Evolution of the upper mantle under the Assab Region (Ethiopia): Suggestions from petrology and geochemistry of tectonitic ultramafic xenoliths and host basaltic lavas

1978 ◽  
Vol 67 (2) ◽  
pp. 547-575 ◽  
Author(s):  
G. Ottonello ◽  
G. B. Piccardo ◽  
J. L. Joron ◽  
M. Treuil
Keyword(s):  
Upper Mantle ◽  
Ultramafic Xenoliths ◽  
Petrology And Geochemistry ◽  
Basaltic Lavas

Petrology of ultramafic xenoliths from Rayfield River, south-central British Columbia

1987 ◽  
Vol 24 (8) ◽  
pp. 1679-1687 ◽  
Author(s):  
Dante Canil ◽  
Mark Brearley ◽  
Christopher M. Scarfe
Keyword(s):  
British Columbia ◽  
Phase Equilibrium ◽  
Partial Melting ◽  
Upper Mantle ◽  
Mantle Xenoliths ◽  
Spinel Lherzolite ◽  
Equilibrium Constraints ◽  
Host Magma ◽  
South Central ◽  
Ultramafic Xenoliths

One hundred mantle xenoliths were collected from a hawaiite flow of Miocene–Pliocene age near Rayfield River, south-central British Columbia. The massive host hawaiite contains subrounded xenoliths that range in size from 1 to 10 cm and show protogranular textures. Both Cr-diopside-bearing and Al-augite-bearing xenoliths are represented. The Cr-diopside-bearing xenolith suite consists of spinel lherzolite (64%), dunite (12%), websterite (12%), harzburgite (9%), and olivine websterite (3%). Banding and veining on a centimetre scale are present in four xenoliths. Partial melting at the grain boundaries of clinopyroxene is common and may be due to natural partial melting in the upper mantle, heating by the host magma during transport, or decompression during ascent.Microprobe analyses of the constituent minerals show that most of the xenoliths are well equilibrated. Olivine is Fo89 to Fo92, orthopyroxene is En90, and Cr diopside is Wo47En48Fs5. More Fe-rich pyroxene compositions are present in some of the websterite xenoliths. The Mg/(Mg + Fe2+) and Cr/(Cr + Al + Fe3+) ratios in spinel are uniform in individual xenoliths, but they vary from xenolith to xenolith. Equilibration temperatures for the xenoliths are 860–980 °C using the Wells geothermometer. The depth of equilibration estimated for the xenoliths using geophysical and phase equilibrium constraints is 30–40 km.

Geochemistry of ultramafic xenoliths from Kapfenstein, Austria: evidence for a variety of upper mantle processes

1980 ◽  
Vol 44 (1) ◽  
pp. 45-60 ◽  
Author(s):  
G. Kurat ◽  
H. Palme ◽  
B. Spettel ◽  
Hildegard Baddenhausen ◽  
H. Hofmeister ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Ultramafic Xenoliths ◽  
Mantle Processes

Xenoliths and their implications for the deep geology of the Midland Valley of Scotland and adjacent region

1984 ◽  
Vol 75 (2) ◽  
pp. 65-70 ◽  
Author(s):  
Brian G. J. Upton ◽  
Peder Aspen ◽  
Robert H. Hunter
Keyword(s):  
Upper Mantle ◽  
Lower Crust ◽  
Retrograde Metamorphism ◽  
Widespread Occurrence ◽  
Peridotite Xenoliths ◽  
Igneous Origin ◽  
Ultramafic Xenoliths ◽  
Lower Palaeozoic ◽  
Lower Crustal ◽  
Alkalic Basalts

