Ophiolitic peridotites in Xigaze (Tibet): Constraints on modes of melt transport in the mantle

2021 ◽  
Author(s):  
Lingquan Zhao ◽  
Sumit Chakraborty ◽  
Hans-Peter Schertl
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Experimental Studies ◽  
Primitive Mantle ◽  
Melt Extraction ◽  
Chemical Signatures ◽  
Element Enrichment ◽  
Spider Diagrams ◽  
Incompatible Trace Elements ◽  
Reverse Zoning

<p>The Xigaze ophiolite (Tibet), which occurs in the central segment of the Yarlung Zangbo Suture Zone, exposes a complete portion of a mantle sequence that consists essentially of fresh as well as serpentinized peridotites. We studied a sequence beneath the crustal section that exposes fresh, Cpx-bearing harzburgites and dunites that are underlain by serpentinized Cpx-bearing harzburgites and dunites. The rocks at the bottom are crosscut by dykes that have undergone different degrees of rodingitization. The modal compositions of peridotite from both fresh and serpentinized sections plot in abyssal upper mantle fields, with clinopyroxene modes less than 5 vol. %. Although harzburgites and dunites indicate that melt has been lost relative to primitive mantle compositions, the trace element patterns carry signatures of enrichment in incompatible elements, such as (i) “bowl-shaped” patterns of trace elements in silicate-Earth normalized spider diagrams, (ii) positive anomalies in highly incompatible trace elements such as Rb, Th, U, Ta, and (iii) enrichment of LREE in the clinopyroxenes from dunites and harzburgites. These features are indicative of complex melt transfer processes and cannot be produced by simple melt extraction. Petrographic studies reveal that harzburgite and dunite contain interstitial polyphase aggregates of olivine + Cpx + spinel + Opx and olivine + Cpx + Spinel, respectively. Experimental studies (e.g. Morgan and Liang, 2003) suggest that these aggregates represent frozen melt-rich components, indicating that fertile melt was percolating through the depleted harzburgite – dunite matrix. Presence of such “melt pods” would explain the trace element enrichment patterns of the bulk rock, as well as features such as reverse zoning (core: Cr, Fe<sup>2+</sup> rich, rim: Al, Mg rich) of spinels in polyphase aggregates in fresh dunites. These results show that melt extraction from the mantle is not a single stage process, and that evidence of multiple melt pulses that propagated through a rock are preserved in the petrographic features as well as in the form of chemical signatures that indicate refertilization of initially depleted rocks.</p>

scholarly journals Nd-Hf isotope geochemistry and lithogeochemistry of the Rambler Rhyolite, Ming VMS deposit, Baie Verte Peninsula, Newfoundland: evidence for slab melting and implications for VMS localization

2021 ◽  
Author(s):  
S J Piercey ◽  
J -L Pilote
Keyword(s):  
Rare Earth ◽  
Trace Element ◽  
Isotope Geochemistry ◽  
Primitive Mantle ◽  
Isotopic Data ◽  
Depleted Mantle ◽  
Element Enrichment ◽  
Felsic Volcanic ◽  
Magmatic History ◽  
Felsic Rocks

New high precision lithogeochemistry and Nd and Hf isotopic data were collected on felsic rocks of the Rambler Rhyolite formation from the Ming volcanogenic massive sulphide (VMS) deposit, Baie Verte Peninsula, Newfoundland. The Rambler Rhyolite formation consists of intermediate to felsic volcanic and volcaniclastic rocks with U-shaped primitive mantle normalized trace element patterns with negative Nb anomalies, light rare earth element-enrichment (high La/Sm), and distinctively positive Zr and Hf anomalies relative to surrounding middle rare earth elements (high Zr-Hf/Sm). The Rambler Rhyolite samples have epsilon-Ndt = -2.5 to -1.1 and epsilon-Hft = +3.6 to +6.6; depleted mantle model ages are TDM(Nd) = 1.3-1.5 Ga and TDM(Hf) = 0.9-1.1Ga. The decoupling of the Nd and Hf isotopic data is reflected in epsilon-Hft isotopic data that lies above the mantle array in epsilon-Ndt -epsilon-Hft space with positive ?epsilon-Hft values (+2.3 to +6.2). These Hf-Nd isotopic attributes, and high Zr-Hf/Sm and U-shaped trace element patterns, are consistent with these rocks having formed as slab melts, consistent with previous studies. The association of these slab melt rocks with Au-bearing VMS mineralization, and their FI-FII trace element signatures that are similar to rhyolites in Au-rich VMS deposits in other belts (e.g., Abitibi), suggests that assuming that FI-FII felsic rocks are less prospective is invalid and highlights the importance of having an integrated, full understanding of the tectono-magmatic history of a given belt before assigning whether or not it is prospective for VMS mineralization.

