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Address : China University of Geosciences, China
Celebration date : 17 Wednesday September 2008
Author name : Ji, Mo; Liu, Junlai; Hu, Ling

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  • Article title : Kalenich, Alexander1; Morozov, Andrey2; Ivanov, Gennady1
    Article type : Tectonic & Seismotectonic
    Location : International Geological Congress,oslo 2008

    Fulltext :

    As the easternmost example of metamorphic core complexes in Sino-Korean Craton, the Liaonan metamorphic core complex (Liaonan mcc) is a typical extensional structure style formed during craton destruction and lithosphere thinning during early Cretaceous. Liaonan mcc is a typical Cordilleran type mcc, that is constituted by three different structural units: a corrugated detachment fault zone which trend varies from NNE to NEE, a lower plate of Archean metamorphic rocks intruded by early Cretaceous synkinematic plutons, and an upper plate of weakly deformed or undeformed Neoproterozoic and upper Paleozoic sedimentary rocks with a Cretaceous supradetachment basin. This paper provides information on the relationships between the corrugated detachment fault zone and the active intrusions. Different stages of exhumation of the lower plate of Liaonan mcc are related to emplacement of three important plutons:
    (1) Zhaotun monzonite pluton was ductilly deformed by regional extension process at a relative deep level, suggesting that the Zhaotun monzonite is of pre-detachment; (2) Yinmawanshan granodiorite-monzogranit batholith is composed of two zones. The hornblendes and its aggregates of marginal zone is strongly orientated to conciliate between magmatic fabric and mylonitic orientation, which presents a synkinemic character; (3) Zhaofang granitic porphyry sheet intruded through the lower plates even in some parts of upper plate, which indicates that the cessation of detachment movement. Zircon SHRIMP U-Pb dating and hornblende-plagioclase geothermometer - geobarometer are applied to the above three plutons. From the geochronological data, the exhumation of the lower plate can be subdivided into three stages. Before the exhumation, Zhaotun pluton emplaced at the depth of >25km during 130±5Ma. In the first stage (~130Ma), the detachment fault and ductile shear zone were formed by regional extension. During the second stage (130~120Ma), the active emplacement of synkinematic granitic and granodioritic plutons contributed to the development of corrugation of detachment fault. Yinmawanshan pluton emplaced at the depth of about 20km at 124±3Ma, representing a peak magma-tectonic activity as also suggested by Wu et al. (2005). The third stage (113~ Ma), the emplacement of Zhaofang granitic porphyry at the depth of less than 3km marks the termination of the extensional movement. We therefore conclude that the total denudation of Liaonan mcc is about 22km in vertical, the initial denudation speed is ≈0.83km/Ma during 130~124Ma, and the terminal denudation speed is ≈1.55km/Ma during 124~113Ma indicating a rapid exhumation. After this complex tectono-magmatic process, the lower plate of Liaonan mcc was exhumed to the earth’s surface by the regional uplift of Liaonan block coupled with the North China Craton.