Search results for "Mantle"
showing 10 items of 322 documents
A geochemical traverse along the “Sperchios Basin – Evoikos Gulf” graben (Central Greece): Origin and evolution of the emitted fluids
2014
The studied area is a 130 km long fast spreading graben in Central Greece. Its complex geodynamical setting includes both the presence of a subduction slab at depth responsible for the recent (Quaternary) volcanic activity in the area and the western termination of a tectonic lineament of regional importance (the North-Anatolian fault). A high geothermal gradient is made evident by the presence of many thermal springs with temperatures from 19 to 82 °C, that discharge along the normal faults bordering the graben. In the period 2004–2012, 58 gas and 69 water samples were collected and their chemical and isotopic analysis revealed a wide range of compositions. Two main groups of thermal water…
The Othris Ophiolite, Greece: A snapshot of subduction initiation at a mid-ocean ridge
2008
The mantle section of the Tethyan-type Othris Ophiolite, Greece, records tectono-magmatic processes characteristic of both mid-ocean ridges and supra-subduction zones. The Othris Ophiolite is a remnant of the Jurassic Neotethys Ocean, which existed between Eurasia and Gondwanaland. Othris peridotites range from fertile plagioclase lherzolites to depleted harzburgites. Abundances of Al2O3 and CaO show well-defined inverse linear correlations with MgO, suggesting that the Othris peridotites formed as residua from variable degrees of partial melting. Peridotites from the Fournos Kaitsa and western Katachloron sub-massifs are similar to abyssal peridotites and can be explained by a multistage m…
Local Earthquake Tomography in the Southern Tyrrhenian Region of Italy: Geophysical and Petrological Inferences on the Subducting Lithosphere
2009
We obtained a high-resolution seismic tomography of the Ionian lithosphere subduction using a new approach based on: (a) the Double-Difference technique for inversions and (b) the statistical post-processing of a great number of preliminary models (Weighted Average Model, WAM method); the latter was used to increase reliability and resolution. In the tomographic model, the high-velocity portion of the steeply dipping Ionian slab is well imaged, as is an underlying low-Vp (≈7.0 km/s) aseismic region. We propose that the low-velocity region can be assigned to a partially hydrated (serpentinized) mantle of the subducting Ionian slab, which progressively dehydrates with depth in dense high-pres…
Minor and trace elements in olivines as probes into early igneous and mantle melting processes
2013
Abstract The trace element composition of olivine is a rapidly growing research area that has several applications of great potential. Mantle olivines can be distinguished from volcanic olivines by lower concentrations of Ca (
Variation of olivine composition in the volcanic rocks in the Songliao basin, NE China: lithosphere control on the origin of the K-rich intraplate ma…
2016
Abstract Lithospheric thickness and the heterogeneity of the mantle lithosphere are two major parameters that play a role in determining the final composition of the mafic melts and their minerals. The Songliao basin in northeast China represents an ideal natural laboratory to study the effect of these two parameters on early Pliocene to Holocene K-rich mafic lavas (K2O > 4 wt.%; K2O/Na2O > 1). A series of Cenozoic volcanic edifices (Erkeshan, Wudalianchi, Keluo and Xiaogulihe) are tentatively divided into three groups (Group 1 — thin, Group 2 — middle, and Group 3 — thick) according to the lithosphere thickness. They are located in the northern region of the Songliao basin extending in a n…
Does second phase content control the evolution of olivine CPO type and deformation mechanisms? A case study of paired harzburgite and dunite bands i…
2021
Abstract We have examined the microstructures and crystallographic preferred orientations (CPOs) of six “paired” harzburgite and dunite samples from a small (~ 1 km2) area in the Ellis Stream Complex, Red Hills Massif, Dun Mountain ophiolite belt in New Zealand. Here, banded peridotites with isoclinal folds, E-W striking vertical foliations and vertical lineations are inferred to result from shear on vertical planes that overprint previous mantle structures. The samples contain five different olivine CPOs: typically known as A, C, D, E and AG-types. The co-located harzburgite and dunite of each pair show different CPOs (e.g., A vs E type). In each pair, dunite generally has larger grain siz…
Lamproites as indicators of accretion and/or shallow subduction in the assembly of south-western Anatolia, Turkey
2010
IntroductionThe Western Anatolian region of Tur-key is tectonically one of the mostcomplex parts of the Alpine–Himala-yan orogenic belt (Fig. 1) because ofits long accretional palaeotectonicevolution. One of the major tectonicfeatures shaping the structure ofwestern Anatolia is the Menderesmetamorphic massif, which consistsof several assembled and imbricatedterranes exhumed during the exten-sion that affected the entire Aegeanprovince during the Late Miocene(Yilmaz et al., 2000; Okay, 2002).The Menderes Massif is usually inter-preted as a core complex delineated bylow-angle detachment faults (Bozkurtand Park, 1994; Hetzel et al., 1995;Ring et al., 2003). An alternativeexplanation associates …
The olivine macrocryst problem: New insights from minor and trace element compositions of olivine from Lac de Gras kimberlites, Canada
2015
This study presents detailed petrographical and geochemical investigations on remarkably fresh olivines in kimberlites from the EKATI Diamond Mine™ located in the Tertiary/Cretaceous Lac de Gras kimberlite field within the Slave craton of Canada. Olivine, constituting about 42 vol.% of the analyzed samples, can be divided into two textural groups: (i) macrocrystic olivines, > 100 μm sub-rounded crystals and (ii) groundmass olivines, < 100 μm subhedral crystals. Olivines from both populations define two distinct chemical trends; a “mantle trend” with angular cores, showing low Ca (< 0.1 wt.% CaO) and high Ni (0.3–0.4 wt.% NiO) at varying Mg# (0.86–0.93), contrasts with a “melt trend” typifie…
Os isotopes and highly siderophile elements (HSE) in the Ligurian Ophiolites, Italy.
2000
The Os isotopic and highly siderophile element (HSE) concentration systematics of the upper mantle have been the focus of much recent interest. However, little systematic study has addressed the combined HSE and Os isotopes in mantle rocks from MOR ophiolites. The Ligurian ophiolites in northern Italy represent an important class of ophiolites representing, like Zabargad or the Galicia margin, crust with clear ocean ridge affinity floored by older mantle with arguably more continental affinities [Rampone et al., J. Petrol. 36, 18–105, 1995; Rampone et al., Contrib. Mineral. Petrol. 123, 61–67, 1996]. We have studied a suite of 15 geochemically and geologically well characterized mantle peri…
Craton reactivation on the Labrador Sea margins: 40Ar/39Ar age and Sr–Nd–Hf–Pb isotope constraints from alkaline and carbonatite intrusives
2007
Abstract The once-contiguous North Atlantic craton (NAC) is crosscut by the Labrador Sea that opened during the Early Cenozoic after extensive Mesozoic continental rifting and removal of cratonic mantle. This large-scale structural change within the cratonic lithosphere was followed at about 150 Ma by the cessation of ultrapotassic and potassic-to-carbonatitic magma production, which had prevailed throughout much of the NAC history. At Aillik Bay, a sequence of olivine lamproites (1374.2 ± 4.2 Ma, 2σ), aillikites/carbonatites (590–555 Ma), and nephelinites (141.6 ± 1.0 Ma, 2σ) erupted through the southern NAC edge on the present-day Labrador Sea margin. Links between these alkaline magma ty…