Search results for "petrology"
showing 10 items of 1516 documents
Pressure-temperature evolution during two granulite-facies metamorphic events (2.62 and 2.02 Ga) in rocks from the Central Zone of the Limpopo Belt, …
2018
Abstract The Central Zone of the Limpopo Belt in southern Africa is a classical example of a polymetamorphic terrane that experienced three metamorphic events at 3.22 Ga (M1), 2.66–2.61 Ga (M2) and 2.02 (M3). However, the geodynamic significance of these events is controversial as their P-T evolution was poorly constrained. We present new petrological and geochronological data for the M2 and M3 events. The Neoarchean M2 event is well-preserved in samples from a newly discovered enclave of supracrustal and magmatic rocks in the 2.612 Ga Bulai pluton that shielded the enclave against a Paleoproterozoic M3 overprint, which is dominant in rocks exposed outside the pluton. P-T pseudosection mode…
The relationship between eruptive activity, flank collapse, and sea level at volcanic islands: A long-term (>1 Ma) record offshore Montserrat, Les…
2016
Hole U1395B, drilled southeast of Montserrat during Integrated Ocean Drilling Program Expedition 340, provides a long (>1 Ma) and detailed record of eruptive and mass-wasting events (>130 discrete events). This record can be used to explore the temporal evolution in volcanic activity and landslides at an arc volcano. Analysis of tephra fall and volcaniclastic turbidite deposits in the drill cores reveals three heightened periods of volcanic activity on the island of Montserrat (∼930 to ∼900 ka, ∼810 to ∼760 ka, and ∼190 to ∼120 ka) that coincide with periods of increased volcano instability and mass-wasting. The youngest of these periods marks the peak in activity at the Soufriere Hills vol…
Advances in Fourier transform infrared spectroscopy of natural glasses: From sample preparation to data analysis
2014
Fourier transform infrared spectroscopy (FTIR) is an analytical technique utilized to measure the concentrations of H and C species in volcanic glasses. Water and CO2 are the most abundant volatile species in volcanic systems. Water is present in magmas in higher concentrations than CO2 and is also more soluble at lower pressures, and, therefore it is the dominant volatile forming bubbles during volcanic eruptions. Dissolved water affects both phase equilibria and melt physical properties such as density and viscosity, therefore, water is important for understanding magmatic processes. Additionally, quantitative measurements of different volatile species using FTIR can be achieved at high s…
Vegetation and environmental changes in tropical South America from the last glacial to the Holocene documented by multiple cave sediment proxies
2019
Abstract δ 18 O values in speleothems have been utilized to document past changes in South American monsoon intensity. However, changes in regional vegetation and ecosystems have not been part of this discussion, and other cave proxies such as speleothem δ 13 C values, a useful proxy for vegetation reconstruction, have been neglected due to interpretive complexities. Here we report δ 13 C values and 87Sr/86Sr ratios in stalagmites, together with XRF-derived elemental chemistry, δ 13 Corg values and carbon content from a sedimentary profile from the same cave where the stalagmites were collected. In combination with a previously published δ 18 O record, this enables us to clarify climate and…
Characterisation and origin of hydrothermal waters at São Miguel (Azores) inferred by chemical and isotopic composition
2017
Abstract This study focuses on the characterisation and origin of hydrothermal waters discharging from three main active volcanoes (Furnas, Fogo and Sete Cidades) at Sao Miguel, where 33 water with temperatures ranging between 13 and 97 °C, and 5 precipitate samples were collected. The developed conceptual model for this active hydrothermal system reveals that all waters can be classified by Na-HCO 3 , Na-Cl and Na-SO 4 types and are of meteoric origin. This is confirmed by the stable hydrogen and oxygen isotope data that are positioned close to the local meteoric water line (− 4.1‰ ≤ δ 18 O H2O ≤ 5.2‰; − 17.6‰ ≤ δD H2O ≤ 20.4‰), except for the Na-Cl type water at Ferraria (Sete Cidades a…
Subduction metamorphism in the Himalayan ultrahigh-pressure Tso Morari massif: an integrated geodynamic and petrological modelling approach
2017
The Tso Morari massif is one of only two regions where ultrahigh-pressure (UHP) metamorphism of subducted crust has been documented in the Himalayan Range. The tectonic evolution of the massif is enigmatic, as reported pressure estimates for peak metamorphism vary from ∼2.4 GPa to ∼4.8 GPa. This uncertainty is problematic for constructing large-scale numerical models of the early stages of India–Asia collision. To address this, we provide new constraints on the tectonothermal evolution of the massif via a combined geodynamic and petrological forward-modelling approach. A prograde-to-peak pressure–temperature–time (P–T–t) path has been derived from thermomechanical simulations tailored for E…
Ultrapotassic Mafic Rocks as Geochemical Proxies for Post-collisional Dynamics of Orogenic Lithospheric Mantle: the Case of Southwestern Anatolia, Tu…
2012
High-Mg ultrapotassic volcanic rock occurrences of lamproitic affinity are exposed in southwestern Anatolia, mostly within the Menderes Massif. From north to south the lamproitic volcanism shows increasingly younger ages ranging from 20 to 4 Ma. Volcanism is contemporaneous with more voluminous shoshonitic, high-K calc-alkaline, and ultrapotassic magmatic activity in the Simav-Selendi, Usak, Kirka, Koroglu, Afyon and Isparta-Golcuk areas. The southward decrease in the age of the volcanism correlates with changes in geochemical composition, particularly a decrease in Sr-87/Sr-86, Pb-207/Pb-204, Zr/Nb and Th/Nb, and an increase in Nd-143/Nd-144, Hf-176/Hf-177, Pb-206/Pb-204, Pb-208/Pb-204 and…
On the Mesozoic Ionian Basin
2001
SUMMARY New seismic reflection profiles of the Italian deep crust project CROP provide new insights on the structure of the Ionian sea. In spite of the Apennines and Hellenides Neogene subduction zones, two conjugate passive continental margins are preserved at the margins of the Ionian sea, along the Malta escarpment to the southwest and the Apulian escarpment to the northeast. The Ionian sea is likely to be a remnant of the Mesozoic Tethys Ocean, confined by these two conjugate passive continental margins. The transition from continental to oceanic crust appears sharper to the northeast than to the southwest. The basin between southeast Sicily and southwest Puglia was about 330 km wide an…
Neoproterozoic-Early Paleozoic Peri-Pacific Accretionary Evolution of the Mongolian Collage System: Insights From Geochemical and U-Pb Zircon Data Fr…
2017
Neoproterozoic to early Paleozoic accretionary processes of the Central Asian Orogenic Belt have been evaluated so far mainly using the geology of ophiolites and/or magmatic arcs. Thus, the knowledge of the nature and evolution of associated sedimentary prisms remains fragmentary. We carried out an integrated geological, geochemical and zircon U–Pb geochronological study on a giant Ordovician metasedimentary succession of the Mongolian Altai Mts. This succession is characterized by dominant terrigenous components mixed with volcanogenic material. It is chemically immature, compositionally analogous to graywacke and marked by significant input of felsic to intermediate arc components, pointi…
Contribution of magmatism, partial melting buffering and localized crustal thinning on the late Variscan thermal structure of the Agly massif (French…
2020
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