Halogens in the mantle beneath the North Atlantic

1980 ◽  
Vol 297 (1431) ◽  
pp. 147-178 ◽  
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Partial Melting ◽  
North Atlantic ◽  
Low Pressure ◽  
The North ◽  
Mid Atlantic Ridge ◽  
Ionic Size ◽  
The North Atlantic ◽  
Incompatible Trace Elements

F, Cl and Br contents of tholeiitic volcanic glasses dredged along the Mid-Atlantic Ridge from 53° to 28° N, including the transect over the Azores Plateau, are reported. The halogen variations parallel those of 87 Sr/ 86 Sr, La/Sm or other incompatible elements of varying volatility. The latitudinal halogen variation pattern is not obliterated if only Mg-rich lavas are considered. Variations in extent of low-pressure fractional crystallization or partial melting conditions do not appear to be the primary cause of the halogen variations. Instead, mantle-derived heterogeneities in halogens, with major enrichments in the mantle beneath the Azores, are suggested. The Azores platform is not only a ‘hotspot’ but also a ‘wetspot’, which may explain the unusually intense Azores volcanic activity. The magnitude of the halogen and incompatible element enrichments beneath the Azores appear strongly dependent on the size of these anions and cations, but independent of relative volatility at low pressure. The large anions Cl and Br behave similarly to large cations Rb, Cs and Ba, and the smaller anion F similarly to Sr and P. Processes involving crystal and liquid (fluid and/or melt), CO 2 rather than H 2 O dominated, seem to have produced these largescale mantle heterogeneities. Geochemical ‘anomalies’ beneath the Azores are no longer apparent for coherent element pair ratios of similar ionic size. Values of such ‘unfractionated’ coherent trace element ratios provide an indication of the mantle composition and its nature before fractionation event (s) which produced the inferred isotopic and trace element heterogeneities apparently present beneath the North Atlantic. The relative trace element composition of this precursor mantle does not resemble that of carbonaceous chondrites except for refractory trace element pairs of similar ionic size. It is strongly depleted in halogens, and to a lesser extent in large alkali ions Rb and Cs relative to refractory Ba. These relative depletions are comparable within a factor of 5 to Ganapathy & Anders’s estimates for the bulk Earth, with the exception of Cs. There is also evidence for removal of phosphorus into the iron core during its formation. With the exception of San Miguel, alkali basalts from the Azores Islands appear to have been derived from the same mantle source as tholeiitic basalts from the ridge transect over the Azores Platform but by half as much degree of partial melting. The Azores subaerial basalts seem to have been partly degassed in Cl, Br and F, in decreasing order of intensity. A working model involving metasomatism from release of fluids at phase transformation during convective mantle overturns is proposed to explain the formation of mantle plumes or diapirs enriched in larger relative to smaller halogen and other incompatible trace elements. The model is ad hoc and needs testing. However, any other dynamical model accounting for the 400 -1000 km long gradients in incompatible trace elements, halogens and radiogenic isotopes along the Mid-Atlantic Ridge should, at some stage, require either (1) some variable extent of mixing or (2) differential migration of liquid relative to crystals followed by re-equilibration (or both), as a diffusion controlled mechanism over such large distances is clearly ruled out, given the age of the Earth.

Trace element evidence for mantle heterogeneity beneath the Scottish Midland Valley in the Carboniferous and Permian

1980 ◽  
Vol 297 (1431) ◽  
pp. 245-257 ◽  
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Partial Melting ◽  
Mantle Source ◽  
Incompatible Element ◽  
Mantle Heterogeneity ◽  
Alkaline Rocks ◽  
Elemental Abundances ◽  
Peridotite Mantle ◽  
Incompatible Trace Elements

The alkaline rocks of Carboniferous to Permian age in the Midland Valley province range in composition from hypersthene-normative, transitional basalts to strongly undersaturated basanitic and nephelinitic varieties. They were formed by varying degrees of equilibrium partial melting of a phlogopite peridotite mantle. Ba, Ce, Nb, P, Sr and Zr were strongly partitioned into the liquid during melting; K and Rb were retained by residual phlogopite for small degrees of melting only. The composition of the mantle source is inferred to have been broadly similar to that from which oceanic alkaline basalts are currently being generated. It was, however, heterogeneous as regards distribution of the incompatible trace elements, with up to fourfold variations in elemental abundances and ratios. The mantle beneath the province may be divisible into several areas, of some hundreds of square kilometres each, which retained a characteristic incompatible element chemistry for up to 50 Ma and which imparted a distinctive chemistry to all the basic magmas generated within them.

