帕米尔构造结公格尔山基岩区第四纪构造变形与剥蚀过程的定量研究

Understanding the long-term evolution of active mountain belts requires precise identification and quantification of the potential couplings between tectonics, climate and erosion(e.g., Beaumont et al., 1992; Willett, 1999; Whipple and Meade, 2006; Whipple, 2009). In the region of the high peak Kongur Shan(7719 m), the correlation between areas of high relief, active normal faulting along the Kongur normal fault (KNF), and deep, rapid exhumation with areas of presumed rapid glacial and fluvial erosion suggests a positive feedback loop...We will use a combination of Be-10 surface exposure dating, and structural and geomorphic mapping to constrain shorter-term slip-rates of the KNF. We will also conduct 40Ar/39Ar dating of hornblende, muscovite, and biotite, (U-Th-Sm)/He and FT dating of zircon and apatite in valley-bottom samples combined with elevation profiles and long transects both across and far from the KNF. With this thermochronologic data, we aim to obtain information on the nature of fault displacements, to identify variations in exhumation rate along and within the footwall of the KNF, including the correlation of shorter-term fault slip-rates to longer term cooling history, to test and constraint as tightly as possible the timing of acceleration in cooling observed by Arnaud et al. (1993) and Robinson et al. (2010) at about 1.5-2 Ma, and to better understand the evolution of topography of Kongur dome on the eastern side of the KNF. We will use a new technique, quartz and feldspar OSL-thermochronology with close temperature of 30-50℃(Herman et al., 2010), to measure how the landscape of a tectonically active range has responded to a change in climatic conditions at the timescale of Quaternary glacial cycles...In order to interpret all the thermochronologic cooling data in terms of exhumation rates, we will use the 3-D thermal-kinematic model Pecube to constrain the influence of extreme topography and rapid advection of crustal rocks on the thermal evolution of these samples, to constrain and understand the relative contributions of tectonics, erosion and climate to both the spatial and temporal exhumation pattern observed in the Kongur Shan, to test whether spatial variations in deformation histories can be explained without a tectonic response to climate or whether the data demand such a response, to check the hypothesis that climate can significantly influence the tectonic and structural evolution of mountain ranges, to discuss potential feedback among normal fault motion, extension-induced topography and topographic enhanced erosion that may lead to fault slip variations.

理解第四纪活动造山带的演化过程亟需精确识别和量化构造、气候和侵蚀之间的耦合作用。本申请试图以"基岩区低角度正断作用与剥蚀过程及其相互作用"为主线，选择海拔7719米、第四纪正断作用强烈、气候变化频繁、冰川作用广泛、高山峡谷发育、冷却速率发生巨变的帕米尔构造结东部公格尔山，通过地质和地貌填图、断错地貌测量及10Be宇宙成因核素测年、角闪石和白/黑云母40Ar/39Ar、锆石和磷灰石裂变径迹(FT)及(U-Th)/He等中-低温热年代学特别是新提出的封闭温度更低(30-50℃)的石英和长石光释光低温热年代学测年研究，采用年龄-高程法、矿物对法和3维热运动学数值模拟，定量限定百万年至千年尺度的正断层滑动速率、断层两盘特别是下盘岩体抬升量与速率和剥蚀速率在时空上的分布与地形演化过程，重建公格尔山第四纪的剥露方式、隆升过程和热演化史，探讨第四纪构造抬升、剥蚀与冰期-间冰期气候旋回间的相互耦合作用。

理解第四纪活动造山带的演化过程亟需精确识别和量化构造、气候和地表过程之间的耦合作用。本项目选择第四纪正断作用强烈、冰川作用广泛、高山峡谷发育的帕米尔构造结东部公格尔山，开展了地质和地貌填图、断错地貌测量及Be-10宇宙成因核素测年、云母Ar-Ar、锆石 (U-Th)/He等中-低温热年代学以及封闭温度更低的长石光释光-石英ESR低温热年代学测年研究。查明了研究区公格尔拉张系空间展布、几何学特征与位移分布特征，全新世垂直抬升速率和东西向拉张速率在公格尔片麻岩穹窿西北麓的公格尔正断层大于16 mm/a和14 mm/a，向北远离穹窿具递减趋势。初步获得了公格尔拉张系数十万年至百万年时间尺度的冷却年龄，估算断层上升盘垂直剥露速率大于3-2.5 mm/a。尝试建立了基岩钾长石光释光与电子自旋共振(ESR)低温热年代学方法，估算的公格尔正断层上升盘长石样品表观IR50℃光释光年龄随高程增加而增加，且明显比断层下降盘的表观年龄要小；估算的石英Al心的表观剥蚀速率与锆石U-Th/He的及黑云母Ar-Ar的近似，但在氧同位素阶段5(约75 ka)存在一明显的拐点，表观剥蚀速率激增至22 mm/a。提出了基于单一钾长石样品多种释光信号热年代计约束岩石冷却速率的数值实验模拟方法，估算公格尔山体的冷却速率与表观剥露速率自180-100ka以来分别为0.8-1.2℃/ka和14至21mm/a，而自45-35 ka以来增加至1.2-1.8℃/ka和21-32mm/a，具有加速冷却与剥露的趋势。这些结果表明，公格尔拉张系及公格尔山的晚第四纪抬升与剥露速率是全球陆内最快的地区之一，且有加速的趋势，以正断抬升作用为主，现今高山峡谷地形是构造变形、冰川及盖孜河快速下切等相互耦合作用的结果。上述结果也表明多种释光(ESR)信号热年代计能够较好地限定过去20万年岩石的冷却历史，为研究晚第四纪构造、气候与地表过程相互作用以及热液演化历史提供了新手段。