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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Evidence of a close link between petrology and isotope records: constraints from SEM, EMP, TEM and in situ ~(40)Ar-~(39)Ar laser analyses on multiple generations of white micas (Lanterman Range, Antarctica)
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Evidence of a close link between petrology and isotope records: constraints from SEM, EMP, TEM and in situ ~(40)Ar-~(39)Ar laser analyses on multiple generations of white micas (Lanterman Range, Antarctica)

机译：岩石学与同位素记录之间紧密联系的证据：来自SEM，EMP，TEM和多代白云母的原位〜（40）Ar-〜（39）Ar激光分析的限制（兰特曼山脉，南极洲）

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摘要

K-Ar ages from white mica are commonly interpreted to record cooling below a certain temperature with the implicit assumption that all the requirements of the volume diffusion theory are fulfilled. Nevertheless, studies on metamorphic white micas have highlighted discrepancies with previously inferred closure temperatures and have evidenced a close link between petrology and argon isotope age records. This study uses the in situ ~(40)Ar-~(39)Ar laserprobe method in conjunction with scanning electron microscopy, electron microprobe and transmission electron microscopy (TEM) techniques to examine the relations between argon isotope records and microtextural, microchemical and microstructural variations in white mica. Gneisses and micaschists belonging to three different tectono-metamorphic complexes of the Lanterman Range (Antarctica) contain multiple generations of potassic white micas and are well-suited to investigate the relation between petrology and argon dating. Texturally resolvable white mica generations show microchemical and microstructural (TEM scale) variations that suggest development under different P-T deformation regimes, ranging from an eclogite facies stage down to low greenschist facies conditions. In situ ~(40)Ar-~(39)Ar laserprobe analyses on white mica samples from the three complexes reveal a complex intragrain and intergrain spatial distribution of argon ages which is closely linked to microtextural, microchemical and microstructural variations: texturally, compositionally and microstructurally older generations yield older ages whereas the younger ones yield younger ages. Results show that in the absence of re-crystallisation, white mica preserves argon isotope records pertaining to the high-pressure stage which survived amphibolite retrogression at temperatures of 550-650 ℃. The texture, petrology and isotope record of white micas in the studied samples preserve a nearly continuous record of P, T and deformation history within the same orogenic cycle.
机译：通常将白云母的K-Ar年龄解释为记录某个温度以下的冷却，这是隐含的假设，即满足体积扩散理论的所有要求。然而，对变质白云母的研究突显了先前推断的封闭温度的差异，并证明了岩石学与氩同位素年龄记录之间的密切联系。这项研究使用原位〜（40）Ar-〜（39）Ar激光探针方法结合扫描电子显微镜，电子显微镜和透射电子显微镜（TEM）技术来研究氩同位素记录与微观组织，微观化学和微观结构之间的关系白云母的变化。属于Lanterman山脉（南极洲）的三种不同构造变质复合体的片麻岩和云母岩，含有多代钾盐白云母，非常适合研究岩石学与氩定年之间的关系。质地上可分辨的白云母世代表现出微化学和微结构（TEM尺度）变化，表明在不同的P-T变形机制下发育，范围从榴辉岩相阶段到低绿片岩相条件。对来自三种配合物的白云母样品的原位〜（40）Ar-〜（39）Ar激光探针分析显示，氩气年龄的复杂晶粒内和晶粒间空间分布与微观结构，微观化学和微观结构变化（在组织，组成和结构上）密切相关。在微观结构上，老一辈人的年龄更大，而年轻一代则年龄较小。结果表明，在没有重结晶的情况下，白云母保留了与高压阶段有关的氩同位素记录，该记录在550-650℃的温度下能抵抗闪石的回生。研究样品中白云母的质地，岩石学和同位素记录在相同的造山周期内保留了几乎连续的P，T和变形历史记录。

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