Differentiation and source of the Nipissing Diabase intrusions, Ontario, Canada

1993 ◽  
Vol 30 (6) ◽  
pp. 1123-1140 ◽  
Author(s):  
P. C. Lightfoot ◽  
H. de Souza ◽  
W. Doherty
Keyword(s):  
Trace Element ◽  
Crustal Contamination ◽  
Primitive Mantle ◽  
Magma Source ◽  
Magma Type ◽  
Ni Content ◽  
Chemical Signatures ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

Major and trace element data are presented for 2.2 Ga Proterozoic diabase sills from across the Nipissing magmatic province of Ontario. In situ differentiation of the magma coupled with assimilation of Huronian Supergroup roof sediments is responsible for the variation in composition between quartz diabase and granophyric diabase seen within many of the differentiated intrusions. Uniform trace element and isotope ratio signatures, such as La/Sm (2.8 – 3.7) and εNdCHUR (−2.7 to −5.9) characterize chilled margins and undifferentiated quartz diabases. These chemical signatures suggest the existence of a single magma source that was parental to intrusions throughout the magmatic province; this magma has higher La/Sm and lower Ti/Y than primitive mantle and is displaced towards the composition of shales. Most chilled diabases and quartz diabases have a similar Mg# (0.64 and 0.60) and Ni content (98 and 127 ppm), and it is argued that the magma differentiated at depth and was emplaced as a uniform low-Mg magma. The Wanapitei intrusion and Kukagami Lake sill are an exception in that although the quartz diabase has La/Sm similar to the Nipissing magma type, which suggests that they came from the same source, the Mg# (0.68–0.71) and Ni content (130–141 ppm) are higher, which may suggest that they are either slightly more primitive examples of the normal Nipissing magma or that cumulus hypersthene has been resorbed. The light rare earth element enriched signature of the Nipissing magmas was perhaps introduced from the continental crust as the magma migrated from the mantle to the surface, but a remarkably constant and large amount (>20%) of crustal contamination would be required. An addition of 1 –3% shale to the source of a transitional mid-ocean ridge basalt type magma can broadly reproduce the compositional features of the Nipissing magma type. The source characteristics were perhaps imparted during subduction accompanying the terminal Kenoran orogeny.

Trace element–enriched mid-Visean dikes in the New Carlisle area of Quebec, Canada: Unusual products of a tholeiitic melt sourced from metasomatized mantle rocks and fractionated in a brine-rich upper-crustal environment

2019 ◽  
Vol 131 (11-12) ◽  
pp. 2079-2093
Author(s):  
Pierre Jutras ◽  
Jaroslav Dostal ◽  
Sandra Kamo
Keyword(s):  
Trace Element ◽  
Magma Chamber ◽  
Early Carboniferous ◽  
High Heat ◽  
Magmatic System ◽  
Eastern Canada ◽  
Mafic Rocks ◽  
Order Of Magnitude ◽  
Element Enrichment ◽  
Incompatible Trace Elements

Abstract Early Carboniferous tholeiitic dikes in the New Carlisle area of Quebec, Canada, are abnormally enriched in high field strength elements (HFSEs), including rare earth elements. The enrichment is systematic and was apparently caused by an enhanced incompatibility of HFSEs during a prolonged episode of crystal fractionation. As a result, HFSE concentrations are up to one order of magnitude higher than those of typical mafic rocks. Very high F and Cl contents suggest that halogen complexing was largely responsible for the trace-element enrichment. The high halogen contents are in part accounted for by a subcontinental lithospheric mantle source that had previously been enriched in these elements by prolonged subduction. Additional Cl enrichment is interpreted to have occurred in a magma chamber that developed within porous and brine-rich country rocks of the upper crust. This conclusion is supported by the observation that HFSE-enriched mafic plutons in the same magmatic province occur in nonmetamorphosed upper-crustal rocks, suggesting high buoyancy and therefore high temperatures. Such evidence for high heat in the late Paleozoic magmatic system of eastern Canada corroborates previous studies suggesting that the transtensional basin in which it evolved was overriding a mantle plume at the time. In the case of the New Carlisle dikes, which are more than twice as enriched in incompatible trace elements as slightly older mafic rocks of the same magmatic system, the regional paleoenvironmental setting suggests that the associated upper-crustal magma chamber may have evolved in rocks with saltier pore water due to long-lasting evaporitic conditions at the surface.

