China is one of the most volcanically active areas in the world, and tengchong volcanic area (98º15'~98º45'e, 24º40'~25º30'n) is located in the southwest of China's Yunnan Province, Tengchong has a total of 97 volcanoes, an area of more than 1,000 square kilometers, its typical characteristics are: large scale, complete type, concentrated distribution and complete preservation, is one of the youngest volcanic areas in China, is the crown of China's volcanoes.
Tengchong Volcanic Group, located in the southern section of the Hengduan Mountain System, on the west side of Gaoligong Mountain, from the Longchuan River in the east, to the Penang River in the west, to the QingliangShan and Xiaobing Alley in the south, with an east-west width of about 40 kilometers and a north-south length of about 90 kilometers. There are 22 craters with volcanic bodies that are completely preserved, 23 with volcanic bodies that are mutilated but have volcanic bodies, and more than 10 craters that are non-volcanic bodies.
The volcanic activity of the volcanic zone is controlled by the tectonic background of the region, which is located in the extension of the Gandhis Middle Plate after the southward turn between the Indian Plate and the Eurasian Plate, and belongs to the Tengchong micro-plate of a secondary tectonic unit of the Yunnan-Burma-Thai Plate. The Tengchong Microplate is bordered by the Myitkyina Suture and the Myanmar Plate in the west and the Nu River Suture and the Baoshan Block in the east. The basal rock system is the Proterozoic Gaoligong Mountain Group, which is a set of granite mixed rocks with a high degree of metamorphism and a small number of shallow metamorphic rock systems, with a total thickness of more than 4000m. The complex tectonic background has produced a large number of active faults in the Tengchong area, mainly north-south faults and supporting north-west and north-east faults.
(Tectonic location and distribution of volcanic rocks in Tengchong volcanic area)
Although the Tengchong seen now is just a group of "extinct volcanoes", it is not dead, just dormant. The volcanic groups are arranged in a north-south direction, among which the more famous volcanoes are: Eagle Mountain, Black Sky Mountain, Empty Mountain and so on.
Mt. Takahak, known as "Little Mt. Fuji", resembles Mount Fuji in Japan. Located about 10 km (98 ° 27 ′e, 25 ° 08 ′n) about the county seat of Tengchong County, with an altitude of 2615 m and a lava area of 29 km2, it is the earliest, largest and highest active volcano among the three volcanoes. Mt. Taying volcano is a composite of multi-stage lava flows, with a slag cone at the top, a late lava lake and a lava cone, and a small central cone in the late lava lake. The volcano is composed of five lava flows, each of which forms lava flows of different compositions, different structures and spread scales, and the magmatic composition evolves from basalt to andes andes andes from early and late. In 1639, Xu Xiake, a famous geographer in China, came here to investigate, and the article "Hitting eagle mountain incident" recorded the scene of the volcanic eruption and field observation that he heard at that time: "The natives said that thirty years ago, there were large trees and giant bamboo on it, blinding the sky. There is a dragon pond, the depth is unpredictable, and the sound of the foot is surging up, and people dare not come closer. After the shepherds arrived, a thunder killed five or six hundred sheep and several shepherds, and the fire was raging day and night, the trees were deep, there was no remains, and the pond became a land... The stone on the top of the mountain, red and frivolous, resembles a hive, and is made of foam, although it is large enough to hug, and two fingers can be carried, but its quality is still strong, but it is also the ashes. "This record indicates that about 400 years ago, there was a recent volcanic eruption in Tengchong. However, after the founding of the People's Republic of China, China's geologists have done detailed scientific research on Daying Mountain, and the absolute age of the volcanic eruption of Daying Mountain has been determined to be 7000 to 10000 years, and there was no and no volcanic eruption in the early 17th century. The native sayings recorded by Xu Xiake can only be the legends of ancient humans.
Located about 25 km (98º30'e, 25º13.8'n) north of Tengchong County, with an altitude of 2072 m and a lava area of about 27 km2, The Volcano is one of the most well-preserved volcanoes in the region (. The lower part of the volcanic cone is a lava cone, the upper part is a slag cone, and the rim of the fire mouth is relatively complete. The Volcano has had many intermittent overflows since the Late Pleistocene, with significant lava overflows on the north and south sides of the cone, and large lava flows from the cone to the west, north and east. The southern lava flows cover the Great Void Mountain lava flows, and the northern side covers the Tuanshan lava flows. Lava tunnels and lava collapses are common.
Big Empty Mountain
The big and small empty mountains and the black sky mountains are the most ornamental volcanoes in the volcanic group, they are evenly arranged, like three perfect volcanic cone models in front of people's eyes, they can really be called the "empty mountain boutique" model. Iron Pot Mountain, a little farther away from here, is more like two large iron pots on a mountain, in spring, lantana blooms and the crater, from a high place, as if the volcano is erupting, where is the history of volcanic eruptions, and what is the form?
