Osmium Isotopic Evidence for Crust–Mantle Interaction in the Genesis of Continental Intraplate Basalts from the Newer Volcanics Province, Southeastern Australia
Osmium Isotopic Evidence for Crust–Mantle Interaction in the Genesis of Continental Intraplate Basalts from the Newer Volcanics Province, Southeastern Australia
复制标题
DOI：
10.1093/petrology/42.6.1197
复制
发表时间：
2001-06
影响因子：
3.9
通讯作者：
Jannene S. McBride;D. Lambert;I. Nicholls;R. Price
中科院分区：
文献类型：
--
作者：
Jannene S. McBride;D. Lambert;I. Nicholls;R. Price
引言 澳大利亚东南部第四纪较新火山省的玄武岩的化学成分和 Nd 具有很大的多样性，在许多大陆板内玄武岩中观察到的丰富地球化学特征的起源具有 Sr 和 Os 同位素组成。 Plains系列橄榄石拉斑玄武岩和Cones系列霞石夏威夷岩具有独特的同位素，引起了相当大的争议。许多研究人员认为，这些特征是子成分的结果，并且显然不通过简单的遗传过程相互关联。 Cones系列霞石夏威夷岩具有痕量大陆岩石圈地幔来源（例如Allegre等，1982；Turner & Hawkesworth，1995；Molzahn等，元素丰度和Nd（Nd = +4·1和+3·8）、Pb（Pb/Pb = 18·62和18·70）和Os（Os = +6和1996；Stewart & Rogers，1996），而其他人（例如 Hawkesworth & Vollmer，1979；Carlson 等人，1981；+7）同位素组成属于大洋岛玄武岩（OIB）范围，相比之下，平原系列橄榄石 tholeiites Brandon 等人，1993； 1998）认为它们反映了软流圈的地壳污染，具有较低的 Nd（+0·9 至 +2·3）、较高的放射性 Sr（Sr/ Sr = 0·7045–0·7053）和相当高的 Os（地幔柱衍生的岩浆在流向地表的过程中 +42。Re-Os 同位素系统是 dis+250 的绝佳工具）。与更“原始”的锥体系列霞石夏威夷岩（Os = 160 和 250 ppt）相比，在 Plains 系列橄榄石拉斑岩中观察到的 Os 浓度相对较低 [Os = 12-45 万亿分之一，这两个独特的富集过程之间存在差异，与更常用的 Sr-Nd-Pb (ppt)] 相比，使它们更容易受到同位素系统的影响，存在强烈的 Re-Os 同位素对比次大陆岩石圈地幔和可能掩盖其原始地幔地壳的污染过程之间。 Os 在熔化过程中表现得兼容，而签名。微量元素趋势和同位素模拟表明，Re 的行为略有不相容，导致在熔体和地壳中的平原系列 Os 内观察到的高 Re/Os 异常地球化学特征以及橄榄石拉斑斑岩中的低 Re/Os 是大陆地壳地幔同化的结果。随着时间的推移，这会导致地幔和地壳具有不同的同位素特征。而Cones系列储层具有高度独特的Os同位素组合-夏威夷岩，其微量元素和同位素组成位置一致。例如，次大陆岩石圈源自地幔柱（OIB地幔通常具有非放射性 Os 同位素来源）或“脉状”次大陆岩石圈地幔的熔化。 Os < 0；Walker 等人，1989；Pearson 等人，1995a，1995b；McBride 等人，1996），而大陆地壳具有高放射性 Os 同位素成分（Os =
INTRODUCTION Basalts from the Quaternary Newer Volcanics Province in southeastern Australia have a large diversity in their chemical and Nd, The origin of the enriched geochemical signatures observed within many continental intraplate basalts has Sr and Os isotopic compositions. Plains series olivine tholeiites and Cones series nepheline hawaiites have distinctive isotopic been the source of considerable controversy. Many workers believe that these signatures are the result of a subcompositions and are clearly not related to each other by a simple genetic process. The Cones series nepheline hawaiites have trace continental lithospheric mantle source (e.g. Allegre et al., 1982; Turner & Hawkesworth, 1995; Molzahn et al., element abundances and Nd ( Nd = +4·1 and +3·8), Pb ( Pb/Pb = 18·62 and 18·70) and Os ( Os = +6 and 1996; Stewart & Rogers, 1996), whereas others (e.g. Hawkesworth & Vollmer, 1979; Carlson et al., 1981; +7) isotopic compositions that fall within the range of oceanisland basalts (OIB). In contrast, the Plains series olivine tholeiites Brandon et al., 1993; Chesley & Ruiz, 1998) believe that they reflect crustal contamination of asthenospheric have lower Nd (+0·9 to +2·3), more radiogenic Sr ( Sr/ Sr = 0·7045–0·7053), and considerably higher Os (+42 to mantleor plume-derived magmas en route to the surface. The Re–Os isotopic system is an excellent tool for dis+250). The relatively low Os concentrations observed in the Plains series olivine tholeiites [Os = 12–45 parts per trillion tinguishing between these two distinctive enrichment processes, as unlike the more commonly used Sr–Nd–Pb (ppt)] compared with the more ‘primitive’ Cones series nepheline hawaiites (Os = 160 and 250 ppt), render them more susceptible isotopic systems, there is a strong Re–Os isotopic contrast between the sub-continental lithospheric mantle and the to contamination processes that can obscure their primary mantle crust. Os behaves compatibly during melting, whereas signatures. Trace element trends and isotopic modelling suggest that Re behaves slightly incompatibly, resulting in high Re/ the unusual geochemical signatures observed within the Plains series Os in melts and the crust and low Re/Os within the olivine tholeiites are the result of assimilation of continental crust mantle. Over time this results in mantle and crustal possessing variable isotopic signatures. However, the Cones series reservoirs with highly distinctive Os isotopic comne-hawaiites have trace element and isotopic compositions consistent positions. For example, the sub-continental lithospheric with their derivation from melting of either a mantle plume (OIBmantle generally has unradiogenic Os isotopic comtype source) or ‘veined’ sub-continental lithospheric mantle. positions ( Os <0; Walker et al., 1989; Pearson et al., 1995a, 1995b; McBride et al., 1996), whereas the continental crust has highly radiogenic Os isotopic compositions ( Os =