ABSTRACTLate Palaeozoic alkalic basalts in and around the Midland Valley of Scotland contain a wide variety of ‘plutonic’ xenoliths. Pyroxene-rich ultramark xenoliths (wehrlites, clinopyroxenites and garnet pyroxenites) may be representative of younger components within a dominantly peridotitic upper mantle represented by ubiquitous magnesian peridotite xenoliths. Glimmerites and other biotite-rich ultramafic xenoliths are probable samples of metasomatised upper mantle facies.Xenoliths composed mainly of plagioclase, clinopyroxene ± orthopyroxene ± magnetite are widespread. These pyroxene granulites may typify the lower crustal layers. Garnet granulites are rare; such rocks may formerly have been important with loss of garnet occurring through retrograde metamorphism. Anorthositic xenoliths are relatively common. The lower crust may consist largely of anhydrous rocks, of gabbroic to anorthositic composition, ccurring as stratiform bodies of metacumulates.Other xenoliths of igneous origin include tonalitic and trondhjemitic gneisses. Although these may play some role in the lower crust, they may be more abundant in the mid-crustal domains underlying the deformed upper Precambrian and lower Palaeozoic supracrustal strata. Xenoliths of quartzofeldspathic, granulitic gneisses containing garnet ± sillimanite ± rutile are also of widespread occurrence; many of these are of metasedimentary provenance and are regarded as being derived from the mid-crustal layers beneath the Southern Highlands, Midland Valley and Southern Uplands and their Irish counterparts.

Ultramafic xenoliths from the Elwin Bay kimberlite: the first Canadian paleogeotherm

1977 ◽  
Vol 14 (6) ◽  
pp. 1202-1210 ◽  
Author(s):  
Roger H. Mitchell
Keyword(s):  
Upper Limb ◽  
Upper Mantle ◽  
Spinel Lherzolite ◽  
Garnet Lherzolite ◽  
Arctic Canada ◽  
Iron Enrichment ◽  
Ultramafic Xenoliths

Ultramafic xenoliths from the Elwin Bay kimberlite provide samples of the upper mantle beneath arctic Canada. The compositions of coexisting pyroxenes have been used to estimate the temperatures and pressures of equilibration of the three texturally and mineralogically distinct types of xenolith, i.e. spinel lherzolite (840–935 °C), coarse garnet lherzolite (925–1085 °C at 39.5–49.5 kbar (3.95–4.95 × 106 kPa)) and porphyroclastic garnet lherzolite (1090–1180 °C at 47.0–51.5 kbar (4.7–5.2 × 106 kPa)). The garnet lherzolite data define an inflected paleogeotherm whose upper limb lies at shallower depths than found for the Thaba Putsoa – Mothae paleogeotherm but which is identical to the Montana paleogeotherm. No evidence is found for iron enrichment of the upper mantle in this region.

A Discussion on volcanism and the structure of the Earth - Plutonic xenoliths and their relation to the upper mantle

1972 ◽  
Vol 271 (1213) ◽  
pp. 313-323 ◽  
Keyword(s):  
Upper Mantle ◽  
Regional Differences ◽  
Primitive Mantle ◽  
Ultramafic Rocks ◽  
Mantle Material ◽  
The Earth ◽  
Ultramafic Xenoliths ◽  
Partial Fusion ◽  
Isotopic Equilibration ◽  
Isotopic Anomalies

The best samples for chemical and petrological studies of the upper mantle are the ultramafic xenoliths carried up during volcanism, and those ultramafic rocks that may be tectonic slices of mantle transplanted into the crust. A geochemical survey of lherzolite xenoliths from a number of different localities fndkates that regional differences do occur in upper mantle material and that dxese differences may be explained by partial fusion and extraction of the liquid phase. In some localities the concentrations of K and U in the xenoliths may be high enough for the xenoliths to represent primitive mantle material There is some evidence that isotopic equilibration between co-existing minerals in the mantle is not attained over very long periods. This might lead to isotopic anomalies in rocks derived from the mantle.

Mössbauer study of phlogopites from upper mantle ultramafic xenoliths /Alcsúcsdoboz, Hungary/

1988 ◽  
Vol 127 (4) ◽  
pp. 289-297 ◽  
Author(s):  
Z. Homonnay ◽  
E. Kuzmann ◽  
A. Vértes ◽  
I. Kubovics ◽  
K. G. Sólymos ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Mössbauer Study ◽  
Ultramafic Xenoliths
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