Influence of Monsoon Climate on Chemical Weathering of Granitic Regoliths

Abstract

Chemical weathering of silicate rocks at the Earth's surface is a fundamental process regulating biogeochemical cycles and modulating global climate over geologic timescales (Berner et al., 1983;West et al., 2005). However, the feedback between weathering and climate still suffers from uncertainty, which mainly originates from the difficult isolation of the respective influences of climate and tectonics on weathering and the use of weathering proxies in sedimentary records (Herman et al., 2013). Moreover, silicate weathering transferring elements from continent to seawater influences the marine sedimentary records, and the flux of elements is primarily controlled by chemical weathering rates (Bataille et al., 2017). Therefore, identifying the controlling factors of chemical weathering is critical to understanding the feedback between weathering and climate and interpreting past climate change by records of weathering. Some studies examined the factors influencing weathering rates of silicate rocks, such as climate, lithology, tectonics, topography, and biota (e.g.,

Characteristics and Influencing Factors of the Granite Weathering Profile: A Case Study of a High Latitude Area in Northeastern China

“…According to the classical weathering theory, in the vertical weathering profile [110,111,125], the weathering degree progressively increases with decreasing depth [191]. However, the chemical weathering degree in the studied profile exhibits the opposite pattern (Figure 7), unique to this region.…”

“…In addition, we selected the CDF value, a stable index that can represent the quality change of profile elements, to calculate the weathering products. The CDF can reflect the mass loss of profile elements, where a CDF < 0 represents the input of foreign substances [110]. The calculated results show that the CDF values of the semi-weathered layer and the saprolite layer are less than 0, which further proves the input of foreign substances in the process of granite weathering.…”

“…K mainly occurs in minerals such as potassium feldspar, biotite, and hornblende, and mineral weathering leads to the loss of K [140]. But τk is abnormally enriched in the semi-weathered layer and saprolite layer, suggesting the possibility of external dust (such as potassium feldspar) input [110]. Compared with τk and τNa, the τCa and τMg present positive values in the profile, indicating the enrichment of Ca and Mg in the profile.…”

“…When CDF = 0, there is no loss of soluble elements in the weathering samples compared with the parent rock; CDF > 0 represents the total mass loss of elements during weathering. The CDF value does not exceed 0.5 because a large proportion of the primary Si is fixed in insoluble quartz and large amounts of Si, Fe, and Al released from the original mineral are retained in the clay minerals, so the CDF value is often considered a reliable indicator of chemical weathering [109][110][111].…”