Discovery of especially large bubble-like miarolitic granites in Laoshan and its geological and geomorphic significance
Recently, some especially large bubble-like miarolitic caves in A-type granites in Laoshan have been discovered with the largest diameter of up to 3.1 m, far exceeding the granitic miarolitic caves previously reported, thus adding new knowledge to geology. This helps to study the primary environment for granites formed in Laoshan and also reveal genesis of “natural-mortar” micro-landform for granites in Laoshan. The existence of a new genesis type—“bubble-like miarolitic caves” of speleology is also confirmed by this discovery. Especially large bubble-like miarolitic caves are rare geological relics with high ornamental, science and tourism value.
Granitic Caves from the Achala Batholith in the Province of Córdoba, Argentina: A Study on Three Particular Stories with a Common Past
The igneous or magmatic rocks, especially those with granitic composition, constitute a special type of geomorphological substrate. As from its exposure on the Earth´s surface and the modelling that eventually takes place on them, different landscapes with specific characteristics emerge where inherited and present shapes coexist making possible to reconstruct the landscape evolution of the massif. Traditionally, in the studies of granitic landscapes, only the forms observed on the surface are described, whereas those that develop underground are not often taken into consideration. In this paper three caves are analysed in order to specify their particular origins and classify it according to its morphological characteristics and the genetic processes involved. These caves are located on the same scarp of the rock massif and, therefore, share a geological and geomorphological common history, which is shown in their hypothesis of evolution. In addition, based on the type of cavity and certain observations of their environments it is possible to establish a relative chronological order in their ages of formation. In this context, it is proven that these underground environments (as the other geographical accidents and granitic landforms) are not chaotic but - on the contrary- they are structured in geological and geomorphological processes over time and they respond to a common evolutionary framework to the entire rock massif. More detailed studies on these environments can develop in new methodological tools to understand the geological history of the granitic landscape they are located in.
40Ar/39Ar geochronology and exhumation of mylonitized metamorphic complex in Changle-Nanao ductile shear zone
New40Ar/39Ar plateau ages from rocks of Changle-Nanao ductile shear zone are 107.9 Ma(Mus), 108.2 Ma(Bi), 107.1 Ma(Bi), 109.2 Ma(Hb) and 117.9 Ma(Bi) respectively, which are concordant with their isochron ages and record the formation age of the ductile shear zone. The similarity and apparent overlap of the cooling ages with respective closure temperatures of 5 minerals document initial rapid uplift during 107–118 Ma following the collision between the Min-Tai microcontinent and the Min-Zhe Mesozoic volcanic arc. The40Ar/39 Ar plateau ages, K-Ar date of K-feldspar and other geochronologic information suggest that the exhumation rate of the ductile shear zone is about 0.18–1.12 mm/a in the range of 107–70 Ma, which is mainly influenced by tectonic extension.