Mineralogical composition of and trace-element accumulation in lower Toarcian anoxic sediments: a case study from the Bilong Co. oil shale, eastern Tethys

2015 ◽  
Vol 153 (4) ◽  
pp. 618-634 ◽  
Author(s):  
XIUGEN FU ◽  
JIAN WANG ◽  
XINGLEI FENG ◽  
WENBIN CHEN ◽  
DONG WANG ◽  
...  
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Oil Shale ◽  
Volcanic Rocks ◽  
Mineralogical Composition ◽  
Geochemical Data ◽  
Anoxic Sediments ◽  
Marine Influence ◽  
High Concentrations ◽  
Element Enrichment

AbstractThe sediments of organic-rich oil shales in the Bilong Co. area can be correlated with those of the early Toarcian anoxic black-shale events in Europe. The Bilong Co. sediments are rich in trace elements Se, Mo, Cd, As and Ni, and, to a lesser extent, Li, F, V, Co, Cu, Cs, Hg and Bi, in comparison to the upper continental crust. Thirty-two oil shale samples were collected from the Bilong Co. oil shale to evaluate the controlling factors of trace-element enrichment in the lower Toarcian anoxic sediments. Minerals identified in the Bilong Co. oil shale include calcite, quartz, illite, feldspar and dolomite, and trace amounts of siderite, magnesite, halite, haematite, zeolite, amphibole, gypsum, anhydrite, apatite, pyrite, sphalerite, barite and mixed-layer illite/smectite. Mineralogical and geochemical data show that seawater and hydrothermal activities are the dominant influences on the mineralogical composition and elevated trace-element concentrations in the oil shale. The clay minerals, quartz and feldspar in the Bilong Co. oil shale were derived from the Nadi Kangri volcanic rocks. Input of sediment from this source may have led to enrichment of trace elements Li, Cr and Cs in the oil shale. Carbonate minerals and nodular- and framboidal-pyrite are authigenic phases formed from seawater. The enrichment of V, Co, Ni, Cu, Mo, As, Se, Bi and U in the oil shale was owing to marine influence. Barite, sphalerite and fracture-filling pyrites were derived from hydrothermal solutions. High concentrations of F, Zn and Cd were probably derived from hydrothermal fluids.

scholarly journals Trace elements in New Zealand ferromanganese nodules: implications for deep sea environments

2021 ◽  
Author(s):  
◽  
Andrea Davies
Keyword(s):  
Trace Elements ◽  
New Zealand ◽  
Trace Element ◽  
Pore Water ◽  
Deep Sea ◽  
Sediment Composition ◽  
Ferromanganese Nodules ◽  
Sediment Profiles ◽  
Element Enrichment ◽  
Trace Element Enrichment

