Argon ratios, 40Ar/39Ar datings and biostratigraphic ages of ODP Leg 165 sites

Drilling in the Caribbean Sea during Ocean Drilling Program Leg 165 has recovered a large number of silicic tephra layers and led to the discovery of three major episodes of explosive volcanism that occurred during the last 55 m.y. on the margins of this evolving ocean basin. The earliest episode is marked by Paleocene to early Eocene explosive volcanism on the Cayman Rise, associated with activity of the Cayman arc, an island arc that was the westward extension of the Sierra Maestra volcanic arc in southern Cuba. Caribbean sediments also document a major mid- to late Eocene explosive volcanic episode that is attributed to ignimbrite-forming eruptions on the Chortis Block in Central America to the west. This event is contemporaneous with the first phase of activity of the Sierra Madre volcanic episode in Mexico, the largest ignimbrite province on Earth. In the Caribbean sediments, a Miocene episode of explosive volcanism is comparable to the Eocene event, and also attributed to sources in the Central American arc to the west. Radiometric 40Ar/39Ar dates have been obtained for biotites and sanidines from 27 tephra layers, providing absolute ages for the volcanic episodes and further constraining the geochronology of Caribbean sediments. Volcanic activity of the Cayman arc is attributed to the northward subduction of the leading edge of the oceanic plate that carried the Caribbean oceanic plateau. Although the factors generating the large episodes of Central American explosive volcanism are unclear, we propose that they are related to contemporary major readjustments of plate tectonic configuration in the Pacific.大洋钻探计划（Ocean Drilling Program）第165航次在加勒比海实施的钻探作业，采获了大量硅质火山碎屑层（silicic tephra layers），并揭示了过去55百万年间，该演化中的大洋盆地边缘发生的三次大规模爆发性火山作用幕。最早的火山作用幕以开曼海隆（Cayman Rise）上的古新世至始新世早期爆发性火山活动为特征，该活动与开曼弧（Cayman arc）的活动相关——开曼弧是古巴南部马埃斯特腊山火山弧（Sierra Maestra volcanic arc）向西延伸的岛弧。加勒比海沉积物还记录了一次重要的中始新世至晚始新世爆发性火山事件，该事件被归因于西侧中美洲乔蒂斯科克地块（Chortis Block）上的熔结凝灰岩喷发（ignimbrite-forming eruptions）。这一事件与墨西哥马德雷山火山幕（Sierra Madre volcanic episode）的第一阶段活动同期，而后者是全球规模最大的熔结凝灰岩省。在加勒比海沉积物中，中新世爆发性火山事件可与始新世事件相媲美，其物源同样来自西侧的中美洲弧。研究人员已对27个火山碎屑层中的黑云母（biotites）和透长石（sanidines）开展了40Ar/39Ar同位素定年，为各火山作用幕提供了绝对年龄数据，并进一步约束了加勒比海沉积物的地质年代学框架。开曼弧的火山活动被归因于携带加勒比洋高原的大洋板块前缘向北俯冲。尽管中美洲大规模爆发性火山作用幕的成因尚不明确，但我们提出其与太平洋板块构造格局同期发生的重大调整存在关联。