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认识风化作用过程的关键在于确定保留于风化剖面中母岩的结构、构造及体积等的变化程度。如果给定元素 (如Ti,Zr或Th)不活动 ,等元素质量平衡法 (IMB)就常用来估算渐进风化过程体积的变化。风化产物的岩石组构常以完全保留原岩组构的原生矿物的假象交代为特征 ,这就意味着等体积风化过程中 ,体积的变化也就是形态的改变 ,因为边界条件不允许有水平方向的应变 ,所以 ,塌陷和膨胀应该导致相应的压实和伸展。风化产物微弱的岩石组构可以通过低场磁化率各向异性技术 (AMS)进行精确的定量测定。首次报道同时利用AMS和IMB法对两种不同环境条件下形成的风化剖面 (产于喀麦隆前寒武纪变质岩上的复杂红土剖面及摩洛哥第四纪玄武岩岩流上的风化剖面 )的研究结果 :其中红土剖面可划分为下部腐泥岩带 (>12m)和上部的富铁结核带 (约 4m) ,其主要特点是有大量的新生磁性矿物 (如针铁矿、赤铁矿和尖晶石 )出现 ,以及弱的但十分一致的磁组构。导致低磁化率值 (50× 10 - 9m3/kg)的腐泥岩化作用保留了片麻岩母岩中的线形构造。AMS关于等体积风化的证据与IMB法Th的结果一致 ,而Ti和Zr却分别显示了明显的塌陷和膨胀 (达 50 % )。导致磁化率增强 (由于尖晶石族矿物出现 ,磁化率高达 (50 0～ 70 0 )×10 - 9m3/kg) ,并使结核?
The key to understanding the weathering process lies in determining the degree of variation in the structure, structure, and volume of the parent rock remaining in the weathering profile. If a given element (such as Ti, Zr, or Th) is inactive, the isobaric mass balance method (IMB) is often used to estimate the change in volume of a progressive weathering process. The rock formation of weathering products is often characterized by the illusion of primary minerals that completely retain the original rock structure, which means that the volume change during the same-volume weathering is also a change in morphology because the boundary conditions do not allow for horizontal orientation Therefore, collapse and expansion should result in corresponding compaction and extension. Weakly weathered rock formations can be accurately quantified by Low Field Magnetic Susceptibility Anisotropy (AMS). It is the first time to report the results of the study on the weathering profiles formed by two different environmental conditions (the laterite-Cambrian metamorphic red clay profile on the Precambrian metamorphic rock in Cameroon and the Quaternary basaltic rock flow in Morocco) by AMS and IMB simultaneously. The red clay profile can be divided into the lower sapropel rock zone (> 12m) and the upper iron-bearing nodule zone (about 4m). The main features of this section are the large number of newborn magnetic minerals (goethite, hematite and spinel) Appear, as well as weak but very consistent magnetic organization. The sapropellation of the low susceptibility values (50 × 10 -9 m 3 / kg) retained the linear structure in the gneiss parent rock. Evidence from the AMS for equal-volume weathering is consistent with the results from the IMB Th, whereas Ti and Zr show significant collapse and swelling (up to 50%), respectively. As a result, the magnetic susceptibility increases (due to spinel minerals, the magnetic susceptibility reaches as high as (50 0 ~ 70 0) × 10 -9 m 3 / kg)