Mantle sources and magma evolution of the Rooiberg lavas, Bushveld Large Igneous Province, South Africa
Mantle sources and magma evolution of the Rooiberg lavas, Bushveld Large Igneous Province, South Africa
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南非布什维尔德大火成岩省 Rooiberg 熔岩的地幔来源和岩浆演化
DOI：
10.1007/s00410-018-1477-y
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发表时间：
2018
影响因子：
3.5
通讯作者：
Teschner
中科院分区：
文献类型：
--
作者：
Günther;Teschner
我们报告了来自 Rooiberg 大陆大型火成岩省 (LIP) 的玄武岩到流纹质熔岩的主量元素和微量元素丰度以及 87Sr/86Sr–143Nd/144Nd 同位素比的新全岩数据集。古元古代鲁伊伯格群的形成与布什维尔德杂岩的层状侵入同时发生并在空间上相关，布什维尔德杂岩在地层上分隔了火山序列。我们的新数据证实存在含 > 4 wt% MgO 的低钛镁铁质和中钛熔岩（玄武岩-安山岩成分），以及 MgO 含量 < 4 wt% 的演化岩石（安山岩-流纹岩成分）。高钛玄武岩熔岩和低钛玄武岩熔岩具有不同的不相容微量元素比（例如（La/Sm）N、Nb/Y和Ti/Y），表明不同的岩石成因。 MELTS 模型表明，演化的熔岩是由镁铁质低钛熔岩在中低压力（~ 4 kbar）下分步结晶形成的。 Rooiberg 岩石的原始地幔标准化微量元素模式显示出大离子亲石元素 (LILE)、稀土元素 (REE) 的富集以及明显的 Nb、Ta、P、Ti 负异常和 Pb 正异常。未改变的鲁伊贝格熔岩具有负 εNdi（− 5.2 至 − 9.4）和放射性 εSri（6.6 至 105）比率（2061 Ma）。这些数据与据称布什维尔德杂岩母体熔体的同位素和微量元素成分重叠，尤其是下部区域。我们认为，Rooiberg 套件的起源与 B1 岩浆的成分类似，被认为是布什维尔德下带的母体，或者熔岩代表了与在深处形成的超镁铁质堆积物相关的分步结晶产物的喷发序列。 Rooiberg 岩浆可能是通过 Kaapvaal 克拉通上地壳内非常原始的地幔衍生熔体的分馏而形成 10-20% 的地壳同化作用。或者，岩浆代表了来自原始亚岩石圈地幔柱和富集的次大陆岩石圈地幔（SCLM）成分的熔体混合物，其中含有方辉岩成分。无论调用这两种情况中的哪一种，鲁伊伯格群的熔岩都显示出与侏罗纪卡鲁溢流玄武岩的地球化学相似性，这意味着太古代岩石圈强烈影响了这两次大规模融化事件。
We report a new whole-rock dataset of major and trace element abundances and87Sr/86Sr–143Nd/144Nd isotope ratios for basaltic to rhyolitic lavas from the Rooiberg continental large igneous province (LIP). The formation of the Paleoproterozoic Rooiberg Group is contemporaneous with and spatially related to the layered intrusion of the Bushveld Complex, which stratigraphically separates the volcanic succession. Our new data confirm the presence of low- and high-Ti mafic and intermediate lavas (basaltic—andesitic compositions) with > 4 wt% MgO, as well as evolved rocks (andesitic—rhyolitic compositions), characterized by MgO contents of < 4 wt%. The high- and low-Ti basaltic lavas have different incompatible trace element ratios (e.g. (La/Sm)N, Nb/Y and Ti/Y), indicating a different petrogenesis. MELTS modelling shows that the evolved lavas are formed by fractional crystallization from the mafic low-Ti lavas at low-to-moderate pressures (~ 4 kbar). Primitive mantle-normalized trace element patterns of the Rooiberg rocks show an enrichment of large ion lithophile elements (LILE), rare-earth elements (REE) and pronounced negative anomalies of Nb, Ta, P, Ti and a positive Pb anomaly. Unaltered Rooiberg lavas have negative εNdi(− 5.2 to − 9.4) and radiogenic εSri(6.6 to 105) ratios (at 2061 Ma). These data overlap with isotope and trace element compositions of purported parental melts to the Bushveld Complex, especially for the lower zone. We suggest that the Rooiberg suite originated from a source similar to the composition of the B1-magma suggested as parental to the Bushveld Lower Zone, or that the lavas represent eruptive successions of fractional crystallization products related to the ultramafic cumulates that were forming at depth. The Rooiberg magmas may have formed by 10–20% crustal assimilation by the fractionation of a very primitive mantle-derived melt within the upper crust of the Kaapvaal Craton. Alternatively, the magmas represent mixtures of melts from a primitive, sub-lithospheric mantle plume and an enriched sub-continental lithospheric mantle (SCLM) component with harzburgitic composition. Regardless of which of the two scenarios is invoked, the lavas of the Rooiberg Group show geochemical similarities to the Jurassic Karoo flood basalts, implying that the Archean lithosphere strongly affected both of these large-scale melting events.
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南非共和国、西南非洲/纳米比亚以及博普塔茨瓦纳共和国、特兰斯凯共和国和文达共和国的岩石地层学
DOI：
--
发表时间：
1980
期刊：
影响因子：
--
作者：
L. Kent
通讯作者：
L. Kent
影响因子：
3.1
作者：
Whitney, Donna L.;Evans, Bernard W.
通讯作者：
Evans, Bernard W.
影响因子：
3.5
作者：
W. Maier;S. Barnes;B. Karykowski
通讯作者：
W. Maier;S. Barnes;B. Karykowski
影响因子：
3.9
作者：
F. Roelofse;L. Ashwal
通讯作者：
F. Roelofse;L. Ashwal
影响因子：
5
作者：
D. Wronkiewicz;K. Condie
通讯作者：
D. Wronkiewicz;K. Condie