Recycling and transport of continental material through the mantle wedge above subduction zones: A Caribbean example
Recycling and transport of continental material through the mantle wedge above subduction zones: A Caribbean example
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DOI：
10.1016/j.epsl.2015.11.040
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发表时间：
2016-02
影响因子：
5.3
通讯作者：
Y. Rojas‐Agramonte;A. Garcia‐Casco;A. Kemp;A. Kröner;J. Proenza;C. Lázaro;Dunyi Liu
中科院分区：
文献类型：
--
作者：
Y. Rojas‐Agramonte;A. Garcia‐Casco;A. Kemp;A. Kröner;J. Proenza;C. Lázaro;Dunyi Liu
对全球大陆地壳增长率的估计在很大程度上取决于对地壳物质在俯冲带被送回地幔，然后作为地幔衍生岩浆的组成部分返回地壳的速度的了解。与俯冲有关的岩浆作用对地壳再循环的量化依赖于间接的化学和同位素示踪剂，并受到大范围潜在熔体来源（例如，俯冲的海洋地壳及其上覆的化学和碎屑沉积物、弧下岩石圈地幔、弧壳）的阻碍，其成分可能无法准确知道。地壳物质如何从俯冲的岩石圈转移并混合到弧岩浆的地幔源中也存在不确定性。我们使用弹性矿物锆石来跟踪加勒比海（大安的列斯群岛）古巴洋内弧的地幔衍生岩石中的地壳循环，其开始是在盘古大陆分裂后触发的。尽管Sr和Nd同位素组成较年轻，但该白垩纪（~ 135-70 Ma）弧的超俯冲带蛇绿岩和火山岩中含有古老的锆石（~ 200-2525 Ma），证明了不同的地壳输入。这些锆石的Hf-O同位素系统表明它们来自中美洲北部（如墨西哥）和南美洲暴露的地壳地体。对大多数基性熔岩中沉积成分的模拟表明，源污染的贡献不超过2%，岩浆对沉积物同化的贡献小于4%。我们讨论了继承锆石存在的几种可能性，并得出结论，它们是通过海洋地壳的俯冲作用作为碎屑颗粒被运送到加勒比海板块下的地幔中。碎屑锆石随后被基性熔体带走，迅速嵌入加勒比海火山弧地壳和超俯冲地幔。这些发现表明，大陆碎屑通过俯冲带上方的地幔楔在岩浆中运输，否则就没有强有力的证据表明地壳输入，这意味着某些弧的地壳再循环率可能比迄今为止所认识到的要高。
Estimates of global growth rates of continental crust critically depend upon knowledge of the rate at which crustal material is delivered back into the mantle at subduction zones and is then returned to the crust as a component of mantle-derived magma. Quantification of crustal recycling by subduction-related magmatism relies on indirect chemical and isotopic tracers and is hindered by the large range of potential melt sources (e.g., subducted oceanic crust and overlying chemical and clastic sediment, sub-arc lithospheric mantle, arc crust), whose composition may not be accurately known. There is also uncertainty about how crustal material is transferred from subducted lithosphere and mixed into the mantle source of arc magmas. We use the resilient mineral zircon to track crustal recycling in mantle-derived rocks of the Caribbean (Greater Antilles) intra-oceanic arc of Cuba, whose inception was triggered after the break-up of Pangea. Despite juvenile Sr and Nd isotope compositions, the supra-subduction zone ophiolitic and volcanic arc rocks of this Cretaceous (∼135–70 Ma) arc contain old zircons (∼200–2525 Ma) attesting to diverse crustal inputs. The Hf–O isotope systematics of these zircons suggest derivation from exposed crustal terranes in northern Central America (e.g. Mexico) and South America. Modeling of the sedimentary component in the most mafic lavas suggests a contribution of no more than 2% for the case of source contamination or less than 4% for sediment assimilation by the magma. We discuss several possibilities for the presence of inherited zircons and conclude that they were transported as detrital grains into the mantle beneath the Caribbean Plate via subduction of oceanic crust. The detrital zircons were subsequently entrained by mafic melts that were rapidly emplaced into the Caribbean volcanic arc crust and supra-subduction mantle. These findings suggest transport of continental detritus, through the mantle wedge above subduction zones, in magmas that otherwise do not show strong evidence for crustal input and imply that crustal recycling rates in some arcs may be higher than hitherto realized.