The lunar crust is a unique window into early planetary differentiation processes in the solar system, bridging the gap between incipient igneous activity in asteroids and the more evolved geodynamics of terrestrial planets like the Earth. Decades after the epic Apollo and Luna missions, the crustal diversity of the Moon remains an outstanding issue which the lunar meteorites - random samples of the lunar surface materials - can contribute to resolve. The new meteorite Mount DeWitt (DEW) 12007 was collected in Victoria Land during the XXVIII PNRA Antarctic Campaign. DEW 12007 is a polymict regolith breccia mainly consisting of glassy impact-melt breccia particles, gabbroic clasts, feldspathic clasts, impact and volcanic glass beads, crystalline basaltic clasts and mingled breccia clasts embedded in a matrix dominated by fine-grained crystals; vesicular glassy veins and rare agglutinates are also present. Main minerals are plagioclase (generally An>85) and clinopyroxene (pigeonites and augites, sometimes interspersed). The presence of tranquillityite, coupled with the petrophysical data, the O-isotope data (Δ 17O=-0.075) and the FeOtot/MnO ratios in olivine (91), pyroxene (65) and bulk rock (77) indicate a lunar origin for DEW 12007. Impactites consist of Al-rich impact melt splashes and plagioclase-rich meta-melt clasts whose parent rocks could be associated to the so-called Mgsuite or to the ferroan anorthosite (FAN) suite of early lunar intrusives. The volcanic products belong to the Very Low Titanium (VLT) or Low Titanium (LT) suites; an unusual subophitic particle could be cryptomare-related. Gabbroic clasts could represent part of a shallow intrusion within a mare volcanic complex with prevailing VLT affinity. DEW 12007 is classified as a mingled regolith breccia which developed on a VLT volcanic complex near a magnesian feldspathic terrane. DEW 12007 is a good compendium of lunar materials which samples a high crustal diversity, comprising clasts from the major Moon terranes (the Feldspathic Highland Terrane, the Procellarum KREEP Terrane and the basaltic maria) and some rare lunar lithologies (i.e., a putative pre-mare basalt and some VLT-like gabbros). DEW 12007 is by now unpaired. A preliminary petrographic and geochemical comparison suggests that a possible launch-pairing relationship between DEW 12007 and other lunar meteorites (Y 793274/981031, QUE 94281 and EET 87521/96008) should be properly investigated. Based on the Clementine remote sensing compositional data, and in light of a comparison with the Apollo and Luna samples, we suggest that a region near the margin of Mare Serenitatis could represent a reliable context for the formation and the ejection of DEW 12007; however, similar locations within Mare Fecunditatis or Mare Crisium could provide an analogous scenario.
The diversity of the lunar crust as told by the new polymict regolith breccia Mount DeWitt 12007 (Antarctica)
Collareta A.
Primo
;D'Orazio M.Secondo
;Gemelli M.;Folco L.Ultimo
2015-01-01
Abstract
The lunar crust is a unique window into early planetary differentiation processes in the solar system, bridging the gap between incipient igneous activity in asteroids and the more evolved geodynamics of terrestrial planets like the Earth. Decades after the epic Apollo and Luna missions, the crustal diversity of the Moon remains an outstanding issue which the lunar meteorites - random samples of the lunar surface materials - can contribute to resolve. The new meteorite Mount DeWitt (DEW) 12007 was collected in Victoria Land during the XXVIII PNRA Antarctic Campaign. DEW 12007 is a polymict regolith breccia mainly consisting of glassy impact-melt breccia particles, gabbroic clasts, feldspathic clasts, impact and volcanic glass beads, crystalline basaltic clasts and mingled breccia clasts embedded in a matrix dominated by fine-grained crystals; vesicular glassy veins and rare agglutinates are also present. Main minerals are plagioclase (generally An>85) and clinopyroxene (pigeonites and augites, sometimes interspersed). The presence of tranquillityite, coupled with the petrophysical data, the O-isotope data (Δ 17O=-0.075) and the FeOtot/MnO ratios in olivine (91), pyroxene (65) and bulk rock (77) indicate a lunar origin for DEW 12007. Impactites consist of Al-rich impact melt splashes and plagioclase-rich meta-melt clasts whose parent rocks could be associated to the so-called Mgsuite or to the ferroan anorthosite (FAN) suite of early lunar intrusives. The volcanic products belong to the Very Low Titanium (VLT) or Low Titanium (LT) suites; an unusual subophitic particle could be cryptomare-related. Gabbroic clasts could represent part of a shallow intrusion within a mare volcanic complex with prevailing VLT affinity. DEW 12007 is classified as a mingled regolith breccia which developed on a VLT volcanic complex near a magnesian feldspathic terrane. DEW 12007 is a good compendium of lunar materials which samples a high crustal diversity, comprising clasts from the major Moon terranes (the Feldspathic Highland Terrane, the Procellarum KREEP Terrane and the basaltic maria) and some rare lunar lithologies (i.e., a putative pre-mare basalt and some VLT-like gabbros). DEW 12007 is by now unpaired. A preliminary petrographic and geochemical comparison suggests that a possible launch-pairing relationship between DEW 12007 and other lunar meteorites (Y 793274/981031, QUE 94281 and EET 87521/96008) should be properly investigated. Based on the Clementine remote sensing compositional data, and in light of a comparison with the Apollo and Luna samples, we suggest that a region near the margin of Mare Serenitatis could represent a reliable context for the formation and the ejection of DEW 12007; however, similar locations within Mare Fecunditatis or Mare Crisium could provide an analogous scenario.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
