Search results for "Peralkaline rock"
showing 10 items of 13 documents
Experimental and thermodynamic constraints on mineral equilibrium inpantelleritic magmas
2020
Abstract Crystallization experiments on two pantellerites from Pantelleria, Italy, provide new evidence for the relationships between mineral phases in pantelleritic rocks as well as the influence of temperature and redox conditions on mineral assemblages. Experiments were performed at 1 kbar with temperature ranging between 750–900°C, and fluid saturation conditions with XH2O (=H2O/H2O+CO2) between 0 and 1. Redox conditions were fixed at, or slightly below, the FMQ buffer. Results show that at temperature of 900 °C pantelleritic magmas are well above the liquidus regardless their water content; we also observed a decrease in liquidus temperature (800°C) with increasingly reducing condition…
Volcanological evolution of Pantelleria Island (Strait of Sicily) peralkaline volcano: a review
2022
International audience; Pantelleria volcano has a particularly intriguing evolutionary history intimately related to the peralkaline composition of its explosively erupted magmas. Due to the stratigraphic complexity, studies over the last two decades have explored either only the pre-Green Tuff ignimbrite volcanism or the post-Green Tuff activity. We here focus on the whole evolutionary history, detailing the achievements since the first pioneering studies, in order to illustrate how the adoption and integration of progressively more accurate methods (40 Ar/ 39 Ar, paleomagnetism, petrography, and detailed field study) have provided many important independent answers to unresolved questions…
The Magmatic to Hydrothermal Evolution of the Intrusive Mont Saint-Hilaire Complex: Insights into the Late-stage Evolution of Peralkaline Rocks
2017
The Cretaceous Mont Saint-Hilaire complex (Quebec, Canada) comprises three major rock units that were emplaced in the following sequence: (I) gabbros; (II) diorites; (III) diverse partly agpaitic foid syenites. The major element compositions of the rock-forming minerals, age-corrected Nd and oxygen isotope data for mineral separates and trace element data of Fe-Mg silicates from the various lithologies imply a common source for all units. The distribution of the rare earth elements in clinopyroxene from the gabbros indicates an ocean island basalt type composition for the parental magma. Gabbros record temperatures of 1200 to 800 degrees C, variable silica activities between 0 center dot 7 …
Phase equilibrium constraints on pre-eruptive conditions of recent felsic explosive volcanism at Pantelleria Island, Italy.
2010
International audience; We present experimental phase equilibria carried out on a pantelleritic bulk-rock composition with a peralkalinity index [PI = molar (Na2O + K2O)/Al2O3] = 1*4, which is representative of the most energetic pumice fall eruption of the resurgent post-caldera volcanism on Pantelleria island. For the explored conditions (P = 25-150 MPa; T = 680-800°C; H2Omelt up to 6 wt %; fO2 ≤ NNO, where NNO is nickel-nickel oxide buffer) clinopyroxene is the liquidus phase followed by alkali feldspar and then quartz. The crystallization of amphibole is limited to temperatures below 700°C. Aenigmatite crystallizes near the liquidus for P ≥ 100 MPa. When clinopyroxene is the sole liquid…
Rare earth elements in apatite as a monitor of magmatic and metasomatic processes: The Ilímaussaq complex, South Greenland
2015
Abstract Textural and compositional variations of apatite from the plutonic Ilimaussaq complex in South Greenland and its surrounding country rocks track magmatic and metasomatic processes. Detailed back-scattered electron (BSE) imaging reveals various types of apatite textures including (i) growth zonation (concentric, oscillatory as well as sector zonation) formed during magmatic differentiation, (ii) resorption and overgrowth textures due to fluid/melt induced metasomatic overprint of precursor apatite and (iii) replacement textures indicating the destabilization of apatite in favor of monazite. In the least evolved rocks of the Ilimaussaq complex, apatite incorporates rare earth element…
