Effects of climatic environment on rock weathering

(1)为研究岩石类型和地貌环境对风化速率的影响，采用微失重技术进行了野外试验。由花岗岩、花岗闪长岩、辉长岩、石灰岩、安山岩、流纹岩、结晶片岩和凝灰岩等八种岩石组成的石片，直径3.5厘米，厚度1厘米，被包裹在尼龙网袋里，放置在日本中部花岗闪长岩山坡上的四个不同地点，历时10年。主要发现：(1)与其他岩石相比，石灰岩具有明显的风化特征；(2)饱和环境中的石灰岩和花岗闪长岩对化学风化的敏感性较高；(3)在地面和非饱和土层中，物理风化作用占主导地位。(2)利用花岗闪长岩片对某集水区进行了10余年的野外风化试验，并在不同风化条件下的3个位置进行了暴露。随着时间的推移，片剂的重量呈线性下降趋势，地表为0.022 wt% yr^<-1>，含水层以上为0.013 wt% yr^<-1>，含水层内为0.42 wt% yr^<-1>。经过10年的风化作用，地表及含水层以上的石片表面仅发生了微小的变化。含水层中的片剂风化作用明显，其中黑云母的风化作用尤为明显，斜长石、钾长石、石英和角闪石的风化作用较轻或中等。花岗闪长岩的风化过程是初始矿物晶界的溶蚀（化学过程）和随后矿物晶界的剥离（物理过程）。为评价化学过程（溶蚀）对该花岗闪长岩片的风化作用，在20℃、pH 6 ~ 7条件下，采用流动反应器对其进行了室内溶蚀试验。得到的速率为0.0078 ~ 0.010 wt% yr^<-1>，比含水层中实际速率慢50倍。结果表明，在花岗闪长岩含水层中，物理过程的作用比化学过程的作用要大得多，在10年的风化过程中，两个过程的相对强度估计为化学：物理= 1∶50。(3)在日本西南部的菊海岛，全新世凸起的珊瑚礁阶地表面发育了许多台地岩，其出现日期已知。基座就在巨石下面形成，这些巨石被认为是被海啸冲走的，在出现之前就在礁滩上沉淀下来了。假设巨石保护下面的石灰岩阶地不受雨水的侵蚀，从基座的高度和它们形成的时期来评估这些石灰岩阶地的表面下降速度。结果表明，6000年的平均下降速率为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