海南岛东部黄竹岭地区原“抱板群”的重新解体

RE-DISINTEGRATION OF THE FORMER“BAOBAN GROUP”IN THE HUANGZHULING AREA,EASTERN HAINAN ISLAND

海南岛东部黄竹岭地区的原“抱板群”早年已被解体为奥陶纪南碧沟组和中元古代戈枕村组、峨文岭组。本研究在原划归早奥陶世南碧沟组中酸性火山岩夹层中获得锆石SHRIMPU-Pb年龄441±10Ma,属于志留纪兰多维列世,且此火山岩的形成年龄可代表该套火山-沉积岩系的形成时代;在原划归抱板群峨文岭组的变质沉积岩系中获得碎屑锆石LA-ICP-MS U-Pb最小峰值年龄438 Ma,指示其形成于志留纪兰多维列世;原划归抱板群戈枕村组的地质体实为泥盆纪片麻状花岗岩类。因此,本文将黄竹岭地区原“抱板群”重新解体为志留纪地层(保脚村组和蒙花岭组),以及泥盆纪侵入岩类。保脚村组(原峨文岭组)变质沉积岩系及蒙花岭组(原南碧沟组)变质火山-沉积岩系均被泥盆纪花岗岩侵入。海南岛东部黄竹岭地区志留纪兰多维列世地层及泥盆纪侵入岩类的厘定,对海南岛东部地区早古生代地层格架的建立、海南地块构造演化等基础性地质问题的研究具有一定意义。

In the past years,the original“Baoban Group”in the Huangzhuling area,eastern Hainan Island,was disintegrated into the Gezhencun and Ewenling formations(Mesoproterozoic),and the Nanbigou Formation(Ordovician).Here we conduct a SHRIMP zircon U-Pb dating of the intermediate acid volcanic rock interlayer,which was previously assigned to the Ordovician Nanbigou Formation.The results show an age of 441±10 Ma,suggesting the age of this set of volcanic sedimentary rock series is of Llandovery age(early Silurian)rather than Ordovician.We also conduct a detrital zircon LA-ICP-MS U-Pb dating of the metamorphic sedimentary rock series,which was originally assigned to the Ewenling Formation of the Baoban Group,and the results indicate a younger peak age of 438 Ma,i.e.Llandovery too,rather than Mesoproterozoic age.The geological body originally assigned to the Gezhencun Formation of the Baoban Group is lithologically re-studied and identified as the Devonian gneissic granite,not metamorphic sedimentary rock.Thus,the original“Baoban Group”in the Huangzhuling area is re-disintegrated into Silurian strata(assigned to Baojiaocun and Menghualing formations)and Devonian intrusive rocks.Our studies also show that the metamorphic sedimentary rock series of the Baojiaocun Formation(originally assigned to the Ewenling Formation)and the metamorphic volcanic sedimentary rock series of the Menghualing Formation(originally assigned to the Nanbigou Formation)were intruded by Devonian granite(formerly misidentified and erroneously assigned to the Gezhencun Formation).This new identification of the Llandovery strata and Devonian intrusive rocks from the former“Baoban Group”in the Huangzhuling area,eastern Hainan Island,provides new information for the establishment of the Early Paleozoic stratigraphic framework of the area,and sheds light on complex tectonic evolution of Hainan Island.