大兴安岭地区德尔布干断裂带北段构造年代学研究

Geochronology in the north segment of the Derbugan fault zone, Great Xing' an Range, NE China.

德尔布干断裂带是大兴安岭隆起西侧NE向的重要断裂带,处在海拉尔-拉布达林-根河盆地西缘,是著名德尔布干成矿区东南边界断裂带。为了确定德尔布干断裂带运动性质、活动时间,深入探讨该断裂带与中生代海拉尔-拉布达林-根河盆地及大兴安岭盆山格局、认识德尔布干断裂带多金属矿床成因等问题,本文应用锆石SHRIMP和云母^(40)At/^(39)Ar定年技术,分别对断裂带内的细粒黑云母花岗岩侵入体、韧性变形的花岗闪长质片麻岩、白云母石英片岩,进行了同位素年代学研究。其中花岗闪长质片麻岩岩浆型锆石SHRIMP谐和年龄300.6±9.3Ma,为花岗闪长质片麻岩海西期的侵位年龄;而花岗闪长质片麻岩中黑云母^(40)At/^(39)Ar坪年龄是130.9±1.4Ma,白云母石英片岩的白云母^(40)Ar/^(39)Ar坪年龄是115.6±1.6Ma,代表早白垩世伸展构造变形年龄;细粒黑云母花岗岩侵入体岩浆型锆石SHRIMP谐和年龄130.1±1.4Ma,为同伸展构造变形侵位的岩浆事件。上述地质年代说明德尔布干断裂带是早白垩世(110～130Ma)该区最年轻的重大伸展构造变形产物。控制NE向大兴安岭隆起和中生代海拉尔-拉布达林-根河等火山沉积盆地的发育格局、以及中生代以来的地壳演化与成矿类型。

Derbugan fault zone, a NE tending fault zone in the West of the Great Xing' an Range uplift and along the western margin of the Hailar-Labudalin-Genhe basins, is the famous zone which is the NS boundary fault zone of the Derbugan metallogenic belt. In order to understanding the character for the activity and timing of this fault, and its relations to the Hailar-Labudalin-Genhe basins, and polymetal ore deposit along this fault, we show the SHRIMP zircon and mica40Ar/39Ar dating for the granule-biotite granitic vein, granodioritic gneiss with ductile deformation and mica-quartz schist in this fault zone. SHRIMP zircon U-Pb dating of the granodioritic gneiss yield concordant age of 300. 6 ±9. 3Ma, together with its igneous zircon in CL image, indicate that age of 300. 6 ±9. 3Ma is the protolith ages for this gneiss. The biotite40Ar/39Ar dating also from this granodioritic gneiss, which yield the plateau age of 130. 9 ± 1. 4Ma, together with the biotite40Ar/39Ar plateau age of 115. 6 ± 1. 6Ma from the mica-quartz schist, indicate that those ages between the 115 ∼130Ma are the extensional event ages at the Early Cretaceous in the Derbugan fault zone. The granule-biotite granitic vein also analyzed by the SHRIMP method, which yield the concordant age of 130. 1 ±1. 4Ma with the igneous zircon in CL image, indicate that age of 130. 1 ± 1.4Ma are the protolith age and incursion due to the syn-extensional event during the Yanshanian in this fault zone. Those results from this study, suggest that the Derbugan fault zone is the youngest extensional structure with the ages between 110∼130Ma during the Yanshanian in this area. Derbugan fault zone has dominated the framework of the Mesozoic volcanism in the Hailar-Labudalin-Genhe basins, the crust evolutions and ore-forming types in the Great Xing'an Range. Therefore the Derbugan fault zone with the extensional event ages of 115∼130Ma are the typical evidence for the intra-continental orogen at Yanshanian during the Mesozoic.