Northern Tibet volcanic field

Coordinates: 35°51′N 91°42′E / 35.85°N 91.7°E / 35.85; 91.7[1] Northern Tibet volcanic field is a volcanic field[lower-alpha 1] in China.

Geography and geomorphology

The volcanic field lies in the Quiangtang plateau, in northern Tibet and the Kunlun mountains. The high altitude, bad terrain and weather make geologic investigations in the region difficult.[2] The volcanic field partly covers the Kangtuo formation.[3]

Local

The Bamaoqiongzong (34°00′N 88°45′E / 34.000°N 88.750°E / 34.000; 88.750[lower-alpha 2]), Yongbohu and Qiangbaqian (35°30′N 88°15′E / 35.500°N 88.250°E / 35.500; 88.250) fields featured Hawaiian eruptions that have formed lava flows. Later erosion has reduced these to flat topped conical hills and table mountains.[4] Other volcanic centres are the cones of Heiguotou (34°15′0″N 90°45′0″E / 34.25000°N 90.75000°E / 34.25000; 90.75000), Kushuihuan-Beishan (34°15′0″N 90°0′0″E / 34.25000°N 90.00000°E / 34.25000; 90.00000) and Yuyiehu (33°15′0″N 90°0′0″E / 33.25000°N 90.00000°E / 33.25000; 90.00000). In addition, the Kekexili (35°51′0″N 91°42′0″E / 35.85000°N 91.70000°E / 35.85000; 91.70000) caldera is considered part of the field.[1] This caldera has a diameter of 4 kilometres (2.5 mi). A volcano named "Debussey" is supposedly also located there.[5]

Bamaoqiongzong covers a surface area of 300 square kilometres (120 sq mi).[6] It forms a 5,400-metre-high (17,700 ft) peak with column-jointed rocks at its top.[6] Two craters lie on this peak, one 230 metres (750 ft) wide and 20 metres (66 ft) deep on the northeastern side with a breach southeast and another less well preserved one on the southeastern side.[7] It is surrounded by lava domes[6] and lava sheets. Originally likely over 300 metres (980 ft) thick, now they reach only several 10 metres (33 ft).[7]

Yongbohu features five vents,[1] the principal one has a height of 150 metres (490 ft). One has the shape of a dragon and another one is conical. Quiangbaqian covers a surface of 55 by 70 kilometres (34 mi × 43 mi) and features lava tube and fissure fed lava flows as well as one 200-metre-high (660 ft) volcano.[5] These volcanics are also known as Yulinshan formation.[3] Sometimes, the chronologically, petrologically and geographically distinct Hoh Xil volcanics are grouped with these fields.[8]

Composition

Bamaoqiongzong, Yongbohu and Qiangbaqian have erupted vitrophyric rocks. Minerals encountered in the vulcanites include andesite, trachyandesite and dacite containing augite,[4] and are subalkaline.[lower-alpha 3] Bamaoqiongzong is potassic,[10] it also contains phonolite and its minerals include aegyrite, alkali feldspar, analcite,[4] foidite,[1] leucite, noselite and titanaugite. This differences may be caused by the position of the centres with respect to the north Tibet block; the last two centres are located on its margin and the first one inside the block.[4]

Eruptive history

The Bamaoqiongzong, Yongbohu and Qiangbaqian volcanoes appear to be of Quaternary age, seeing as their deposits lie above Pliocene-Pleistocene rocks.[4] Lava flows from Bamaoqiongzong lie on Quaternary lake deposits.[1] Argon-argon dating has yielded ages of 30-26, 18 and 15-14 million years ago for the fields respectively however.[10] Potassium-argon dating of Bamaoqiongzong has yielded ages ranging from 20 to 28.6 million years ago.[2]

There is no evidence for Holocene eruptions. A satellite photo supposedly showing activity from[1] a crater (35°51′N 91°42′E / 35.850°N 91.700°E / 35.850; 91.700) on a 1.5-kilometre-wide (0.93 mi) cone on the ring fault[5] of the Kekexili caldera in 1973 was later discarded.[1]

References

  1. 1 2 3 4 5 6 7 8 "Unnamed". Global Volcanism Program. Smithsonian Institution.
  2. 1 2 Wanming 1991, p. 140.
  3. 1 2 Ding, Jikai; Zhang, Shihong; Chen, Weiwei; Zhang, Junhong; Yang, Tianshui; Jiang, Gaolei; Zhang, Kexin; Li, Haiyan; Wu, Huaichun (2015-05-15). "Paleomagnetism of the Oligocene Kangtuo Formation red beds (Central Tibet): Inclination shallowing and tectonic implications". Journal of Asian Earth Sciences. Special issue on Development of the Asian Tethyan Realm. 104: 59. doi:10.1016/j.jseaes.2014.10.006.
  4. 1 2 3 4 5 Wanming, Deng (February 1978). "A PRELIMINARY STUDY ON THE PETROLOGY AND PETROCHEMISTRY OF THE QUARTERNARY[sic] VOLCANIC ROCKS OF NORTHERN TIBET AUTONOMOUS REGION". Acta Geological Sinica. Retrieved 2017-04-05.
  5. 1 2 3 Whitford-Stark, J. L. (1987-01-01). "A survey of Cenozoic volcanism on mainland Asia". Geological Society of America Special Papers. 213: 11. doi:10.1130/SPE213-p1. ISSN 0072-1077.
  6. 1 2 3 Wanming 1991, p. 141.
  7. 1 2 Wanming 1991, p. 142.
  8. ↑ Deng, J. F; Mo, X. X; Zhao, H. L; Wu, Z. X; Luo, Z. H; Su, S. G (2004-05-01). "A new model for the dynamic evolution of Chinese lithosphere: 'continental roots–plume tectonics'". Earth-Science Reviews. 65 (3–4): 240. doi:10.1016/j.earscirev.2003.08.001.
  9. ↑ Daly, Reginald A. (1918-01-01). "Genesis of the Alkaline Rocks". The Journal of Geology. 26 (2): 98. JSTOR 30080727.
  10. 1 2 "Publication insights: Types of volcanic rocks for the Bamaoqiongzong, Yongbocuo and Qiangbaqian in the Northern Tibet, the dating of 40Ar-39Ar and its geological implications". Retrieved 2017-04-05.

Sources

  • Wanming, Deng (1991-04-01). "Cenozoic volcanism and intraplate subduction at the northern margin of the Tibetan Plateau". Chinese Journal of Geochemistry. 10 (2): 140–152. doi:10.1007/BF02837714. ISSN 1000-9426.

Notes

  1. ↑ The Global Volcanism Program considers them together.[1]
  2. ↑ Individual coordinates are given by Global Volcanism Program in the Synonyms & Subfeatures tab
  3. ↑ "Lime alkaline" is a different name for "subalkaline".[9]
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