5C and 5D) and unlike the orthopyroxene
present in the blocks, they do not form kelyphitic rims.
We have determined in situ concentrations of 28 trace elements (REE, Ba, Rb, Sr, Th, U, Nb, Ta, Pb, Zr, Hf, Y, Sc, V, Co and Cr) in olivine, plagioclase, orthopyroxene
, clinopyroxene, amphibole and phlogopite on two polished thick sections (130 [micro]m) by laser ablation ICP-MS at the Natural History Museum of London, using a New Wave UP193FX gas laser source operating at 193 nm coupled to an Agilent 7500CS ICP-MS.
The dyke is everywhere porphyritic with abundant euhedral to subhedral orthopyroxene
crystals several mm or more in length (Figs.
MINERALS Level of abundance JSO-1/JSO-2 JSO-2 * Contamination soils Allophane +++ +++ + Quartz + + - + Plagioclase - + X K-feldspar X - X Augite - + X Gibbsite + - + X Hematite - - X Magnetite - - + 7A halloysite X - X Orthopyroxene
X X + - Hydrated halloysite X - X Olivine - - + Glass + - + - +++ abundant; + -: common; +: existent; -: rare, X: not detected * Terashima et al.
The high contents of MgO (up to 30 wt%) coupled with low abundances of incompatible trace elements in komatiites suggest that the komatiitic magma was generated by a high degree of partial melting when Mg-rich olivine and orthopyroxene
were dominant phases entering the melts.
Diamonds are known to occur in three peridotite subtypes: dunite (90% olivine), harzburgite (40-90% olivine, the rest orthopyroxene
and garnet), and lherzolite (at least 40% olivine, with orthopyroxene
and clinopyroxene in a wide range of proportions, and minor garnet).
8] Magnetite 50,000 Ilimenite 100 Hematite 60-600 Pyrrhotite 10-1000 Orthopyroxene
50 Biotite 80 TABLE 3.
Two other minor assemblages occur in distinct areas of the body: a chromite prospect consisting of massive and banded chromite deposits, and an area consisting of 5-10% orthopyroxene
Abundant indicator minerals were recovered from both kimberlites and include pyrope garnets, chromites, picroilmenites, Cr-diopside orthopyroxene
These rocks are rich in diopside and orthopyroxene
is very rare.
Traces of initial minerals like Olivine, Orthopyroxene
, and Chrome Spinel are observed in the form of isolated islands.
These crystals such as plagioclase, biotite, hornblende and orthopyroxene
are easily identified as phenocrysts because they do not correspond to the mineral phase association observed in peralkaline magmatism.
releases its silica into the magma, and as the silica content rises, the magma's ability to hold dissolved carbon dioxide drops.
Mineral compositions for plagioclase (N = 93), clinopyroxene (N = 65) and orthopyroxene
(N = 48) cores were obtained with a Cameca SX-50 microprobe, using wavelength-dispersive spectrometry (WDS) with count times between ~10-20 seconds.
1) 2) 3) 4) 5) Quartz 30 35 34 28 - alkali feldspar 60 57 63 58 - (perthite) calcic - - - - 49 plagioclase Biotite <1 <1 - 1 1 alkali 9 8 6 11 - amphibole calcic - - - - 26 hornblende Clinopyroxene - - - - 9 Orthopyroxene
- - - - 7 Olivine - - - - 3 Ore - <1 - 1 4 Accessory 1 <1 <1 1 1 minerals IUGS rock a-fG a-fG a-fGl a-fG G-N classification Abbreviations: a-fG = alkali-feldspar granite.