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.    

Platinum-group element geochemistry of intraplate basalts from the Aleppo Plateau, NW Syria

2012 ◽  
Vol 150 (3) ◽  
pp. 497-508 ◽  
Author(s):  
GEORGE S.-K. MA ◽  
JOHN MALPAS ◽  
JIAN-FENG GAO ◽  
KUO-LUNG WANG ◽  
LIANG QI ◽  
...  
Keyword(s):  
Partial Melting ◽  
Middle Miocene ◽  
Primitive Mantle ◽  
Element Geochemistry ◽  
Alkali Basalts ◽  
Melt Extraction ◽  
Mid Ocean Ridge ◽  
Order Of Magnitude ◽  
Platinum Group ◽  
Ocean Ridge

AbstractEarly–Middle Miocene intraplate basalts from the Aleppo Plateau, NW Syria have been analysed for their platinum-group elements (PGEs). They contain extremely low PGE abundances, comparable with most alkali basalts, such as those from Hawaii, and mid-ocean ridge basalts. The low abundances, together with high Pd/Ir, Pt/Ir, Ni/Ir, Cu/Pd, Y/Pt and Cu/Zr are consistent with sulphide fractionation, which likely occurred during partial melting and melt extraction within the mantle. Some of the basalts are too depleted in PGEs to be explained solely by partial melting of a primitive mantle-like source. Such ultra-low PGE abundances, however, are possible if the source contains some mafic lithologies. Many of the basalts also exhibit suprachondritic Pd/Pt ratios of up to an order of magnitude higher than primitive mantle and chondrite, an increase too high to be attributable to fractionation of spinel and silicate minerals alone. The elevated Pd/Pt, associated with a decrease in Pt but not Ir and Ru, are also inconsistent with removal of Pt-bearing PGE minerals or alloys, which should have concurrently lowered Pt, Ir and Ru. In contrast, melting of a metasomatized source comprising sulphides whose Pt and to a lesser extent Rh were selectively mobilized through interaction with silicate melts, may provide an explanation.

Geochemical evidence for the emplacement of the Whin Sill complex of northern England

1985 ◽  
Vol 122 (4) ◽  
pp. 389-396 ◽  
Author(s):  
R. S. Thorpe ◽  
R. Macdonald
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Partial Melting ◽  
Sedimentary Rocks ◽  
Crustal Contamination ◽  
Mantle Peridotite ◽  
Chemical Characteristics ◽  
Heterogeneous Mantle ◽  
Magma Pulses ◽  
Significant Chemical

AbstractThe Whin Sill comprises a major quartz tholeiite sill of late Carboniferous age underlying an area of c. 5000 km2 and with a volume of c. 200 km3, associated with contemporaneous dykes emplaced within Carboniferous sedimentary rocks in northeast England. New trace element analyses of chilled margins, sill interiors and dykes indicate that the Whin Sill complex magmas show significant chemical variations in terms of the relatively stable trace elements Th, Ce, Y, Zr, Nb and Ni. These data indicate that the complex was fed by a large number of compositionally distinct magma pulses, and that certain of the dykes may have formed feeder channels for the sill. The chemical characteristics of the sill and dyke samples are consistent with derivation by extensive polybaric fractional crystallization of olivine tholeiite magma derived by partial melting of compositionally heterogeneous mantle peridotite and/or crustal contamination of mantle-derived magmas.

scholarly journals Elemental and Sr–Nd–Pb isotopic geochemistry of Mesozoic mafic intrusions in southern Fujian Province, SE China: implications for lithospheric mantle evolution

2007 ◽  
Vol 144 (6) ◽  
pp. 937-952 ◽  
Author(s):  
JUN-HONG ZHAO ◽  
RUIZHONG HU ◽  
MEI-FU ZHOU ◽  
SHEN LIU
Keyword(s):  
Trace Element ◽  
Mantle Source ◽  
Lithospheric Mantle ◽  
Type A ◽  
Primitive Mantle ◽  
Trace Element Geochemistry ◽  
Spinel Lherzolite ◽  
Fujian Province ◽  
Mafic Rocks ◽  
Se China

