云南卓潘碱性杂岩体岩浆演化富稀土机制:来自磷灰石地球化学的证据
投稿时间:2024-03-08  修订日期:2024-04-09  点此下载全文
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作者单位邮编
马飞 昆明理工大学 650093
王蝶* 昆明理工大学 
基金项目:国家自然科学基金项目(41963003)和云南省“兴滇人才”项目资助
中文摘要:云南卓潘碱性杂岩体具有较高的稀土元素含量(约1319ppm),具有较高程度的稀土元素找矿前景,然而,对于卓潘碱性岩的岩浆演化过程和稀土元素富集机制有待深入研究。本研究选取卓潘岩体中的出露岩体(正长辉石岩和辉石正长岩),对其中主要的富稀土矿物磷灰石进行主、微量测试,深入剖析磷灰石的地球化学特征,旨在探讨碱性岩岩浆演化过程和稀土元素富集机制。电子探针(EPMA)和激光剥蚀等离子质谱(LA-ICP-MS)分析结果表明,正长辉石岩和辉石正长岩中磷灰石均为氟磷灰石,F含量分别为2.92%和3.35%;磷灰石稀土元素含量存在差异,平均值分别为12288 ppm和16503 ppm;稀土模式配分图均表现出富集轻稀土元素,强烈亏损重稀土元素特征。磷灰石Mn温度计估算结果结合SO3含量的相对高低,氧逸度结果表明正长辉石岩相对低于辉石正长岩;磷灰石中高的Ce/Pb和低的Th/U特征,表明岩浆演化过程中流体活动性较强,并且前者流体活动性高于后者;磷灰石中的挥发分(F、Cl)含量及其比值特征指示岩浆源区受到大洋俯冲作用相关的交代作用。基于上述研究结果,卓潘碱性杂岩体稀土元素的富集过程:岩浆演化早期,辉石、榍石以及黑云母等大量硅酸盐矿物结晶,由于早期硅酸盐矿物的结晶,岩浆房中磷酸盐达到饱和,大量磷灰石析出并作为早期正长辉石岩中富稀土矿物;岩浆演化晚期,由于残余岩浆结晶中磷酸盐和稀土元素的相对亏损,磷灰石少量析出并作为晚期辉石正长岩中富稀土矿物。因此,卓潘碱性杂岩体中正长辉石岩和辉石正长岩均具有一定程度的稀土找矿前景。
中文关键词:磷灰石  主微量元素成分  稀土富集  卓潘碱性杂岩体
 
Rare earth enrichment mechanism in the magmatic evolution of the Zhuopan alkaline complex in Yunnan: evidence from mineral geochemistry
Abstract:The Zhuopan alkaline complex in Yunnan is characterized by a relatively high content of rare earth elements (approximately 1319 ppm), showing a high potential for rare earth element exploration. However, the magmatic evolution process and the enrichment mechanism of rare earth elements within the Zhuopan alkaline rocks warrant further investigation. This study selects exposed rock bodies within the Zhuopan complex (syenite-pyroxenolite and gabbro-syenite) and conducts major and trace element analyses on apatite, a key rare earth-bearing mineral found therein. By deeply dissecting the geochemical characteristics of apatite, the aim is to explore the magmatic evolution process of alkaline rocks and the enrichment mechanism of rare earth elements. The results from Electron Probe Microanalysis (EPMA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) analyses indicate that the apatite found in both syenite-pyroxenolite and gabbro-syenite is fluorapatite, with fluorine contents of 2.92% and 3.35%, respectively. There are differences in the rare earth element (REE) content of apatite between the two rock types, with average values of 12288 ppm and 16503 ppm, respectively. The REE distribution patterns for both types of apatite show an enrichment in light rare earth elements (LREEs) and a strong depletion in heavy rare earth elements (HREEs). The estimation results of the apatite Mn thermometer, combined with the relative levels of SO3 content, suggest that the oxygen fugacity in the syenite-pyroxenolite is relatively lower than that in the gabbro-syenite. The high Ce/Pb and low Th/U characteristics in apatite indicate a strong fluid activity during the magmatic evolution process, with the former exhibiting higher fluid activity than the latter. The content and ratio characteristics of volatiles (F, Cl) in apatite indicate that the magma source region was influenced by metasomatism associated with oceanic subduction. Based on the aforementioned research findings, the enrichment process of rare earth elements (REEs) in the Zhuopan alkaline complex can be summarized as follows: During the early stages of magmatic evolution, a significant crystallization of silicate minerals such as pyroxene, sphene, and biotite occurs. Due to the early crystallization of these silicate minerals, phosphate in the magma chamber reaches saturation, leading to the extensive precipitation of apatite, which acts as an early REE-rich mineral in the syenite-pyroxenolite. In the later stages of magmatic evolution, due to the relative depletion of phosphate and REEs in the residual magma, only a small amount of apatite precipitates, serving as a late-stage REE-rich mineral in the gabbro-syenite. Therefore, both syenite-pyroxenolite and gabbro-syenite in the Zhuopan alkaline complex have a certain degree of rare earth prospecting prospect.
keywords:Apatite  Petrogenesis and mineralization  Rare earth enrichment  Chopan alkaline complex  
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