摘要
在内蒙古西部图古日格地区发现东西向延伸约20km、南北宽约2—4km的变形带，由奥陶纪白云山组石英片岩、白云母石英片岩、片理化大理岩和石英砂岩组成。片理稳定倾向南东，但透入性不均，从北向南可分为四个强和弱变形亚带。石英组构分析表明强变形带中发生了动态重结晶向静态重结晶的转变。据石英组构推测强变形亚带的变形温度范围约为350—500℃之间。这一温度区间高于或近于白云母的封闭温度，因此白云山组强变形带中白云母的年龄可以代表变形年代。采自强变形亚带白云母的Ar／Ar等时线年龄为440．3±7．2Ma。考虑到样品所在地构造位置为造山带的弧前或岛弧地区，是板块俯冲作用的高应变带，因此该年龄应代表与俯冲有关的挤压变形事件的发生时代，即反映早古生代末期造山作用的时代。这条变形带的发现为解释图古日格地区造山带格局提供了构造变形方面的证据。研究区变形带的形成时代与温都尔庙地区高压变质事件在误差范围内相同，表明两个地区都受到早古生代末期造山作用的影响，也表明兴蒙造山带的南造山带从西部图古日格地区向东沿延至温都尔庙地区。
Xing＇ an Mongolian Orogenic Belt is located in the eastern part of the Central Asia Orogenic Belt, composed of the Paleozoie opposite subduction orogenic belt that includes a northern orogenic belt （NOB） and southern orogenic belt （SOB）. The NOB extends ca. 550km from Xilinhot in the east to Airgin Sum in the west. The SOB outcrops from Ondor Sum in the east, via Bater, to Tugurige in the west. Songliao-Hunshandake block and oceanic crust called Ondor Sum Group located between NOB and SOB. In recent years, the Early Paleozoic structural deformation in the Ondor Sum-Hongqi area has been recognized, which suggests that a subduction of the Songliao-Hunshandake block beneath the North China craton. But, how to extend the subduction belt from Ondor Sum-Hongqi area to neighbor area and geochronology evidences related with the subduction is still unsolved. In Tugnrige area, ca. 150km to the west of Ondor Sum-Hongqi area of the SOB, six tectonic units have been recognized, which includes, from north to south, fold belt of subducted oceanic crust, melange, fore-arc belt, island arc belt, back arc foreland basin and North China craton. In the fore-arc belt a deformation zone is found that is 20km long from east to west and 2 - 4km wide from north to south. The deformation zone is composed of the Ordovician Baiyunshan Formation including quartz schists, muscovite quartz schists, foliated marbles and quartz sandstones. Widespread sonth-dipping foliation, but penetrative inequality, can be observed in the zone. From north to south, the deformation zone can be divided into four strong and weak deformed sub-zones. The strong deformed sub-zone, with the thickness exceeded 450m, is characterized by two phase deformations, in which fabric analysis of quartz reveal change from dynamic recrystallization to static recrystallization. Analysis of microscopic photographs indicates that most quartz grains show different boundary shapes and subgrains show a bulgy recrystallization in weak deformed zone. The subgrain rotation recrystallization representing higher temperature can been observed from the samples of strong deformed zone. There are some static recrystallization grains, which show approximate equigranular, straight edge and triple point structure. According to these quartz fabric the temperature range of the strong deformed sub-zone is about 350 - 500℃, which is near or higher than the muscovite closure temperature. So the muscovite age of strong deformed zone in the Baiyunshan Formation can represent the deformation age. A muscovite Ar/Ar isochron age of 440. 3 ±7.2Ma has been acquired from the strong deformed sub-zone. Considering the sample located in fore-are or island arc area of the SOB, which is a high strain zone of plate subduetion, the age should suggest a deformation event related with the subduction during the late Early Paleozoic. The deformation zone, therefore, provides structural deformation evidence for the SOB in Tugnrige area. The formation age of deformation zone correlates with the high-pressure metamorphic event age in Ondor Sum area, which suggests that two regions are affected by the late Early Paleozoie orogeny and the SOB extends from Ondor in the east to Tugnrige in the west.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2015年第1期80-88,共9页
Acta Petrologica Sinica
基金
国家重点基础研究发展计划(2013CB429806)
国家自然科学基金项目(40872145
41121062)
中国地质调查局项目(1212011220906)联合资助
关键词
强变形带
白云母Ar/Ar年龄
构造岩石学
内蒙古
兴蒙造山带
Strong deformation zone
Muscovite Ar/Ar age
Structural petrology
Inner Mongolia
Xing＇ an Mongolian orogenic belt
