1,721,069 research outputs found
X-ray tomography of tourmaline nodules in granitoid rocks: fractal analysis and petrological implications
No full textChaotic advection, fractals and diffusion during mixing of magmas:evidence from lava flows
No full textDevelopment of viscous fingering between enclaves and host magma: evidence from Vegetation Island (Terra Nova Intrusive Complex, Antarctica)
No full textA wide range of types of contact morphology among mafic and felsic magmas are observed in outcrops on Vegetation Island (Terra Nova Intrusive Complex, Antarctica). Image analysis and fractal geometry techniques were applied for in-depth study of the mafic/felsic interface, with the aim of studying the origin of the varied morphologies. In particular, the length (IPN) and fractal dimension (D-box) of interfaces were measured. Results indicate that there is a close exponential dependence of IPN on D-box.
The observed morphologies are identical to those observed during viscous fingering processes induced by the displacement of a more viscous fluid by a less viscous one. To test if viscous fingering was responsible in this case too, IPN and D-box values were measured on viscous fingering structures obtained experimentally using various viscosity ratios (V-R) from the literature. Results indicate that, as in the natural case, there is an exponential dependence of IPN on D-box, leading to the conclusion that the varied interface morphologies between mafic and felsic magmas are the result of viscous fingering dynamics. In addition, experimental studies clearly show that there is an exponential relationship between the viscosity ratio of fluids and the interface fractal dimension (D-box), and the ratio between the two types of magma was estimated using this relationship. It is shown that viscosity contrasts between mafic and felsic magmas varied considerably, ratios ranging from ca. 6 to 49. These results, together with outcrop evidence, provide indications regarding the evolution of the magmatic system, which generated the actual mafic/felsic associations on Vegetation Island
Machine Learning Thermo-Barometry: Application to Clinopyroxene-Bearing Magmas
No full textWe introduce a new approach, based on machine learning, to estimate pre-eruptive temperatures and storage depths using clinopyroxene-melt pairs and clinopyroxene-only chemistry. The model is calibrated for magmas of a wide compositional range, it complements existing models, and it can be applied independently of tectonic setting. Additionally, it allows the identification of the main chemical exchange mechanisms occurring in response to pressure and temperature variations on the base of experimental data without a priori assumptions. After the validation process, performances are assessed with test data never used during the training phase. We estimate the uncertainty using the root-mean-square error (RMSE) and the coefficient of determination (R2). The application of the best performing algorithm (trained in the range 0–40 kbar and 952–1882 K) to clinopyroxene-melt pairs from primitive to extremely differentiated magmas of both subalkaline and alkaline systems returns a RMSE on the order of 2.6 kbar and 40 K for pressure and temperature, respectively. We additionally present a melt- and temperature-independent clinopyroxene barometer in the range 0–40 kbar, characterized by a RMSE of the order of 3 kbar. Tested for tholeiitic compositions in the range 0–10 kbar, the melt- and temperature-independent clinopyroxene barometer has a RMSE of 1.7 kbar. We finally apply the proposed approach to clinopyroxenes from Iceland, providing new, independent, insights about pre-eruptive storage depths of Icelandic volcanoes. The general applicability of this model will promote the comparison between the architecture of plumbing systems across tectonic settings and facilitate the comparison between petrologic and geophysical studies
Rheological changes in melts and magmas induced by crystallization and strain rate
