| 中亚造山带中的燃烧变质事件及其年代学研究 |
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| 作者姓名： | Igor S. Novikov Ellina V. Sokol |
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| 作者单位： | Institute of Geology and Mineralogy,Siberian Branch of the Russian Academy of Sciences,3,Koptyug av.,Novosibirsk,630090,Russia |
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| 基金项目： | The study was supported by grant SS-4922.2006.5 from the president of the Russian Federation for leading science schools ("Siberian metamorphic school")and grants 05-05-65036 from the Russian Foundation for Basic Research;it was carried out as part of Integration Project 105of the Siberian Branch of the Russian Academy of Sciences. |
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| 摘 要： | Combustion metamorphic(pyrometamorphic)complexes produced by prehistoric natural coal fires are widespread inCentral Asia,namely at the interfaces between mountain systems and the flanking sedimentary basins.Large-scale and prolonged firesaccompanied the initial orogenic stages as unweathered coal-bearing formations became exposed into the aeration zone.Pyrometamorphic rocks are comparable to sanidinite facies rocks in formation conditions and in alteration of sedimentary material but,unlike these,their protolith underwent different melting degrees to produce either ferrous basic paralavas or glazed clinkers.The phasecomposition of the newly-formed melted rocks are favorable for~(40)Ar/~(39)Ar dating of combustion metamorphic events which are coeval tothe onset of the main stage of recent orogenic events.We suggest a new algorithm providing correct ~(40)Ar/~(39)Ar dating ofpyrometamorphic rocks followed by well-grounded geological interpretation.We studied pyrometamorphic rocks in the western Salairzone of the Kuznetsk coal basin where combustion metamorphism under temperatures above 1000℃acted upon large volumes of coal-bearing sediments.Samples of paralavas were dated by the step heating ~(40)Ar/~(39)Ar method checked against internal(plateau andisochrone ages)and external("criterions of couple")mineralogical criterions,and against preliminary dating from geological andstratigraphic evidence.As a result,we distinguished two groups of dates for combustion metamorphic events.The first one(1.2±0.4Ma)is drawn towards the west boundary of Prokopyevsk-Kiselevsk block of Salair zone,while the second one(0.2±0.3Ma)isconfined to its east boundary.The former ages represent rocks in the western edge of the Prokopievsk-Kiselevsk block of the Salair zoneand the latter ages correspond to those in its eastern edge.The dates record the time when the fault boundaries of the blocks wererejuvenated during recent activity and the block accreted to the Salair orogenic area as a piedmont step.These are the first absolute agesobtained for the onset of uplift of the northern edge of the Ahai-Sayan area,the key event of its neotectonic history.The suggestedapproach to the choice of objects,classification of rocks,and interpretation of~(40)Ar/~(39)Ar data is universal and can be practiced in anyarea subjected to combustion metamorphism.
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| 关 键 词： | 同位素年代学 40 Ar/39 Ar定年 新构造 燃烧变质杂岩 似熔岩 接触变质煤 Kuznetsk盆地 Altai-Sayan地区 |
| 文章编号： | 1000-0569/2007/023（07）-1561-72 |
| 修稿时间： | 2006-12-24 |
Combustion metamorphic events as age markers of orogenic movements in Central Asia |
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| Igor S. Novikov Ellina V. Sokol.Combustion metamorphic events as age markers of orogenic movements in Central Asia[J].Acta Petrologica Sinica,2007,23(7):1561-1572. |
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| Authors: | Igor S Novikov Ellina V Sokol |
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| Institution: | Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences , 3, Koptyug av. , Novosibirsk, 630090, Russia |
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| Abstract: | Combustion metamorphic (pyrometamorphic) complexes produced by prehistoric natural coal fires are widespread in Central Asia, namely at the interfaces between mountain systems and the flanking sedimentary basins. Large-scale and prolonged fires accompanied the initial orogenic stages as unweathered coal-bearing formations became exposed into the aeration zone.Pyrometamorphic rocks are comparable to sanidinite facies rocks in formation conditions and in alteration of sedimentary material but,unlike these, their protolith underwent different melting degrees to produce either ferrous basic paralavas or glazed clinkers. The phase composition of the newly-formed melted rocks are favorable for 40Ar/39Ar dating of combustion metamorphic events which are coeval to the onset of the main stage of recent orogenic events. We suggest a new algorithm providing correct 40 Ar/39 Ar dating of pyrometamorphic rocks followed by well-grounded geological interpretation. We studied pyrometamorphic rocks in the western Salair zone of the Kuznetsk coal basin where combustion metamorphism under temperatures above 1000℃ acted upon large volumes of coalbearing sediments. Samples of paralavas were dated by the step heating 40 Ar/39 Ar method checked against internal (plateau and isochrone ages) and external ("criterions of couple") mineralogical criterions, and against preliminary dating from geological and stratigraphic evidence. As a result, we distinguished two groups of dates for combustion metamorphic events. The first one (1.2±0.4 Ma) is drawn towards the west boundary of Prokopyevsk-Kiselevsk block of Salair zone, while the second one (0.2±0.3 Ma) is confined to its east boundary. The former ages represent rocks in the western edge of the Prokopievsk-Kiselevsk block of the Salair zone and the latter ages correspond to those in its eastern edge. The dates record the time when the fault boundaries of the blocks were rejuvenated during recent activity and the block accreted to the Salair orogenic area as a piedmont step. These are the first absolute ages obtained for the onset of uplift of the northern edge of the Altai-Sayan area, the key event of its neotectonic history. The suggested approsch to the choice of objects, classification of rocks, and interpretation of 40 Ar/39 Ar data is universal and can be practiced in any area subjected to combustion metamorphism. |
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| Keywords: | Geochronology 40 Ar/39 Ar dating Neotectonics Combustion metamorphic complexes Paralava Clinker Kuznetsk basin Altai-Sayan area |
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