Mafic, Large‐Volume, Pyroclastic Density Current Deposits from Phreatomagmatic Eruptions in the Ferrar Large Igneous Province, Antarctica
Mafic, Large‐Volume, Pyroclastic Density Current Deposits from Phreatomagmatic Eruptions in the Ferrar Large Igneous Province, Antarctica
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南极洲费拉大火成岩省的岩浆喷发产生的镁铁质、大体积、火山碎屑密度流沉积物
DOI：
10.1086/449324
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
J. White
中科院分区：
文献类型：
--
作者：
P. Ross;J. White
镁铁质火山碎屑矿床日益被认为是大陆泛滥玄武岩省的重要组成部分，但这些矿床的成因模式以及形成它们的喷发可能对环境的影响仍然缺乏约束。莫森组(费拉尔大火成岩省，侏罗纪)包含了世界上任何洪水玄武岩省最著名的大型镁铁质原生火山碎屑矿床。在Allan丘陵南部，与其他地点不同，Mawson组主要由近水平的、横向连续的、米厚的层组成，分为四个相：(1)分选较差的粗大的火山灰凝灰岩或凝灰岩角砾岩层；(2)凝灰岩或细碎的火山灰凝灰岩层；(3)富块层；和(4)含增生的火山灰岩层。我们将第一相解释为高浓度火山碎屑密度流(PDC)的沉积，这些沉积是由于岩浆喷发岩柱的坍塌而产生的，其中一些来自可能几公里外的库姆斯山。细粒层可能是由稀释的PDC沉积的，而富块层主要来自局部来源，主要是侧向抛射和弹道坠落。稀薄、潮湿的湍流也可能是形成和沉积大型(高达4.5厘米)的边缘型吸积青金石的原因。建议在至少100-200平方公里的面积上侵位几米厚的玄武岩PDC矿床，单个矿床的体积约为1立方公里。费拉尔镁铁质岩浆的前火山碎屑喷发是爆炸性的，产生了大量的喷发云，并将其产物分布在大量地区。
Mafic volcaniclastic deposits are increasingly recognized as important components of continental flood basalt provinces, but the mode of origin of these deposits and the possible environmental influence of the eruptions that formed them remain poorly constrained. The Mawson Formation (Ferrar large igneous province, Jurassic) contains the best‐known examples of large‐scale, mafic, primary pyroclastic deposits from any flood basalt province worldwide. At southern Allan Hills, in contrast with other sites, the Mawson Formation consists predominantly of subhorizontal, laterally continuous, meter‐thick layers that fall into four facies: (1) poorly sorted, coarse lapilli‐tuff or tuff‐breccia beds; (2) tuff or fine lapilli‐tuff beds; (3) block‐rich layers; and (4) accretionary lapilli‐bearing beds. We interpret the first facies as deposits of high‐concentration pyroclastic density currents (PDCs) resulting from the collapse of phreatomagmatic eruption plumes, some from a source probably several kilometers away in Coombs Hills. The finer‐grained layers were probably deposited by dilute PDCs, whereas block‐rich layers originated from local sources predominantly by lateral ejection and ballistic fall. Dilute, moist turbulent currents were also likely responsible for the generation and deposition of large (up to 4.5 cm) rim‐type accretionary lapilli. Emplacement of meters‐thick basaltic PDC deposits over areas of at least 100–200 km2 is suggested, with individual deposit volumes on the order of a cubic kilometer. Prelava pyroclastic eruptions of the Ferrar mafic magmas were explosive, produced significant eruption clouds, and distributed their products over substantial areas.