汕头市礐石花岗岩地貌特征及其成因

Granite Landforms and Their Origins in the Queshi Area of Shantou,Guangdong,China

以广东汕头礐石地区景区内各类花岗岩地貌为研究对象,利用地表调查和洞穴调查,在国内外已有研究的基础上,对礐石地区花岗岩的地貌特征、成因及形成年代进行探讨。结果表明:礐石山由燕山晚期花岗岩构成,于中更新世晚期之前就受风化作用;礐石花岗岩石节理的性质和礐石地区高温多雨的热带季风气候下产生的风化作用,是形成礐石花岗岩地貌的基本因素;礐石地区花岗岩山体主要分为石蛋山、峰林山、馒头山3种类型;洞穴可划分石核洞,崩塌洞穴,裂隙洞和龛4类。

Granite,a principal component of continental crust,emerges at the Earth's surface through crustal movements,creating diverse landforms.The Queshi region,comparable to Huangshan in its granite hilly landscape,stands as a representative granite landform in China,yet its origin remains incompletely studied.This investigation utilizes surface landscape and cave analyses to elucidate the characteristics and determining factors of granite landforms in the Queshi region,to comprehend the formation mechanisms of these unique landforms.In the surface investigation,field surveys and aerial photography,employing a DJI Phantom 4 RTK drone,were utilized to measure the morphology and dimensions of exposed rock egg sizes on cliff faces and joint spacing.The survey results facilitated an overall classification of surficial landscapes,encompassing the proportion of rock egg sizes on the mountain and the spacing between the vertical and horizontal joints.To assess mountain development concerning stone eggs,cave orientation and elevation were determined using a rangefinder and GPS measurements,while different contact relationships between stone eggs were investigated.By amalgamating domestic and international granite development theories with field investigation results,this study delves into the geological structure of the surrounding areas,the characteristics of granite landforms,and the factors governing the landform formation of granite geomorphology in the Queshi area.The findings indicate that 1)rocks in the Queshi scenic area have evolved into various rock eggs through subsequent weathering processes,manifesting as grotesque formations resembling humans,genies,or animals,and 2)granite mountain bodies in the Queshi region can be categorized into three types:rock egg mountains,peak forest mountains,and steamed bun mountains.Stone egg mountains exhibit a unique form with round,large stone eggs stacked atop each other,peak forest mountains comprise elongated rock eggs or blocks due to narrowly spaced vertical joints,while steamed bun mountains lack obvious joints and fractures,presenting gently rounded mountain shapes.Furthermore,3)granite caves in the Queshi scenic area are classified into four categories based on different formation processes:core stone caves,collapsed caves/rock egg caves,fissure caves,and niches.Core stone caves form when weathered material in the gaps between stone cores is carried away by flowing water without causing any movement of the core stones.Fissure caves,relatively rare and small in scale in the Queshi scenic area,are formed along large fractures created by bedrock breaks.Niches are concave grooves formed at the base of rock bodies or rock eggs,buried by rock debris or soil,storing more rainwater than bare rock surfaces and enhancing chemical weathering.After external runoff removed the debris,the rock base became exposed and formed concave grooves.Finally,4)the weathering crusts of the Queshi region formed before the subsidence of the Rongjiang fault,during which the Queshi Mountains experienced relative uplift.Consequently,the weathering crusts continued to weather,forming the present granite landforms.Weathering occurs through the rock joints of the parent rock of the weathered crusts,with the degree of damage to the rock determined by joint density.The greater the joint density,the more extensive the damage;conversely,the smaller the joint density,the less the damage.Therefore,mountain morphological differences in the Queshi region are primarily caused by variations in joint spacing rather than climate or rock-type influences.