青藏高原东南缘大理地区晚新生代构造地貌过程以点

青藏高原东南缘大理地区晚新生代构造地貌过程以点苍山和玉龙雪山为例摘要：炼铁盆地位于青藏高原东南缘的点苍山西北，是剑川左行走滑断裂与点苍山-罗坪山西坡断裂系的交接部位。通过对该盆地进行详细地层测量和构造变形调查表明，罗坪山西坡正断层控制了炼铁盆地的发育，盆地为半地堑，内部沉积了一套生长地层，其沉积物源可能为西侧的兰坪-思茅盆地。正断作用开始于上新世，并且可能持续到第四纪，磷灰石裂变径迹热年代学分析表明，罗坪山西坡正断层在距今 0.15 Ma 仍在活动。研究最终得出，炼铁盆地演化可以划分为两个阶段：（一）上新世剑川左行走滑断裂在其南部转换为伸展构造，形成了炼铁半地堑盆地，并且控制了盆地的沉积过程。 （二）更新世澜沧江及其支流黑惠江的快速下切，袭夺了炼铁湖盆使其消亡，形成炼铁盆地今日之面貌。 玉龙雪山位于青藏高原东南缘，其顶部存在一个残留剥蚀面。地质上，该山体的东西两侧被年轻的正断层围限, 形成一个孤立的菱形断块山，与大理地区的点苍山构成一个 Z 字型地垒的南北两端。根据该区地质地貌特征，我们运用岩石圈弹性挠曲地壳均衡理论，以古残留面为当时金沙江下切玉龙雪山的基准面，研究分析得出，在 9-13 Ma金沙江水系快速下切玉龙雪山，造成虎跳峡大规模物质剥蚀时，该山体没有发生差异性隆升,其顶部作为第三纪的剥蚀残山而存在。在晚新生代（5-2.5 Ma） ，红河右行走滑断裂发生,其北西端转换为伸展构造，玉龙雪山地区发生近东西向伸展，激发了地壳均衡反弹, 峰顶由此隆升了 468 m，加大了山体与周围地区的地势高差。而玉龙雪山与周围地区的剩余地势高差主要由构造作用（如正断层）完成，因此晚新生代玉龙雪山的隆升是由构造与侵蚀作用共同控制的结果。玉龙雪山的南东延伸部分点苍山（4122 m）同样也发生了构造伸展，但是山体没有遭受类似虎跳峡的剥蚀作用，不足以产生相当的均衡反弹 因此其海拔相对要低很多。这进一步证实了地壳均衡反弹导致玉龙雪山隆升，并加大了玉龙雪山与点苍山的地势高差。Abstract：Liantie basin is located on the west of the NNW trending Luoping Shan, northwest part of the Diancang Shan with a general definition, at the southeastern margin of the Tibetan Plateau. It is just the place where the left-lateral strike-slip fault of Jianchuan meets the normal faults on the west slope of the Diancang-Luoping Shan. Detailed measurement of the strata and investigation of structural deformation within the basin, indicate that normal faults bounding on the west slope of the Luoping Shan has controlled the development of the Lian basin, which is a half-graben and deposited with a suite of growth strata whose source is very likely from the Lanping-Simao basin, west of Liantie basin. The normal faulting on the west slope of Luoping Shan started at the time of Sanying Formation, which is of Pliocence time, and continues to Quaternary. And our apatite fission track analyses indicate that normal faults on the west slope of the Luoping Shan are still active at about 0.15 Ma. The final indication of this work is that the Liantie basin experienced two stages of evolution: (1) Jianchuan left-lateral strike-slip fault, was transformed into extensional structure in its southwestern end in Pliocene time and formed the Liantie basin as a half graben; and the extension has controlled the depositional process of the basin; (2) the Pleistocene rapid incision of Lancang River and its important tributary-the Heihuijiang River captured the original Liantie basin, and therefore resulting in the basin from lacustrine close environment into present open system. The Yulong Snow Mountain is located in the southeastern margin of the Tibetan Plateau. And its top is considered a relict surface. In geological setting, the Yulong Snow Mountain is bounded as a rhombus block by young normal faults, and together with the Diancang Shan within the Dali block composes the two end members of the Z-type horst on the north and south, respectively. According to the geologic and geomorphologic characteristics in this area and the elevation of the relict surface (4250 m) referenced as the initial incision surface, the analyses by isostasy of the lithospheric elastic flexural model, indicate that there existed no differential uplift for the Yulong Snow Mountain when the Jinsha River was rapidly incising it during 9-13 Ma and cause the mass lose in the Tiger Leap Gorge, and the mountain was still an eroded relict hill. It is only after the normal faulting was developed at 5-2.5 Ma on both the east and the west sides of the mountain that it triggered the local isostasy within this small area, thereby resulting in the uplift of the snow mountain by 468 m. and the increase of relief between the Yulong Snow Mountain and its surrounding area. But the other relief existing in the two areas is caused by tectonic forcing, such as the normal faulting. Therefore, Late Cenozoic uplift of the Yulong Snow Mountain is controlled by both erosion and tectonic forcing. The Diancang Shan, 4122 m of highest elevation and as the part continuing southward from the Yulong Snow Mountain, was also experienced the tectonic extension at 5-2.5 Ma, but had little erosion like that in the Tiger Leap Gorge, which further prove that the existence of the isostatic rebound occurred in the Yulong Snow Mountain and that this rebound also increased the modern high relief between the two mountains.