Geochemical analysis of minerals from sediment core CRP-2 in the Ross Sea, Antarctica

Distribution patterns, petrography, whole-rock and mineral chemistry, and shape and fabric data are described for the most representative basement lithologies occurring as clasts (granule to bolder grain-size class) from the 625 m deep CRP-2/2A drillcore. A major change in the distribution pattern of the clast types occurs at c. 310 mbsf., with granitoid-dominated clasts above and mainly dolerite clasts below; moreover, compositional and modal data suggest a further division into seven main detrital assemblages or petrofacies. In spite of this variability, most granitoid pebbles consist of either pink or grey biotite±hornblende monzogranites. Other less common and ubiquitous lithologies include biotite syenogranite, biotite-hornblende granodiorite, tonalite, monzogranitic porphyries (very common below 310 mbsf), microgranite, and subordinately, monzogabbro, Ca-silicate rocks, biotite-clinozoisite schist and biotite orthogneiss (restricted to the pre-Pliocene strata). The ubiquitous occurrence of biotite±hornblende monzogranite pebbles in both the Quaternary-Pliocene and Miocene-Oligocene sections, apparently reflects the dominance of these lithologies in the onshore basement, and particularly in the Cambro-Ordovician Granite Harbour Igneous Complex which forms the most extensive outcrop in southern Victoria Land. The petrographical features of the other CRP-2/2A pebble lithologies are consistent with a supply dominantly from areas of the Transantarctic Mountains facing the CRP-2/2A site, and they thus provide further evidence of a local provenance for the supply of basement clasts to the CRP-2/2A sedimentary strata.本数据集对取自625米深CRP-2/2A钻探岩心（drillcore）中、以碎屑（clasts，粒级范围为细砾至巨砾（granule to bolder grain-size class））形式产出的典型基底岩性（basement lithologies），系统阐述了其分布规律、岩石学（petrography）特征、全岩化学（whole-rock chemistry）与矿物化学（mineral chemistry）数据，以及形态与组构数据（fabric data）。碎屑类型的分布模式在约310 mbsf（meters below seafloor，海底以下米数）处发生显著转变：其上覆层以花岗岩类（granitoid）碎屑为主，下伏层则以辉绿岩（dolerite）碎屑占主导；此外，成分与矿物百分含量数据（modal data）表明，可进一步划分为7种主要碎屑组合（detrital assemblages）或岩相（petrofacies）。尽管存在上述岩性分异，绝大多数花岗岩类砾石均为粉色或灰色的黑云母±角闪石二长花岗岩（biotite±hornblende monzogranites）。其他相对少见且广泛分布的岩性包括黑云母正长花岗岩（biotite syenogranite）、黑云母-角闪石花岗闪长岩（biotite-hornblende granodiorite）、英云闪长岩（tonalite）、二长花岗岩斑岩（monzogranitic porphyries，在310 mbsf以下极为常见）、细晶花岗岩（microgranite），以及次要产出的二长辉长岩（monzogabbro）、钙硅酸盐岩（Ca-silicate rocks）、黑云母-斜黝帘石片岩（biotite-clinozoisite schist），还有仅赋存于上新统之前地层（pre-Pliocene strata）的黑云母正片麻岩（biotite orthogneiss）。在第四纪-上新统（Quaternary-Pliocene）与中新世-渐新统（Miocene-Oligocene）地层中，黑云母±角闪石二长花岗岩砾石均广泛产出，这一现象直观反映出此类岩性在陆上基底（onshore basement）中占据主导地位，尤其是在维多利亚地南部（southern Victoria Land）分布最广的寒武-奥陶纪花岗岩港火成杂岩（Cambro-Ordovician Granite Harbour Igneous Complex）中。CRP-2/2A钻探岩心其余砾石岩性的岩石学特征，均与横贯南极山脉（Transantarctic Mountains）面向CRP-2/2A钻孔位点区域的物源供给特征相符，从而进一步佐证了CRP-2/2A沉积地层中基底岩屑的物源为当地邻近区域。