Rates of subcritical cracking and long-term rock erosion
Rates of subcritical cracking and long-term rock erosion
复制标题
DOI：
10.1130/g45256.1
复制
发表时间：
2018-11-01
期刊：
影响因子：
5.8
通讯作者：
Whitten, J.
中科院分区：
文献类型：
--
作者：
Eppes, M. C.;Hancock, G. S.;Whitten, J.
基岩破裂是岩石侵蚀和随后的地表过程的关键因素。在这里，我们测试的假设，岩石的敏感性亚临界开裂，一种特定类型的压裂，显着驱动和限制岩石侵蚀。我们测量了Be-10衍生的侵蚀速率，抗压强度，和裂纹特性20露头的不同岩石单位（石英岩，花岗岩，和两个变质砂岩）在北方蓝岭山脉的弗吉尼亚州（美国）。我们还测量了亚临界开裂指数（n），查尔斯定律的速度常数（A），和断裂韧性（K-IC）的样品从四个相同的露头，每种岩石类型的代表。侵蚀率从1.16 +/- 0.67到32.3 +/- 7.8米/年不等。我们发现，在四个岩石单元中，平均侵蚀速率与三个亚临界开裂参数之间存在很强的相关性（R-2 > 0.85，p < 0.05），但与抗压强度无关（R-2 = 0.6; p > 0.1）。同时发现，裂缝长度与n之间存在相关关系（R-2 = 0.91，p < 0.05）。后者的相关性与已发表的模型预测是一致的，进一步表明亚临界开裂和岩石侵蚀之间的机械联系。我们推断，亚临界开裂参数密切相关的侵蚀率，因为亚临界开裂是机械风化的主导过程，导致正反馈有关亚临界开裂率，裂纹长度，孔隙度和水的可及性。这些数据是第一个直接测试和支持亚临界开裂可以设定长期岩石侵蚀速度的假设。
Bedrock fracture is a key element of rock erosion and subsequent surface processes. Here, we test the hypothesis that rock's susceptibility to subcritical cracking, a specific type of fracturing, significantly drives and limits rock erosion. We measured Be-10-derived erosion rates, compressive strength, and crack characteristics on 20 outcrops of different rock units (quartzite, granite, and two metasandstones) in the northern Blue Ridge Mountains of Virginia (USA). We also measured the subcritical cracking index (n), Charles's law velocity constant (A), and fracture toughness (K-IC) of samples from four of the same outcrops, representative of each rock type. Erosion rates range from 1.16 +/- 0.67 to 32.3 +/- 7.8 m/m.y. We find strong correlations- across the four rock units-between average erosion rates and the three subcritical cracking parameters (R-2 > 0.85, p < 0.05), but not compressive strength (R-2 = 0.6; p > 0.1). We also find a correlative relationship between n and outcrop fracture length (R-2 = 0.91; p < 0.05). The latter correlation is consistent with that of published model predictions, further indicating a mechanistic link between subcritical cracking and rock erosion. We infer that subcritical cracking parameters closely tie to erosion rates, because subcritical cracking is the dominant process of mechanical weathering, leading to positive feedbacks relating subcritical cracking rates, crack length, porosity, and water accessibility. These data are the first that directly test and support the hypothesis that subcritical cracking can set the pace of long-term rock erosion.