摘要
首次对北山地区的乌珠尔嘎顺、额勒根、雀儿山、黑鹰山、狼娃山、明水和石板井等花岗岩体开展了高精度^(40)Ar/^(39)Ar同位素年代测定,共分析了10件样品,其中有6件获得了比较可靠的^(40)Ar/^(39)Ar 同位素年龄数据,基本能够代表岩体的侵位年龄,分别为352.3±3.8Ma、271.76±0.88Ma、286.2±3.4Ma、272.0±4.7Ma、294.1±2.9Ma 和255.2±4.1Ma;其他4件样品尽管受后期热扰动较为强烈,但是也能够获得一些有价值的年龄信息。另外,受后期构造-热事件的影响,本文有6件样品发生了不同程度的 Ar 丢失,其中样品 NSS01-13钾长石 Ar 丢失最为严重,不能获得可靠的年龄,其他样品发生 Ar 丢失的时间主要集中在燕山期,少量在印支期。获得的这些^(40)Ar/^(39)Ar 测年数据与已经发表的其他^(40)Ar/^(39)Ar 测年数据记录下了北山地区多期次的构造-岩浆侵入活动事件。根据这些年龄数据,可以将北山地区自海西中期以来的岩浆活动归纳为5个阶段,分别是:①330～360Ma,海西中期花岗岩类侵入活动;②270～310Ma,与西伯利亚、哈萨克斯坦和塔里木三大板块碰撞的时间同期或稍晚的花岗岩类侵入活动;③250～270Ma,明显晚于主碰撞发生的时间,为海西晚期碰撞后花岗岩类侵入活动;④210～250Ma,印支期构造-岩浆活动;⑤169～195Ma,燕山早期岩浆活动。其中270～310Ma 同碰撞期花岗岩类最为发育,分布范围最广。尽管北山地区从前寒武纪到燕山期花岗岩类均有产出,但是规模最大、影响范围最广的岩浆侵入活动发生在海西晚期,反映了海西晚期西伯利亚、哈萨克斯坦和塔里木三大板块碰撞对接的构造事件。印支期和燕山期花岗岩类可能是在统一大陆形成之后由陆内强烈活化形成的。北山地区花岗岩类的高精度年代学测量可以构筑本区花岗岩类时空演化的精细格架,对于重塑本区大地构造演化历史、指导区域金属矿床的寻找具有重要的意义。
The Beishan Mountain is located in north-western China and eastern-central part of the Central Asian Orogenic Belt. The granitoid intrusions are well developed and associated with copper, tungsten, gold and molybdenum mineralization in the region. In this paper, ten potassium-bearlng minerals separates from granitoid samples are analyzed for the ^40Ar/^39 Ar dating, of which six samples obtained reliable ^40Ar/^39Ar plateau age data, i.e. 352.3 ± 3.8Ma, 271.76 ± 0.88Ma, 286.2 ± 3.4Ma, 272.0 ± 4.7Ma, 294. 1 ± 2.9Ma and 255.2 ± 4.1 Ma, respectively. They represent the emplacement age of the intrusions. Some useful age information can also be obtained from other four samples, even though they experienced strong late thermal disturbing. In addition, the Ar loss has been identified in six samples presented in this paper, mainly due to the late tectono-thermal events. Since the K-feldspar of the sample NSS01-13 lost much At, its reliable plateau age cannot be obtained. The Ar loss predominantly occurred during the time period of early Yanshanian, and partly of Indosinian. The ^40Ar/^39Ar age data in this paper, together with other published ^40Ar/^39Ar age data, indicate that multiple tectono-magmatic events occurred in Beishan region. Based on these age data, the magmatic activities in study area can be ascribed to five stages as follows since middle Hercynian movement ： （ 1 ） 330 - 360MaMa, the middle Hercynian magmatic activity prior to the collision of Siberia, Kazakhstan and Tarim plates; （2） 270 - 310Ma, syn-collision granitoids associated with the collision of three plates; （3） 250 -270Ma, post-collisional granitoids; （4） 210 - 250Ma, Indosinian tectono-magmatic activity; （5） 169- 195Ma, early Yanshanian tectono-magmatic activity. Among these five stages, the granitoids occurring in the second stage, i.e. 270 -310Ma, are predominant, with the largest outcrop area. Combined with other age data published by other authors, the most widespread granitoids of the Beishan region emplaced in late Hercynian, consistent with the collision time of the Siberia, Kazakhstan and Tarim plates. In contrast, the Indosinian and Yanshanian granitoids may be the products of the continental reactivation after the forming of the united continent. It can be concluded that the high precise age dating for granitoids in Beishan region is the key for building up the regional tectonic framework and re-constructing the tectono-magmatic evolutionary history. Meanwhile, these age data can also be used to direct the regional mineral exploration.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2006年第11期2719-2732,共14页
Acta Petrologica Sinica
基金
国家重点基础研究发展规划(973)项目(2002CB412606)
国家地质大调查项目(200310200001-01)
内蒙古自治区项目(内地研2004-01)的联合资助。
