南秦岭石泉北部将军河地区中酸性岩脉锆石U-Pb 年代学及其构造意义
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Zircon UPb Geochronology of IntermediateFelsic Dykes from the Jiangjunhe Area in Northern Shiquan, South Qinling Mountains and Its Geological Significance
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    摘要:

    南秦岭石泉北部中酸性岩脉发育,大部分岩脉与地层之间为构造接触关系,其形成时代及与区域金矿化的关系一直存在疑问。本研究采集石泉北部将军河地区中酸性岩脉13件,通过详细野外观察与室内鉴定,确定岩脉的岩性主要为闪长岩类。主量元素分析数据表明闪长岩的SiO2含量为53.19%~68.48%,铝饱和指数A/CNK值为0.67~1.28,里特曼指数σ值介于1.4~2.93之间;微量元素分析数据表明中酸性闪长岩脉的稀土总量较低(ΣREE=44.54×10-6~253.23×10-6),REE球粒陨石标准化图呈轻、重稀土高度分馏的右倾型(HREE/LREE=6.15~14.87,(La/Yb)N=5.97~38.67),具有弱负Eu异常(δEu=0.68~0.88);微量元素蛛网图显示富集大离子亲石元素(Ba、K、Sr)与高场强元素(Zr、Hf),相对亏损高场强元素(HREE、Ti、P、Th),岩脉可能来自于与消减作用有关的下地壳物质重熔。闪长岩脉的单颗粒锆石UPb年龄为771.9±3.4Ma,与汉南杂岩、安康北部的凤凰山内新元古代的岩浆活动具有同步性,指示区域伸展裂解的构造背景。根据野外填图推测南秦岭石泉北部将军河地区新元古代的岩脉对金矿的形成没有直接关系。

    Abstract:

    Numerous intermediatefelsic dykes are present in the northern part of Shiquan County in the South Qinling region. Most of the dykes have a structural contact relation with strata. But the relationship between formation age and gold mineralization in this area has been debated. In this study, a total of 13 rock samples were collected from several intermediatefelsic dykes in the northern part of Shiquan County. Field observation and indoor identification suggest that these dykes belong to diorite. The major elements analysis shows that diorite has a SiO2 content of 53.19%~68.48%, with A/CNK value of 0.67~1.28 and Rittman index (σ) of 1.4~2.93. The REE compositions indicate that intermediatefelsic dykes have a lower content of total REE (ΣREE=(44.54~253.23)×106) and are characterized by significant light REE enrichments relative to heavy REE (HREE/LREE=6.15~14.87, with (La/Yb)N=5.97~38.67) and weak negative Eu anomaly(δEu=0.68~0.88). Trace element analysis shows an obvious enrichment of lithophile elements (such as Ba, K, Sr), and depletion of high field strength elements (such as HREE, Ti, P, Th), indicating that these dykes were the products of lower crust remelting induced by the oceanic lithosphere subduction. Single zircon UPb dating age (771.9 ± 3.4 Ma) of diorite dykes is synchronous to that of the complex in southern Hanzhong and the Neopaleozoic magmatic activity at Fenghuangshan Mts north of Ankang, indicating a tectonic setting of regional extension breakup. Field geological mapping indicates that the Neoproterozoic dikes in the Jiangjunhe area has no direct genetic relation with the formation of gold deposits.

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段少帅,焦建刚,罗德智,黄喜峰,王硕,陈炳龙.2017.南秦岭石泉北部将军河地区中酸性岩脉锆石U-Pb 年代学及其构造意义[J].地质学报,91(4):748-761.
DUAN Shaoshuai, JIAO Jiangang, LUO Dezhi, HUANG Xifeng, WANG Shuo, CHEN Binglong.2017. Zircon UPb Geochronology of IntermediateFelsic Dykes from the Jiangjunhe Area in Northern Shiquan, South Qinling Mountains and Its Geological Significance[J]. Acta Geologica Sinica,91(4):748-761.

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  • 在线发布日期: 2017-04-25