Investigations on volcanic rocks in sediment core CRP-3 from the Ross Sea, Antarctica

The petrography, mineralogy and geochemistry of volcanic and subvolcanic rocks in CRP-3 core have been examined in detail in order to characterise and to compare them with volcanic and subvolcanic rocks cropping out in the Victoria Land area, and to define the clast provenance or to establish possible volcanic activity coeval with deposition. Clasts with sizes ranging from granule to boulder show geochemical and mineralogical features comparable with those of Ferrar Supergroup rocks. They display a subalkaline affinity and compositions ranging from basalts to dacite. Three different petrographic groups with distinct textural and grain size features (subophitic, intergranular-intersertal, and glassy-hyalopilitic) are recognised and are related to the emplacement/cooling mechanism. In the sand to silt fraction, the few glass shards that have been recognised are strongly altered: however chemical analyses show they have subalkalic magmatic affinity. Mineral compositions of the abundant free clinopyroxene grains found in the core, are less affected by alteration processes, and indicate an origin from subalkaline magmas. This excludes the presence, during the deposition of CRP-3 rocks of alkaline volcanic activity comparable with the McMurdo Volcanic Group. Strong alteration of the magmatic body intruded the Beacon sandstones obliterates the original mineral assemblage. Geochemical investigations confirm that intrusion is part of the Ferar Large Igneous Province.

已对CRP-3岩心（CRP-3 core）内火山岩与次火山岩的岩石学、矿物学及地球化学特征开展了详细研究，旨在对其进行特征刻画，并与维多利亚地（Victoria Land）区域出露的火山岩及次火山岩进行对比，同时明确碎屑物源，或是确定与沉积作用同期的火山活动可能性。粒径范围从颗粒状至巨砾状的碎屑，其地球化学与矿物学特征与费拉超群（Ferrar Supergroup）岩石的特征具有可比性。这些岩石表现出亚碱性亲和性，成分跨度从玄武岩至英安岩。研究识别出三类具备独特结构与粒度特征的岩石学组：亚辉绿结构（subophitic）、粒间-填间结构（intergranular-intersertal）以及玻璃质-玻基交织结构（glassy-hyalopilitic），各组分别对应不同的就位/冷却机制。在砂级至粉砂级组分中，已识别出的少量玻璃质碎屑已发生强烈蚀变，但化学分析结果显示其具有亚碱性岩浆亲和性。岩心中大量游离的单斜辉石颗粒的矿物成分受蚀变过程影响较小，表明其源自亚碱性岩浆。这排除了CRP-3岩心沉积时期存在与麦克默多火山群（McMurdo Volcanic Group）相当的碱性火山活动的可能性。侵入比肯砂岩（Beacon sandstones）的岩浆体遭受了强烈蚀变，其原始矿物组合已被彻底破坏。地球化学调查证实，该侵入体属于费拉大火成岩省（Ferar Large Igneous Province）的一部分。