Trace element partitioning in lamproitic magmas—the Gaussberg olivine leucitite
2004
Abstract Partition coefficients for compatible and incompatible trace elements for use in modelling the origin and evolution of lamproitic and other potassic rocks are reported. These are based on values obtained by in situ determination using laser ablation microprobe-inductively coupled plasma-mass spectrometry (LAM-ICP-MS) on mineral/glass pairs in examples of the Gaussberg olivine leucitite, a classic leucite lamproite. Leucite/melt partition coefficients for 32 elements show values above 1 only for Cs and Rb, whereas values for Ni, Ga and Co are 0.4–0.1. DLc/Lq for most other elements are in the range 0.07–0.0005, and delineate a gently sloping pattern to lower values for elements gene…
Explosive eruptive history of Pantelleria, Italy: Repeated caldera collapse and ignimbrite emplacement at a peralkaline volcano
2018
A new, pre-Green Tuff (46 ka) volcanic stratigraphy is presented for the peralkaline Pantelleria Volcano, Italy. New 40Ar/39Ar and paleomagnetic data are combined with detailed field studies to develop a comprehensive stratigraphic reconstruction of the island.We find that the pre-46 ka succession is characterised by eight silicarich peralkaline (trachyte to pantellerite) ignimbrites,many ofwhich blanketed the entire island. The ignimbrites are typically welded to rheomorphic, and are commonly associated with lithic breccias and/or pumice deposits. They record sustained radial pyroclastic density currents fed by lowpyroclastic fountains. The onset of ignimbrite emplacement is typically prec…
A revision of the structure and stratigraphy of pre-Green Tuff ignimbrites at Pantelleria (Strait of Sicily)
2013
International audience; At Pantelleria, peralkaline silicic magmas were erupted across a range of eruptive typologies and magnitudes: pyroclastic flows, Plinian to strombolian pumice fallout and lava flows. In this paper we focus on the intermediate cycle of eruptive activity which is bracketed by ignimbrite units slightly older than the two caldera collapses which marked the volcanological activity of the island. This age interval (180-85 ka) was punctuated by six ignimbrite-forming eruptions (silicic and variably peralkaline) for a cumulative erupted magma volume of approximately 6 km3 dense rock equivalent. Based on new 40Ar/39Ar (Na,K)-feldspar ages and petrographic data, we propose an …
Age and evolution of late Mesozoic metamorphic core complexes in southern Siberia and northern Mongolia
2008
Numerous Cretaceous metamorphic core complexes (MCCs) extend from Transbaikalia in Russia to northern Mongolia within the Central Asian Orogenic Belt. We investigated the Buteel and Zagan MCCs in detail. Shear sense indicators in mylonitized rocks show footwall-to-the-NW tectonic transport. Single zircon dating of footwall rocks in the Buteel MCC establishes the emplacement of granitoid orthogneiss precursors at 240–211 Ma, a felsic metavolcanic rock at 265.0 ± 1.2 Ma, a syenite at 265.5 ± 1.2 Ma and a metarhyolite of the pre-granitoid basement at 553.6 ± 2.9 Ma. A peralkaline granite intruding orthogneisses of the Zagan MCC has a new U–Pb zircon age of 151.6 ± 0.7 Ma. 40Ar/39Ar ages of 133…
Potassic dyke swarm in the Sapucai Graben, Eastern Paraguay: Petrographical, mineralogical and geochemical outlines.
1992
Abstract The western side of the Parana Basin of Brazil extends to central Paraguay, where repeated and widespread magmatic activity developed from Lower Cretaceous to Oligocene, associated with late Mesozoic crustal extension trending NE-SW. In central Paraguay this trend is characterized by a zone of NW-SE normal faults which formed the Asuncion-Sapucai graben, up to 45 km wide and 200 km long, where alkaline rocks occur as volcanic domes, complexes, lava-flows and dykes. These rocks, 128 Ma aged, are dominantly potassic and ne-normative. A swarm of at least 200, mainley NW-SE trending, dykes occurs in the Sapucai region and seems to be formed by two main lineages: tephrite to phonolite (…