Geochemical constraints on the Cenozoic, OIB-type alkaline volcanic rocks of NW Turkey: Implications for mantle sources and melting processes
Geochemical constraints on the Cenozoic, OIB-type alkaline volcanic rocks of NW Turkey: Implications for mantle sources and melting processes
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DOI：
10.1016/j.lithos.2005.04.003
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发表时间：
2006
期刊：
影响因子：
3.5
通讯作者：
E. Aldanmaz;N. Köprübaşı;Ö. F. Gürer;Nuretdin Kaymakçi;A. Gourgaud
中科院分区：
文献类型：
--
作者：
E. Aldanmaz;N. Köprübaşı;Ö. F. Gürer;Nuretdin Kaymakçi;A. Gourgaud
土耳其西北部的火山区包含许多内陆碱性火山喷发序列，这些序列沿着与晚新生代伸展过程有关的局部伸展盆地形成。火山岩套包括提取的地幔绝热减压熔融的熔融产物，其代表是小体积的碱性橄榄玄武岩和玄武质的大陆板内火山岩，其成分代表幔源的原生（或近原生）熔体。火山岩具有近均匀的87 Sr/86 Sr（0.70316-70353）和143 Nd/144 Nd（0.51291-0.51297; Nd=5.08-6.32）比值，具有洋岛玄武岩（OIB）型微量元素模式特征，相对于N-MORB，大离子亲石、高场强和轻稀土元素明显富集，重稀土元素略有亏损。个别玄武岩喷发序列的微量元素的变化表明，每个熔岩序列显示出非常相似的时间组成的趋势，其特征在于不相容元素和MgO的增加，减少SiO2，熔体生产的收益。系统的变化不兼容的微量元素浓度（和比例）的熔岩的同位素比值没有反映，导致的时间组成的趋势不是由源的变化引起的建议。熔体化学随时间的变化并不反映结晶分离，也不能用地幔中两个（或多个）成分不同的来源的不同程度的部分熔融所产生的熔体之间的混合比例来解释。相反，所观察到的趋势是一致的熔融程度从早期形成的碱性橄榄石玄武岩到后来的玄武岩和系统的混合增量之间的熔融来自同一来源，但可能在不同的深度逐渐减少。分馏校正后的微量元素定量模拟结果表明，镁铁质碱性岩浆起源于不同程度的熔融混合（0.2%至8%）的成分均匀、富含所有不相容元素的含挥发分地幔域的增量部分熔融（例如LILE、HFSE和L-MREE）相对于假设的耗尽MORB地幔（DMM）和/或原始地幔（PM）组成的变化。
The volcanic province of North-West Turkey contains a number of intra-continental alkaline volcanic eruption sequences formed along the localized extensional basins developed in relation with the Late Cenozoic extensional processes. The volcanic suite comprises the extracted melt products of adiabatic decompression melting of the mantle that are represented by small-volume intra-continental plate volcanic rocks of alkaline olivine basalts and basanites with compositions representative of mantle-derived, primary (or near-primary) melts. The volcanic rocks have near-uniform87Sr/86Sr (0.70316–70353) and143Nd/144Nd (0.51291–0.51297; ɛNd=5.08–6.32) ratios and are characterized by Ocean Island Basalt (OIB)-type trace element patterns with significant enrichment in LILE, HFSE and L-MREE, and a slight depletion in HREE, relative to N-MORB. Trace element variations of individual basaltic eruption sequences indicate that each lava sequence shows remarkably similar temporal–compositional trends that are characterized by an increase in incompatible elements and MgO, with decreasing SiO2, as melt production proceeds. Systematic change in incompatible trace element concentrations (and ratios) of the lavas is not reflected by the isotopic ratios, leading to the suggestion that the temporal–compositional trends are not caused by source variations. The variations in melt chemistry with time does not reflect fractional crystallization nor can it be explained by variable proportions of mixing between melts produced by different degrees of partial melting of two (or more) compositionally distinct sources in the mantle. Instead, the observed trends are consistent with a progressive decrease in degree of melting from early-formed alkali olivine basalts to later basanites and systematic mixing between increments of melt derived from the same source but probably at different depths. Quantitative trace element modeling of fractionation-corrected data indicates that the mafic alkaline magmas originated from mixing of melts produced by variable degrees (∼2% to 8%) of incremental partial melting of a compositionally uniform, volatile-bearing mantle domain that is enriched in all incompatible elements (e.g. LILE, HFSE and L-MREE) relative to hypothetical Depleted MORB Mantle (DMM) and/or Primitive Mantle (PM) compositions.