摘要
里尔峪组是古元古界南辽河群早期沉积地层,其成因对探讨辽-吉造山/活动带的大地构造属性具有重要意义。论文以辽东黄花甸地区里尔峪组为研究对象,对其进行了详细的野外地质填图和室内岩相学、地球化学以及同位素年代学研究工作。里尔峪组主体岩石类型为含不等量磁铁矿、电气石的黑云母变粒岩类夹斜长角闪岩。变粒岩中锆石阴极发光(CL)图像显示其具有震荡环带,说明其具有岩浆成因的碎屑锆石特征,LA-ICP-MS锆石U-Pb年龄数据具有1936Ma、2082Ma、2178Ma和2574Ma的年龄峰值,主峰与区内古元古代花岗质岩石的形成年龄一致,反映其物源主要来自于古元古代花岗质岩石,少量来自于太古宙克拉通结晶基底。其中1800~2000Ma的锆石年龄极可能是受变质作用改造的结果。斜长角闪岩呈夹层或透镜体状产出于里尔峪组变粒岩中,地球化学特征显示:(1)SiO_2含量为48.83%~51.50%,具有较低TiO_2含量(0.95%~1.33%)、低MgO含量(6.67%~9.49%)特征;(2)Mg#值为48~59,低于原生玄武质岩浆Mg#值,说明原岩岩浆经历了原始岩浆的结晶分异作用;(3)稀土元素总量(ΣREE)值为59.87×10^(-6)~82.83×10^(-6),LREE/HREE值介于3.58~4.88,(La/Yb)_N值为2.33~4.50,稀土元素配分模式具有岛弧火山岩的特征而不同于MORB型火山岩。微量元素Ba、U、Sm相对富集,亏损高场强元素Th、Nb、P、Ta等,Nb、Ta相对亏损,贫Cr、Ni,说明原岩为形成于岛弧环境或活动大陆边缘的高铁拉斑玄武岩。斜长角闪岩中锆石阴极发光图像具有两类特征,第一类具有核边结构,锆石核部主要呈暗色,内部结构比较复杂,部分保留岩浆环带特征;第二类锆石其内部结构比较均一,为典型的变质锆石,并且具有继承性锆石核以及变质增生边。LA-ICP-MS锆石U-Pb定年得出两件斜长角闪岩的原岩年龄分别为1995±13Ma、2150±21Ma,大致代表了里尔峪组的形成时代。综上所述,黄花甸地区里尔峪组原岩为形成于岛弧或活动大陆边缘的碎屑岩夹基性火山岩沉积建造,物源主要来自于辽-吉造山/活动带内的古元古代花岗岩和南北两侧的太古宙的变质基底,该套地层在~1.88Ga遭受了变质作用的改造。结合前人对胶-辽-吉古元古代岩石构造变形、变质作用等研究成果,本文研究认为南辽河群所在的胶-辽-吉活动带在~2.2Ga发生了从东部陆块拉张弧后裂解,2.0~2.15Ga发生有洋壳的俯冲,在~1.88Ga发生造山变质作用形成区域上的胶-辽-吉造山带。
The Lieryu Formation of the South Liaohe Group is an Early Paleoproterozoic stratum unit in previous geological mapping and has great significance to study the tectonic setting of the Liao-Ji orogenic/activity belt. We conducted a detailed field geological survey and petrography, geochemistry and geochronology studies on the Lieryu Formation in the Huanghuadian area of the Liaodong Peninsula. The Lieryu Formation consists of magnetite and tourmaline bearing gneisses, and amphibolite lenses occasionally. Most detrital zircons from the gneiss in the formation show oscillatory zones under Cathodoluminescenee （CL） image, which indicate a magmatic origin. Four peak-ages have been obtained by zircon U-Pb LA-ICP-MS dating： 1936Ma, 2082Ma, 2178Ma and 2574Ma. The third-peak of 2178Ma is very similar to the age of Liaoji Paleoproterozoic granite, which might be a major provenance for the zircons in the Lieryu Formation. Another peak-age of 1800- 2000Ma should be a metamorphic age compared to the regional metamorphic events. The amphibolite in the formation, exposed as boudinages or lenses, have the following geochemical characteristics ： （ 1 ） SiO2 contents of 48. 83% -51.50%, low TiO2 contents （0. 95% - 1.33% ） and MgO contents （6. 67%-9.49% ） ; （2） Mg# values of 48 - 59, lower than that of the primary basaltic magma, indicating that the original magma has undergone the crystallization differentiation of the primitive magma; （3） The total amount of rare earth element of 59. 87 × 10-6 - 82. 83 × 10-6, the ratios of LREE/HREE of 3.58 - 4. 88 and （La/Yb）N value is between 2. 33 - 4. 50; （4） relatively enriched Ba, U and Sm, and relatively depleted high field strength elements such as Th, Nb, P and Ta. The distribution patterns of REE show that protoliths of the amphibolites should be formed in an arc-related or active continental margin-related setting. Zircons CL image from the amphibolites in the Lieryu Formation can be divided into two types, the first type has dark color, and core-rim concentric oscillatory zones with sharp boundaries, the inner structure is relatively complicate; the second type contains an overgrowth margin, which indicates a typical type of metamorphic zircon. Two kinds of age have been obtained using zircon U-Pb LA-ICP-MS dating method： 1995± 13Ma and 2150± 21Ma, the latter of which roughly indicate a formation age of the Lieryu Formation. Overall, the protoliths of Lieryu Formation might be formed in an arc-related or active continental margin-related tectonic setting; the provenance of the Formation should be from the Liaoji granitic rocks and basements in two sides. Combined with regional geological data, the study area which contains the Liaohe Group might rifted from a continental margin as a back-arc basin at the age of 2. 2Ga, underwent a subduction setting in 2. 15 -2. 0Ga and orogenetic event in - 1.88Ga forming the Jiao-Liao-Ji orogenic belt at last.
作者
高铂森
董永胜
李富强
王鹏森
甘宜成
陈木森
田忠华
GAO BoSen DONG YongSheng LI FuQiang WANG PengSen GAN YiCheng CHEN MuSen(College of Earth Science, Jilin University, Changchun 130061, China Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2017年第9期2725-2742,共18页
Acta Petrologica Sinica
基金
国家自然科学基金重点项目(41430210)
中国地质调查局地质调查项目(DD20160121)联合资助
关键词
里尔峪组
南辽河群
地质年代学
岛弧
黄花甸
辽东
Lieryu Formation
South Liaohe Group
Geochronology
Island arc environment
Huanghuadian area
Eastern Liaoning
