Petrochemistry of late Palaeozoic alkali lamprophyre dykes from N Scotland

1987 ◽  
Vol 77 (4) ◽  
pp. 267-277 ◽  
Author(s):  
A. N. Baxter
Keyword(s):  
Lithospheric Mantle ◽  
Incompatible Element ◽  
Fluid Phase ◽  
Spinel Lherzolite ◽  
Lower Carboniferous ◽  
Scottish Highlands ◽  
Basic Series ◽  
Dyke Swarms ◽  
Element Variation ◽  
Primary Magmas

ABSTRACTThe lower Carboniferous–late Permian dyke swarms of the Scottish Highlands and Islands comprise a mild-strongly alkaline basic series of dolerites, camptonites and monchiquites. Differentiation within the suite was largely controlled by olivine + clinopyroxene fractionation. Major and trace element data indicate that dolerites and camptonites chemically overlap, their mineralogical contrasts resulting from differential loss of an H2O, CO2-rich fluid phase during ascent. By contrast most monchiquites have high Mg-values and are relatively primitive compositions, some being near-primary magmas which have risen rapidly from mantle levels with little chemical modification.HREE-buffered incompatible element profiles imply a garnet–lherzolite source, which must underlie the lithospheric mantle region represented by spinel lherzolite xenoliths found in some monchiquites. C. 0·5–2·0% partial melting can account for the gross incompatible element variation in the suite, but relative fluctuations in K, Ba, Rb, Sr, P and Zr imply chemical heterogeneity controlled either by refractory mantle accessory phases or by modification of magmas during ascent through variably metasomatised lithospheric mantle.

Lherzolite - carbonatite melt interaction in the presence of additive CO2 and H2O: Experimental data at 5.5 GPa and 1200-1450°C

2021 ◽  
Author(s):  
Aleksei Kruk ◽  
Alexander Sokol
Keyword(s):  
Experimental Data ◽  
Lithospheric Mantle ◽  
Fluid Phase ◽  
Experimental Results ◽  
Silicate Melt ◽  
Silicate Melts ◽  
Garnet Lherzolite ◽  
Russian Science ◽  
Continental Lithospheric Mantle

<p>We study the reaction of garnet lherzolite with carbonatitic melt rich in molecular CO<sub>2</sub> and/or H<sub>2</sub>O in experiments at 5.5 GPa and 1200-1450°C. The experimental results show that carbonation of olivine with formation of orthopyroxene and magnesite can buffer the CO<sub>2</sub> contents in the melt, which impedes immediate separation of CO<sub>2</sub> fluid from melt equilibrated with the peridotite source. The solubility of molecular CO<sub>2</sub> in melt decreases from 20-25 wt.% at 4.5-6.8 wt.% SiO<sub>2</sub> typical of carbonatite to 7-12 wt.% in more silicic kimberlite-like melts with 26-32 wt.% SiO<sub>2</sub>. Interaction of garnet lherzolite with carbonatitic melt (2:1) in the presence of 2-3 wt.% H<sub>2</sub>O and 9-13 wt.% molecular CO<sub>2</sub> at 1200-1450°С yields low SiO<sub>2</sub> (<10 wt.%) alkali‐carbonatite melts, which shows multiphase saturation with magnesite-bearing garnet harzburgite. Thus, carbonatitic melts rich in volatiles can originate in a harzburgite source at moderate temperatures common to continental lithospheric mantle (CLM).</p><p>Having separated from the source, carbonatitic magma enriched in molecular CO<sub>2</sub> and H<sub>2</sub>O can rapidly acquire a kimberlitic composition with >25 wt.% SiO<sub>2 </sub>by dissolution and carbonation of entrapped peridotite. Furthermore, interaction of garnet lherzolite with carbonatitic melt rich in K, CO<sub>2</sub>, and H<sub>2</sub>O at 1350°С produces immiscible kimberlite-like carbonate-silicate and K-rich silicate melts. Quenched silicate melt develops lamelli of foam-like vesicular glass. Differentiation of immiscible melts early during ascent may equalize the compositions of kimberlite magmas generated in different CLM sources. The fluid phase can release explosively from ascending magma at lower pressures as a result of SiO<sub>2</sub> increase which reduces the solubility of CO<sub>2</sub> due to decarbonation reaction of magnesite and orthopyroxene.</p><p>The research was performed by a grant of the Russian Science Foundation (19-77-10023).</p>

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.

scholarly journals Zircon Xenocrysts from Cenozoic Alkaline Basalts of the Ratanakiri Volcanic Province (Cambodia), Southeast Asia—Trace Element Geochemistry, O-Hf Isotopic Composition, U-Pb and (U-Th)/He Geochronology—Revelations into the Underlying Lithospheric Mantle

