珠江口盆地西江主洼珠琼运动的沉积响应及构造意义

Sedimentary Response and Tectonic Significance of Zhuqiong Movement in Xijiang Main Sag,Pearl River Mouth Basin

珠江口盆地西江主洼经历了早—中始新世的珠琼运动一幕和晚始新世—早渐新世的珠琼运动二幕,期间分别沉积了文昌组和恩平组。为研究两幕运动的差异,通过对古近系沉积岩样品主微量元素分析来判断物源成分,从而理清珠琼两幕运动期间西江主洼的物源转换规律。结果表明:西江主洼珠琼运动一幕晚文昌期主要为风化酸性火成岩,缓坡处文一、二段顶部出现中性火成岩成分;珠琼运动二幕恩平组在主洼中部和东部主要表现为中性火成岩风化产物,28洼恩四段底部由长英质变为中性岩母岩,洼陷西部则未出现中性岩母岩,珠海期由酸性火成岩向石英岩母岩成分过渡。基底岩性研究表明,研究区古近系存在珠一坳陷内低凸起酸性花岗岩和坳陷南部隆起带中性花岗岩两类不同局部物源区,文昌期珠一坳陷内低凸起为主要物源区,在珠琼运动二幕时洼陷中部和东部物源区发生转换,物源来自珠一坳陷南部东沙隆起带,洼陷西部物源在恩平期没有转换,直到珠海期南海运动时与中、东部共同转变为接受北部统一的区域物源控制。洼陷不同部位物源转换存在差异,说明珠琼运动两幕之间存在物源的继承性发育,但具有不同的沉积演化特征。

The Xijiang main sag in the Pearl River Mouth basin experienced the first episode of the Zhuqiong movement in the Early Middle Eocene and the second episode of the Zhuqiong movement in the Late Eocene-Early Oligocene,during which the strata of Wenchang Formation and Enping Formation were deposited respectively.In order to study the difference between the two episodes,the major and trace elements of the Paleogene sedimentary rocks were analyzed to determine the provenance composition,so as to clarify the provenance transformation law of Xijiang main sag during the two episodes of Zhuqiong movement.The results show that the provenance of the first episode is mainly from weathered felsic rocks in the late Wenchang period,and the composition transformed to intermediate igneous rocks at the top of Wen-1 and Wen-2 Members at the gentle slope;The Enping Formation in the second episode of the Zhuqiong movement consists of mainly weathered by intermediate igneous rocks in the middle and east of the Xijiang Main Sag,the bottom of the Fourth Member of Enping Formation in the 28 subsag changed from felsic to intermediate igneous rocks,and no intermediate igneous rocks appear in the west of the sag.In the Zhuhai period,the parent composition transitioned from acidic igneous rocks to quartzites.The study of the basement lithology shows that there are two different local provenance areas in the Paleogene of the study area,the low uplift acid granite in the Zhu-1 sag and the intermediate granite in the southern uplift belt of the sag.The low uplift in the Zhu-1 sag is the main provenance area in the Wenchang period,and the central and eastern provenance areas of the sag were transformed during the second episode of the Zhuqiong movement,and the provenance comes from the Dongsha uplift belt in the south of the Zhu-1 sag.The provenance of the western part of the sag did not change during the Enping period,until the South China Sea movement in Zhuhai period changed,together with the central and eastern parts,changed to be controlled by the unified regional provenance in the north.The difference in provenance transformation in different parts of the sag indicates that there is an inherited development of provenance between the two episodes of the Zhuqiong movement,but with different sedimentary evolution characteristics.