| The rock base that constitutes Lieyu and Kinmen is the Mesozoic Era granite gneiss, intruded with different kinds of igneous rock. On top of the laccolith are the Kinmen layer, red soil layer, basalt layer, and modern sedimentary layer. The basalt molten rock from the Tertiary Period covers the weathered granite gneiss or the Tertiary Period sedimentary rock, and they are mostly exposed in the hills and southern coastlines of Lieyu.
During the Ice Age in the Quaternary Period, Lieyu and Kinmen were connected to mainland China since the sea level dropped down by more than 100 meters. At the end of the Ice Age, global climate warmed up again, and the melted ice in the Arctic and Antarctic caused the global sea level to rise back up, resulting in Lieyu and Kinmen being separated from Mainland China. After tectonic movements and sea level changes, the smooth gneiss hills formed Lieyu’s backbone, among which are plateaus and lowlands. The complex rocks, geological structures, and years of weathering and terrain changes have given Lieyu’s coastlines and mountains their exciting appearances.
The birth of Lieyu and Kinmen started near the end of the Triassic period. The wrinkle area in Nanling experienced a series of tectonic movements such as the Indo-China movement, Yanshan movement, and Himalayas movement, the island of Lieyu and Kinmen took shape at the eastern edge of the wrinkle (the southeast coastline of China).
As for the history of the geology, the Yanshan movement took place between 1000 to 2000 million years ago resulted in fierce faulting in the southeastern region of Fuchien Province with pervasive lava activities. This resulted in several deep faults which controlled volcanism and allowed magma to intrude and form hidden, gigantic bodies of granite. Lieyu and Kinmen are located at the right side of the deep fault between Changle and Nan-ao; at the center of the metamorphic rock belt in the east of Fuchien, the granite that forms the base is the product of the Yanshan movement. Therefore, Lieyu, Kinmen, and the nearby Fuchien coastline are of the same geological structure and igneous rock. They have similar rock formation, which is mainly gneiss, mixed rocks, and granite (Fuchien Geology Magazine, 1985).
According to dating, the age of granite gneiss base is about 139 million years, and the age of the intruding granite is about 101 million, making them both a product of the Mesozoic Era. When this rock base formed deep under the crust, pegmatite and basic rocks also intruded. Through the argon method, geologists have determined that the age of the basic rocks in Fuchien area (including Kinmen) is about 76-91 million years, and it was also determined that after the Yanshan movement, the ground structure became a product of wearing and tearing, which can be seen as an age indicator for the Yanshan movement and related acidic granite that formed magma. Afterwards, the base was covered by the Kinmen layer and red soil layer. In the Miocene epoch (about 13 million years ago), the expansion of Nanhai caused lava activities in the ground gaps and resulted in the basalt magma eruption in Lieyu and the flow in Yangshan, Dashanding, and Nanshantou. The sedimentary material on the surface is mostly the product of the weathering, transferring, and sedimentation formed since the Quaternary Period.
|