Effects of climatic environment on rock weathering

(1)为了研究岩石类型和地貌环境对风化速率的影响，采用微量失重技术进行了野外试验。八种类型的岩石：花岗岩，花岗闪长岩，辉长岩，石灰岩，安山岩，流纹岩，结晶片岩和凝灰岩，直径为3.5厘米，厚度为1厘米，被装入尼龙网袋，并放置在日本中部花岗闪长岩山坡上的四个不同位置10年。结果表明：（1）灰岩具有明显的风化特征;（2）饱和环境下的灰岩和花岗闪长岩对化学风化的敏感性较高;（3）地面和非饱和土层的物理风化作用占主导地位。(2)在一个集水区进行了10年以上的野外风化试验。将片剂暴露在具有不同风化条件的三个位置。片剂重量随时间线性下降 关于我们 地表<-1><-1>、含水层和含水层中的土壤水污染率分别为0.022wt%yr ^、0.013wt%yr ^和0.42wt%yr <-1>^。在地面和含水层上方风化10年后，仅观察到片剂表面的微小变化。相比之下，含水层中的岩片风化明显，黑云母的风化尤为明显，而斜长石、钾长石、石英和角闪石的风化则为轻微/中度。花岗闪长岩的风化作用是通过矿物颗粒边界的初始溶解（化学过程）和随后的矿物颗粒的剥离（物理过程）进行的。为了评价仅由化学过程（溶解）引起的风化量，使用流通式反应器在20 ℃和pH 6-7下对Granodiazole片剂进行了实验室溶解实验。所获得的速率为0.0078-0.010 wt% yr^<-1>，比含水层中的现场速率慢1.50倍。这一结果表明，物理过程的贡献，在含水层中的花岗闪长岩风化，是非常大的化学过程相比，和两个过程的相对强度在10年的风化过程中估计为化学：物理= 1：50。(3)在日本西南部的纪海岛，许多基座岩石在全新世上升的珊瑚礁阶地的表面上发育，其出现日期已知。基座形成于巨砾下方，巨砾被认为是由海啸搬运而来，并在出现之前就沉积在礁坪上。假设巨石保护下面的石灰岩梯田从降雨溶液，这些石灰岩梯田的表面降低率进行了评估，从高度的岩石和他们的形成时期。结果表明，6000年来平均下降速率为205 mm/ky。少

(1) To study the effect of rock type and geomorphic setting on weathering rates, field experiments were performed using the microweight loss technique. Tablets of eight types of rock : granite, granodiorite, gabbro, limestone, andesite, rhyolite, crystalline schist and tuff with a diameter of 3.5 cm and a thickness of 1 cm, were enclosed in nylon mesh bags and placed in four distinct locations on a granodiorite hillslope in central Japan for 10 years. The main findings are that (1) limestone has distinctive weathering characteristics compared to other rocks ; (2) limestone and granodiorite in a saturated environment have high susceptibility to chemical weathering ; and (3) physical weathering is dominant on the ground and in unsaturated soil layers.(2) Field weathering experiments using granodiorite tablets were conducted at a catchment over 10 yr. The tablets were exposed at three positions having different weathering conditions. The weight of the tablets linearly decreased with time … More and the rates were 0.022 wt% yr^<-1> for the ground surface, 0.013 wt% yr^<-1> for above the aquifer and 0.42 wt% yr^<-1> for in the aquifer. Only minor change of the tablet surface was observed after 10 yr of weathering at the ground surface and above the aquifer. In contrast, the tablets in the aquifer were remarkably weathered, and weathering of biotite was particularly noticeable while those of plagioclase, K-feldspar, quartz, and hornblende were minor/moderate. The weathering of granodiorite is inferred to proceed by initial dissolution of mineral grain boundary (chemical process) and subsequent detachment of the mineral grain (physical process). To evaluate the amount of weathering caused only by the chemical process (dissolution), a laboratory dissolution experiment was conducted on the granodiorite tablet using a flow through reactor at 20 ℃ and pH 6-7. The obtained rates, 0.0078-0.010 wt% yr^<-1>, were 〜50 times slower than the field rate in the aquifer. This result shows that the contribution of the physical process, in granodiorite weathering in the aquifer, is very large compared to the chemical process, and relative intensities of the two processes during the 10 yr weathering are estimated to be chemical : physical = 1 : 〜50.(3) In Kikai-jima, southwestern Japan, many pedestal rocks develop on the surface of Holocene raised coral-reef terraces with known dates of emergence. Pedestals are formed just under boulders which are considered to have been transported by tsunami and settled on a reef flat before emergence. On the assumption that boulders protect underlying limestone terrace from rainfall solution, the rate of surface lowering of these limestone terraces was evaluated from the height of pedestals and the period of their formation. The result showed that the mean lowering rate during 6000 years is 205 mm/ky. Less