哀牢山-红河断裂带哀牢山-大象山段渐新世-早中新世热史演化及成因

Thermal Evolution History and Its Genesis of the Ailao Shan-Red River Fault Zone in the Ailao Shan and Day Nui Con Voi Massif during Oligocene-Early Miocene

哀牢山-红河断裂带范围内样品热史演化的系统构建工作偏少;部分学者往往将样品的冷却年龄简单地归因于断裂带的事件年龄,而没有考虑热扰动因素,致使以往研究结论仍然存在分歧及不合理之处.利用断裂带中高温测年资料,构建了Tt变化曲线,结合压力-温度-深度(P-T-D)变化趋势及地层恢复,对T-t变化的成因提出了较为合理的解释.中高温热史演化表明断裂带SE端(大象山段)与NW端(哀牢山段)皆经历2期冷却过程;在地层剥蚀或构造剥露作用诱导下,SE端、NW端于32~30Ma、32~22Ma分别经历第1期冷却过程,而其在26~24Ma、22~20Ma分别经历的第2期冷却过程中,由于断裂活动减弱这一因素,致使该期冷却速率明显增大(尤其是断裂带NW端).伴随着印支地块的顺时针旋转挤出,断裂带中南部左旋转换拉张构造活动向北迁移.在断裂带T-t演化的第1个阶段内,受断裂带转换拉张强度NW向减弱的影响,断裂带SE端正断活动所致的山体隆升效应明显强于NW端,致使SE端样品冷却过程较早,同时冷却速率明显偏大;而在第2个阶段,伴随着青藏高原进入中新世早期的隆升阶段,作为高原东南缘板块调节边界的哀牢山-红河断裂带其活动性由SE端开始减弱,使得冷却过程由SE端向NW端传递.

In spite of much research focused on thermal evolution history-tectonic activity of the Ailao Shan-Red River fault zone（ASRR）during Late Oligocene-Early Miocene,its thermal reconstruction is limited.Moreover,the related thermal disturbance factors are often ignored and the measured ages（cooling ages）are generally irrationally recognized as the timing of tectonic events in the existing studies.Combined with the pressure-temperature-depth paths（P-T-D）and paleogeomorphology reconstruction,the T-t paths of the ASRR are constructed to explore the genesis of T-t paths and the evolutionary characteristics of the fault zone systematically.The cooling process of the metamorphic massif can be divided into two phases：for Day Nui Con Voi is 32-30 Ma and 26-24 Ma,while for the Ailao Shan is 32-22 Ma and 22-20 Ma.In the first phase,the rapid cooling may have been caused by the strata denudation or tectonic denudation,followed by the more rapid cooling of the second phase,in which the intensity weakening of the fault has been more dominant,compared with the denudation and other factors.With the clockwise rotation and extrusion of the Indochina terrane relative to the South China block,the sinistral tensile transformation zone in the south propagated northwards.Additionally,the spatial differences in the tectonic activities induced the variedcooling processes for the southeastern and northwestern part.In phaseⅠ,the tectonic uplift in the southeastern part presented earlier and stronger than the northwestern one,with the northwestward propagation and weakening of the sinistral tensile transformation.So the cooling process of the southeastern part was much earlier and more rapid,compared with the northwestern process.In phase Ⅱ,the activity of the ASRR which acted as the boundary of the plate extrusion became weak northwards,along with a new period of Tibet uplift in early Miocene.Then the change stimulated another rapid cooling process,showing the northwestward decreasing trend.