青藏高原北部构造发展的主要阶段

MAIN STAGES OF STRUCTURAL EVOLUTION OF NORTHERN QINGHAI-XIZANG(TIBET)PLATEAU

青藏高原北部构造发展经历了元古宙、早古生代、晚古生代—三叠纪、侏罗纪—新生代四个阶段。元古宙地壳演变是由活动带向稳定区变化.早元古代活动带经吕梁期地质热事件固结(克拉通化),结晶基底形成;长城系—青白口系为类盖层沉积,晋宁事件使其稳定,塔里木、柴达木、国祁连、阿拉善地块集结而成西北大陆地壳。早古生代地壳发展进入到裂陷槽为主阶段。北祁连、拉鸡山、柴达木周边裂陷槽经加里东期地质事件形成祁连山造山带,并使柴达木周边裂陷槽封闭,构成青藏高原北部大陆,拼接于欧亚板块南缘.晚古生代时在活动大陆边缘南侧存在一个广阔的北特提斯海,覆盖青南、藏北,漫及中祁连、西秦岭。三叠纪扩张海进入全盛时期,沉积了型相多变的地层。早印支期地质事件与晚印支期地质事件相继形成二条造山带、三条构造推挤带,至此,欧亚大陆增生至唐古拉山.燕山期地质事件使印巴板块前缘微陆块与欧亚板块碰接(东巧-怒江缝合带),唐古拉抬升,海相侏罗系褶皱,并有中酸性岩带.从白垩纪起构造发展进入到强烈隆升、走滑断裂与推覆构造为主的发育时期。晚第三纪泛湖区的出现,大陆相火山喷溢,近代地震的强烈活动、成盐事件都是新生代时期重要地质特征。

The structural evolution of northern Qinghai-Xizang(Tibet)plateau went through four stages,Proterozoic,early Palaeozoic,later Palaeozoic to Trassi and Jurassic to Cenozoic. The crustal evolution trended towards stable region from mobile zone in Proterozoic. the mobile zone of early Proterozoic formed crystalline basement consolidation through the geological heating evet during Luliang perild(Cratonization),and Jinning event made it steady the seeming cover deposition of Changeheng System -Qingbaikou System ,then Tarim,Qaidam,middle Qilian,Alashan massif collected and solidified to form northwest cgntinental crust. The crustal evolution of early Palaeozoic was generally rift geosyneline stage,so north Qilian,Lajishan,peripheral Qaidam rift geosyncline became Qilianshan orogenic zone through the geological event of Caledonian period with the rift geosyneline of peripheral Qaidam being trapped to compose the north continent of Qinghai-Tibet plateau and to connect with south margin of Europe—Asia platetectonics. In the palaeozoic wide northern Tethys on the south of active continental margin covered south Qinghai and northern Xizang(Tiebt)towards middle Qilian and western Qinling. The expanded sea entered a prime period in Triassic having varied types and facies sedinentary strata. Two orogenic zones and three structural nappind-compressed belts had been formed during the geolongical events of early and later Indosinian period,as a result Europe-Asia continent was acereting to become Tanggula mountains. In yanshan geological event the front magin microcontientalblock of Yenba platetectonics collided and connected with Eruope-Asia platetectonies(Dongqao-Nujiang suture belt),Tanggula uplifted and the Jurassic system of marine facies folded accompanying with the intrusion of intermediate-acidity rock belt. Since Cretaceous structural evolution was violently uplifting,strike-slip fault and nappe structural period. The important geological characters of cenozoic include the appearing of panlake-area in Neogene volcanic outburst of Continental facies,the violent action of recent earthquakes and depositing salt event.