Full text linkThis review highlights the rheological and phase proportions variation induced by cooling events from superliquidus temperature (melt) to subliquidus temperatures. It provides a comprehensive view of the rheological response of magmatic systems undergoing dynamic cooling and shear deformation. The two main parameters which are of importance to model the rheological properties of such crystallizing systems and which are simultaneously poorly investigated so far are crystallization and strain rates. The response to relatively high deformation rates results in shear thinning behavior in partly crystallized systems under variable shear rate and it should be considered in magmatic processes. Due to the sluggish crystallization of SiO2-rich melts, data are mainly available for mafic systems, which does not allow a general reappraisal. An attempt to model available literature data for less evolved systems in dynamic scenarios and a comparison with MELTS algorithm approach (thermodynamic equilibrium conditions) is provided. Since there are difficulties in comparing experimental data gained using different methodologies, we focus mainly on data obtained with the concentric cylinder technique. This highlights the fact that a general experimental protocol is needed in order to compare and model viscosity data to predict the dynamic rheological evolution for volcanic rocks
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Miocene to Recent plutonism and volcanism in the Tuscan Magmatic Province (central Italy). Eurogranites 2002, European Network of Laboratories “Granites”, Field Meeting Guide, 15-21 settembre 2002
No full textMagmatic Processes at Euganean Hills (Veneto Volcanic Province, Italy): Clinopyroxene Investigation to Unravel Magmatic Interactions
No full textThe Euganean Hills (NE Italy) magmatic district represents the final volcanic activity of the Veneto Volcanic Province. Alkaline to subalkaline magmatic suite dominated by intermediate to felsic volcanic rocks characterises the latest volcanic activity of the Euganean Hills. Magmatic (intrusive and volcanic) enclaves are common in Euganean Hills trachytes. We used the ability of clinopyroxene to record variations of P, T, and fO2 to reconstruct the geological history of the volcanic enclaves and trachytic host. Despite similar major and trace elements composition, clinopyroxene from host is higher in Ca and Na (and Fe3+) and lower in Mg than enclaves and is slightly enriched in trace elements but with the same pattern distribution. Minor differences in geochemistry and crystal structure of clinopyroxene from enclaves and trachytic host suggest similar parental magmas that differs by small degrees of fractional crystallisation. Clinopyroxene geobarometry performed combining X-ray diffraction with mineral geochemistry for volcanic enclaves–trachytic host combined with amphibole geobarometry for intrusive enclaves and crystal mushes points to a crystallisation pressure range between 4.8–2.0 kbars. Our data support the model of a complex system of magma chambers at intermediate to shallow crustal level where mafic magma accumulated, evolved by fractionation processes and mixed
Viscosity behaviour of silicate melts during cooling under variable shear rates
No full textThe viscosity of a crystal-bearing shoshonite from Vulcanello (Aeolian Archipelago, Italy) was measured using the concentric cylinder method. Experiments were performed in the temperature interval from superliquidus (1573 K) to 1373 K with the aim to investigate the rheological response of the magma during variable cooling rate (i.e. 1000, 100 and 10 K/h) and shear rate (0.01, 0.1 and 1 s−1). In one experiment, with a cooling rate of 10 K/h and shear rate of 1 s−1, clinopyroxenes (ca. 11 vol.%) with hopper texture crystallized. One further experiment was performed for a longer time with a cooling rate of 100 K/h and shear rate of 1 s−1 to the final temperature of 1323 K. In this case, the final product showed skeletal crystals of pyroxenes (ca. 17 vol.%) and an apparent viscosity of 1.10 × 104 Pa s, which was very close to the experiment performed at 10 K/h and shear rate of 1 s−1 to 1373 K (1.18 × 104 Pa s). The comparison between experiments performed at cooling rate of 100 K/h, and finally quenched at to 1373 and 1323 K, respectively, showed that a temperature decrease of 50 K produces an increase in the apparent viscosity of ca. 1 log unit due to the transition from crystal-free to crystal-bearing melts. This study provides new data on apparent viscosity variation as cooling and shear rates vary in a crystallizing magmatic system. Results show that, on average, the viscosity of a shoshonitic system can increase by about two orders of magnitude due to temperature decrease from 1573 to 1373 K and the incipient crystallization occurring at the lowest temperatures. Finally, the results confirm that crystal nucleation and growth kinetics, as well as magma viscosity, are controlled by the dynamic state of the system. © 2020 Elsevier B.V
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