冀东地区新太古代晚期的岩浆事件与地壳增生:来自岩石地球化学和锆石年龄及Hf同位素的制约  

Late Neoarchean magmatism and crustal growth in eastern Hebei:Constraint from geochemistry,zircon U-Pb ages and Hf isotope

作　　者：耿元生[1] 杨崇辉[1] 杜利林[1] 任留东[1] 宋会侠[1] GENG YuanSheng;YANG ChongHui;DU LiLin;REN LiuDong;SONG HuiXia(Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China)

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《岩石学报》2018年第4期1058-1082,共25页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41572175);地质调查项目(DD20160121-04;DD20160120-04)联合资助

摘　　要：在华北克拉通东部冀东的遵化-迁西-迁安地区广泛分布有新太古代晚期的斜长角闪岩(基性火山岩)、TTG片麻岩和紫苏闪长岩/紫苏花岗岩。锆石U-Pb同位素测定表明,该区的斜长角闪岩、TTG片麻岩和紫苏闪长岩/紫苏花岗岩几乎同时形成于2529±30Ma到2555±14Ma期间。这是华北克拉通新太古代晚期一次重要的岩浆事件,并紧随有2.5Ga左右的麻粒岩相变质作用。阴极发光图像显示,TTG片麻岩和紫苏闪长岩/紫苏花岗岩中一些锆石的核部为灰黑色,具杉树叶结构或无内部结构,意味着这些锆石核部的U-Th-Pb同位素体系在变质作用期间受到了干扰或重置,因此岩浆锆石核部的207Pb/206Pb加权平均年龄通常被解释为代表岩浆事件最年轻的年龄。新太古代晚期TTG片麻岩和紫苏闪长岩/紫苏花岗岩的岩浆锆石具有正的εHf(t)值(-0.08~9.49),计算的tDM1(Hf)模式年龄介于2572~2896Ma之间,峰值年龄为2.72Ga。这表明,TTG片麻岩和紫苏闪长岩/紫苏花岗岩的母岩浆是从亏损地幔源分异出来的,且2.7Ga是研究区和华北克拉通最重要的一次地壳增生事件。地球化学和岩石成因研究表明,本区的TTG片麻岩和紫苏闪长岩/紫苏花岗岩是由来自新生地壳基性岩石部分熔融形成的岩浆通过结晶分离形成的,其中角闪石是主要的分离相矿物。地幔柱模式更有利于解释本区TTG片麻岩和紫苏闪长岩/紫苏花岗岩的成因以及冀东地区的许多其他地质特征。Amphibolites（ basic volcanics）,TTG gneisses and hypersthene-diorite/charnockite of Late Neoarchean age are widely distributed throughout the Zunhua-Qianxi-Qian＇an area in eastern Hebei,North China Craton. SHRIMP zircon U-Pb isotopic dating reveals that amphibolites,TTG gneisses and hypersthene-diorite/charnockites were synchronously from 2529 ± 30 Ma to 2555 ± 14 Ma,reflecting an important Late Neoarchean magmatic event in the North China Craton, followed by sequential granulite facies metamorphism at - 2. 5Ga. CL images exhibed that some cores of zircons from TTG gneisses and hypersthene-diorite/charnockites are black-gray with fir-leaf structure or structureless,implying that the U-Th-Pb isotopic system of the cores of the zircons have been turbulenced or reseted during metamorphism,so the -（207）Pb/-（206）Pb weighted mean ages in cores of magamatic zircons are generally interpreted as the youngest age of magmatic event. Magmatic zircons of the Late Neoarchean TTG gneisses and charnockites have positive εHf（ t） values of-0. 08 - 9. 49 and calculated t_（DM1）（ Hf） ages from 2572 Ma to 2896 Ma with a peak age of 2. 72 Ga,suggesting that the TTG gneissic and charnockitic magma were direved from depleted mantal source,and 2. 7Ga was an important crustal growth event in the studed area and the North China Craton. Geochemical and petrogenetic studies revel that the TTG gneisses and hypersthene-diorite/charnockites in the area were formed by fractional crystaollization in the magmas direved from juvenile crustal rocks with hornblende as the primary frantionated phase. A mantle plume model is favored from petrogenesis of TTG gneisses and hypersthene-diorite/charnockite which explains the many other gellogical features in the eastern Hebei of the North China Craton as well.

关 键 词：新太古代晚期岩浆事件 SHRIMP锆石U-PB定年 锆石Hf同位素 TTG片麻岩 紫苏闪长岩/紫苏花岗岩 冀东 华北克拉通 

分 类 号：P588.345[天文地球—岩石学] P597.3[天文地球—地质学]