Search results for "magmatism"

Vestiges of the Mesoproterozoic Events in the Neoproterozoic Mozambique Belt: the East African Perspective in the Rodinia Puzzle

2003

Abstract Most of the geological and palaeogeographical models consider the Neoproterozoic supercontinent Gondwana (∼650-550 Ma) as the direct offspring of the disintegrated Mesoproterozoic supercontinent Rodinia (∼1300-750 Ma). One of the main classical sutures along which the dispersing Rodinia fragments were fused into a new supercontinent (Godwana) is identified as the Mozambique belt of East Africa. The calc-alkaline magmatism (∼1200-950 Ma) in northern Mozambique, southern Malawi and southern Tanzania is regarded as the sole evidence for fragmentation of Rodinia, which is traced within this Neoproterozoic orogenic belt. There are no unequivocal Mesoproterozoic (Kibaran) sediments in th…

1999

The tholeiitic dolerites that crop out in three diapirs of the SE of the Iberian Chain (Alfarp, Quesa and Lugar Nuevo de Fenollet, Valencia), are the expression of evolved (low Ni, Cr and mg* values) basic magmas, injected into poorly lithified sediments (lutites, marls and gypsum) which represent the Upper Triassic (Keuper facies)-Hettangian boundary, developing sills with reduced thickness. Their mineral and whole-rock geochemical compositions indicate a continental tholeiitic affinity and certain similarities to a MORB composition and, on the other hand, show that the Alfarp dolerites represent the less evolved compositions, whereas the Fenollet dolerites show a significantly greater dif…

U-Pb data on zircons for the thermal peak of metamorphism in the Variscan Odenwald, Germany

1995

U-Pb data are presented for zircons from metamorphic rocks of the crystalline Odenwald that comprises part of the Mid-German Crystalline Rise. The Odenwald can be divided into four principal domains with different magmatic and metamorphic histories on the basis of published structural and petrological data and the presented ages. In the eastern (Boll-stein) Odenwald the metasedimentary rocks contain zircons derived from basement rocks that exceed 2.2 Ga in age. The intrusion of granitic magmas into these metasedimentary rocks took place before or close to the end of the thermal peak of metamorphism at 375 ± 5 Ma ago. Rapid uplift of the Bollstein Odenwald occurred at about 320 Ma bp, later …

Age of initial oceanic magmatism in the Late Proterozoic Arabian Shield

1992

Lead isotopic data for zircons from a dacite clast in a volcanic breccia of the oldest oceanic assemblage (immature arc or oceanic plateau) of the southwestern Arabian Shield (Baish group), acquired with the single-grain evaporation technique, yielded a mean 207 Pb/ 206 Pb age of 842 ±17 Ma. Earlier published Rb-Sr data for Baish rocks yielded a three-point isochron of 1165 ±110 Ma. This age has been repeatedly cited as evidence for pre-1 Ga arc magmatism in the Arabian Shield. However, more recent Rb-Sr data and zircon ages for clastic metasedimentary rocks are in agreement with our new zircon age, suggesting that initial oceanic magmatism in the Arabian Shield did not begin until after 90…

In situ quantification of the nitrogen content of olivine-hosted melt inclusions from Klyuchevskoy volcano (Kamchatka): Implications for nitrogen rec…

2021

International audience; Assessing the N content of arc magmas and their mantle source remains a challenge because the volatile element composition of melts and gases can be modified during magma ascent, storage, and eruption. Given that melt inclusions (MIs) in Mg-rich olivine represent the best proxies for primary arc melts, we applied, for the first time, an in situ high-resolution secondary ion mass spectrometry (SIMS) method to determine the N concentration in olivine-hosted MIs from Klyuchevskoy volcano in Kamchatka. To reverse the effects of post-entrapment modification processes (i.e., exsolution of volatiles into a fluid bubble), the MIs were partially to completely homogenized at h…

Geochemical characteristics of Cretaceous carbonatites from Angola

1999

Abstract The Early Cretaceous (138–130 Ma) carbonatites and associated alkaline rocks of Angola belong to the Parana-Angola-Etendeka Province and occur as ring complexes and other central-type intrusions along northeast trending tectonic lineaments, parallel to the trend of coeval Namibian alkaline complexes. Most of the Angolan carbonatite-alkaline bodies are located along the apical part of the Mocamedes Arch, a structure representing the African counterpart of the Ponta Grossa Arch in southern Brazil, where several alkaline-carbonatite complexes were also emplaced in the Early Cretaceous. Geochemical and isotopic (C, 0, Sr and Nd) characteristics determined for five carbonatitic occurren…

Geochemical characteristics of lawsonite blueschists in tectonic mélange from the Tavşanlı Zone, Turkey: Potential constraints on the origin of Medit…

2019

The barren Messinian Tripoli in Sicily and its palaeoenvironmental evolution: suggestions on the exploration potential

2016

New observations on the Sicily Messinian Tripoli have yielded a variably thick diatomitic, calcareous and shaly rock interval marked by an upwards disappearance of calcareous and siliceous plankton (barren lithosome), coexisting with a variability in vegetal remains and significant amounts of amorphous organic matter (AOM). Facies analysis associated with biostratigraphy and palaeoecology of the several field and borehole sections has been framed in a well-accepted chronological scheme that points to this barren interval coinciding with the stratigraphic upper and younger part of some Tripoli sections (bituminous Tripoli) located in the northern part of the study area. Biostratigraphically,…

An anorogenic pulse in a typical orogenic setting: The geochemical and geochronological record in the East Serbian latest Cretaceous to Palaeocene al…

2013

Abstract This study focuses on the East Serbian latest Cretaceous to Palaeocene Mafic Alkaline Rocks (hereafter, ES-MAR). This alkaline magmatism developed along the Eurasian border after the closure of the Mesozoic Tethys in the Balkan sector. Olivine(± clinopyroxene)-phyric and olivine- and nepheline-normative basanite, tephrite and theralite rocks are studied using Ar/Ar ages and major elements, trace elements and Sr–Nd–Pb isotopes. The ES-MAR are geochemically similar to other alkaline rocks of the Circum-Mediterranean Anorogenic Cenozoic Igneous (CiMACI) province, showing elevated contents of high field strength elements (HFSE) (e.g., Nb = 50–100 ppm) and high HFSE/LILE (large ion lith…

Potassic and sodic igneous rocks from eastern Paraguay: their origin from the lithospheric mantle and genetic relationships with the associated Paran…

1997

3 DIPARTIMENTO DI SCIENZE DELLA TERRA, UNIVERSITY OF TRIESTE, VIA E. WEISS 8, I-34127 TRIESTE, ITALY 4 INSTITUTO DE GEOCIENCIAS, UNIVERSIDADE DE SAO PAULO, C.P. 30627, 01051 SAO PAULO, SP, BRAZIL 5 DIPARTIMENTO DI SCIENZE DELLA TERRA, ‘LA SAPIENZA’ UNIVERSITY, PIAZZALE ALDO MORO 5, I-00185, ROME, ITALY 6 ISTITUTO DI MINERALOGIA, PETROGRAFIA E GEOCHIMICA, UNIVERSITY OF PALERMO, VIA ARCHIRAFI 36, I-90100,