自然演化碎屑锆石裂变径迹的初始径迹长度及径迹长度的影响因素探究

Due to the lack of the effective thermal indicator, it was hard to reconstruct the thermal history of the deep basin with high temperature, which causing a significant impact on the study of the deep hydrocarbon source rocks evolution. Zircon fission track thermochronometry, with the higher annealing temperature, can be used as an effective method to study thermal history of the deep sedimentary basin with high temperature. Due to the special annealing character of fission track, annealing rate was used to reflect the annealing degree of fission track. Thus, the initial track length is very important parameter for the study of annealing rate, annealing behavior and annealing model. However, the value of the initial track length in zircon found in literature were uncertainty and difficulty for the calculation of annealing rate. Distinguished from previous research using the standard igneous zircon samples, this study plan to use natural borehole samples from the Cenozoic strata in the sedimentary basin to investigate the annealing behavior of zircon fission track. Based on the measured track lengths of detrital zircon samples in the shallow, we apply the maximum value method, average value method and calibration method to determine the initial track length, and further explore the influence of the source thermal event, radiation damage and heating rate on the track length. The main purpose of this project is to study the initial track length of detrital zircon fission track, and preliminarily solve the controversial issues about value of the initial track length in zircon fission track, and provide an important foundation for studying annealing rate.

沉积盆地深层较高温度的热历史由于缺乏有效古温标进行热史恢复，一直是困扰深部烃源岩演化研究的难题。锆石裂变径迹热定年技术具有较高退火温度，能揭示深层较高温度的热历史。裂变径迹具有退火特性，常用退火率来表示其退火程度。初始径迹长度是研究裂变径迹退火率、退火行为、退火模型的重要参数。然而，国际上关于锆石裂变径迹的初始径迹长度并未确定和统一值。区别于前人使用的火成岩锆石标准样品，本课题拟利用沉积盆地新生界地层的钻井自然演化样品探讨碎屑锆石裂变径迹的退火行为。运用浅层未受退火作用影响的碎屑锆石实测径迹长度，结合最大值法、平均值法和校正值法确定锆石裂变径迹的初始径迹长度，并进一步探究母源区热事件、辐射损伤和增温速率等对径迹长度的影响。本文旨在通过探究自然演化碎屑锆石裂变径迹的初始径迹长度，初步解决锆石裂变径迹的初始径迹长度存在争议的问题，从而为锆石裂变径迹退火率的研究提供重要基础。

沉积盆地深层较高温度的热历史由于缺乏有效古温标进行热史恢复，一直是困扰深部烃源岩演化研究的难题。锆石裂变径迹热定年技术具有较高退火温度，能揭示深层较高温度的热历史。裂变径迹具有退火特性，常用退火率来表示其退火程度。初始径迹长度是研究裂变径迹退火率、退火行为、退火模型的重要参数。然而，国际上关于锆石裂变径迹的初始径迹长度并未确定和统一值。区别于前人使用的火成岩锆石标准样品，本课题利用沉积盆地新生界地层的钻井自然演化样品探讨碎屑锆石裂变径迹的退火行为。运用浅层未受退火作用影响的碎屑锆石实测径迹长度，结合最大值法、平均值法和校正值法确定了自然演化碎屑锆石裂变径迹的初始径迹长度（L0）为12.97 µm。高温热背景渤海湾盆地深钻孔样品的锆石裂变径迹开始发生退火的温度（220 °C）高于低温热背景塔里木盆地深钻孔样品的锆石裂变径迹开始发生退火的温度（170 °C），揭示了增温速率是导致不同热背景下自然演化碎屑锆石裂变径迹开始退火温度和退火行为存在差异的原因。明确了径迹的各向异性、母源区热事件、沉积盆地热事件、辐射损伤和实验室蚀刻条件等对锆石裂变径迹长度的影响。本文旨在通过探究自然演化碎屑锆石裂变径迹的初始径迹长度，初步解决锆石裂变径迹的初始径迹长度存在争议的问题，从而为锆石裂变径迹退火率的研究提供重要基础。