青藏高原北缘银石山地区地貌年代学初步研究

PRELIMINARY STUDY OF LANDFORMS CHRONOLOGY IN YINSHISHAN,NORTHERN EDGE OF QINGHAI-TIBET PLATEAU

青藏高原北缘银石山地区可划分出7类一级地貌类型:强抬升断块区、弱抬升断块区、低丘区、早期夷平面残留区、晚期准夷平面分布区、冲洪积平原、残积缓丘区等。通过相关沉积物的光释光和石英电子自旋共振年龄以及覆于早期夷平面、后期山丘、夷平低地或堆积台面等之上的火山岩年龄测年,重塑了晚新生代以来的地貌演化过程:中新世中晚期—上新世中期为主夷平面发育时期,上新世晚期(3.7Ma)主夷平面解体,强(弱)抬升断块区和低丘山地等开始形成。早更新世早期在低丘区中形成夷平低地或堆积台面,中后期抬升断块区与低丘区相间的地表形貌特征进一步强化。中更新世早期(0.64Ma)残积缓丘区形成,中期(0.43Ma)嵩华山北面形成一级冰斗,中后期(0.365Ma)低丘区主要斜坡地貌成型,末期(0.178Ma)强抬升断块区的主要沟谷地貌基本成型。晚更新世以来主要河流阶地形成,其间在0.037Ma前后冲洪积平原形成。

The landforms can be divided into seven first-order types in Yinshishan area, northern edge of Qinghai-Tibet plateau,namely:strongly-uplifted fault-block, inferior-uplifted fault-block, low-hillock area, distributive area for rudimental early planation surface, distributive area for late subplanation surface, diluvium-alluvial plain and eluvium slow-hillock.The evolution process of the landforms since late Neozoic is reconstructed on the basis of OSL,ESR ages of correlative sediments and ages of the volcanics covering the early planation surface,late hillocks and low planation or cumulate platform.The reconstruction shows that the primary planation surfaced mainly developed in Mid-Late Miocene-Middle Pliocene and disintegrated in late Pliocene(3.7 Ma B.P.),along with the launching of strongly-uplifted faulted-blocks and weakly-uplifted fault-blocks,while the low planation or cumulate platform formed in early Early Pleistocene.The landform features of the uplifted faulted block alternated with the low-hillock areas were strengthened in Mid-Late Pleistocene.Eluvium slow-hillock area formed in early Middle Pleistocene (0.64 Ma B.P.); the first-degree ice-cirque,in middle Middle Pleistocene (0.43 Ma B.P.) in the north of Songhuashan; and primary slopes in the low-hillock area in Mid-Late Middle Pleistocene (0.365 Ma B.P.).The primary gullies shaped up basically in the end of Middle Pleistocene(0.178 Ma B.P.); primary river terraces formed since the Late Pleistocene, and diluvium-alluvial plains formed at about 0.037 Ma B.P..