<p>Ferromanganese nodules are authigenic marine sediments that form over millions of years from the precipitation of Fe oxyhydroxides and Mn oxides from seawater (hydrogenetic-type growth) and sediment pore-water (diagenetic-type growth). Fe-Mn (oxyhydr)oxides grow in layers about nuclei, effectively scavenging minor metals such as Ni, Cu and Co from the waters they grow in. The uptake of different elements into the ferromanganese nodules reflects their environment and mechanism of growth, and these deposits are of interest both as a potential source of metals of economic interest, and as records of changing ocean conditions. This study investigates the composition of 77 ferromanganese nodules from the seafloor around New Zealand. Samples analysed come from locations several thousand kilometres apart under the same water mass (Lower Circumpolar Deep Water – LCDW), but with varying depth, current velocity, and sediment type. The outermost 1 mm rim of each nodule, representing near-modern growth, was sampled to compare with modern environmental parameters including substrate sediment composition and chemical and physical oceanography. Major, minor, and trace element analysis of nodule rims were undertaken, and the authigenic and detrital components examined via leaching experiments to evaluate their relative influence on growth mechanisms. Overall, New Zealand ferromanganese nodules are hydrogenetic in origin. However, there are systematic variations in composition that reflect variable diagenetic influence. Hydrogenetic endmember compositions are defined by samples from two localities in the Southern Ocean that have no evidence for diagenetic influence. Diagenetic influence on nodule composition is exemplified by samples from the two locations in the Tasman Sea, but also include nodules from the Campbell nodule field. Nodules from the Campbell nodule field come from two transects perpendicular to the Campbell Plateau, and the Deep Western Boundary Current (DWBC). Both sediment composition and nodule rim chemistry vary systematically across both transects. Areas closest to the slope have sediment profiles indicating high energy, erosive environments, continental-sourced sand components, and are dominated by nodules with hydrogenetic chemical characteristics similar to those of the Southern Ocean. Further from the slope, the sediment profiles indicate silt dominated sediments of a more oceanic crustal provenance, lower energy environment, and increased influence of oxic diagenetic processes on the major, minor and trace element profiles of the nodules. No hydrothermal contribution was identified in the chemistry of any of the nodules analysed. The physical and chemical properties of the sediment, along with current velocities, were found to be the key influences in diagenetic enrichment in the nodules. The influence of seawater chemistry was difficult to determine due to the lack of direct analyses in the area. Ferromanganese nodule chemistry is a function of the nodule environment, including water body, sediment composition and depth. The authigenic components of nodules can therefore be used to investigate the deep-sea environment. The redox conditions of sediments and the productivity of the overlying water will affect the trace metal constituents of the pore-waters of a sediment (Kuhn et al., 2017). Sediments with a larger fraction of labile organic matter may result in trace element enrichment of the pore-water. Sediments below the CCD will be higher in trace elements than sediments below the CCD (U1413, U1406B, U1402, U1398, U1398, and U1378) due to carbonate matter acting as a dilutant that can limit the supply of trace elements mobilised in the pore-water during diagenesis (Glasby, 2006). Terrigenous clasts such as quartz (Chester, 1990), will also reduce trace element enrichment in the pore-water due to their low reactivity, e.g. for the sediment U1406B, which has a high lithic component (Table 3.2). Sediments with a higher biogenic silica component (such as U1373, U1374, and U1378) (Table 3.2, Table 3.4) are predicted to produce nodules with higher trace element contents (ISA, 2010). In contrast to both the CCZ and Indian Ocean nodules, the Campbell nodule field samples formed above the CCD, and hence in sediments that include a significant carbonate component. This minimises the trace element pore-water enrichment and can account for the lower Cu+Ni+Co contents observed in the Campbell nodule field nodules compared with those that formed below the CCD (CCZ and Indian Ocean).</p>

Mineralogic reaction zones at a calc-silicate/metapelite interface: an example of trace element mobility in a metamorphic environment

1994 ◽  
Vol 58 (391) ◽  
pp. 205-214 ◽  
Author(s):  
J. V. Owen ◽  
J. Dostal ◽  
B. N. Church
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Rare Earths ◽  
Fluid Phase ◽  
Aqueous Fluid ◽  
Silicate Rock ◽  
Element Mobility ◽  
Trace Element Mobility ◽  
Reaction Zones ◽  
Incompatible Trace Elements

AbstractMetasomatic interaction on a cm scale between calc-silicate pods and the enclosing sillimanite + biotite + tourmaline gneiss at Partridge Breast Lake, northern Manitoba, Canada, led to the development of an inner (by calc-silicate rock), hornblende-rich reaction zone and an outer, biotite-rich zone. The boundary between the reaction zones is interpreted as the original calc-silicate/metapelite interface. Compared with its metapelitic protolith, the biotite zone shows a two- to twenty-fold depletion in the concentrations of incompatible trace elements (notably the light rare earths, U, Th, Nb, Ta, Zr and Hf). In contrast, the relative concentrations of trace elements remained nearly constant during the mineralogical transformation of the calc-silicate rock to the hornblende zone. The depletion of trace elements in the biotite zone is attributed to the dissolution of accessory phases (e.g. monazite). Although stable at the metamorphic conditions (∼600–650°C at ∼ 4.5 kbar) prevalent during metasomatism, Mg-rich tourmaline is absent in the biotite zone, suggesting that either the pH or composition (e.g. the (Al + Si)/(Ca + Mg + Fe) ratio) of the aqueous fluid phase was inappropriate for the preservation of this mineral.

