Supplementary materials for PhD thesis 'The Origin and Petrogenesis of the Ethiopian Flood Basalts': Data Tables

<i>This dataset comprises the files contained on a CD-ROM which was attached to the thesis when it was submitted in 2009. It was uploaded to ORDO in 2025 for preservation purposes. For more information, please refer to the thesis “</i><i>The Origin and Petrogenesis of the Ethiopian Flood Basalts</i><i>”</i><i> via ORO</i><i>.</i><b>Abstract</b>The volcanic rocks of the Afro-Arabian volcanic province chart the nature and evolution of the mantle plume source responsible for a major continental flood basalt event and the manner in which it interacted with the lithosphere over the course of continental separation. The flood basalts of the Ethiopian Plateau constitute the larger part of this province and are associated with melting in the head of the Afar Plume. High-Ti picrites from the eastern part of the NW Plateau are among the earliest uncontaminated outpourings of flood volcanism; their compositions are therefore considered to be close to that of the primary melt. These are exposed in a stratigraphically coherent sequence with variably porphyritic high-Ti olivine-rich basalts and ankaramites, which together provide a continuous record of volcanism reflecting a transition from high- to low-flux magmatism. Phase-relations differ fromthose in other tholeiitic flood basalts in that clinopyroxene and magnetite crystallisebefore plagioclase. This is typical of ferropicrites and reflects a high-Fe-Ti-, and low AI-source. The olivine phenocrysts exhibit a range of morphologies and compositions which reflect fractionation and magma-mixing at varying depths prior to eruption, and the introduction of water into the magmas at shallow levels is evident from pervasive iddingsitization. The lavas have similar major element chemistry to MORB but show higher concentrations of incompatible elements inherited from a HIMU-type lithospheric component. and enrichments in LREE relative to HREE which reflect the presence of residual garnet in the source. The picrites and ankaramites have lower AI₂O₃ and higher K₂O, P₂O₅, TiO₂ and Fe₂O₃^(tot) contents than any reported lavas with equivalent MgO content from other flood basalt provinces. These least evolved lavas were derived from oxidised (QFM+1), deep-seated magmas generated by different degrees of partial melting of the primary melt, whereas the olivine basalt magmas evolved by crystal fractionation at a shallow level from a melt similar in composition to the ankaramites. The MgO content of the primary melt calculated from the most Mg-rich olivines (Fo₉₀) is between 17 and 18 %, and it is likely that this ponded at the base of the crust where it evolved at pressures near to 1.2 GPa. Primary melt fractions of 3 - 6 % were generated in the plume at pressures of 4 - 5 GPa and temperatures in excess of 1600 °C, implying that melting occurred beneath thick (120- 150 km) lithosphere prior to extension. Sub-chondritic initial ¹⁸⁷Os/¹⁸⁸Os ratios (0.125 - 0.126) indicate derivation from a depleted mantle source, and high ³He/⁴He (18.6 R_a) and solar-like Ne isotopic ratios imply an origin in undegassed mantle.<br>

本数据集包含2009年提交学位论文时随附的光盘所载全部文件，于2025年上传至ORDO以进行长期保存。如需获取更多详细信息，请通过ORO查阅学位论文《埃塞俄比亚溢流玄武岩的成因与岩石成因》。

摘要
非洲-阿拉伯火山省的火山岩记录了引发大型大陆溢流玄武岩事件的地幔柱（mantle plume）源区的性质与演化过程，以及该源区在大陆裂解过程中与岩石圈（lithosphere）的相互作用方式。埃塞俄比亚高原的溢流玄武岩是该火山省的主体部分，其成因与阿法尔地幔柱（Afar Plume）头部的部分熔融作用密切相关。西北高原东部产出的高钛苦橄岩（High-Ti picrites）是溢流火山作用中最早的未受污染喷发产物之一，因此其化学成分被认为与原生熔体接近。该类高钛苦橄岩与不等斑状高钛富橄榄玄武岩及安卡岩（ankaramites）共同产出在地层连续的序列中，完整记录了火山作用从高通量岩浆活动向低通量岩浆活动的转变过程。该套岩石的矿物相变关系与其他拉斑玄武质溢流玄武岩（tholeiitic flood basalts）不同：单斜辉石（clinopyroxene）与磁铁矿（magnetite）的结晶顺序早于斜长石（plagioclase），这一特征是铁质苦橄岩（ferropicrites）的典型标志，反映其源区具有高Fe-Ti、低Al的特点。橄榄石斑晶具有多种形态与化学成分，反映了喷发前不同深度下发生的结晶分异与岩浆混合作用；普遍发育的伊丁石化作用（iddingsitization）则证明岩浆在浅部阶段曾有水介质加入。这套熔岩的主量元素化学成分与洋中脊玄武岩（Mid-Ocean Ridge Basalt, MORB）相近，但继承了HIMU型岩石圈组分（HIMU-type lithospheric component）的特征，不相容元素含量更高；且相对重稀土元素而言，轻稀土元素（Light Rare Earth Element, LREE）出现富集，这反映源区存在残留石榴子石。相较于其他溢流玄武岩省中报道的同等MgO含量的熔岩，本研究的苦橄岩与安卡岩具有更低的Al₂O₃含量，以及更高的K₂O、P₂O₅、TiO₂和全Fe₂O₃（Fe₂O₃^(tot)）含量。这些最未经历演化的熔岩源自氧化状态为QFM+1的深部岩浆，该岩浆由原生熔体经不同程度的部分熔融作用形成；而橄榄玄武岩岩浆则由成分与安卡岩相近的熔体在浅部经结晶分异作用（crystal fractionation）演化而来。根据最富镁的橄榄石（Fo₉₀）计算得到的原生熔体MgO含量为17%~18%，该熔体可能在地壳底部发生堆积，并在约1.2 GPa（吉帕斯卡）的压力条件下完成演化。地幔柱内于4~5 GPa压力、1600 ℃以上温度条件下发生的部分熔融产生了3%~6%的原生熔体组分，这意味着熔融作用发生在拉伸事件之前的厚达120~150 km的岩石圈下方。初始¹⁸⁷Os/¹⁸⁸Os比值为亚球粒陨石级（sub-chondritic，0.125~0.126），表明其源区为亏损地幔源区（depleted mantle source）；高³He/⁴He比值（18.6 Rₐ）与类太阳氖同位素组成则证明其源自未脱气地幔（undegassed mantle）。