| 词条 | Vitim Plateau |
| 释义 |
Vitim Plateau is a volcanic landform in Russia. It consists of a plateau with a number of cinder cones and volcanoes, the last of which was active about 810,000 years before present. Geography and geomorphologyThe Vitim Plateau lies along the headwaters of the Vitim River.{{sfn|Litasov|Foley|Litasov|2000|p=85}} It covers a surface area of {{convert|10000|km2}},[1] and is heavily forested.[3] About five circular groups of volcanoes occur in the field, which is in turn subdivided into two major provinces.{{sfn|Litasov|Foley|Litasov|2000|p=85}} Both central volcanoes and cinder cones occur in the volcanic field, with the largest volcanoes reaching heights of {{convert|150|m}} and diameters of {{convert|1.5|km}}.[4] GeologySince the Oligocene and especially the Pliocene, the Asian Plate has been rifting apart in the Baikal Rift where the Siberian craton and a Paleozoic assembly of terranes (ancient microcontinents) form a contact zone. This rifting process is associated with volcanism in the neighbourhood of the rift zone, and this volcanism has produced about {{convert|5000|km3}} of volcanic rock in several volcanic fields,[3] including the Udokan Plateau and the Vitim Plateau which are the largest volcanic fields of the Baikal Rift.{{sfn|Litasov|Foley|Litasov|2000|p=84}} The reasons for the rifting process aren't well known. One theory holds that the collision between India and Asia and other tectonic processes triggered the pull-apart in the Baikal Rift. Another one postulates the existence of thermal anomalies such as a mantle plume beneath the Baikal Rift as the driving force of the rifting.[3] The basement beneath the Baikal Rift is granitic and up to {{convert|20|km}} thick. It may be of Paleozoic age. Other rocks in the region are sediments close to river valleys and Mesozoic volcanic rocks.[3] CompositionVitim Plateau volcanic rocks are mainly alkaline to subalkaline basalts, nephelinites and melanephelinites, with phenocryst phases containing clinopyroxene, olivine and plagioclase. Younger rocks have a tendency towards alkaline compositions.[3] The melts that give rise to Vitim Plateau magmas appear to originate in the lithospheric mantle, starting from garnet pyroxenite and peridotite and leaving phlogopite as residual phase when starting from pyroxenite.[3] Petrology indicates that a complex magma production process takes place beneath the Vitim Plateau, including remelting and crystallization.{{sfn|Litasov|Foley|Litasov|2000|p=111}} Eruption historyTwo volcanic phases have been identified in the Vitim Plateau. The first took place during the Miocene;[1] potassium-argon dating has yielded ages of 10.65 - 6.6 million years ago.[3] The second occurred during the Pleistocene with the most recent eruption dated 810,000 years ago.[1] Later volcanic activity was concentrated in river valleys and cones on the surface of the plateau. References1. ^1 {{cite book|last1=Whitford-Stark|first1=J.L.|title=A survey of Cenozoic volcanism on mainland Asia|date=1987|publisher=Geological Society of America|location=Boulder, Colorado|isbn=9780813722139|page=26|url=https://books.google.com/?id=85AmC4hnDlMC&pg=PR7&dq=%22vitim+volcanic%22+OR+%22vitim+plateau%22+AND+cones#v=onepage&q=%22vitim%20volcanic%22%20OR%20%22vitim%20plateau%22%20AND%20cones&f=false|language=en}} [1][2][3]2. ^1 2 3 4 5 6 7 {{cite journal|last1=JOHNSON|first1=J. S.|last2=GIBSON|first2=S. A.|last3=THOMPSON|first3=R. N.|last4=NOWELL|first4=G. M.|title=Volcanism in the Vitim Volcanic Field, Siberia: Geochemical Evidence for a Mantle Plume Beneath the Baikal Rift Zone|journal=Journal of Petrology|date=1 July 2005|volume=46|issue=7|pages=1309–1344|doi=10.1093/petrology/egi016|url=https://academic.oup.com/petrology/article/46/7/1309/1546617|language=en|issn=0022-3530}} 3. ^1 2 3 4 {{Cite GVP|name=Vitim Plateaz|vn=302040}} }} Sources{{refbegin}}
3 : Pleistocene volcanoes|Volcanoes of Russia|Plateaus of Russia |
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