Tectono-magmatic Interplay and Related Metasomatism in Gabbros of the Chenaillet Ophiolite (Western Alps)

2019 ◽  
Vol 60 (12) ◽  
pp. 2483-2508 ◽  
Author(s):  
R Tribuzio ◽  
G Manatschal ◽  
M R Renna ◽  
L Ottolini ◽  
A Zanetti
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Western Alps ◽  
Fine Grained ◽  
Ductile Shearing ◽  
Trace Element Signature ◽  
High Concentrations ◽  
Incompatible Trace Elements ◽  
Detachment Faulting ◽  
Ocean Ridge

Abstract The Jurassic Chenaillet ophiolite in the Western Alps consists of a gabbro–mantle association exhumed to the seafloor through detachment faulting and partly covered by basaltic lavas. One of the Chenaillet gabbroic bodies includes mylonites that are transected by a network of felsic veins, thereby testifying to the interplay of ductile shearing and magma emplacement. The deformed gabbros preserve clinopyroxene porphyroclasts of primary magmatic origin, which are typically mantled by amphibole (titanian edenite) and minor secondary clinopyroxene. Titanian edenite and secondary clinopyroxene also occur as fine-grained syn-kinematic phases locally associated with fine-grained plagioclase. The felsic veins are made up of anorthite-poor plagioclase and minor titanian edenite. Geothermometric investigations document that the ductile gabbro deformation and the crystallization of the felsic veins occurred at 765 ± 50 °C and 800 ± 55 °C, respectively. With respect to undeformed counterparts, the deformed gabbros are variably enriched in SiO2 and variably depleted in Mg/(Mg + Fetot2+) and Ca/(Ca + Na). In addition, the deformed gabbros show relatively high concentrations of incompatible trace elements such as rare earth elements (REE), Y, Zr and Nb. The felsic veins are characterized by low Mg/(Mg + Fetot2+) and Ca/(Ca + Na), high SiO2 and high concentrations of incompatible trace elements. Relict clinopyroxene porphyroclasts from the deformed gabbros display a rather primitive, mid-ocean ridge-type geochemical signature, which contrasts with the trace element fingerprint of titanian edenite from both the deformed gabbros and the felsic veins. For instance, titanian edenite typically has relatively high REE abundances, with chondrite-normalized REE patterns characterized by a pronounced negative Eu anomaly. A similar trace element signature is shown by secondary clinopyroxene from the deformed gabbros. Amphibole from both the deformed gabbros and the felsic veins displays high F/Cl values. We show that the SiO2-rich hydrous melts feeding the felsic veins were involved in the high-temperature gabbro deformation and that melt–gabbro reactions led to major and trace element metasomatism of the deforming gabbros.

scholarly journals Behavior of the clinopyroxenes trace elements in spinel-lherzolite xenoliths from Liri (Kapsiki plateau, Cameroon line)

2020 ◽  
Vol 8 (2) ◽  
pp. 259
Author(s):  
Nguihdama Dagwai ◽  
Kamgang Pierre ◽  
Mbowou Gbambié Isaac Bertrand ◽  
Chazot Gilles ◽  
Ngounouno Ismaïla
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Partial Melting ◽  
Rare Earths ◽  
Titanium Content ◽  
Primitive Mantle ◽  
Spinel Lherzolite ◽  
Alkali Basalts ◽  
Hydrated Minerals

Spinel-lherzolite xenoliths trapped within the alkali basalts flow in the Liri region (Kapsiki Plateau) have a protogranular texture and consist of olivine, orthopyroxene, clinopyroxene and spinel crystals. These xenoliths are residues of partial melting of the primitive mantle, with the low titanium content in clinopyroxene crystals (TiO2 < 0.5 wt.%). The clinopyroxene of the spinel-lherzolite xenoliths from Liri, are divided into two distinct groups according to their trace element characteristics. The variations in the rare earths elements make it possible to classify the different clynopyroxenes in two groups: the first group consisting of the samples of Liri (Liri 1, Liri 02, Liri 3, Liri 05 and Liri 5) rich in light rare earths elements (LREEs), with ratios (Ce/Yb)N normalized which vary between 3.00 and 7.78. It is probably a cryptic metasomatism due to the absence of hydrated minerals (such as amphibole) which caused these enrichments. The second group comprises samples of Liri (Liri 01, Liri 2, Liri 04, Liri 4) depleted in light rare earths elements, with the ratio in (Ce/Yb) N < 1.2. This depletion in rare earths elements results from the extraction of the melting liquid.    

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