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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Large volume recycling of oceanic lithosphere over short time scales: geochemical constraints from the Caribbean Large Igneous Province
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Large volume recycling of oceanic lithosphere over short time scales: geochemical constraints from the Caribbean Large Igneous Province

机译：短时间内大规模回收岩石圈：来自加勒比大火成岩省的地球化学限制

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摘要

Oceanic flood basalts are poorly understood, short-term expressions of highly increased heat flux and mass flow within the convecting mantle. The uniqueness of the Caribbean Large Igneous Province (CLIP, 92-74 Ma) with respect to other Cretaceous oceanic plateaus is its extensive sub-aerial exposures, providing an excellent basis to investigate the temporal and compositional relationships within a starting plume head. We present major element, trace element and initial Sr-Nd-Pb isotope composition of 40 extrusive rocks from the Caribbean Plateau, including onland sections in Costa Rica, Colombia and Curacao as well as DSDP Sites in the Central Caribbean. Even though the lavas were erupted over an area of ～3 * 10~6 km~2, the majority have strikingly uniform incompatible element patterns (La/Yb = 0.96 ± 0.16, n = 64 our of 79 samples, 2σ) and initial Nd-Pb isotopic compositions (e.g. ~(143)Nd/~(144)Nd_(in) = 0.51291 ± 3, ε_(Ndi) = 7.3 ± 0.6, ~(206)Pb/~(204)Pb_(in) = 18.86 ± 0.12, n = 54 out of 66, 2σ). Lavas with endmember compositions have only been sampled at the DSDP Sites, Gorgona Island (Colombia) and the 65-60 Ma accreted Quepos and Osa igneous complexes (Costa Rica) of the subsequent hotspot track. Despite the relatively uniform composition of most lavas, linear correlations exist between isotope ratios and between isotope and highly incompatible trace element ratios. The Sr-Nd-Pb isotope and trace element signatures of the chemically enriched lavas are compatible with derivation from recycled oceanic crust, while the depleted lavas are derived from a highly residual source. This source could represent either oceanic lithospheric mantle left after ocean crust formation or gabbros with interlayered ultramafic cumulates of the lower oceanic crust. High ~3He/~4He in olivines of enriched picrites at Quepos are ～12 times higher than the atmospheric ratio suggesting that the enriched component may have once resided in the lower mantle. Evaluation of the Sm-Nd and U-Pb isotope systematics on isochron diagrams suggests that the age of separation of enriched and depleted components from the depleted MORB source mantle could have been ≤500 Ma before CLIP formation and interpreted to reflect the recycling time of the CLIP source. Mantle plume heads may provide a mechanism for transporting large volumes of possibly young recycled oceanic lithosphere residing in the lower mantle back into the shallow MORB source mantle.
机译：人们对海洋洪水玄武岩了解甚少，这是对流地幔内热通量和质量流量高度增加的短期表现。加勒比大火成岩省（CLIP，92-74 Ma）相对于其他白垩纪海洋高原的独特之处在于其广泛的地下暴露，为研究始发羽状头内的时间和成分关系提供了极好的基础。我们介绍了来自加勒比高原的40个挤压岩的主要元素，微量元素和Sr-Nd-Pb同位素组成，包括哥斯达黎加，哥伦比亚和库拉索岛的陆上剖面以及中加勒比的DSDP站点。即使熔岩在〜3 * 10〜6 km〜2的区域喷发，大多数熔岩仍具有明显一致的不相容元素模式（La / Yb = 0.96±0.16，n = 79个样品中的64个样品，2σ）和初始Nd -Pb同位素组成（例如〜（143）Nd /〜（144）Nd_（in）= 0.51291±3，ε_（Ndi）= 7.3±0.6，〜（206）Pb /〜（204）Pb_（in）= 18.86 ±0.12，n = 54（66，2σ）。具有末端成员组成的熔岩仅在随后的热点轨道的DSDP站点，哥戈纳岛（哥伦比亚）和65-60 Ma增生的克波斯和奥萨火成岩复合体（哥斯达黎加）采样。尽管大多数熔岩的成分相对均匀，但同位素比率之间以及同位素与高度不相容的痕量元素比率之间仍存在线性关系。化学富集熔岩的Sr-Nd-Pb同位素和痕量元素特征与回收海洋地壳的衍生相容，而贫化熔岩则来自高度残留的来源。该来源可以代表洋壳形成后留下的岩石圈地幔，也可以代表下洋壳中间层状超镁铁质累积的辉长岩。克波斯富橄榄岩橄榄石中〜3He /〜4He高，比大气比高〜12倍，表明富集成分可能曾经存在于下地幔中。在等时线图上对Sm-Nd和U-Pb同位素系统进行的评估表明，在CLIP形成之前，从贫化MORB源地幔中富集和贫化组分的分离年龄可能≤500 Ma，并被解释为反映了该物质的回收时间。 CLIP来源。地幔柱头可能提供一种机制，将位于下部地幔中的大量可能是年轻的回收海洋岩石圈运回浅层MORB源地幔。

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