The Varre-Sai chondrite, a Brazilian fall: petrology and geochemistry

The Varre-Sai meteorite fell along the border of the states of Espirito Santo and Rio de Janeiro, Brazil; on 19 June 2010 at 5:40 pm. Petrography and X-ray powder diffraction (XRD) indicate that the rock is an L5 S4 chondrite, with blastoporphyritic texture that has not been previously described. Geochemical data based on major and rare-earth elements (REEs) show that Varre-Sai is highly similar to the other L chondrites. In Harker diagrams, Varre-Sai, L, and LL chondrites form a single group, suggesting no significant chemical differences between them and contributing to the long-standing debate of whether LL chondrites form a distinct group or whether they are a subset of the L group. Harker diagrams also define a trend from E to H and L/LL chondrites, similar to the cosmochemical trends suggested by other authors. The behaviour of Fe₂O_3t and NiO indicates a relationship with Fe-Ni alloys, and their trend in the diagram suggests some chemical differentiation in the ordinary chondrite parental bodies. The REE content in Varre-Sai, normalized to C chondrites, falls in the field of L chondrites and others, but with slight REE enrichment. The chemical differences in chondrites, mainly in REEs, Fe₂O_3t and NiO could be alternatively interpreted as variations in the inherited agglutinated materials as chondrules, Ca–Al-rich inclusions and Fe–Ni nodules.

瓦雷-赛伊（Varre-Sai）陨石于2010年6月19日下午5时40分，坠落于巴西圣埃斯皮里图州与里约热内卢州的交界地带。岩石学与X射线粉末衍射（X-ray powder diffraction, XRD）分析表明，该陨石为L5 S4型球粒陨石，其具有此前未被报道过的爆破斑状结构（blastoporphyritic texture）。基于主量元素与稀土元素（rare-earth elements, REEs）的地球化学数据显示，瓦雷-赛伊陨石与其他L型球粒陨石具有极高的相似性。在哈克图解（Harker diagrams）中，瓦雷-赛伊陨石、L型与LL型球粒陨石共同构成一个聚类，表明三者之间不存在显著化学差异，这为长期存在的学术争议提供了新的支撑：即LL型球粒陨石是否为独立的分类群，或是L型球粒陨石的一个子类。哈克图解同样呈现出从E型球粒陨石到H型、L/LL型球粒陨石的演化趋势，这与其他学者提出的宇宙化学趋势相一致。三氧化二铁总量（Fe₂O₃t）与氧化镍（NiO）的分布特征表明其与铁镍合金存在关联，且二者在图解中的演化趋势暗示，普通球粒陨石（ordinary chondrite）的母体天体曾发生过一定程度的化学分异。以C型球粒陨石为标准进行归一化处理后，瓦雷-赛伊陨石的稀土元素含量落在L型及其他类型球粒陨石的分布区间内，但存在轻微的稀土元素富集现象。球粒陨石之间的化学差异（主要体现在稀土元素、三氧化二铁总量与氧化镍上）也可被解释为继承的胶结物质（如球粒（chondrules）、富钙铝包裹体（Ca–Al-rich inclusions）与铁镍结核（Fe–Ni nodules））的成分变化。