Age constraint on Burmese amber based on U-Pb dating of zircons
Age constraint on Burmese amber based on U-Pb dating of zircons
复制标题
DOI：
10.1016/j.cretres.2012.03.014
复制
发表时间：
2012-10-01
影响因子：
2.1
通讯作者：
Li, Xianhua
中科院分区：
文献类型：
--
作者：
Shi, Guanghai;Grimaldi, David A.;Li, Xianhua
缅甸北方的琥珀已经被商业开发了几千年，它也保存了世界上七个主要的白垩纪琥珀矿床中最多样化的古生物群。最近的估计年龄从Albian到Cenomanian不等，基于孢粉学，一种arnmonoid，以及保存在琥珀中的中生代昆虫分类群。含burmite岩石为沉积岩，主要由圆形岩屑碎屑（直径0.03 - 0.15 mm）和少量石英和长石碎片组成。岩屑碎屑中大部分是火山岩。从琥珀基质中分离出来的锆石可分为两组：第一组锆石生长过盛，具有变化的CL模式，形成后经历了轻微的地质扰动，其离子探针Pb-206/U-238年龄落在很窄的范围内，近似于102 Ma-108 Ma; II组锆石是典型的岩浆锆石，具有韵律性平坦带，推测其来源于火山岩碎屑，获得了98.79 ± 0.62Ma的Pb-206/U-238年龄。第一组锆石的测年仅针对其内部，因此隐藏了过度生长可能导致的年龄偏移。考虑到近岸海洋环境和1-m厚的含勃姆石沉积物，以及火山碎屑的同喷发和喷发后沉积，因此98.79 +/- 0.62 Ma的年龄可以用作勃姆石的最大极限（无论是在或之后），建立了最早的塞诺曼时代的包体。年龄还表明，火山喷发发生在98.79 +/- 0.62 Ma的湖岗谷附近。(C)2012爱思唯尔有限公司保留所有权利。
Amber from northern Myanmar has been commercially exploited for millennia, and it also preserves the most diverse palaeobiota among the worlds' seven major deposits of Cretaceous amber. Recent estimated ages vary from Albian to Cenomanian, based on palynology, an arnmonoid, and Mesozoic insect taxa preserved within the amber. The burmite-bearing rock is sedimentary and consists mainly of rounded lithic clasts (0.03 similar to 0.15 mm in diameter), with minor fragments of quartz and feldspar. Among the lithic clasts are mostly volcanic rocks. Zircons separated from the amber matrix form two groups: Group-1 zircons are overgrown and have variable CL patterns, experienced slight geological disturbances after they formed, and their Ion microprobe Pb-206/U-238 ages fall into a very narrow range of similar to 102 Ma- similar to 108 Ma; Group-II zircons are typical magmatic ones with rhythmically flat zones, inferred to be derived from volcanic rock clasts, and yielded a concordia Pb-206/U-238 age of 98.79 +/- 0.62 Ma. The dating on Group-1 zircons is only for their interiors, thus hiding what age excursion might come from the overgrowth. Considering the nearshore marine environment and 1-m thickness of the burmite-bearing sediments, and the syn- and post-eruption deposition of volcanic clasts, the age of 98.79 +/- 0.62 Ma therefore can be used as a maximum limit for the burmite (either at or after), establishing an earliest Cenomanian age for the fossilized inclusions. The age also indicates that volcanic eruption occurred at 98.79 +/- 0.62 Ma in the vicinity of the Hukawng Valley. (C) 2012 Elsevier Ltd. All rights reserved.