Minerals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 556 ◽  
Author(s):  
Paula Piilonen ◽  
F. Sutherland ◽  
Martin Danišík ◽  
Glenn Poirier ◽  
John Valley ◽  
...  
Keyword(s):  
Lithospheric Mantle ◽  
Incompatible Element ◽  
Trace Element Geochemistry ◽  
Ocean Water ◽  
Element Geochemistry ◽  
Alkali Basalts ◽  
Low Degree ◽  
Host Basalt ◽  
Peridotitic Mantle ◽  
Hf Isotopic Composition

Zircon xenocrysts from alkali basalts in Ratanakiri Province, Cambodia represent a unique low-Hf zircon within a 12,000 km long Indo-Pacific megacryst zone. Colorless, yellow, brown, and red crystals ({100}, {101}, subordinate {211}, {1103}), with hopper growth and corrosion features range up to 20 cm in size. Zircon chemistry indicates juvenile, Zr-saturated, mantle-derived alkaline melt (Hf 0.6–0.7 wt %, Y <0.2 wt %, U + Th + REE (Rare-Earth Elements) < 600 ppm, Zr/Hf 66–92, Eu/Eu*N ~1, positive Ce/Ce*N, HREE (Heavy REE) enrichment). Incompatible element depletion with increasing Yb/SmN from core to rim at ~ constant Hf suggests single stage growth. Ti-in-zircon temperatures (~570–740 °C) are lower than predicted by crystal morphology (800–900 °C) and decrease from core to rim (ΔT = 10–50 °C). The δ18O values (4.88 to 5.01‰ VSMOW (Vienna Standard Mean Ocean Water)) are relatively low for xenocrysts from the zircon Indo-Pacific zone (ZIP). The 176Hf/177Hf values (+ εHf 4.5–10.2) give TDepleted Mantle model source ages of 260–462 Ma and TCrustal ages of 391–754 Ma. The source magmas reflect variably depleted lithospheric mantle with little supracrustal input. Zircon U-Pb (0.88–1.56 Ma) and (U-Th)/He (0.86–1.02 Ma) ages are older than host basalt ages (~0.7 Ma), which suggests limited residence before transport. Zircon genesis suggests Zr-saturated, Al-undersaturated, carbonatitic-influenced, low-degree partial melting (<1%) of peridotitic mantle at ~60 km beneath the Indochina terrane.

Geochemistry of Precambrian basaltic rocks from the Central African Republic (Equatorial Africa)

1985 ◽  
Vol 22 (5) ◽  
pp. 653-662 ◽  
Author(s):  
J. Dostal ◽  
C. Dupuy ◽  
J. L. Poidevin
Keyword(s):  
Upper Mantle ◽  
Central African Republic ◽  
Incompatible Element ◽  
Dolerite Dyke ◽  
Basaltic Rocks ◽  
Incompatible Elements ◽  
Equatorial Africa ◽  
Metavolcanic Rocks ◽  
Greenstone Belts ◽  
Dyke Swarms

The two Archaean greenstone belts (Bandas and Bogoin) in the Central African Republic (Equatorial Africa) are 250 and 150 km long. The metavolcanic rocks in the belts are predominantly komatiitic and tholeiitic basalts. Komatiites include both Al-depleted and Al-undepleted types. The komatiites and light-REE-depleted tholeiites were probably derived from a similar upper mantle source. However, the tholeiitic basalts enriched in light REE from the upper volcanic strata of the Bandas belt were generated from a different source. The dolerites from Proterozoic dyke swarms and sills differ from the basalts mainly in their abundances and ratios of several incompatible elements such as K, Rb, Th, and light REE. They were derived from a distinct, incompatible-element-enriched upper mantle source.The average background gold levels in the Bandas belt and dolerite dyke swarms are comparable to those in equivalent rocks from North America. The exception is the Bogoin greenstone belt, which has anomalously high gold abundances.

The Early Cretaceous Shangzhuang layered mafic intrusion and its bearing on decratonization of the North China Craton

2017 ◽  
Vol 155 (7) ◽  
pp. 1475-1506 ◽  
Author(s):  
XUE-MING TENG ◽  
M. SANTOSH ◽  
LI TANG
Keyword(s):  
Early Cretaceous ◽  
North China Craton ◽  
Lithospheric Mantle ◽  
North China ◽  
Layered Intrusion ◽  
Parent Magma ◽  
Spinel Lherzolite ◽  
The North ◽  
Layered Mafic Intrusion ◽  
Lithospheric Destruction

