A Complex History for the Caribbean Plateau: Petrology, Geochemistry, and Geochronology of the Beata Ridge, South Hispaniola
A Complex History for the Caribbean Plateau: Petrology, Geochemistry, and Geochronology of the Beata Ridge, South Hispaniola
复制标题
加勒比高原的复杂历史：南伊斯帕尼奥拉岛贝阿塔海岭的岩石学、地球化学和地质年代学
DOI：
--
复制
发表时间：
2000
期刊：
影响因子：
--
通讯作者：
R. Duncan
中科院分区：
文献类型：
--
作者：
S. Révillon;E. Hallot;N. Arndt;C. Chauvel;R. Duncan
贝阿塔海岭是加勒比盆地中部一个突出的南西南向地形结构。它的特点是异常厚的洋壳（长达20公里），据信是加勒比海洋高原的一部分。在 Nautica-Beata 航行期间通过潜水器回收的样本显示，该山脊主要由辉长岩、辉绿岩和稀有的枕状玄武岩组成。纹理差异很大，反映了冷却速率的差异，并暗示了地下、浅深环境。辉长岩和辉绿岩的主要元素组成遵循简单的趋势，对应于橄榄石、单斜辉石和斜长石的分步结晶。微量元素比率接近球粒晶 [(Nb/Zr)N 0.85–1.1]，稀土元素模式 (REE) 几乎平坦 [(La/Yb)N 0.63–1.02]。然而，该源的同位素已耗尽（ϵNd +7.4 至 +9.5）。为了解释这些地球化学特征，我们提出岩浆是通过尖晶石橄榄岩的部分熔融物汇集形成的。回收的稀有玄武岩具有较高的微量元素比例和富集的稀土元素模式[(Nb/Zr)N 3.45； (La/Yb)N 28–30]。它们可能是通过同位素贫乏源（ϵNd +5）的低度熔化形成的。通过 40Ar-39Ar 方法对整个岩石或分离的斜长石上的几个样品进行了年代测定。大多数样本的年龄在 80 至 75 Ma 之间，这与该省以前的年龄一致，但其他样本的年龄却出奇地年轻，约为 55 Ma。辉长岩-辉绿岩族的化学特征与加勒比海其他地区和其他海洋高原的玄武岩非常相似。这一特征的持续存在引发了人们对普遍接受的海洋高原形成地幔柱模型的有效性的质疑。根据加勒比板块的地球动力学重建评估了替代假设。两个地球动力学模型可以解释贝阿塔海脊样本的地球化学和同位素特征。在一种解释中，加勒比高原在加拉帕戈斯热点以南的太平洋约 80-90 Ma 形成，可能位于萨拉戈麦斯热点上方。在此模型中，76 Ma 事件与加拉帕戈斯羽流有关。在第二种解释中，加拉帕戈斯地幔柱是 90 Ma 与地幔柱相关的主要岩浆事件的原因，而 76 Ma 事件归因于岩石圈减薄。在这两种解释中，55 Ma 事件都与贝亚塔海脊局部岩石圈减薄有关。
The Beata Ridge is a prominent SSW‐trending topographic structure in the central Caribbean basin. It is characterized by unusually thick oceanic crust (up to 20 km) and is believed to form part of the Caribbean oceanic plateau. Samples recovered by submersible during the Nautica‐Beata cruise show the ridge to be composed mainly of gabbros, dolerites, and rare pillow basalts. Textures, which vary significantly, reflect differences in cooling rates and suggest a subsurface, hypabyssal environment. Major‐element compositions of gabbros and dolerites plot on simple trends that correspond to fractional crystallization of olivine, clinopyroxene, and plagioclase. Trace‐element ratios are close to chondritic [(Nb/Zr)N 0.85–1.1] and rare earth element patterns (REE) are almost flat [(La/Yb)N 0.63–1.02]. The source, however, was isotopically depleted (ϵNd +7.4 to +9.5). To explain these geochemical features, we propose that the magmas formed through pooling of fractional melts of spinel peridotite. The rare basalts recovered have higher trace‐element ratios and enriched REE patterns [(Nb/Zr)N 3.45; (La/Yb)N 28–30]. They possibly formed through lower‐degree melting of an isotopically less depleted source (ϵNd +5). Several samples were dated by the 40Ar‐39Ar method, either on whole rocks or separated plagioclases. Most samples have ages between 80 and 75 Ma, which are consistent with previous ages within the province, but others are surprisingly young, around 55 Ma. The chemical signature of the gabbro‐dolerite group is very similar to that of basalts from other parts of the Caribbean and from other oceanic plateaus. The persistence of this signature raises questions about the validity of generally accepted mantle‐plume models for the formation of oceanic plateaus. Alternative hypotheses are evaluated in the light of geodynamic reconstructions of the Caribbean plate. Two geodynamic models may account for the geochemical and isotopic characteristics of the Beata Ridge samples. In one interpretation, the Caribbean plateau formed ∼80–90 Ma in the Pacific south of the Galapagos hot spot, possibly above the Sala y Gomez hot spot. In this model, the 76‐Ma episode is related to the Galapagos plume. In the second interpretation, the Galapagos plume was responsible for the main plume‐related magmatic event at 90 Ma and the 76‐Ma episode is attributed to lithospheric thinning. In both interpretations, the 55‐Ma episode is related to lithospheric thinning localized on the Beata Ridge.