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Northern Tibet volcanic field

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Coordinates: 35°51′N 91°42′E / 35.85°N 91.7°E / 35.85; 91.7[1]
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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[a] in China.

Geography and geomorphology

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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

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The Bamaoqiongzong (34°00′N 88°45′E / 34.000°N 88.750°E / 34.000; 88.750[b]), 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

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Bamaoqiongzong, Yongbohu and Qiangbaqian have erupted vitrophyric rocks. Minerals encountered in the vulcanites include andesite, trachyandesite and dacite containing augite,[4] and are subalkaline.[c] 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

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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

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  1. ^ a b c d e f g h "Unnamed". Global Volcanism Program. Smithsonian Institution.
  2. ^ a b Wanming 1991, p. 140.
  3. ^ a b 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. ^ a b c d e 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. ^ a b c Whitford-Stark, J. L. (1987-01-01). "A Survey of Cenozoic Volcanism on Mainland Asia". Vol. 213. p. 11. doi:10.1130/SPE213-p1. ISBN 978-0-8137-2213-9. ISSN 0072-1077. {{cite book}}: |journal= ignored (help); Missing or empty |title= (help)
  6. ^ a b c Wanming 1991, p. 141.
  7. ^ a b 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): 97–134. doi:10.1086/622576. JSTOR 30080727. S2CID 128642330.
  10. ^ a b "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

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Notes

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  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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