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董春艳,王晨,颉颃强,白文倩,万渝生. 2018. 冀东新太古代晚期界岭口闪长岩成因:U-Pb-Nd-Hf-O同位素研究. 岩石学报, 34(9): 2793-2810
冀东新太古代晚期界岭口闪长岩成因:U-Pb-Nd-Hf-O同位素研究
作者单位E-mail
董春艳 中国地质科学院地质研究所北京离子探针中心, 北京 100037  
王晨 中国地质科学院地质研究所北京离子探针中心, 北京 100037  
颉颃强 中国地质科学院地质研究所北京离子探针中心, 北京 100037  
白文倩 中国地质科学院地质研究所北京离子探针中心, 北京 100037  
万渝生 中国地质科学院地质研究所北京离子探针中心, 北京 100037 wanyusheng@bjshrimp.cn 
基金项目:本文受国家自然科学基金项目(41472169)和中国地质调查局重点项目(DD20160121-03、121201102000150012、121201102000150010-04)联合资助.
摘要:
      本文报道了华北克拉通东部冀东地区界岭口闪长岩及其中基性岩包体的锆石定年结果和地球化学组成。界岭口闪长岩是华北克拉通规模最大的太古宙闪长质侵入体,总面积约650km2。界岭口闪长岩由闪长岩和石英闪长岩组成,两者渐变过渡。在界岭口闪长岩中存在基性岩包体,包括辉绿岩、细粒辉长岩和辉长岩,一些基性岩包体边部存在冷凝边。石英闪长岩和细粒辉长岩包体的岩浆锆石年龄分别为2533±5Ma和2534±8Ma。闪长岩和石英闪长岩元素组成类似(13个样品),主要区别是后者SiO2相对较高一些。它们稀土总量较高(TREE=93.0×10-6~234.2×10-6),轻重稀土分异程度不强((La/Yb)N=10.4~23.9),无明显铕异常(Eu/Eu*=0.80~1.05)。在MORB标准化的微量元素图解上,大离子亲石元素相对富集,高场强元素相对亏损。全岩εNdt)和tDM1(Nd)分别为-1.20~2.13和2.73~2.95Ga(7个样品),岩浆锆石εHft)和tDM1(Hf)分别为1.66~4.37和2.60~2.78Ga(13个数据点),δ18O值为5.00‰~6.83‰(13个数据点)。相对于闪长岩-石英闪长岩,基性岩包体(3个样品)的MgO和CaO含量明显增高。岩石稀土总量偏低(TREE=82.4×10-6~155.7×10-6),轻重稀土分离不强((La/Yb)N=3.3~6.0),出现较弱的负铕异常(Eu/Eu*=0.71~0.88),在MORB标准化的微量元素图解上,大离子亲石元素相对富集,高场强元素相对亏损。全岩εNdt)和tDM1(Nd)分别为-0.70和2.97Ga(1个样品),岩浆锆石εHft)和tDM1(Hf)分别为0.52~4.72和2.66~2.82Ga(16个数据点),δ18O值为4.88‰~6.72‰(13个数据点)。结合前人研究,可得出如下结论:1)界岭口闪长岩是基性岩浆结晶分异和陆壳物质影响双重作用的产物,而陆壳物质参与可能起了更重要的作用;2)界岭口闪长岩形成于新太古代晚期总体上仍处于挤压的岛弧构造环境;3)在华北克拉通,至少一部分具有中太古代晚期-新太古代早期Nd-Hf模式年龄的新太古代晚期TTG岩石形成与新太古代晚期富集地幔添加有关或是新太古代晚期亏损地幔添加与陆壳物质影响共同作用的结果。
英文摘要:
      This paper reports zircon geochronology and whole-rock geochemistry of Jielingkou diorite and its basic enclaves in eastern Hebei, eastern North China Craton. Jielingkou diorite is the largest diorite intrusive body with a total area of~650km2 in the North China Craton. It is composed of diorite and quartz diorite, with both showing gradual transformation. There are some basic enclaves in Jielingkou diorite, including diabase, fine-grained gabbro and gabbro, with some diabase enclaves with chilling margins. SHRIMP U-Pb dating reveals that quartz diorite and fine-grained gabbro enclave have magmatic zircon ages of 2533±5Ma and 2534±8Ma. Diorite and quartz diorite are similar in composition (13 analyses), with the main difference being that the latter is higher in SiO2 content. They are relatively high in TREE (93.0×10-6~234.2×10-6) and (La/Yb)N ratios (10.4~23.9) with no obvious Eu anomalies (0.80~1.05). In the MORB-normalized trace element plot, they are enriched in LILE and show negative Nb (Ta) anomalies. Whole-rock εNd(t) and tDM1(Nd) are -1.20~2.13 and 2.73~2.95Ga (7 analyses), respectively, and magmatic zircon has εHf(t) and tDM1(Hf) of 1.66~4.37 and 2.60~2.78Ga (13 analyses) and δ18O of 5.00‰~6.83‰ (13 analyses). Compared with diorite and quartz diorite, basic enclaves (3 analyses) are obviously higher in MgO and CaO contents, lower in TREE (82.4×10-6~155.7×10-6) and (La/Yb)N ratios (3.3~6.0) and show weak Eu anomalies (0.71~0.88). In the MORB-normalized trace element plot, they are also enriched in LILE and show negative Nb (Ta) anomalies. Whole-rock εNd(t) and tDM1(Nd) are -0.70 and 2.97Ga (1 analyses), respectively, and magmatic zircon has εHf(t) and tDM1(Hf) of 0.52~4.72 and 2.66~2.82Ga (16 analyses) and δ18O of 4.88‰~6.72‰ (13 analyses). Combined with previous studies, some conclusions can be drawn as follows:1) Jielingkou diorite resulted from a combined process of basic magmatic crystallization and continental material addition, with the latter playing an more important role; 2) Jielingkou diorite was formed in an arc environment at the end of the Neoarchean; 3) in the North China Craton, at least some of the Late Neoarchean TTG rocks with Late Mesoarchean to Early Neoarchean Nd-Hf model ages were formed as a result of enriched mantle addition to continent or combined depleted mantle addition and continental contamination at the end of the Neoarchean.
关键词:闪长岩  U-Pb-Nd-Hf-O同位素  新太古代  冀东  华北克拉通
投稿时间:2017-11-05  修订日期:2018-02-06
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