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J4 ›› 2010, Vol. 16 ›› Issue (3): 294-308.

• 矿物·岩石·地球化学 • 上一篇    下一篇

宁芜盆地浅成侵入岩的锆石U-Pb年代学和Hf同位素研究及其地质意义

 胡劲平, 蒋少涌   

  1. 内生金属矿床成矿机制研究国家重点实验室(南京大学),南京大 学 地球科学与工程学院,南京 210093
  • 收稿日期:2009-06-23 修回日期:2010-03-15 出版日期:2010-09-20 发布日期:2010-09-20
  • 通讯作者: 蒋少涌,E-mail: shyjiang@nju.edu.cn
  • 作者简介:胡劲平,男,1988年生,地球化学专业本科生
  • 基金资助:

      江苏省自然科学基金重点课题(BK2008026);国家自然科学基金 (40221301)

Zircon U-Pb Dating and Hf Isotopic Compositions of Porphyrites from
the Ningwu Basin and Their Geological Implications

 HU Jin-ping, JIANG Shao-yong   

  1. tate Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing 210093, China
  • Received:2009-06-23 Revised:2010-03-15 Online:2010-09-20 Published:2010-09-20

摘要:

宁芜火山岩盆地是长江中下游成矿带中最重要的矿集区之一,以产出玢岩型铁矿而著称。盆地内的岩浆活动产物可
分为龙王山组,大王山组,姑山组和娘娘山组4个旋回火山岩及相关浅成侵入岩。本文对该盆地中凹山铁矿的成矿母岩——
辉长闪长玢岩进行了精确的锆石U-Pb定年和Hf同位素组成测定。3个样品的锆石U-Pb年龄分别为(123±1) Ma,(127±3)
Ma和(125±2)Ma。前人已对该盆地中火山岩开展过较多的定年工作,获得大王山组的锆石U-Pb年龄为127~131 Ma。 因此,
与成矿密切相关的辉长闪长玢岩与第二旋回大王山组火山岩同期,形成年龄相近或略晚于火山岩。辉长闪长玢岩中锆石εHf
(t) 值为-6.3~-8.6, 结合前人的地球化学数据,该岩石的形成可能与软流圈地幔上涌、富集岩石圈地幔熔融并与地壳物质
混合有关,这一过程发生于华南约125 Ma时岩石圈强烈伸展时期。同位素组成特征表明,与盆地内火山岩相比,宁芜浅成
侵入岩形成过程中有更多的地壳物质加入

关键词: 宁芜火山岩盆地, 辉长闪长玢岩, 锆石U-Pb年龄, Hf同位素

Abstract:

Ningwu volcanic basin is one of the most important basins related to mineral deposits in middle-lower reaches of the
Yangtze River belt. Four volcanic units occur in the basin, in an ascending order, the Longwangshan Formation, the Dawangshan
Formation, the Gushan Foramtion and the Niangniangshan Formation, with some high-level sub-volcanic igneous rocks intruding
them. Detailed zircon U-Pb dating and Hf  isotopic composition measurement were performed on  the host  rocks  (gabbro-diorite
porphyrites) of  the Washan  iron deposit. The zircon U-Pb ages of  three samples are  (123±1) Ma,  (127±3) Ma and  (125±2)
Ma, respectively.Together with previously published precise zircon U-Pb dating results for volcanic rocks (127 to 131Ma), these
results have placed a better constraint on  the magmatic and mineralization activity duration of  the Ningwu volcanic basin. The
zircons  from  the Ningwu porphyrites have εHf
( t ) values  from -6.3  to -8.6. Together with other available geochemical data,  the
Hf  isotope data  indicate  that  the Ningwu porphyrites may have derived  from upwelling depleted asthenospheric mantle mixed
with enriched mantle and crust, which was controlled by the extensive lithosphere extension at around 125 Ma. The lower εHf(t)
values and slightly younger ages of  the gabbro-diorite porphyrites  than  their hosting volcanic  rocks may  indicate more crust
material involvement in the porphyrite petrogenesis.

Key words: :Ningwu volcanic basin, grabbro-diorite porphyrite, zircon U-Pb age, Hf isotopes

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