西藏阿里札达盆地上新世-早更新世沉积相及其构造演化特征

札达盆地新近系上新统一第四系下更新统地层可划分为下更新统香孜组(Qp^1x)、新近系上新统古格群(N2gg)，其中后者又细分为上新统札达组(N2^2z)和上新统托林组(N1^2t)，属地堑型湖盆沉积，主要发育冲洪积相、冰缘相、冰湖相、湖相及河流相。札达盆地的构造演化经历了早期裂陷(N2^1t)、持续裂陷(N2^2z)、湖盆外泻(Qp^1z)、稳定隆升(Qp^2f)和强烈快速隆升(Qp^3～Qh)等5个阶段。盆地南北两侧数条相向正断层的活动性控制着该区的沉积相展布格局：断层活动强烈时，湖盆水域扩大，湖水加深，主要发育深湖—半深湖沉积，断层活动减弱时，水体变浅或干涸，湖盆被充填，主要发育河流相、冲洪积沉积。第四纪以来，随着青藏高原的快速隆升，札达盆地周缘高山区冰川活动加剧，主要发育冰缘相和冰湖相。

FEATURES OF PLIOCENE-LOWER PLEISTOCENE SEDIMENTARY FACIES AND TECTONIC EVOLUTION IN THE ZANDA BASIN,NGARI AREA,TIBET

The Neogene Pliocene-Quaternary lower Pleistocene strata in the Zanda basin, Ngari area, Tibet, may be divided into the lower Pleistocene Qangzü (Q_p¹x) Formation and the Neogene upper Pliocene Guge Group (N₂gg) and the latter may be further divided into the Pliocene Zanda Formation (N₂²z) and the Pliocene Toling Formation (N₂¹t).The strata belong to graben-type lake-basin deposits and consist predominantly of alluvial-proluvial, paraglacial, glaciolacustrine, lacustrine and fluvial facies.The tectonic evolution of the basin went through five stages, i.e.:the early-rifting stage (N₂¹t), sustained rifting (N₂²z), lake basin outflow (Q_p¹x), steady uplift (Q_p²f) and rapid strong uplift (Q_p³-Qh).The activities of several normal faults on the southern and northern sides of the basin control the distribution pattern of the sedimentary facies:when fault activities were strong, the water bodies of the lake basin enlarged, the water became deep and mainly deep-and semi-deep lake deposits occurred; when fault activities weakened, the water bodies became shallow or dried up, the lake basin was filled up and there mainly occurred fluvial and alluvial-proluvial deposits.Since the beginning of the Quaternary, alpine glacial activities around the Zanda basin have intensified with the rapid uplift of Qinghai-Tibet Plateau, and then paraglacial and glaciolacustrine deposits have developed.