摘要
40Ar/39Ar年代学是同位素地质年代学中重要的两个"金钉子"手段之一(另一个为U-Pb法),广泛应用于重大地质事件、地质界线的精确定年,是确定地质年表的主要手段。40Ar/39Ar年代学测定的母体元素钾为常量元素,且实现分析时由于只需测定Ar同位素的比值,因而具有很高的分析精度,因此可以测定非常年轻(数千年)地质体的年龄。此外,由于在自然界中不易发生(物理、化学)反应的特性,Ar在矿物中的扩散可被准确地定量描述,因此40Ar/39Ar年代学也是热年代学的重要支柱,被广泛应用于地球深部物质上涌、折返、剥露、变质的冷却历史,率先提供了解析造山带、地壳作用过程等热历史的定量模型。这些特点使得40Ar/39Ar年代学成为地质年代学的三大支柱之一。那么,近年来该方法发展到了什么程度,其精确度和准确度达到了怎样的高度?为何年轻火山样品中极少发现过剩Ar?高压环境中的样品过剩Ar为何难以辨认?压力影响矿物的封闭温度吗?缓慢冷却K-长石的年龄谱是否可以真实地反映岩体所经历的热历史?多重扩散域模型(MDD)遇到了哪些挑战、该如何应用?40Ar/39Ar法和U-Pb法在构造热过程研究中有何不同的应用?本文对这些问题进行了思考和讨论,以期推动大家对40Ar/39Ar年代学的深入探索,推动其在我国地质研究中的应用。
As an important tool in geochronology,40Ar /39Ar method plays a role in both precise dating and thermochronology. Compared with U-Pb method,40Ar /39Ar geochronology is more widely applied in thermal history and geodynamic process of the crust. Because of the high potassium content in nature and only isotopic ratios to be analyzed during experiment,40Ar /39Ar method has a high analytical precision,therefore,it can be used to date very young（ e. g.,thousands of years） samples. Moreover,based on the nature of chemical inertia and describable behavior,40Ar /39Ar technique is widely used to quantitatively calculate thermal history of uplift, denudation and metamorphism of deep crustal material,which are important in understanding orogeny and crust-mantle reaction. Nevertheless,how well has40Ar /39Ar technique developed at present？ How exactly can it date natural geological sample？ Why seldom was excess argon recognized within yang samples and those from high-pressure belt？ Does pressure affect the closure temperature of argon isotope system？ Can the age spectrum of K-feldspar reflect the thermohistory truly？ What should we be ware when using40Ar /39Ar and UPb method？ These problems are discussed carefully in this paper in order to stimulate a broader discussion on40Ar /39Ar geochronology.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2014年第2期326-340,共15页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41025010
41221002)
中国科学院战略性先导科技专项(XDB03020203)联合资助
