近日，美国犹他州立大学教授Alexis K. Ault及其小组研究了用褐铁矿（U-Th）/He热年代学追踪古代不整合发育。这一研究成果于2025年3月4日发表在《地质学》杂志上。

岩石记录中的不一致性反映了构造、气候和/或沉积路线系统的变化。确定亚不整合面岩石何时到达近地表环境（<1公里深度）仍然是一个挑战，阻碍了因果关系的确定。研究组使用（U-Th）/He分析褐铁矿（磁铁矿后的赤铁矿假晶）的新方法解决了这个问题。褐铁矿化重置了（U-Th）/He系统，并将岩石与近地表的居住联系起来。

研究组应用这个工具来记录深层不整合发育的时间。他们整合了褐铁矿（U-Th）/He（褐铁矿He）和电子背散射衍射（EBSD）数据，以限制美国西部科罗拉多前线山脉主要不一致性正下方结晶基底中褐铁矿化的最小时间。褐铁矿由赤铁矿晶粒组成，没有残留的磁铁矿，并表现出晶体学取向关系，表明褐铁矿化是通过近地表的氧化发生的。单个火星的He测年范围为1042±24 Ma至127±8 Ma（n=52）。褐铁矿He日期与成冰纪之前近地表的褐铁矿化和相关基底居住一致，可能早在约1040 Ma。

热历史模型表明，该褐铁矿He定年光谱合理地反映了显生宙埋藏和再加热过程中不同大小的He扩散域的部分He损失。该工作突出了科罗拉多前缘山脉不整合发育的古老性。研究组建议将成对褐铁矿He EBSD分析作为一种新的地质鉴识工具，用于量化低温蚀变、古地形演化和不整合发育的时空模式。

附：英文原文

Title: Tracking ancient unconformity development with martite (U-Th)/He thermochronometry

Author: Jordan L. Jensen, Alexis K. Ault

Issue&Volume: 2025-03-04

Abstract: Unconformities in the rock record reflect change(s) in tectonics, climate, and/or sediment routing systems. Pinpointing when sub-unconformity rocks reached the near-surface environment (<1 km depth) remains a challenge that inhibits assignment of causality. We addressed this problem with a new approach using (U-Th)/He analyses of martite (hematite pseudomorph after magnetite). Martitization resets the (U-Th)/He system and links rocks to residence in the near surface. Here, we applied this tool to document the timing of unconformity development in deep time. We integrated martite (U-Th)/He (martite He) and electron backscatter diffraction (EBSD) data to constrain the minimum timing of martitization in crystalline basement directly below a major nonconformity in the Colorado Front Range, western United States. Martite comprises hematite crystallites with no remnant magnetite and exhibits crystallographic orientation relationships that suggest martitization occurred by oxidation in the near surface. Individual martite He dates range from 1042 ± 24 Ma to 127 ± 8 Ma (n = 52). Martite He dates are consistent with martitization and associated basement residence in the near surface prior to the Cryogenian, potentially as early as ca. 1040 Ma. Thermal history models show that our spectrum of martite He dates reasonably reflects partial He loss from variably sized He diffusion domains during Phanerozoic burial and reheating. Our work highlights the antiquity of unconformity development in the Colorado Front Range. We suggest paired martite He-EBSD analysis as a new forensic tool for quantifying spatiotemporal patterns of low-temperature alteration, paleotopographic evolution, and unconformity development.

DOI: 10.1130/G53010.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G53010.1/652553/Tracking-ancient-unconformity-development-withredirectedFrom=fulltext