都庞岭-九嶷山地区早元古代地壳存在证据

都庞岭-九嶷山地区出露的南华纪至第四纪地层最大厚度累加为18.5km,物探推测的地壳厚度为32~40km,两者相减尚应有13.5~18.5km厚的硅铝质地壳物质;地表基性-超基性火山岩中已发现有年龄值为1141~2707M a的片麻岩、麻粒岩、辉长岩、尖晶石二辉橄榄岩、片岩等沉积岩和岩浆岩变质结晶岩类;源岩主要属地壳成分的花岗岩,钕同位素t2DM值为1790~1380M a;花岗岩内磨圆状残留锆石SHRIMP法年龄值912~2669M a。推测南华系-奥陶系仅属上地壳基底,南华系之下还存在元古代甚至太古代的变质结晶基底。

The proofs of existing earth crust's double foundation in the area of Duoponglin-Jiuyan mountainous

The strata's thickness from Cryogenian Period to Quaternary Period is 18.5km in the area of Duoponglin-Jiuyan Mountainous;the physical exploration's data related that the earth crust's thickness is 32-40km. Therefore,under the Cryogenian System,exists salic material which thickness is about 13.5-18.5km.In the terrestrial basic-ultrabasic volcanic rock,exists metamorphous-crystalline rock whose ages between 1141Ma and 2707Ma such as gneiss,granulite,gabbro,spinel lherzolite and schist.The values of Nd isotope's t_2DM of granite whose source rock belonged to earth crust are between 1790Ma and 1380Ma.SHIMP ages of Zircon's porphyroclast in granite are between 912 Ma and 2699Ma.So we propose a conclusion that from the Cryogenian System to Ordovician System is only the upper foundation of the earth crust,under the Cryogenian System exists the under foundation consisted of the metamorphous-crystalline rock which belong to the Proterozoic PR Eonothem even the Neoarchean Erathem.