Geochemical characteristics of Carboniferous greenstones in the Inner Zone of Southwest Japan
Geochemical characteristics of Carboniferous greenstones in the Inner Zone of Southwest Japan
复制标题
日本西南部内带石炭系绿岩地球化学特征
DOI：
10.1046/j.1440-1738.2000.00263.x
复制
发表时间：
2000
期刊：
影响因子：
1.5
通讯作者：
K. Tazaki
中科院分区：
文献类型：
--
作者：
S. Sano;Y. Hayasaka;K. Tazaki
摘要绿岩代表古洋壳的残余，产于日本西南弧内带的二叠纪和侏罗纪增生杂岩中。根据上覆石灰岩的化石年龄和绿岩本身的Sm-Nd同位素年龄，大多数绿岩的形成年龄是早石炭世。这些绿岩的地球化学性质类似于今天的海洋岛屿。二叠纪增生杂岩（秋吉带）的绿岩成分为碱性和拉斑玄武岩。一些碱性玄武岩显示出来自EM‐1地幔源的特殊特征，例如南大西洋的戈夫岛和特里斯坦-达春哈玄武岩。侏罗纪增生杂岩（Tamba带）的绿岩也是碱性玄武岩和拉斑玄武岩，Tamba带北方部分的两种玄武岩类型来自类似于洋中脊玄武岩源地幔的强烈亏损特征。大洋玄武岩的可变地球化学是由石炭纪地幔柱的存在下的扩张脊，划分Farallon和Izanagi板块的假说解释。Farallon板块的Akiyoshi带海山和/或洋岛以及Izanagi板块的Tamba带海山和/或洋岛是由热羽流上涌同时形成的。部分秋吉带玄武岩局部起源于EM-1地幔源，而Tamba带北方部分的玄武岩具有正常类型的洋中脊玄武岩（N-MORB）源成分。N-MORB特征的存在与石炭纪“太平洋”中的扩张中心的存在是一致的，该扩张中心导致Farallon和Izanagi板块分离。二叠纪和侏罗纪玄武岩增生年龄的差异可能是由于两个板块相对运动的差异造成的。
Abstract Greenstones, representing remnants of paleo‐oceanic crust, occur in Permian and Jurassic accretionary complexes of the Inner Zone in the Southwestern Japan arc. The formation age of most of the greenstones is early Carboniferous, based on fossil ages for overlying limestones and Sm‐Nd isotope ages of the greenstones themselves. The geochemistry of such greenstones is similar to those of present‐day oceanic islands. Greenstones of the Permian accretionary complex (Akiyoshi belt) are alkalic and tholeiitic in composition. Some alkali basalts show peculiar features from an EM‐1 mantle source, such as the Gough Island and Tristan da Chunha basalts in the South Atlantic. Greenstones of the Jurassic accretionary complex (Tamba belt) are also alkali and tholeiitic basalts with both basalt types in the northern part of the Tamba belt coming from strongly depleted characters similar to a mid‐ocean ridge basalt source mantle. The variable geochemistry of the oceanic basalts is explained by hypothesis on existence of a Carboniferous mantle plume below the spreading ridge which divides the Farallon and Izanagi plates. The Akiyoshi belt seamounts and/or oceanic islands of the Farallon plate and Tamba belt seamounts and/or oceanic islands of the Izanagi plate formed simultaneously by the upwelling of the thermal plume. Some part of the Akiyoshi belt basalts originated locally from an EM‐1 mantle source, while basalts from the northern parts of the Tamba belt have a normal‐type mid‐ocean ridge basalt (N‐MORB) source component. Existence of an N‐MORB signature is consistent with the presence of a spreading center in a Carboniferous ‘Pacific Ocean’ that caused separation of the Farallon and Izanagi plates. Disparity in accretion ages of the basaltic rocks in the Permian and Jurassic may have been caused by differences in the relative motion of the two plates.
影响因子：
1.5
作者：
Maruyama, S;Isozaki, Y;Terabayashi, M
通讯作者：
Terabayashi, M