Minor-Element Distribution in Olivine

1970 ◽  
Vol 78 (3) ◽  
pp. 304-325 ◽  
Author(s):  
Tom Simkin ◽  
J. V. Smith
Keyword(s):  
Minor Element ◽  
Element Distribution

Rare-earth and minor element distribution and petrographic features of fluorites and associated Mesozoic limestones of northwestern Sicily

1981 ◽  
Vol 32 (1-4) ◽  
pp. 255-269 ◽  
Author(s):  
A. Bellanca ◽  
P. Di Salvo ◽  
P. Möller ◽  
R. Neri ◽  
F. Schley
Keyword(s):  
Rare Earth ◽  
Minor Element ◽  
Element Distribution

Deformation-controlled cation diffusion in compositionally zoned tourmaline

2005 ◽  
Vol 69 (4) ◽  
pp. 471-489 ◽  
Author(s):  
S. H. Büttner
Keyword(s):  
Plastic Deformation ◽  
Microprobe Analysis ◽  
Electron Microprobe Analysis ◽  
Volume Ratio ◽  
Minor Element ◽  
Element Distribution ◽  
Dislocation Creep ◽  
Dominant Deformation Mechanism ◽  
Growth Zones ◽  
Compositional Zonation

AbstractThe compositional zonation of both undeformed and plastically deformed tourmaline crystals from an amphibolite-facies mylonitic pegmatite from the Sierras Pampeanas (NW Argentina) has been investigated using electron microprobe analysis (EMPA). Undeformed tourmaline shows optical and compositional major and minor element growth zonation with a Ca- and Mg-rich rim zone and an Fe- rich core zone. The tourmaline population of the mylonite consists of crystals which appear undeformed at microscopic scale, and of weakly, moderately, and strongly deformed crystals. Depending on the intensity of plastic deformation, the optical zonation is blurred or absent, and the compositional zonation is less pronounced or destroyed. Plastic deformation mobilizes small cations (Fe2+, Mg2+) more efficiently and at lower deformation intensity than larger cations (Na+, Ca2+). In addition to intra-crystal homogenization, plastic deformation caused variable but generally minor Fe, Mg, Si, Al, Ca, and Na exchange between deformed tourmaline domains and co-existing fluid or solid phases. Dislocation creep is interpreted as the dominant deformation mechanism leading to the homogenization of the initial tourmaline growth zonation. The composition and the degree of homogeneity of deformed tourmaline domains depend on the initial composition of the growth zones, their initial volume ratio, the intensity and homogeneity of plastic deformation, and the size of the mobilized cation. Consequently, the composition of and the element distribution within plastically deformed crystals is not entirely controlled by intensive variables (P-T-X), and therefore not suitable for petrogenetic interpretation.

Petrology of a plagioclase-bearing olivine websterite from the Gorringe Bank (northeastern Atlantic Ocean)

1988 ◽  
Vol 25 (4) ◽  
pp. 557-569 ◽  
Author(s):  
Giancarlo Serri ◽  
Réjean Hébert ◽  
Roger Hekinian
Keyword(s):  
Solidus Temperature ◽  
Parental Magma ◽  
Minor Element ◽  
Element Distribution ◽  
Rock Composition ◽  
Natural Systems ◽  
S 100 ◽  
Compositional Variations ◽  
A Minor ◽  
Northeastern Atlantic

Samples of plagioclase olivine websterite included in variously serpentinized harzburgite and lherzolite tectonites were collected by submersible on the northwest flank of the Gettysburg Seamount near 36°N in the northeastern Atlantic. The websterite exhibits a coarse porphyroclastic texture (70% porphyroclasts), and the composition of the pyroxene shows a progressive re-equilibration with decreasing temperature (and probably pressure) under anhydrous conditions from a near-solidus temperature of ~1250 °C (porphyroclasts) down to ~700 °C (granoblasts). In situ observations, as well as textural, mineralogical, and chemical evidence, suggest that the websterite can best be interpreted as a heteradcumulate rock that crystallized on the walls of narrow conduits from a MORB type magma flowing through the residual tectonites.The Mg #'s (= 100 × Mg/(Mg + Fe2+)) of coexisting clinopyroxene, orthopyroxene, and olivine (91.5–90.5, 90.0–89.7, and 89.5–88.5, respectively), the plagioclase composition (An88.7–87.9), and the mineral minor-element distribution are not compatible with the crystallization at low pressure of the websterite from N-MORB type parental magma. Instead, the calculated composition of the liquid in equilibrium with the websterite's most magnesian minerals and the bulk-rock composition are more akin to those of a poorly differentiated T-MORB than of N-MORB parental magma. Phase relations and mineral compositions produced by anhydrous melting experiments for synthetic and natural systems indicate that the pressure of crystallization of the plagioclase olivine websterite is constrained within the narrow range of 7–10 kbar. It is thought that fractionation of websterite is probably a minor but significant petrologic factor of MORB type magma differentiation. It could explain some of the compositional variations observed in magnesian MORB.

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