AbstractCretaceous mafic dykes in Fujian province, SE China provide an opportunity to examine the nature of their mantle source and the secular evolution of the Mesozoic lithospheric mantle beneath SE China. The mafic rocks have SiO2 ranging from 47.42 to 55.40 wt %, Al2O3 from 14.0 wt % to 20.4 wt %, CaO from 4.09 to 11.7 wt % and total alkaline (K2O+Na2O) from 2.15 wt % to 6.59 wt %. Two types are recognized based on their REE and primitive mantle-normalized trace element patterns. Type-A is the dominant Mesozoic mafic rock type in SE China and is characterized by enrichment of light rare earth elements (LREE) ((La/Yb)n = 2.85–19.0) and arc-like trace element geochemistry. Type-P has relatively flat REE patterns ((La/Yb)n = 1.68–3.43) and primitive mantle-like trace element patterns except for enrichment of Rb, Ba and Pb. Type-A samples show EMII signatures on the Sr-Nd isotopic diagram, whereas type-P rocks have high initial 143Nd/144Nd ratios (0.5126–0.5128) relative to the type-A rocks (143Nd/144Nd = 0.5124–0.5127). The type-A rocks have 207Pb/204Pb ranging from 15.47 to 15.67 and 206Pb/204Pb from 18.26 to 18.52. All the type-A rocks show a negative correlation between 143Nd/144Nd and 206Pb/204Pb ratios and a positive relationship between 87Sr/86Sr and 206Pb/204Pb ratios, indicating mixing of a depleted mantle source and an EMII component. Geochemical modelling shows that the parental magmas were formed by 5–15 % partial melting of a spinel lherzolite, and contaminated by less than 1 % melt derived from subducted sediment. The type-P magmas were derived from a mantle source unmodified by subduction components. The wide distribution of type-A dykes in SE China suggests that subduction-modified lithospheric mantle was extensive beneath the Cathaysia Block. Geochemical differences between Mesozoic and Cenozoic mafic rocks indicate that lithospheric thinning beneath SE China occurred in two episodes: firstly by heterogeneous modification by subducted components in early Mesozoic times, and later by chemical–mechanical erosion related to convective upwelling of the asthenosphere during Cenozoic times.

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.

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

&lt;p&gt;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) &amp;#8220;bowl-shaped&amp;#8221; 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 &amp;#8211; dunite matrix. Presence of such &amp;#8220;melt pods&amp;#8221; would explain the trace element enrichment patterns of the bulk rock, as well as features such as reverse zoning (core: Cr, Fe&lt;sup&gt;2+&lt;/sup&gt; 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.&lt;/p&gt;

Megacrysts and salic xenoliths in Scottish alkali basalts: derivatives of deep crustal intrusions and small-melt fractions from the upper mantle

2009 ◽  
Vol 73 (6) ◽  
pp. 943-956 ◽  
Author(s):  
B. G. J. Upton ◽  
A. A. Finch ◽  
E. Słaby
Keyword(s):  
Trace Elements ◽  
Coarse Grained ◽  
Partial Replacement ◽  
Spinel Lherzolite ◽  
Alkali Basalts ◽  
Deep Crust ◽  
Basaltic Magmatism ◽  
Potassic Feldspar ◽  
Trace Element Contents ◽  
Early Primary

AbstractCa-poor and typically Na-rich feldspar megacrysts are common associates of spinel lherzolitic and pyroxenitic xenoliths in Scottish alkalic basalts. Associated megacrysts and composite megacrysts and salic xenoliths include apatite, magnetite, zircon, biotite, Fe-rich pyroxene(s) and corundum. The salic xenoliths and related megacrysts are referred to collectively as the ‘anorthoclasite suite': the majority of the samples are inferred to derive from the disaggregation of coarse-grained, typically Na-rich, syenitic protoliths at depth. Rare occurrences of euhedral anorthoclase megacrysts, together with zircon dating, imply that the suite crystallized at, or very shortly before, their entrainment by the basaltic host magmas. Some evidence suggests that the anorthoclasite suite protoliths lie within ultramafic (pyroxenitic) domains in the deep crust. The latter are inferred to be pegmatites, crystallized from carbonated trachytic magmas with widely variable Ca, Na, K, Ba and trace-element contents, and to have ranged from metaluminous to peraluminous. Crystal zonation and resorption textures within the salic xenoliths imply that the crystallization of the parent magmas was complex. Confirmation of this comes from cathodoluminescence studies of the feldspars showing that early ('primary’) anorthoclases and potassian albites exhibit partial replacement by a more potassic feldspar. A third generation of potassic feldspar (enriched in an assortment of trace elements and deduced to have crystallized from a carbonated high-K melt) forms transecting zoned veins in which carbonate fills the axial zone.Whereas most of the anorthoclasite suite materials are inferred to have grown from metaluminous magmas, the occurrence of magmatic corundum in salic xenoliths indicates crystallization from magmas that were peraluminous. The corundum-bearing samples also contain Nb-rich oxide minerals and their associated feldspars have the highest rare-earth element(REE)contents. Accordingly, the peraluminous trachyte magmas are deduced to have been specifically enriched in high field-strength trace elements. It is proposed that formation of the anorthoclasite suite protoliths is a phenomenon closely related to that of salic glass ‘pockets', well known from spinel lherzolite xenoliths around the world. Not only are there compositional affinities, but both sets of phenomena appear to have closely pre-empted the ascent of alkali basalt (host) magmas. We propose that the two sets of phenomena are linked and that the anorthoclasite suite derived from coarse-grained sheets, generated by the aggregation of salic melt fractions rising from the shallow mantle and heralding the onset of basaltic magmatism.

