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Filiberto, J, Chin E, Day JMD, Franchi IA, Greenwood RC, Gross J, Penniston-Dorland SC, Schwenzer SP, Treiman AH.  2012.  Geochemistry of intermediate olivine-phyric shergottite northwest Africa 6234, with similarities to basaltic shergottite northwest Africa 480 and olivine-phyric shergottite northwest Africa 2990. Meteoritics and Planetary Science. 47(8):1256-1273.   10.1111/j.1945-5100.2012.01382.x   Abstract

The newly found meteorite Northwest Africa 6234 (NWA 6234) is an olivine (ol)-phyric shergottite that is thought, based on texture and mineralogy, to be paired with Martian shergottite meteorites NWA 2990, 5960, and 6710. We report bulk-rock major- and trace-element abundances (including Li), abundances of highly siderophile elements, Re-Os isotope systematics, oxygen isotope ratios, and the lithium isotope ratio for NWA 6234. NWA 6234 is classified as a Martian shergottite, based on its oxygen isotope ratios, bulk composition, and bulk element abundance ratios, Fe/Mn, Al/Ti, and Na/Al. The Li concentration and δ7Li value of NWA 6234 are similar to that of basaltic shergottites Zagami and Shergotty. The rare earth element (REE) pattern for NWA 6234 shows a depletion in the light REE (La-Nd) compared with the heavy REE (Sm-Lu), but not as extreme as the known “depleted” shergottites. Thus, NWA 6234 is suggested to belong to a new category of shergottite that is geochemically “intermediate” in incompatible elements. The only other basaltic or ol-phyric shergottite with a similar “intermediate” character is the basaltic shergottite NWA 480. Rhenium-osmium isotope systematics are consistent with this intermediate character, assuming a crystallization age of 180 Ma. We conclude that NWA 6234 represents an intermediate compositional group between enriched and depleted shergottites and offers new insights into the nature of mantle differentiation and mixing among mantle reservoirs in Mars.

Franz, HB, Kim ST, Farquhar J, Day JMD, Economos RC, McKeegan KD, Schmitt AK, Irving AJ, Hoek J, Dottin J.  2014.  Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars. Nature. 508:364-+.   10.1038/nature13175   AbstractWebsite

The geochemistry of Martian meteorites provides a wealth of information about the solid planet and the surface and atmospheric processes that occurred on Mars. The degree to which Martian magmas may have assimilated crustal material, thus altering the geochemical signatures acquired from their mantle sources, is unclear(1). This issue features prominently in efforts to understand whether the source of light rare-earth elements in enriched shergottites lies in crustal material incorporated into melts(1,2) or in mixing between enriched and depleted mantle reservoirs(3). Sulphur isotope systematics offer insight into some aspects of crustal assimilation. The presence of igneous sulphides in Martian meteorites with sulphur isotope signatures indicative of mass-independent fractionation suggests the assimilation of sulphur both during passage of magmas through the crust of Mars and at sites of emplacement. Here we report isotopic analyses of 40 Martian meteorites that represent more than half of the distinct known Martian meteorites, including 30 shergottites (28 plus 2 pairs, where pairs are separate fragments of a single meteorite), 8 nakhlites (5 plus 3 pairs), Allan Hills 84001 and Chassigny. Our data provide strong evidence that assimilation of sulphur into Martian magmas was a common occurrence throughout much of the planet's history. The signature of mass-independent fractionation observed also indicates that the atmospheric imprint of photochemical processing preserved in Martian meteoritic sulphide and sulphate is distinct from that observed in terrestrial analogues, suggesting fundamental differences between the dominant sulphur chemistry in the atmosphere of Mars and that in the atmosphere of Earth(4).

Furi, E, Hilton DR, Murton BJ, Hemond C, Dyment J, Day JMD.  2011.  Helium isotope variations between Reunion Island and the Central Indian Ridge (17 degrees-21 degrees S): New evidence for ridge-hot spot interaction. Journal of Geophysical Research-Solid Earth. 116   10.1029/2010jb007609   AbstractWebsite

We report new helium abundance and isotope results for submarine basaltic glasses from the Central Indian Ridge (CIR) between the Marie Celeste (16.7 degrees S) and Egeria fracture zones (FZ) (20.6 degrees S); the adjacent Gasitao, Three Magi, and Rodrigues ridges; and for olivine separates from lavas and cumulate xenoliths from the Mascarene Islands (Reunion, Mauritius, and Rodrigues). Helium isotope ratios in basaltic glasses range from 7.1 to 12.2 R(A) (where R(A) = air (3)He/(4)He) and lie between values of Mid-Ocean Ridge Basalt (MORB) (8 +/- 1 R(A)) and samples from Reunion Island (11.5 to 14.1 R(A)). The highest (3)He/(4)He values (up to 12.2 R(A)) are found in glasses recovered off axis from the Three Magi and Gasitao ridges. Along the CIR axis, MORB-like (3)He/(4)He ratios are found near the Egeria FZ, and there is a marked increase to values of similar to 11 R(A) between similar to 19 degrees and 20 degrees S. The lowest (3)He/(4)He values (< 8 R(A)) are found immediately south of the Marie Celeste FZ, where incompatible trace element ratios (e. g., La/Sm) are highest. These low (3)He/(4)He ratios can be explained by closed system radiogenic (4)He ingrowth in either (1) a "fossil" Reunion hot spot mantle component, embedded into the subridge mantle when the CIR migrated over the hot spot at similar to 34 Ma or (2) trace element enriched MORB mantle. In contrast, the high (3)He/(4)He ratios observed on the CIR axis adjacent to the Gasitao Ridge, and along the off-axis volcanic ridges, are consistent with flow of hot spot mantle material from Reunion (similar to 1100 km to the west) toward the CIR.