A very hydrous mantle under the western Pacific region: Implications for formation of marginal basins and style of Archean plate tectonics
A very hydrous mantle under the western Pacific region: Implications for formation of marginal basins and style of Archean plate tectonics
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DOI：
10.1016/j.gr.2006.02.006
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发表时间：
2007
影响因子：
6.1
通讯作者：
T. Komiya;S. Maruyama
中科院分区：
文献类型：
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作者：
T. Komiya;S. Maruyama
西太平洋地区自450 Ma以来一直受到俯冲冷洋板块的冷却。然而，该地区的特点也是存在许多小于1300公里的海洋微板块，以及活跃的岩浆活动;菲律宾海板块是代表。通过对菲律宾海板块DSDP钻孔玄武岩岩石化学特征的整理和分析，认为大洋玄武岩的源区地幔富含水，其源区地幔中的水主要来源于大洋玄武岩。0.2重量百分比，比MORB低50-60 ℃。大规模熔融是由于源区地幔含水量高所致。众所周知，一些边缘盆地的深度显然大于主要海洋。我们根据瞬态半空间冷却模型计算了年龄-深度相关性，参数为地幔和地表温度1280 ° C和0 °C，热扩散率1 mm 2s −1。计算结果表明，菲律宾海洋中脊的年龄-剩余深度的相关系数为367岁（m），与测深资料一致。此外，大洋中脊可能相对较深，因为这一区域下面是较冷的地幔。地幔橄榄岩中水的加入降低了固相线温度和粘度。水合橄榄岩的熔融实验表明，加入0.2wt.% H2O含量使固相线温度降低150 °C。因此，该地区下的地幔实际上可能对应于一个ca。在岩浆作用和流变学方面，比正常MORB源地幔热90 °C。对更热地幔的数值模拟表明，许多小板块的形成是由于活跃岩浆活动的广泛热释放，与该地区许多微板块相一致。许多大洋微板块的存在可能类似于太古代的板块构造，其特征是更热的地幔。
The western Pacific region has been refrigerated by the subducting cold oceanic plates since 450 Ma. However, the region is also characterized by the presence of many oceanic microplates less than 1300 km across, as well as active magmatism; the Philippine Sea plate is representative. We have compiled and examined petrochemical characters of drilled basalts of DSDP from the Philippine Sea plate, and conclude that the source mantle for oceanic basalts is rich in water ca. 0.2 wt.%, and is 50–60 °C lower than that for MORB. The extensive melting is due to the high water content in the source mantle. It is well known that some marginal basins apparently have greater depths than the major oceans. We calculated the age–depth correlation based on a model of transient half-space cooling at given parameters of temperatures of mantle and surface, 1280 and 0 °C, and the thermal diffusivity, 1 mm2s−1. The calculation shows the correlation of age-residual depth from a mid-oceanic ridge is 367 age(my) for the Philippine Sea, consistent with the bathymetric data. Moreover, the mid-oceanic ridge may be relatively deep because this region is underlain by the cooler mantle. Addition of water to the mantle peridotite lowers the solidus temperature and viscosity. Melting experiments of hydrous peridotite show that addition of 0.2 wt.% H2O content lowers the solidus temperature by 150 °C. As a result, the mantle under the region may practically correspond to a ca. 90 °C hotter mantle than normal MORB-source mantle in terms of magmatism and rheology. Numerical simulation for a hotter mantle suggests that many small plates should be formed because of extensive heat release by active magmatism, consistent with many microplates in this region. The presence of many oceanic microplates may be analogous to Archean plate tectonics, characterized by a hotter mantle.