(Black Sky Mountain)
After scientific research, the age of Tengchong volcanic rocks ranges from millions to hundreds of years, and the comprehensive age data of the volcanic rocks of the predecessors divide the eruption of Tengchong volcano into five stages: the first stage, the Pliocene, after a long period of weathering, its vertebral body damage is serious, and only the volcano of the dome landform or volcanic mountain body can be seen, and the volcanic rock is an overflow phase or an erupting phase bedrock. It is mainly distributed in the southern part of the volcanic area, and a small number is distributed in the northern part of the volcanic area. In the second phase, the early Pleistocene, most of the volcanic mechanisms have been destroyed, and the crater is no longer obvious, but the cone-shaped mountain is visible. In the middle Pleistocene of the third period, the volcanic rock was an eruptive phase or an eruptive phase, and the volcano developed from both ends of the basin to the center, and the volcanic rocks were mostly acidic Anglo-an rocks, of which the Daliuchong area was the most typical. The volcanic mechanisms of the Mesopleistan volcanoes are well preserved, and most of them can still be seen in the crater. In the fourth period of late Pleistocene, the eruption range was reduced, mainly distributed in the center of the basin, erupting in Daying Mountain, Ma On Shan, Black Sky Mountain and its nearby Big Empty Mountain, Little Empty Mountain and other places. The fifth phase is holocene volcanoes, the three volcanoes of Black Sky Mountain, Daying Mountain and Ma'anshan continue to erupt in the Holocene, and the volcanic mechanism is well preserved, all of which are truncated cone-shaped volcanic cones, oval craters, eruption-eruption phases, and neutral rocks.
The eruption forms of tengchong volcanic groups are mainly fissure type and central type. Central eruptions, which erupt in the Pleistocene and Holocene. According to the chronological order of eruption and the difference in lithology, it is divided into two types: one is basalt or partial basalt, which constitutes a widely distributed multi-stage lava platform, and the truncated cone-like volcano, the material has a layered structure, lava, slag and pyroclastic material are stacked in layers, the volcanic cone is toped by pumice, and the crater and its vicinity are scattered with spindle-like and rope-like volcanic bombs, volcanic ash, volcanic gravel and debris. Such volcanoes include Daying Mountain, Dakong Mountain, Lao Gui Po, Ma'an Shan and other volcanoes, and their eruptive nature is semi-violent - tranquil; one is neutral or acidic Andesan rock and Ying'an rock, with many rhyolary structures or strip structures, such as Alpine Yubi Slope, Beilaifeng Mountain, West Dapotou, Half Mountain, Large and Small Liuchong, etc. The current volcanic body is mostly damaged, but there are some volcanic tops, there are still crater remains, and the eruption nature is violent.
(Center eruption)
Fissure eruption, its eruption time in the Pliocene and early Pleistocene, the nature is relatively quiet, mainly for the basal lava flow, viscous small flow is large, columnar joint development, mainly exposed in the Valley of the Daying River and Longchuan River, mostly the bottom of the riverbed bedrock and the base of the river terrace.
(Slit eruption)
According to the morphology of volcanic groups and their material composition, they are divided into the following categories:
Cone volcano its composition is mainly basalt, andesan basalt, volcanic cone relative height difference is larger, can reach 50 meters ~ 750 meters, the overall slope of the outer wall is relatively gentle, between 15 ° ~ 30 °, the shape of a truncated cone, its fire crater is well preserved, most of the volcanic cone has more than one crater, its depth is between 30 meters to 70 meters, often developed volcanic central mound, also known as "fire plug", the central mound is more rounded, 10 meters to 30 meters high, the crater inside and outside the wide spread of pumice, volcanic ash, Volcanic bombs. Parasitic volcanic cones are also developed on some main volcanic vertebrae, with relatively small height differences. Typical such as Eagle Mountain, Xiaotuan Mountain, Black Sky Mountain, etc.
Bell-shaped volcanoes belong to this category of Laifeng Mountain, Tieguo Mountain, Laoyanghe Mountain, Linjia Mountain, Dasong Mountain, etc., composed of rhyolite, Andesian rock, tuff, of which the slope is gentle parallel flow development, the rock structure is more delicate. Its magma is acidic, viscosity, weak fluidity, and accumulates around the crater, forming bell-shaped hills. The relative height of the bell-shaped volcano is 150 meters to 300 meters, due to the early formation era, it is damaged by late erosion, and the top crater is no longer obvious. Rulai Fengshan, the appearance is a standing bell shape, stacked on top of the granite hills, the top altitude is 1903 meters, the relative height difference is about 240 meters, the bottom diameter is about 1.5 km to 2 km, the top is flat and round, composed of andesite and tuff, with obvious rhyolus structure.
Mortar volcano is also known as "Mal-style" volcano, the cone is relatively gentle, the slope is about 5 °, the relative height difference is less than 30 meters, the diameter of the bottom is about 1500 meters, the crater is mortar-shaped, the depth is generally about 5 meters to 25 meters, and the diameter is about 50 meters to 140 meters. For example, the Qinghai Giant Fire Mouth, which is 40 meters to 100 meters lower than the surrounding mountains, has accumulated water into a lake, the circumference is not large, the diameter is about 50 meters, the water depth is more than 20 meters, there is no cone, and there is no volcanic debris deposition around it.
The top of the shield volcano is generally gentler, the crater usually appears shallow butterfly-like, the depth is between 5 meters and 30 meters, the relative height difference is 50 meters to 200 meters, the overall uphill slope is slow, and the bottom of the shield volcano is mostly elliptical, with a diameter between 300 meters and 1500 meters. Tengchong lava terraces, widely distributed around volcanic cones or non-volcanic cones, as well as in river valleys and basins, are much larger than the area occupied by volcanic cones.
Rich geological resources, so that the Tengchong volcanic group is well-known at home and abroad, in 1994 the State Council listed the Tengchong volcanic group as a national scenic spot. In order to make full use of this valuable resource, in 1997 the state approved the Tengchong volcanic community as a national park.
At present, Tengchong County adheres to the principle of "protection first, development as a supplement", plans and rectifies Tengchong Volcano National Park, and maintains the original appearance of volcanic groups in the demarcated tertiary protection area. In the near future, a living "Museum of Volcanic Geology" will be presented here.