滇西南那邦变质基性岩地球化学与俯冲板片裂离

中缅边界那邦麻粒岩相变质基性岩地球化学特征表明其原岩是岩浆岩，并具有ＭＯＲＢ的特性，其岩石化学具有以下特征：岩石的ＴＦｅ／ＭｇＯ值低（１．１０～２．１７），ＡＦＭ图解上显示拉斑玄武岩演化趋势；ＴｉＯ２含量（１．１４％～１．８１％）高稀土亏损、重稀土较有富集的配分形式，稀土元素和总量（∑ＲＥＥ）值十倍于球粒陨石（２４～５０μｇ／ｇ），（Ｌａ／Ｓｍ）Ｎ＝０．４３～０．７５（Ｌａ／Ｙｂ）Ｎ＝０．４５～０

Geochemistry and genesis of Nabang metamorphic basalt, southwest Yunnan, China: implications for the subducted slab break-off

The Nabang metamorphic basalt is discovered recently on the border of China and Burma. The majoy, trace and rare earth element characteristics of Nabang metamorphic basalt have been investigated. All studied rocks are depleted in light rare earth elements(LREE) with REE=24-50g/g, (La/Sm)N=0.43~0.75 the same and (La/Yb)N=0.45-0.74. Ti2O, Nb and Ta show that the Nabang metamorphic rocks are different from islandarc basalt as shown by the geochemical diagrams. The NdSr isotope data show a clear signature of a depleted mantle source similar to NMORB with 87Sr860.704-0.705,143Nd144Nd= 0.5129~0.5132, Nd= 4.85~ 9.67. Combining with its geochronological results and geological background, it can be concluded that the Nabang metamorphic basalt is related to Myitkyina suture, east Burma. The Nabang metamorphic basalt may be an evidence of slabbreakoff of NeoTethys subducted upper oceanic crust.