Cathodoluminescence images and trace element compositions of fluorapatite from the Hongge layered intrusion in SW China: A record of prolonged crystallization and overprinted fluid metasomatism
Cathodoluminescence images and trace element compositions of fluorapatite from the Hongge layered intrusion in SW China: A record of prolonged crystallization and overprinted fluid metasomatism
复制标题
中国西南红格层状岩体氟磷灰石的阴极发光图像和微量元素组成：长期结晶和叠印流体交代作用的记录
DOI：
10.2138/am-2017-6028
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发表时间：
2017-07
影响因子：
3.1
通讯作者：
Wang Christina Yan
中科院分区：
文献类型：
--
作者：
Xing Chang Ming;Wang Christina Yan
摘要对中国西南红格含铁钛氧化物镁铁质-超镁铁质层状侵入体上部辉长岩和铁钛氧化物矿石中的氟磷灰石进行了阴极发光和微量元素分析。氟磷灰石与铁钛氧化物密切共生，并与斜长石和单斜辉石形成间隙。一个薄片中的氟磷灰石颗粒宽度为~10 ~ 800 mm，长度为~50 ~ 1200 μm。粗粒氟磷灰石晶体（宽度>200）在同一薄切片中显示简单和复杂的CL图像。具有简单CL图像的粗粒氟磷灰石晶体显示沿晶界沿着的不连续的薄暗边，而具有复杂图像的那些显示横跨晶粒的清楚明亮的细脉。另一方面，细粒氟磷灰石晶体（宽度<200 μm）显示复杂的CL图像，并可分为四种类型，即，同心的、混乱的、带状的和整体黑暗的。同心型显示出明显明亮的核心，周围环绕着不规则分区的黑暗地幔，而混乱型则显示出内部无序的明亮和黑暗部分，并带有薄的黑暗边缘。带状型的亮带和暗带分布不均匀。整体暗型显示相对较暗且不均匀的图像。氟磷灰石颗粒含有1.84-2.74重量%的F、0.07-0.19重量%的Cl和0.86-1.63重量%的OH。粗粒氟磷灰石颗粒的总稀土元素（REE）浓度范围为2278至3008 ppm，Sr/Y为9至13。在CL成像下，细粒氟磷灰石颗粒在明亮的核、扇区和条带中具有相对高的REE（2242-4687 ppm）和低的Sr/Y（6 - 14），而在黑暗的地幔、扇区和边缘中具有相对低的REE（1881-2728 ppm）和高的Sr/Y（9 - 15）。在薄片尺度上，细粒氟磷灰石CL成像亮层的稀土元素含量远高于粗粒氟磷灰石CL成像亮层。氟磷灰石颗粒间和单颗氟磷灰石内部的稀土元素含量差异很大，这是由于长期的结晶过程和流体交代作用的叠加。粗粒氟磷灰石可能比细粒氟磷灰石更早结晶。然后，不同程度的热液交代释放稀土元素的细粒氟磷灰石，使不同的CL图像开发的晶体。研究结果表明，层状侵入体中岩浆磷灰石的微量元素组成和CL图像结构均受到后期流体交代作用的强烈改造。因此，使用层状侵入体中的磷灰石重建原始熔体成分时应谨慎对待。
Abstract Cathodoluminescence (CL) and trace element analyses were performed for fluorapatite from the gabbro and Fe-Ti oxide ores in the upper zone of the Hongge Fe-Ti oxide-bearing, mafic-ultramafic layered intrusion in SW China. The fluorapatite is closely associated with Fe-Ti oxides and interstitial to plagioclase and clinopyroxene. The fluorapatite grains in one thin section vary from ~10 to 800 mm in width and ~50 to 1200 μm in length. Coarse-grained fluorapatite crystals (>200 in width) in the same thin section show both simple and complex CL images. The coarse-grained fluorapatite crystals with simple CL images show discontinuous, thin dark rims along grain boundaries, whereas those with complex images show clearly bright veinlets across the grains. On the other hand, fine-grained fluorapatite crystals (<200 μm in width) show complex CL images and can be divided into four types, i.e., concentric, chaotic, banded, and overall dark. The concentric type shows distinctly bright core surrounded by dark mantle that is irregularly zoned, whereas the chaotic type shows disordered bright and dark sectors in the interior with a thin dark rim. The banded type shows unevenly distributed bright and dark bands. The overall dark type shows a relatively dark and uneven image. Fluorapatite grains contain 1.84–2.74 wt% F, 0.07–0.19 wt% Cl, and 0.86–1.63 wt% OH. Coarse-grained fluorapatite grains have total rare earth elements (REE) concentrations ranging from 2278 to 3008 ppm and Sr/Y of 9 to 13. Fine-grained fluorapatite grains have relatively high REE (2242–4687 ppm) and low Sr/Y of 6 to 14 in the bright cores, sectors, and bands and relatively low REE (1881–2728 ppm) and high Sr/Y of 9 to 15 in the dark mantles, sectors, and rims under CL imaging. On the thin section scale, the bright sections under CL imaging for fine-grained fluorapatite have much higher REE contents than those for similar bright CL images for coarse-grained fluorapatite. The highly variable REE concentrations among fluorapatite grains and the sections within a single fluorapatite are attributed to a prolonged crystallization process and overprint by fluid metasomatism. The coarse-grained fluorapatite may have crystallized earlier than fine-grained fluorapatite. Then variable degrees of hydrothermal metasomatism released REE from the fine-grained fluorapatite so that diverse CL images developed in the crystals. This study reveals that magmatic apatite from a layered intrusion can be intensively modified by later-stage fluid-induced metasomatism in both trace element composition and CL image texture. Reconstruction of primary melt compositions using apatite from layered intrusions should therefore be treated with caution.
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影响因子：
5.8
作者：
J. R. Murray;N. Oreskes
通讯作者：
J. R. Murray;N. Oreskes
影响因子：
3.3
作者：
Yuwei She;Xie‐Yan Song;Songyue Yu;Liemeng Chen;W. Zheng
通讯作者：
Yuwei She;Xie‐Yan Song;Songyue Yu;Liemeng Chen;W. Zheng
影响因子：
5
作者：
Bindeman, IN;Davis, AM;Drake, MJ
通讯作者：
Drake, MJ
影响因子：
3.9
作者：
D. Harlov;Ulf B. Andersson;H. Förster;J. Nyström;P. Dulski;C. Broman
通讯作者：
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影响因子：
3.5
作者：
NIELSEN, RL;GALLAHAN, WE;NEWBERGER, F
通讯作者：
NEWBERGER, F