华北克拉通山西省晚石炭世基性岩墙成因:锆石U-Pb年龄、地球化学和Sr-Nd同位素证据(英文)  

Zircon U-Pb age,geochemical,and Sr-Nd isotopic constraints on the origin of Late Carboniferous mafic dykes of the North China Craton,Shanxi Province,China

作　　者：刘燊[1] 冯彩霞[1] 江博明 胡瑞忠[3] 翟明国[1] 赖绍聪[1] 

机构地区：[1]大陆动力学国家重点实验室、西北大学地质学系,西安710069 [2]台湾国立大学地质科学系,中国台北 [3]矿床地球化学国家重点实验室、中国科学院地球化学研究所,贵阳550002

出　　处：《岩石学报》2014年第6期1707-1717,共11页Acta Petrologica Sinica

基　　金：supported by the Opening Project(201206) of State Key Laboratory of Ore deposit Geochemistry;National Natural ScienceFoundation of China(41373028)

摘　　要：作为岩石圈伸展拉张背景侵位的特征岩石，基性岩墙群（煌斑岩、辉绿岩和辉绿玢岩等）地质和地球化学研究日益受到地质研究者的关注。研究显示，基性岩墙在全球范围主要分布在美国、加拿大、巴西、澳大利亚和中国等地区，且年代格架主要集中在前寒武纪时期（2．4Ga、2．1Ga、1．8Ga、1．4Ga、1．0Ga）。目前，国内中生代以来基性岩墙群主要出露于华北克拉通、华南、西藏和塔里木盆地。本研究基性岩墙来自山西省大同附近，对于该套岩墙，本文给出了锆石u—Pb定年、地球化学和Sr-Nd同位素证据。LA．ICP．MS锆石u．Pb年龄为293bla，岩石具有变化较小的主元素变化特征（Si02=50．78％～51．35％，TiO，=2．16％-2．32％，Al2O3=14．53％-15．08％，Fe203=12．42％～12．66％，MnO=0．13％～0．16％，MgO=5．14％-5．35％，CaO=7．93％～8．25％，N如O=3．52％～3．78％，K20=1．01％～1．14％和P205=0．24％-0．36％）。另外，基性岩墙富集轻稀土元素、大离子侵石元素（Ba，K和sr）和高场强元素（Nb，Ta和zr），亏损Th、Pb和Ti。同时，基性岩墙具有相对一致的（87Sr／86Sr）；比值（0．70422～0．70423），正的￡Nd（f）值（5。8—6．1）和变化较小的Nd模式年龄（tDMI=0．67～0．72Ga，tDM2=0．57～0．59Ga）。以上特征表明，基性岩墙来自亏损软流圈地幔的分布熔融作用，岩浆侵位过程中发生了橄榄石、辉石和含Ti相矿物的分离结晶作用，但没有受到地壳物质的混染作用影响。基性岩墙的成因上与华北克拉通和西伯利亚板块碰撞后的拉伸作用有密切联系。As the special result of lithospheric extension, nowadays, the invistigation on geology and geochemistry of the marie dykes （e. g. , lamprophyre, delerite, diabase porphyrite, etc. ） has been given special attention. The mafic dykes mainly distribute in America, Canada, Brazil, Australian and China. In addition, the ages of these dykes are between 2. 4Ga and 1.0Ga. At present, the Mesozoic and Cenozoic mafic in China were found in North China Craton （NCC）, southern China, Tibet and Tarim basin. The studied mafic dykes came from Shanxi Province, northern NCC. Herein, we report U-Pb zircon ages, whole-rock geochemistry, and Sr-Nd isotopic data for representative samples of these dykes. Laser ablation-inductively coupled plasma-mass spectrometry （LA-ICP-MS） U- Pb analysis of zircons yielded a consistent Late Carboniferous （293.4 ±1.7Ma） age for one sample of the rocks analyzed during this study. Dolerites within the study area have a narrow range of compositions （ SiO2 = 50. 78% ~ 51.35%, TiO2 = 2. 16% ~ 2. 32%, A1203 = 14.53% ~ 15.08%, Fe203 = 12. 42% - 12. 66%, MnO =0. 13% ~0. 16%, MgO =5.14% -5.35%, CaO =7.93% ~ 8. 25%, Na20 =3.52% -3.78%, K20 = 1.01% - 1.14%, and P205 =0. 24% -0. 36% ）. The dolerites are enriched in light rare earth elements （LREE）, large ion lithophile elements （LILE; i. e. , Ba, K, and Sr） and high field strength elements （Nb, Ta, and Zr）, and depleted in Th, Pb, Nb, P, and Ti. These mafic dykes have relatively uniform （STSr/S6Sr）i values （0. 70422 ~0. 70423）, positive 8Nd （t） values （5. 8 ~ 6. 1 ）, and invariant neodymium model ages （ tDMl = 0. 67 ~ 0. 72Ga, tvM2 = 0. 57 ~ 0. 59Ga）. These data suggest that these dykes formed from magmas derived from partial melting of a depleted asthenospheric mantle source that fractionated olivine, pyroxene, and Ti-bearing phases without assimilating significant amounts of crustal material. In summary, the generation and emplacement of mafic magmas in Shanxi Province, northern NCC can be attributed to pos

关 键 词：晚石炭世 基性岩墙 成因 华北克拉通北部 西伯利亚板块 

分 类 号：P588.134[天文地球—岩石学] P597.3[天文地球—地质学]