Tectonomagmatic Constraints on the Sources of Eastern Mediterranean K-rich Lavas
Tectonomagmatic Constraints on the Sources of Eastern Mediterranean K-rich Lavas
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DOI：
10.1093/petrology/egr055
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发表时间：
2012
影响因子：
3.9
通讯作者：
M. Kirchenbaur;C. Münker;S. Schuth;D. Garbe‐Schönberg;P. Marchev
中科院分区：
文献类型：
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作者：
M. Kirchenbaur;C. Münker;S. Schuth;D. Garbe‐Schönberg;P. Marchev
富钾镁铁质熔岩，特别是高钾系列玄武岩，是俯冲带火山作用的重要终端成员。两种岩石成因模型可以解释镁铁质富钾熔岩的生成，涉及古代富集岩石圈地幔源的熔融（单阶段模型）或由来自俯冲沉积物或洋壳的俯冲相关成分最近再受精引发的熔融（多阶段模型）。基于新的主量元素、微量元素和 Sr-Nd-Hf-Pb 同位素数据，对这两个模型进行了来自保加利亚东南部罗多彼斯的始新世-渐新世碰撞后高钾岩石的测试。单阶段模型通过 Sr-Nd 同位素模型进行评估，假设存在古代丰富的岩石圈域，而多阶段模型则通过比较保加利亚熔岩与圣托里尼熔岩的成分进行评估。圣托里尼熔岩被认为是对长期存在的爱琴海俯冲带系统当前的微量元素和同位素库存进行采样的。这个朝北的系统很可能自侏罗纪晚期或白垩纪早期以来就一直活跃，并且可能参与了保加利亚熔岩地幔源的再肥化。除了保加利亚熔岩的数据外，我们还提供了圣托里尼岛的新主量元素、微量元素和 Sr-Nd-Hf-Pb 同位素数据。这些数据与之前发布的数据一起进行评估，以推断爱琴海地区的源富集模式。保加利亚熔岩表现出从中钾到高钾和钾玄岩的多种成分，具有放射性 Sr-87/Sr-86 (0.706-0.709)，以及非放射性 epsilon Nd (-5.7 至 -1.9) 和 epsilon Hf (-3 至 +3) 同位素特征。正如微量元素和 Sr-Nd 同位素系统学所记录的那样，微量元素预算显然对浅层地壳同化有很好的缓冲。保加利亚熔岩的 Sr-Nd 同位素组成模型支持近期（中生代至新生代）源头富集。因此，可以自信地排除涉及古代（>1 Ga）岩石圈地幔熔化的单阶段模型，这与该地区的构造模型一致。富集的同位素特征，加上不相容元素的明显富集，表明地幔再受精作用是由类似于目前在希腊海沟俯冲的大陆沉积物的俯冲成分进行的。与圣托里尼熔岩相比，保加利亚熔岩记录了俯冲流体成分的主要流入。总的来说，保加利亚熔岩的数据显然支持多阶段模型。
Potassium-enriched mafic lavas, and in particular basalts of the high-K series, are important end-members of subduction zone volcanism. Two petrogenetic models can explain the generation of mafic K-rich lavas, involving either melting of ancient, enriched lithospheric mantle sources (single-stage model) or melting triggered by recent refertilization by subduction-related components derived from subducted sediments or oceanic crust (multi-stage model). These two models are tested for post-collisional high-K rocks of Eocene-Oligocene age from the Rhodopes, SE Bulgaria, based on new major element, trace element and Sr-Nd-Hf-Pb isotope data. The single-stage model is evaluated by Sr-Nd isotope modelling assuming the presence of ancient enriched lithospheric domains whereas the multi-stage model is assessed by comparing the compositions of the Bulgarian lavas with those of lavas from Santorini. Santorini lavas are considered to sample the current trace element and isotope inventory of the long-lived Aegean subduction zone system. This northward facing system has been active most probably since late Jurassic or early Cretaceous times and was potentially involved in refertilizing the mantle sources of the Bulgarian lavas. In addition to the data for Bulgarian lavas, we present new major element, trace element and Sr-Nd-Hf-Pb isotope data for Santorini. These are evaluated together with previously published data to infer the mode of source enrichment in the Aegean realm. The Bulgarian lavas exhibit a broad range of compositions from medium-K to high-K and shoshonitic with radiogenic Sr-87/Sr-86 (0.706-0.709), and unradiogenic epsilon Nd (-5.7 to -1.9) and epsilon Hf (-3 to +3) isotope signatures. The trace element budget was apparently well buffered against shallow-level crustal assimilation as documented by the trace element and Sr-Nd isotope systematics. Modelling of the Sr-Nd isotope compositions of the Bulgarian lavas argues for recent (Mesozoic to Cenozoic) source enrichment. Therefore single-stage models involving melting of ancient (>1 Ga) lithospheric mantle can be confidently ruled out, in agreement with tectonic models for the region. The enriched isotope signatures, together with a pronounced enrichment of incompatible elements, rather indicate mantle refertilization by a subduction component similar to continent-derived sediments subducted at the Hellenic Trench at present. The Bulgarian lavas record a predominant influx of subduction fluid components in comparison with the Santorini lavas. Collectively, the data presented for the Bulgarian lavas are clearly in favour of a multi-stage model.