郯庐断裂安徽段桴槎山韧性剪切带的形成时限初探

测算全新世之前地质事件过程时间(需要精度万年级),没有现行可以采用的定年方法(误差精度百万年级),因此有必要探索构造地质自组织的时限定年方法(万年级)。本文以滨西太平洋构造系郯庐断裂带为实例,通过石英位错密度法测得差异应力σ分别为:糜棱岩化岩石为141.17MPa,糜棱岩为191.88MPa,超糜棱岩为223.31MPa;相应的应变速率分别为3.760×10^-13s^-1、7.705×10^-13s^-1和1.087×10^-12s^-1;体积因子f_v相应依次为0.7923、0.6340和0.5886;所得构造形成时限t依次为2.08×10⁴a、1.83×10⁴a和1.44×10⁴a。为检查精度,对同一剪切带不同应变强度样品进行系统内的比较分析,剪切带边缘样品的t值明显大于剪切带中心部位,在目前尚无地球化学方法可供借用检验的条件下,本文首次提出的自检验方法是一种提高精度的有效尝试。文中有关时限定年的系统讨论,是对以往时限定年的校正和总结,这有助于构造地质学定量化的发展,也是对构造年代学的一项补充。

DURATION OF STRUCTURAL DEFORMATION OF DUCTILE SHEAR ZONE IN FUCHASHAN HILL, ANHUI SECTOR OF THE TAN-LU FAULT

So far there is no practical method to determine the duration of geological event before Holocene, and it is necessary to explore the determination means in tectonic field. In this paper, we took the Fuchashan ductile shear zone, Anhui sector of the Tan(cheng)-Lu(jiang) fault as an example to study the duration, and got the following conclusions by the work. The differential stresses of the mylonitized rock, mylonite and ultra-mylonite were 141.17 MPa, 191.88 MPa and 223.31 MPa respectively, the corresponding strain rates were 3.760?10^-13 s^-1, 7.705?10^-13s^-1 and 1.087?10^-12s^-1 respectively. The volumetric factors for the three were 0.7923, 0.6340 and 0.5886 respectively, and the corresponding duration were 2.08?10⁴ a, 1.83?10⁴ a and 1.44?10⁴ a respectively. Checking up by analyzing and comparing varied strain intensities of different samples from the same ductile shear zone, we found that the duration of the sample from marginal position was evidently longer than that from central part. The self-test method might be a new attempt in enhancing the precision as to the situation in case of without available geochemical methods. The systematic discussion about duration determination was revision and summarization of the work ever before, which should benefit for the quantification of tectonic geology and tectono-chronology.