Research On Volcanic Geology And New Tectonics In Wulanhada Region, Inner Mongolia

Quaternary Volcanic Cluster of Wulanhada belongs to the south edge in the Plateau, lying from the city of Baiyinchagan to Wulanhada of Chahaeryouyihouqi in Inner Mongolia. As an active volcano, it has experienced many volcanic actions over a long period of time. The chronology of its eruptions can be divided into two phrases including the late Pleistocene explosion phrase and the Holocene explosion phrase. It is also the only volcanic cluster which has erupted in Holocene. The rock types are tephrite and alkali olivine basalt.They are low-part-melt primary magma in the upper mantle,continent rift vally basalt , which are not mixed with any substance from the Crust.The activity of the volcano cluster in Wulanhada began in the late stage of late Pleistocene and stopped in the Holocene. The volcano cluster includes 30 volcanoes, seventeen of which are late Pleistocene and thirteen are Holocene. All of these consist of basaltic materials and lava flows. These volcanoes extend in line from northeast to southwest, and strictly controled by basement faults. Volcanoes which erupted in Late Pleistocene, consist of splashing down cone which is in small scale, and basalt lava flow. However, most of the cones are not typical craters, but are crevice volcanoes or crevice-central volcanoes. The default extends by 40°, with a width of 12km, including 17 craters. These craters are similar to Mount Laki of the Iceland , but with a smaller intensity eruption, and the area is limited. Volcanoes which erupted in Holocene had two phases: early intensely eruption and later magma eruption in large scale, which belong to strombolian-type. Three bigger of these volcanoes are called "Liandanlu" by local people, and No.1, No.2 and No.3 "Liandanlu" are along from northeast to southwest. All of the three volcanoes have similar consistence and characters, and consist of basalt cinder and lava flow. They all have a large scale, and volcano cones and craters preserved well. Small cones in the crater formed in the late stage of volcanism are also preserved very well. They are roundness in plane. Cone mainly consist of basaltic pumice , and main body is landing cinder cone with few splashing down accumulations formed in the late stage. Lava flow which is bareness, and has a large distribution in an area of 220 km~2, consisting the main bodyof Quaternary Volcanic Cluster. Lava flow which along the lower belt to the southeast, is dominated by modern terrain, and formed a dammed lake after blocking the water system of Holocene. This type lava flow is mainly pahoehoe lava, and the subsidiary is aa Lava.Lava flows have collapse crater, and lava graves and whiff cone structure can be seen in front of the lava flow.The spatial distribution reflects the new tectonics skeleton , the intruding of deep magma is the main cause of controlling new tectonically activities.