ISSN 1009-6248CN 61-1149/P 双月刊

主管单位:中国地质调查局

主办单位:中国地质调查局西安地质调查中心
中国地质学会

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    巴西圣弗朗西斯科克拉通Gaviao地块Jussiape杂岩中太古代二长花岗岩的识别及其地质意义

    Identification and Its Geological Significance of Mesoarchean Monzogranite in the Jussiape Complex of the Gaviao Block, Sao Francisco Craton, Brazil

    • 摘要: Jussiape杂岩是巴西圣弗朗西斯科克拉通Gaviao地块内古元古代重要的岩浆岩单元,被认为由Jussiape Ⅰ花岗岩(2 121 Ma)和Jussiape Ⅱ正长花岗岩(2 052 Ma)构成。为了进一步厘清Jussiape杂岩的侵入时代、查明其岩体特征和对区域岩浆活动、构造背景及成矿的指示意义,笔者对Jussiape花岗岩开展了岩石学、锆石U−Pb同位素年代学和Lu−Hf同位素研究,在Jussiape Ⅰ花岗岩内识别出了一组中太古代的二长花岗岩侵入岩,其锆石U−Pb同位素年龄为(3 108±22) Ma。SiO2含量为72.23%~72.50%,Al2O3含量为14.68%~15.09%,TiO2含量约为0.24%,Na2O含量为5.29%~5.66%,K2O含量小于2%,K2O/Na2O均值为0.29,TFeO+MgO均值为2.42%;具有较为明显的Nb、Ta、P、Ti、Sr负异常,Ni、Cr等相容元素含量很低,Hf−Rb−Ta图解显示其为碰撞大地构造背景下的花岗岩;稀土元素配分曲线为较为平缓的右倾斜型,轻稀土富集,La/Yb值大于15,具Ce、Eu负异常。εHf(t)值为−18.31~−0.53,二阶段模式年龄TDM2为3 523~4 063 Ma。这些地质特征指示Jussiape中太古代的二长花岗岩源于古老地壳物质循环再造,其成岩受区域Barra do Mendes−Joao Correa线状构造控制,是对中太古代Gaviao地块南部西侧岩浆弧活动的响应,与区域中太古代短暂存在的自西向东的俯冲、碰撞造山大地构造背景一致。Barra do Mendes−Joao Correa线状构造在古元古代持续活动,控制或影响了Jussiape Ⅰ花岗岩、Jussiape Ⅱ正长花岗岩和Ibitiara花岗闪长岩的侵位和展布,构成了区内重要的构造−岩浆−成矿带,具有IOCG型矿床(铁氧化物铜−金矿床)成矿潜力,是Gaviao地块内该类型矿床勘查突破的关键区带。

       

      Abstract: The Jussiape Complex developed in Gaviao Block of Sao Francisco Craton is composed by Jussiape Ⅰ granite and Jussiape Ⅱ syenogranite with intrusion ages of 2 121 Ma and 2 052 Ma respectively. In order to determination the intrusive age and petrological characteristics of the Jussiape Complex, and discuss the significance to regional magmatic activity, tectonic setting, and mineralization,petrology,zircon U−Pb isotope chronology, and Lu−Hf isotope studies of the jussiape granite are carried out. Finally, a group of mesoarchean monzogranite intrusions with zircon U−Pb isotopic age of (3108±22 )Ma were identified in the jussiape Ⅰ granite. Petrogeochemical date show that, the samples SiO2 content is 72.23%–72.50%, Al2O3 content is 14.68%–15.09%, TiO2 content is 0.24%, Na2O content ranges from 5.29%–5.26%,K2O content is less than 2% with K2O/Na2O value is 0.29, the average value of TFeO+MgO is 2.42%. The samples exhibit depletion in Nb, Ta, P, Ti, Sr, and compatible elements such as Ni and Cr, the Hf−Rb−Ta diagram shows a collision tectonic granite feature; The rare earth element distribution curve shows a relatively gentle right tilt type and the La/Yb ratio is greater than 15, with enrichment of LREE and negative Ce andEu anomalies. Lu−Hf isotope analysis show that the εHf (t) value range from −18.31 to −0.53 and the value of TDM2 is 3 523–4 063 Ma,indicating that the Jussiape monzogranite originated from the recycling of ancient crustal materials and controlled by the Barra do Mendes−Joao Correa lineament which is responding to the magmatic arc activity in the west of the southern part of the Gaviao Block.It is consistent with the subduction and collisional orogeny tectonic background that briefly existed in the southern part of the Gaviao Block during the Mesoarchean. The Barra do Mendes−Joao Correa lineament reactivated during the period of 2.1–1.9 Ga, forming a series of granite bodies such as Jussiape Ⅰ granite,Jussiape Ⅱ syenogranite and Ibitiara granodiorite that spread in a NNW direction.It is the most important structral−magmatic−metallogenetic belt in the region and has potential for IOCG-type deposits.

       

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