AbstractThe North China Craton (NCC) is one of the classic examples of decratonization through extensive lithospheric destruction during Mesozoic time. Among the various pulses of magmatism associated with cratonic erosion are the rare mafic intrusions in the Yanshan Belt. Here we investigate the Shangzhuang layered intrusion belonging to this suite, which is characterized by compositional layering with troctolite, noritic gabbro and gabbro/gabbroic anorthosite/gabbrodiorite from the bottom to top. The different lithologies of this intrusion exhibit close field relationships, similar chemical patterns and overall identical Lu–Hf isotopes indicating a co-magmatic nature. The fine-grained gabbros occurring near the margin of the intrusion display U–Pb ages similar to those of the other rocks and are considered to represent the composition of the parent magma, characterized by Fe, Mg and Ti enrichment. The magma was sourced from low-degree partial melting of spinel lherzolite sub-continental lithospheric mantle, which had been enriched by crust–mantle interaction and metasomatic fluids derived from the Mongolian oceanic slab subduction beneath the NCC during Late Palaeozoic time. In addition, limited asthenospheric or deeper-mantle materials were also locally mixed with the enriched mantle as the final source component. Our zircon U–Pb data constrain the emplacement age of this intrusion as c. 128–123 Ma in Early Cretaceous time, and correlates with the regional extensional tectonics between c. 135 and 115 Ma in the eastern and central NCC. Mantle upwelling associated with this event resulted in the thermal and chemical erosion of the lithospheric mantle, and emplacement of the parent magma of this layered intrusion.

Petrological and geochemical characteristics of Mesoproterozoic dyke swarms in the Gardar Province, South Greenland: Evidence for a major sub-continental lithospheric mantle component in the generation of the magmas

2015 ◽  
Vol 79 (4) ◽  
pp. 909-939 ◽  
Author(s):  
Alexander Bartels ◽  
Troels F. D. Nielsen ◽  
Seung Ryeol Lee ◽  
Brian G. J. Upton
Keyword(s):  
Rare Earth ◽  
Lithospheric Mantle ◽  
Source Region ◽  
Crustal Contamination ◽  
Coarse Grained ◽  
Stability Field ◽  
Time Interval ◽  
Continental Lithospheric Mantle ◽  
Melt Generation ◽  
Dyke Swarms

AbstractThe Mesoproterozoic Gardar Province in South Greenland developed in a continental rift-related environment. Several alkaline intrusions and associated dyke swarms were emplaced in Archaean and Ketilidian basement rocks during two main magmatic periods at 1300–1250 Ma and 1180–1140 Ma. The present investigation focuses on mafic dykes from the early magmatic period ('Older Gardar') and the identification of their possible mantle sources.The rocks are typically fine- to coarse-grained dolerites, transitional between tholeiitic and alkaline compositions with a general predominance of Na over K. They crystallized from relatively evolved, mantle-derived melts and commonly show minor degrees of crustal contamination. Selective enrichment of the large ion lithophile elements Cs, Ba and K and the light rare-earth elements when compared to high field-strength elements indicate significant involvement of a sub-continental lithospheric mantle (SCLM) component in the generation of the magmas. This component was affected by fluid-dominated supra-subduction zone metasomatism, possibly related to the Ketilidian orogeny ∼500 Ma years prior to the onset of Gardar magmatism. Melt generation in the SCLM is further documented by the inferential presence of amphibole in the source region, negative calculated εNd(i) values (–0.47 to –4.40) and slightly elevated87Sr/86Sr(i) (0.702987 to 0.706472) ratios when compared to bulk silicate earth as well as relatively flat heavy rare-earth element (HREE) patterns ((Gd/Yb)N= 1.4 –1.9) indicating melt generation above the garnet stability field.The dyke rocks investigated show strong geochemical and geochronological similarities to penecontemporaneous mafic dyke swarms in North America and Central Scandinavia and a petrogenetic link is hypothesized. Considering recent plate reconstructions, it is further suggested that magmatism was formed behind a long-lived orogenic belt in response to back-arc basin formation in the time interval between 1290–1235 Ma.

scholarly journals The age and evolution of the lithospheric mantle in the East Antarctic Craton: osmium isotope composition and the distribution of the platinum group elements in spinel lherzolite nodules

2019 ◽  
Vol 485 (6) ◽  
pp. 726-731
Author(s):  
R. Sh. Krymsky ◽  
A. V. Antonov ◽  
B. V. Belyatsky ◽  
N. M. Sushchevskaya ◽  
S. A. Sergeev
Keyword(s):  
Lithospheric Mantle ◽  
Isotope Composition ◽  
Platinum Group Elements ◽  
Mantle Xenoliths ◽  
Spinel Lherzolite ◽  
Thermal Erosion ◽  
Rift Propagation ◽  
Mantle Section ◽  
Partial Destruction ◽  
Osmium Isotope

The mantle xenoliths of lherzolite composition from Mesozoic alkaline-ultrabasic diatremes of the Jetty Oasis were studied. The studied xenoliths represent the mantle section of the East Antarctic Craton down to depths of 60-80 km. The osmium isotope composition of these nodules testifies to the beginning of the formation of the lithospheric mantle in the considered region at about 2400 Ma. The absence of any signs of Early Archean lithosphere points either to partial destruction of the lithosphere at the convergent boundary of the plates in the Late Archean or to thermal erosion of the Archean lithosphere under the deep-seated plume impact at the Mesozoic time during rift propagation.

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