辽西建平变质杂岩中花岗岩类岩石的锆石蒸发年龄及其地质意义

Zircon Evaporation Ages and Their Geological Significance from Granitoid of the Jianping Metamorphic Complex, Western Liaoning Province

建平变质杂岩是辽宁西都太古代最下部地质单元，是华北地台北缘麻粒岩相带的重要组成部分。它由少量连续性很差的表壳岩及大量的ＴＴＧ岩石和其他深成侵入体组成。采用单颗粒锆石Ｐｂ蒸发法对其中的ＴＴＧ岩石及其他侵入岩进行了年龄测定。结果表明：本区ＴＴＧ花岗质岩浆约于２５２１Ｍａ开始活动，并于２５００Ｍａ左右达到高峰，形成了大量的ＴＴＧ质侵入体（包括部分喷出岩）；紧随其后，本区发生强烈的高级变质变形事件，此事件约于２４８３～２４９０Ｍａ达到高峰，使得已形成的岩石变成麻粒岩、紫苏花岗岩及斜长紫苏花岗岩等；于２４７２Ｍａ就位的与退变质作用有关的后构造花岗岩标志着本区高级变质变形事件的结束。据此，可以推测建平变质杂岩可能形成于陆块形成后不久即发生大陆碰撞和地壳加厚的晚太古活动大陆边缘的环境中。

Jianping metamorphic Complex,the lowest section of the Archaean terrain from the Western Liaoning Province,is composed of discontinuous supra crustal rocks,an amount of TTG rocks and some other plutons.Single zircon ages for TTG series and some other plutons obtained by the Pb evaporation method show that intrusion of TTG series began at 2?521?Ma and reached a peak at about 2?500?Ma.This was foll owed by high grade metamorphic and deformed event,transforming the above assemb lages into graulites,charnockites and enderbites some 2?483～2?490?Ma.The int rusi on of post tectonic granites in 2?472?Ma associated with regional retrogre ssion ends the evolution of this area.A likely tectonic setting in which the Jianpin g metamorphic Complex was formed is an active continental margin that is involv ed in continental collision and crustal thickening shortly after its formation.