| 蒙古国呼勒德地区正长岩锆石SHRIMP铀-铅年龄及其地质意义 |
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| 引用本文：云飞,刘翼飞,江思宏,白大明.2010.蒙古国呼勒德地区正长岩锆石SHRIMP铀-铅年龄及其地质意义[J].地球学报,31(3):365-372. |
| DOI：10.3975/cagsb.2010.03.10 |
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| 基金项目:国家科技支撑课题(编号: 2007BAB25B02) ; 地质调查项目(编号: 1212010911029) |
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| 中文摘要:呼勒德稀土元素矿化区位于蒙古国中戈壁省南部, 区内稀土元素和金矿(化)点星罗棋布, 为蒙古中南部最重要的金属矿化集中区之一。在所有上述矿床(点)中, 稀土元素矿化在下二叠统火山-沉积岩内呈似层状、脉状和透镜体状产出, 并且与呼勒德碱性正长岩株具有密切空间分布关系。本次研究对呼勒德正长岩进行了锆石SHRIMP铀-铅同位素年龄测定, 所获同位素年龄值为(214.3 ± 2.5)Ma, MSWD值为0.52, 属中生代印支期。根据上述同位素年代学数值, 同时结合其他地质与地球化学证据, 可以推测, 中生代时期, 受古陆块内部构造应力调整作用影响, 呼勒德地区一带及东西两侧曾发生过强烈构造-岩浆活动, 并且形成碱性正长岩株及相关的稀土元素矿(化)点。印支期碱性岩浆活动不仅为稀土元素矿(化)点的形成提供了物质、动力和热力来源, 而且是成矿流体对流循环的“发动机”。对比分析结果表明, 呼勒德碱性正长岩体的形成时间与南蒙古鲁金郭勒碱性花岗斑岩脉及相关稀土元素矿床形成时代大体相似, 它们均是地壳演化特定阶段混源(壳、幔源)岩浆活动的产物。 |
| 中文关键词:碱性正长岩 锆石SHRIMP年龄 呼勒德稀土元素矿化区 印支期 中南蒙古 |
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| Zircon SHRIMP U-Pb Dating of the Alkaline Syenite Stock in the Khuld Rare Earth Element Mineralized District of Central-South Mongolia and Its Geological Implications |
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| Abstract:Located on the southern margin of the Siberian Platform, the Khuld district is one of the most important REE, gold and uranium mineralized districts in Central-South Mongolia. Mineralization occurs both in the Late Paleozoic volcano-sedimentary sequence and in the Paleozoic-Mesozoic intrusions. Among these intrusions, the Khuld alkaline syenite stock shows an intimate spatial relationship with the REE ore spots. It intruded into the Permian volcano-sedimentary rocks, and has an outcrop of 15 km2. The stock consists mainly of alkaline porphyritic syenite in the central phase and fine- to medium-grained alkaline syenite in the marginal phase. A fresh alkaline porphyritic syenite sample from the Khuld stock was selected for SHRIMP U-Pb age dating. The zircon grains separated from the fresh whole rock sample have given a weighted mean 206Pb/238U age of 214.3±2.5Ma, with a MSWD value of 0.52. Comparative studies indicate that the Khuld alkaline syenite stock and related REE ore spots are similar to REE-bearing Lugiin Gol nepheline syenite complex which also occurs in Central-South Mongolia. Both Khuld and Lugiin Gol REE-bearing alkaline syenite intrusions have ?Nd(t) values ranging from 1.22 to 2.26 with an average of 1.62. The Khuld stock is similar to Paleozoic and Mesozoic granitoid intrusions in petrology, geochemistry and isotopic geology, with positive ?Nd(t) values occurring within the Da Hinggan Ling-Mongolia orogenic belt. Based on the zircon SHRIMP U-Pb age data mentioned above, in combination with other geological evidence, it is suggested that the Khuld alkaline syenite stock and its related REE mineralized belt were formed within a re-working deep-rooted fault zone to the north of the collision zone of the North China continental massif and Siberian platform. The Khuld alkaline syenite stock, which was probably produced by Mesozoic Indosinian tectonic-magmatic activities, might have played an important role in the ore-forming process of the REE ore spots. The rock-forming materials of the Khuld alkaline syenite stock were derived from a mixed source comprising mantle- and crustal-related components. |
| keywords:alkaline syenite zircon SHRIMP U-Pb dating Khuld REE mineralized district Indosinian Central-South Mongolia |
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