中亚造山带中的燃烧变质事件及其年代学研究(英文)

• 作 者: IgorS.Novikov EllinaV.Sokol
• 机 构: Institute of Geology and Mineralogy,Siberian Branch of the Russian Academy of Sciences,3,Koptyug av.
• 出 处: 岩石学报
• 发表日期: 2007年07期
• 关键词: 同位素年代学 40Ar/39Ar 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

<正> 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 for⁴⁰Ar/³⁹Ar 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 ⁴⁰Ar/³⁹Ar 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 ⁴⁰Ar/³⁹Ar 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 of⁴⁰Ar/³⁹Ar data is universal and can be practiced in anyarea subjected to combustion metamorphism.