The chronology and tectonic style of landscape evolution along the elevated Atlantic continental margin of South Africa resolved by joint apatite fission track and (U-Th-Sm)/He thermochronology
The chronology and tectonic style of landscape evolution along the elevated Atlantic continental margin of South Africa resolved by joint apatite fission track and (U-Th-Sm)/He thermochronology
复制标题
联合磷灰石裂变径迹和 (U-Th-Sm)/He 热年代学解决了南非大西洋隆起大陆边缘景观演化的年代学和构造风格
DOI：
10.1002/2015tc004042
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发表时间：
2016
期刊：
影响因子：
4.2
通讯作者：
Wildman M
中科院分区：
文献类型：
--
作者：
Wildman M
大西洋型大陆边缘长期以来一直被认为是整个后裂陷阶段的“被动”构造环境。最近的研究对这些边缘的长期稳定性提出了质疑，并表明裂后隆起和先前存在的结构的重新激活可能是大陆边缘演化的共同特征。南非西部大陆边缘的纳马夸兰地区的特点是普遍存在断层基底，但缺乏保存较年轻的地质地层来限制裂后构造断层活动。在这里，我们提出了第一个系统的研究，使用联合磷灰石裂变径迹和磷灰石（U-Th-Sm）/He热年代学，以更好地了解整个地区的景观演化的年代学和构造样式。磷灰石裂变径迹年龄范围为58.3 ± 2.6 ~ 132.2 ± 3.6 Ma，平均径迹长度为10.9 ± 0.19 ~ 14.35 ± 0.22 µm，平均（U-Th-Sm）/He样品年龄范围为55.8 ± 31.3 ~ 120.6 ± 31.4 Ma。这些数据的联合反演模型揭示了两个不同的冷却事件在大约150-130 Ma和110-90 Ma的有限冷却在新生代。基于这些热历史的剥蚀估计预测约1-3公里的剥蚀与两个主要的构造事件相吻合。第一个事件发生在早白垩世，是由大陆裂谷作用和同生裂谷地形的发展和移除所驱动的。第二个事件发生在晚白垩世，包括基底结构的局部再活化以及区域性地幔驱动的隆升。相对构造稳定性占主导地位，在新生代，并在此期间的区域剥蚀被限制在1公里以内。
Atlantic‐type continental margins have long been considered “passive” tectonic settings throughout the entire postrift phase. Recent studies question the long‐term stability of these margins and have shown that postrift uplift and reactivation of preexisting structures may be a common feature of a continental margin's evolution. The Namaqualand sector of the western continental margin of South Africa is characterized by a ubiquitously faulted basement but lacks preservation of younger geological strata to constrain postrift tectonic fault activity. Here we present the first systematic study using joint apatite fission track and apatite (U‐Th‐Sm)/He thermochronology to achieve a better understanding on the chronology and tectonic style of landscape evolution across this region. Apatite fission track ages range from 58.3 ± 2.6 to 132.2 ± 3.6 Ma, with mean track lengths between 10.9 ± 0.19 and 14.35 ± 0.22 µm, and mean (U‐Th‐Sm)/He sample ages range from 55.8 ± 31.3 to 120.6 ± 31.4 Ma. Joint inverse modeling of these data reveals two distinct episodes of cooling at approximately 150–130 Ma and 110–90 Ma with limited cooling during the Cenozoic. Estimates of denudation based on these thermal histories predict approximately 1–3 km of denudation coinciding with two major tectonic events. The first event, during the Early Cretaceous, was driven by continental rifting and the development and removal of synrift topography. The second event, during the Late Cretaceous, includes localized reactivation of basement structures as well as regional mantle‐driven uplift. Relative tectonic stability prevailed during the Cenozoic, and regional denudation over this time is constrained to be less than 1 km.