Abstract: In the eastern section of the Qinling geotectonic belts, the authors discovered an ancient subduction zone at the northern foot of the Mt. Dabie near Xinyang, Henan province. The subduction complex consists of ophiolites, melanges and low-T/high-P metamorphic rocks. The melanges are composed of native blocks (dolomite-marble, olisto-strome), exotic blocks (serpentinite, issite, hornblendite, granite, gabbro, chert, etc.) and argillo-arenaceous matrix. The suite of ophiolite includes metamorphosed basic volcanic rocks, diabase dykes, metamorphic pelites, basic and ultrabasic magmatic rocks. The essential characteristics of the suite are coincident with those of the island-arc ophiolites. 3T-phengites and C-type eclogites have been found in the low-T/high-P zone of meta-morphism. According to their general tectonic character the subduction complex was produced by a marginal sea floor underthrusting southwards beneath an island-arc. The acorites, sampled from the low-T/high-P zone, have been dated at 693-603 Ma by U-Pb age determination. The quartz-diorites, which intruded into the ophiolitic suite, have been dated at 413.5 Ma by K-Ar age determination. These ages imply that the subduction zone was formed in the end of Late Proterozoic.We suggest that the structural evolution of the ancient convergent plate margins should be divided into following three episodes.(1) During Late Proterozoic (about 700-800 m.y. B.P.), the oceanic crust of the East Qinling Sea underthrusting northwards beneath the continental block of North China, which gave rise to the Tongbai island, is associated with a marginal sea.(2) Nearly in the end of Late Proterozoic (about 700-600m.y. B.P.), a polarity reversal of this subduction zone occurred. The oceanic crust of the marginal sea was consumed beneath the Tongbai island arc, which resulting in the Xinyang subductio ncomplex.(3) During Early paleozoic (about 600-500m.y. B.P.), the oceanic crust of the East Qinling Sea was subducted northwards again beneath the accreted continental margin along a new Benioff zone.

摘要： 在秦岭构造带东段大别山北麓的河南信阳附近,作者发现了一个古消减带,其中消减杂岩由蛇绿岩:混杂岩及低温高压变质带的岩石组成。推断古板块会聚边缘的构造发育史可以划分为以下三个阶段: Ⅰ、晚元古代(约800—7000百万年前),东秦岭古洋壳向北朝华北古陆之下俯冲,产生了初始的桐柏岛弧及弧后的边缘海。 Ⅱ、元古代末(约700—600百万年前),俯冲带极性反向,边缘海洋壳向南朝桐柏岛弧之下消减,从而产生了信阳消减杂岩。 Ⅲ、早古生代初(约600—500百万年前),边缘海闭合,桐柏岛弧增生于华北古陆的南缘,东秦岭古洋壳沿岛弧之南的一个新贝尼奥夫带再次向北俯冲。