Oceanic mafic magmatism in the Siletz terrane, NW North America: Fragments of an Eocene oceanic plateau?
Oceanic mafic magmatism in the Siletz terrane, NW North America: Fragments of an Eocene oceanic plateau?
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北美西北部 Siletz 地体的海洋镁铁质岩浆作用：始新世海洋高原的碎片？
DOI：
10.1016/j.lithos.2017.01.005
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发表时间：
2017
期刊：
影响因子：
3.5
通讯作者：
D. Weis
中科院分区：
文献类型：
--
作者：
B. Phillips;A. Kerr;E. Mullen;D. Weis
Siletz 地体是一个主要由镁铁质增生的海洋地体，位于俄勒冈州、华盛顿州和温哥华岛的卡斯卡迪亚弧前地区。该地体代表了古新世晚期至始新世的大型火成岩省，由枕状熔岩、大量熔岩流和侵入岩层组成。此前有人提出，Siletz 地体代表了增生的海洋高原、热点岛链、弧后盆地、岛弧或一系列板窗火山岩。对全省范围内的地体进行地球化学重新评估，包括新的高精度 Sr-Pb-Nd-Hf 同位素数据，已用于评估所提出的 Siletz 地体构造岩浆模型的有效性。微量元素数据几乎没有显示出地壳污染或弧特征的证据，并且样品具有平坦到轻稀土富集的稀土元素 (REE) 模式。这些特征与其他海洋高原相似，例如翁通爪哇和加勒比海。初始同位素比范围为 206Pb/204Pb：18.751 至 19.668，207Pb/204Pb：15.507 至 15.661，208Pb/204Pb：38.294 至 39.2128，176Hf/177Hf：0.28300 至0.28316（εHf：9.0至 14.5)，143Nd/144Nd：0.51282至0.51299(εNd：5.0至8.1)和87Sr/86Sr：0.70302至0.70380。这些数据与 Siletz 地体的地幔源一致，该地幔源似乎是非均质的且稍微富集。丰富的特征具有 EM2 和 HIMU 成分的特征，结合计算出的地幔潜在温度远高于周围地幔，表明 Siletz 岩浆活动源自地幔柱，可能是黄石热点。因此，我们得出结论，Siletz 地体代表了一个增生的海洋高原。
The Siletz terrane, a predominantly mafic accreted oceanic terrane, is located in the Cascadia forearc region of Oregon, Washington and Vancouver Island. The terrane represents a late Palaeocene–Eocene large igneous province that consists of pillow lavas, massive flows and intrusive sheets. Previously it has been proposed that the Siletz terrane represents either an accreted oceanic plateau, hotspot island chain, backarc basin, island arc, or a sequence of slab window volcanics. A province-wide geochemical reassessment of the terrane, including new high precision Sr-Pb-Nd-Hf isotope data, has been used to assess the validity of the proposed tectonomagmatic models for the Siletz terrane. The trace element data show little evidence of crustal contamination, or an arc signature, and the samples have rare earth element (REE) patterns that are flat to light REE enriched. These features are similar to other oceanic plateaus such as the Ontong Java and the Caribbean. Initial isotope ratios range from206Pb/204Pb: 18.751 to 19.668,207Pb/204Pb: 15.507 to 15.661,208Pb/204Pb: 38.294 to 39.2128,176Hf/177Hf: 0.28300 to 0.28316 (εHf: 9.0 to 14.5),143Nd/144Nd: 0.51282 to 0.51299 (εNd: 5.0 to 8.1) and87Sr/86Sr: 0.70302 to 0.70380. These data are consistent with a mantle source of the Siletz terrane that appears to have been heterogeneous and slightly enriched. The enriched signature has characteristics of both EM2 and HIMU components and this, combined with a calculated mantle potential temperature well above ambient mantle, indicates derivation of the Siletz magmatism from a mantle plume, possibly the Yellowstone Hotspot. We therefore conclude that the Siletz terrane represents an accreted oceanic plateau.