The Lithospheric Mantle beneath Continental Margins: Melting and Melt-Rock Reaction in Canadian Cordillera Xenoliths   总被引：3，自引：0，他引：3  

PESLIER  ANNE H.; FRANCIS  DON; LUDDEN  JOHN 《Journal of Petrology》2002,43(11):2013-2047

Seven alkali basalt centers in the southern Canadian Cordilleracontain mantle xenolith suites that comprise spinel Cr-diopsideperidotites, spinel augite-bearing wehrlites and orthopyroxene-poorlherzolites, and minor pyroxenites. The Cr-diopside peridotitesappear to be residues of the extraction of Mg-rich basalts byup to 15% partial melting (median 5–10%) of a pyrolite-likesource in the spinel stability field. The xenoliths are similarto other mantle xenolith suites derived from beneath convergentcontinental margins, but are less depleted, less oxidized, andhave lower spinel mg-number than peridotites found in fore-arcsettings. Their dominant high field strength element depletedcharacter, however, is typical of arc lavas, and may suggestthat fluids or melts circulating through the Canadian Cordilleralithosphere were subduction related. Modeling using MELTS isconsistent with the augite-bearing xenoliths being formed byinteraction between crystallizing alkaline melts and peridotite.Assimilation–fractional crystallization modeling suggeststhat the trace element patterns of liquids in equilibrium withthe augite xenoliths may represent the initial melts that reactedwith the peridotite. Moreover, the compositions of these meltsare similar to those of some glasses observed in the mantlexenoliths. Melt–rock interaction may thus be a viablemechanism for the formation of Si- and alkali-rich glass inperidotites. KEY WORDS: Canadian Cordillera; mantle xenolith; peridotite; wehrlite; melt–rock reaction  相似文献   

Petrogenesis of basaltic shergottite Northwest Africa 5298: Closed‐system crystallization of an oxidized mafic melt     

Hejiu HUI  Anne H. PESLIER  Thomas J. LAPEN  John T. SHAFER  Alan D. BRANDON  Anthony J. IRVING 《Meteoritics & planetary science》2011,46(9):1313-1328

Abstract– Northwest Africa (NWA) 5298 is an evolved basaltic shergottite that has bulk characteristics and mineral compositions consistent with derivation from an oxidized reservoir in Mars. Chemically zoned clinopyroxene (64.5%, augite and pigeonite), with interstitial lath‐shaped plagioclase (29.4%, An₄₀ to An₅₅), constitutes the bulk of this meteorite. The plagioclase has been converted by shock to both isotropic maskelynite and spherulitic, birefringent feldspar representing a quenched vesicular melt. The remainder of the rock consists of minor amounts of Fe‐Ti oxides (ilmenite and titanomagnetite), phosphates (merrillite and apatite), silica polymorph, fayalite, pyrrhotite, baddeleyite, and minor hot desert weathering products (calcite and barite). Oxygen fugacity derived from Fe‐Ti oxide thermobarometry is close to the quartz‐fayalite‐magnetite (QFM) buffer indicating that the late stage evolution of this magma occurred under more oxidizing condition than those recorded in most other shergottites. Merrillite contains the largest abundances of rare earth elements (REE) of all phases, thereby controlling the REE budget in NWA 5298. The calculated bulk rock REE pattern normalized to CI chondrite is relatively flat. The evolution of the normalized REE patterns of the bulk rock, clinopyroxene, plagioclase, and phosphate in NWA 5298 is consistent with closed‐system chemical behavior with no evidence of crustal contamination or postcrystallization disturbance of the REE contents of these phases.  相似文献