( ρ a , ρ rd ), voids ( H ), water absorption (WA 24h ) and compressive strength ( S ) had been determined. All mixtures showed bloating potential taking into consideration the gases released at high temperatures, two of which were located inside and close to the “area of bloating”. The products obtained were lightweight aggregates (LWAs) in accordance with norm UNE-EN-13055-1 ( ρ b  ≤ 1.20 g/cm 3 or particle density ≤2.00 g/cm 3 ). LWAs manufactured with 75%:25% and 50%:50% proportions of washing aggregate sludge:fly ash, heated at different temperatures and dwell times, were expanded LWAs (BI > 0). They showed the lowest loose bulk density, the lowest dry and apparent particle density, the lowest water absorption and the highest compressive strength. It was possible to establish three groups of LWAs depending on their properties in comparison to Arlita G3 and/or F3 , a commercially available lightweight aggregate manufactured in Spain. Our LWAs could have the same or similar applications of these commercial products, such as insulation, geotechnical applications, horticulture, gardening and/or prefabricated lightweight structures and insulation lightweight concretes.

Characterization of lightweight aggregates manufactured from washing aggregate sludge and fly ash

The Cameros Basin in Central Spain is an intraplate rift
basin that developed from Late Jurassic to Middle Albian time along
NW–SE trending troughs. The sedimentary basin fill was deposited
predominantly in continental environments and comprises several depositional
sequences. These sequences consist of fluvial sandstones that
commonly pass upward into lacustrine deposits at the top, producing
considerable repetition of facies. This study focused on the western
sector of the basin, where a total of seven depositional sequences (DS-
1 to DS-7) have been identified.
The composition of sandstones permits the characterization of each
sequence in terms of both clastic constituents and provenance. In addition,
four main petrofacies are identified. Petrofacies A is quartzosedimentolithic
(mean of Qm85F2Lt13) and records erosion of marine
Jurassic pre-rift cover during deposition of fluvial deposits of DS-1
(Brezales Formation). Petrofacies B is quartzofeldspathic (mean of
Qm81F14Lt5) with P/F > 1 at the base. This petrofacies was derived
from the erosion of low- to medium-grade metamorphic terranes of
the West Asturian–Leonese Zone of the Hesperian Massif during deposition
of DS-2 (Jaramillo Formation) and DS-3 (Salcedal Formation).
Quartzose sandstones characterize the top of DS-3 (mean of
Qm92F4Lt4). Petrofacies C is quartzarenitic (mean of Qm95F3Lt2) with
P/F > 1 and was produced by recycling of sedimentary cover (Triassic
arkoses and carbonate rocks) in the SW part of the basin (DS-4, Pen˜ -
acoba Formation). Finally, depositional sequences 5, 6, and 7 (Pinilla
de los Moros–Hortiguela, Pantano, and Abejar–Castrillo de la Reina
formations, respectively) contain petrofacies D. This petrofacies is
quartzofeldspathic with P/F near zero and a very low concentration of
metamorphic rock fragments (from Qm85F11Lt4 in Pantano Formation
to Qm73F26Lt1 in Castrillo de la Reina Formation). Petrofacies D was
generated by erosion of coarse crystalline plutonics located in the Central
Iberian Zone of the Hesperian Massif. In addition to sandstone
petrography, these provenance interpretations are supported by clay
mineralogy of interbedded shales. Thus, shales related to petrofacies
A and C have a variegated composition (illite, kaolinite, and randomly
interlayered illite–smectite mixed-layer clays); the presence of chlorite
characterizes interbedded shales from petrofacies B; and Illite and kaolinite
are the dominant clays associated with petrofacies D.
These petrofacies are consistent with the depositional sequences and
their hierarchy. An early megacycle, consisting of petrofacies A and B
(DS-1 to DS-3) was deposited during the initial stage of rifting, when
troughs developed in the West Asturian–Leonese Zone. A second stage
of rifting resulted in propagation of trough-bounding faults to the SW,
involving the Central Iberian Zone as a source terrane and producing
a second megacycle consisting of petrofacies C and D (DS-4, DS-5, DS-6, and DS-7). Sandstone composition has proven to be a powerful tool
in basin analysis and related tectonic inferences on intraplate rift basins
because of the close correlation that exists between depositional
sequences and petrofacies.

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Sandstone petrography of continental depositional sequences of an intraplate rift basin: western Cameros Basin (North Spain)

Three duricrust types (calcretes, palycretes and silcretes) have been distinguished in the Lower Paleogene arkosic materials from the margins of the Duero and Tajo basins (central Spain). In the calcretes the cements are composed of calcite plus palygorskite, whereas palygorskite is the only cement in the palycretes. In the silcretes, the cement consists chiefly of opal and chalcedony, with minor quartz. The important duricrust development in the Paleogene detrital materials can be correlated with a drastic climatic change towards colder and more arid conditions during this time, as inferred from the sedimentological features and the clay mineral evolution. The origin of calcretes and palycretes is related to the movement of alkaline phreatic waters generated from dolomitic rocks of Cretaceous age cropping out in the near surroundings. Silcretes originated from the vertical transfer of silica from supersaturated groundwaters, from the Hercynian granitic rocks, up to the surface. Silcretes are developed either on unconsolidated arkosic materials or replace previous calcrete or palycrete levels.

M. Rodas

Papers

Natural fluid-deposited graphite: Mineralogical characteristics and mechanisms of formation

Production of lightweight aggregates from mining and industrial wastes.

Characterization of lightweight aggregates manufactured from washing aggregate sludge and fly ash

Sandstone petrography of continental depositional sequences of an intraplate rift basin: western Cameros Basin (North Spain)

Calcretes, palycretes and silcretes in the Paleogene detrital sediments of the Duero and Tajo basins, central Spain