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.

Lower Palaeozoic convergent plate margin volcanism on Bømlo, southwest Norwegian Caledonides: geochemistry and petrogenesis

1986 ◽  
Vol 123 (2) ◽  
pp. 123-142 ◽  
Author(s):  
Harald Furnes ◽  
Harald Brekke ◽  
Jan Nordås ◽  
Jan Hertogen
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Spinel Lherzolite ◽  
Continental Flood Basalts ◽  
Element Abundances ◽  
Upper Cambrian ◽  
Lower Silurian ◽  
Range Type ◽  
Lower Palaeozoic ◽  
Norwegian Caledonides

AbstractMajor and trace element analyses of a Lower Palaeozoic metavolcanic sequence of convergent plate type from Bømlo, southwest Norwegian Caledonides, are presented and discussed. This sequence ranges in age from the Upper Cambrian through the Lower Silurian. Petrogenetic models for the lavas in terms of partial melting and crystal fractionation are discussed. Two models are presented for the metabasalts in order to explain their different trace element abundances and ratios:(1) REE modelling, assuming a mantle source with REE abundances twice chondritic, suggests progressively more varied sources with time. Thus the metabasalts from the oldest (Upper Cambrian–Lower Ordovician) Geitung Unit of primitive island arc type, and those of the mid-Ordovician Siggjo Complex of ‘Basin and Range’ type can be modelled in terms of high (around 25%) and moderate (around 5%) degrees of partial melting of spinel lherzolite, respectively. The metabasalts of the post-Ashgillian Vikafjord Group of typical continental flood basalts are compatible with moderate (c. 5–10%) degrees of partial melting of spinel- and garnet-lherzolite sources. The supposed Lower Silurian Langevåg Group of calc-alkaline ‘Andean’ type metabasalts, grading into alkaline to tholeiitic metabasalts of early marginal basin (youngest) character, require low (<5%) to moderate degrees of partial melting of amphibole-, garnet- and spinel-lherzolite sources, respectively.(2) Source heterogeneity, produced by subduction zone-derived enrichment of LIL elements, and contemporaneous stabilization of minor phases which accommodate HFS elements. This process, combined with possible continental contamination, may possibly yield the trace element concentrations and ratios of the different metabasalts by partial melting of modally similar mantle sources.

Mineral/melt partition coefficients of oceanic alkali basalts determined on natural samples using laser ablation-inductively coupled plasma-mass spectrometry (LAM-ICP-MS)

2000 ◽  
Vol 64 (1) ◽  
pp. 85-94 ◽  
Author(s):  
G. M. Thompson ◽  
J. Malpas
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Inductively Coupled Plasma ◽  
Partition Coefficients ◽  
Dominant Factor ◽  
Alkali Basalts ◽  
Compositional Evolution ◽  
Icp Ms ◽  
D Values ◽  
The Impact

AbstractIn order to limit the range of possible differentiation mechanisms and the impact of these processes on the trace element signatures of igneous suites, it is important to be able to predict or model the compositional evolution of the primary and/or parental magmas. Part of the problem in understanding these relationships in basalts from ocean islands is the paucity of reliable trace element mineral/melt partition coefficients, particularly for undersaturated magmas. Consequently, we have measured mineral/groundmass partition coefficients for Rb, Sr, Y, Zr, Nb, Hf, Ta, Th and REE, in situ, in clinopyroxene, Fe-Ti oxides and olivine in primitive basalts from Rarotonga, Cook Islands using LAM-ICP-MS.Analyses of these mafic rocks show high concentrations of most incompatible trace elements (e.g. Sr, Th, Y, REE, etc.) in pyroxenes relative to the other phases, suggesting that fractionation of pyroxenes was the dominant factor in the distribution of these trace elements during crystal fractionation. In such cases, the highly incompatible elements (D <0.01) are Ba, Cs and Nb. Elements that could also be classified as strongly incompatible (D <0.1) are Rb, Ta and Th. The remaining trace elements have bulk partition coefficient values that range from ∼.0.1 up to ∼.0.8 (Sr, Hf, Zr, Y and REE). Magnetites incorporate greater amounts of Nb and Ta than the titanaugites, and any significant fractionation of magnetite would have affected the bulk distribution of Nb and Ta. The LREE have lower Kd values than other REE, with the HREE having Kd values close to unity. Consequently, with the separation of titanaugite an overall enrichment of REE in the residual liquid with an increase in the La/Yb ratio is produced.

Sign in / Sign up

Export Citation Format

Share Document