Evolution of the Lithospheric Mantle beneath the Marsabit Volcanic Field (Northern Kenya): Constraints from Textural, P–T and Geochemical Studies on Xenoliths
Evolution of the Lithospheric Mantle beneath the Marsabit Volcanic Field (Northern Kenya): Constraints from Textural, P–T and Geochemical Studies on Xenoliths
复制标题
马萨比特火山田（肯尼亚北部）下方岩石圈地幔的演化：捕虏体结构、P-T 和地球化学研究的限制
DOI：
--
复制
发表时间：
2006
期刊：
影响因子：
--
通讯作者：
T. Pettke
中科院分区：
文献类型：
--
作者：
B. Kaeser;A. Kalt;T. Pettke
来自马萨比特（肯尼亚北部）的第四纪玄武岩和碱性玄武岩所含的捕虏体代表了元古代岩石圈地幔的碎片，这些碎片在中生代（安扎地堑）和第三纪-第四纪（肯尼亚裂谷）裂谷期间变薄和化学改变。研究了四种类型的橄榄岩捕虏体，以限制岩石圈地幔的热和化学演化。 I、III 和 IV 组橄榄岩提供了寒冷、高度变形和异质上地幔的证据。矿物的结构、温压和微量元素特征表明，尖晶石稳定场的低温（750–800Ca t<1.5 GPa）是通过石榴石稳定场（970–1080Ca t 2.3–2.9 GPa）最初的高压和高温减压和冷却而获得的。冷却、减压和穿透变形与岩石圈减薄一致，可能与中生代至古近纪 Anza Graben 的发育有关。再平衡和重结晶橄榄岩捕虏体（第二组）记录加热（从 800 ℃ 到 1100 ℃）。矿物微量元素特征表明，镁铁质硅酸盐熔体富集，是第四纪主体玄武岩和碱性玄武岩的母体。矿物结构、P-T 平衡条件和地球化学之间的关系可以通过与肯尼亚裂谷形成相关的交代作用和岩石圈加热来解释，该裂谷位于热上涌地幔区域上方。
Xenoliths hosted by Quaternary basanites and alkali basalts from Marsabit (northern Kenya) represent fragments of Proterozoic lithospheric mantle thinned and chemically modified during rifting in the Mesozoic (Anza Graben) and in the Tertiary–Quaternary (Kenya rift). Four types of peridotite xenoliths were investigated to constrain the thermal and chemical evolution of the lithospheric mantle. Group I, III and IV peridotites provide evidence of a cold, highly deformed and heterogeneous upper mantle. Textures, thermobarometry and trace element characteristics of minerals indicate that low temperatures in the spinel stability field (� 750– 800 � Ca t<1.5 GPa) were attained by decompression and cooling from initially high pressures and temperatures in the garnet stability field (970–1080 � Ca t 2.3–2.9 GPa). Cooling, decompression and penetrative deformation are consistent with lithospheric thinning, probably related to the development of the Mesozoic to Paleogene Anza Graben. Re-equilibrated and recrystallized peridotite xenoliths (Group II) record heating (from � 800 � Ct o � 1100 � C). Mineral trace element signatures indicate enrichment by mafic silicate melts, parental to the Quaternary host basanites and alkali basalts. Relationships between mineral textures, P–T conditions of equilibration, and geochemistry can be explained by metasomatism and heating of the lithosphere related to the formation of the Kenya rift, above a zone of hot upwelling mantle.