基于激光U-Pb定年的埋藏白云岩形成过程——以塔里木盆地永安坝剖面下奥陶统蓬莱坝组为例  

Laser ablated U-Pb dating-based determination of burial dolomitization process: A case study of Lower Ordovician Penglaiba Formation of Yonganba Outcrop in Tarim Basin

作　　者：乔占峰 张哨楠[1] 沈安江[2,3] 胡安平 梁峰[2,3] 罗宪婴 佘敏[2,3] 吕学菊 QIAO ZhanFeng;ZHANG ShaoNan;SHEN AnJiang;HU AnPing;LIANG Feng;LUO XianYing;SHE Min;LV XueJu(State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu 610500,China;PetroChina Hangzhou Research Institute of Geology,Hangzhou 310023 China;Key Laboratory of Carbonate Reservoir,CNPC,Hangzhou 310023 China)

机构地区：[1]西南石油大学,油气藏地质及开发工程国家重点实验室,成都610500 [2]中国石油杭州地质研究院,杭州310023 [3]中国石油天然气集团公司碳酸盐岩储层重点实验室,杭州310023

出　　处：《岩石学报》2020年第11期3493-3509,共17页Acta Petrologica Sinica

基　　金：国家科技重大专项(2016ZX05004-002);中国石油天然气股份有限公司科学研究与技术开发项目(2019B-0406)联合资助。

摘　　要：埋藏白云石化作用是形成厚层块状白云岩的主要机制之一,但其形成过程一直存在争议。本文以塔里木盆地永安坝剖面蓬莱坝组为例进行解剖,在露头和薄片岩石学研究的基础上,利用激光U-Pb定年和同位素分析,剖析了蓬莱坝组白云岩形成时期及演化过程,取得三个方面的认识:(1)蓬莱坝组发育四种类型白云岩:藻纹层白云岩、自形-半自形细中晶白云岩、雾心亮边自形中晶白云岩和他形粗晶白云岩,不同类型白云岩垂向互层发育;(2) U-Pb定年结果显示蓬莱坝组受三期云化作用改造,分别为准同生期云化作用、晚奥陶世到志留纪浅埋藏云化作用(464±12Ma到433±22Ma)及泥盆纪埋藏云化作用(382±29Ma),浅埋藏云化作用会对准同生白云石造成重结晶,而埋藏云化作用表现为白云石次生加大,存在寒武系云化流体卷入,影响U-Pb定年;(3)规模白云岩的发育为沉积环境和构造埋藏演化史共同作用的结果,提出塔中北斜坡和塔北南缘为规模白云岩发育区,这对本区油气勘探具有重要的指导意义。Burial dolomitization is the major mechanism for the formation of massive dolomite,but its process has been of a dispute for a long time. In this paper,we took the Lower Ordovician Penglaiba Formation outcropped at Yonganba profile in Tarim Basin as an example,and studied the timing and process of dolomitization of the Penglaiba Formation by using laser ablated U-Pb dating and isotope analysis on the basis of detailed observation of the outcrop and thin sections of collected samples from this profile. It’s concluded that:( 1) the Penglaiba Formation consists of four types of dolomite,including microbial dolomite,euhedral to subhedral fine to medium crystalline dolomite with zonation under CL,enhedral medium crystalline dolomite with cloud core and bright edges,and anhedral coarse crystalline dolomite,and these four types of dolomites are interbedded vertically in the profile;( 2) U-Pb dating revealed that three stages of dolomitization,including penecontemporaneous dolomitization,shallow burial dolomitization during Late Ordovician to Silurian( 464 ± 12 Ma ~ 433 ± 22 Ma),and burial dolomitization during Devonian( 382 ± 29 Ma). Shallow burial dolomitization tends to cause recrystallization of penecontemporaneous dolomite,and burial dolomitization leads to the overgrowth of pre-existing dolomite in certain degree. Additionally,involvement of Cambrian dolomitized fluids probably exist;( 3) it’s proposed that the formation of massive dolomite is controlled by depositional environment and tectonic-burial evolution,and as a result,the north slope of Tazhong uplift and the south slope of Tabei uplift could be favorable to the development of massive dolomite,which is meaningful to guide the hydrocarbon exploration.

关 键 词：激光铀铅定年 埋藏白云石化作用 规模白云岩 蓬莱坝组 塔里木盆地 

分 类 号：P588.245[天文地球—岩石学] P597.3[天文地球—地质学]