Alkali-halogen metasomatism of the CM carbonaceous chondrites
Alkali-halogen metasomatism of the CM carbonaceous chondrites
复制标题
CM碳质球粒陨石的碱卤交代作用
DOI：
10.1111/maps.13405
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发表时间：
2019
影响因子：
2.2
通讯作者：
Lee M
中科院分区：
文献类型：
--
作者：
Lee M
Meteorite Hills（MET）01075在CM碳质陨石中是独一无二的，因为它包含了一种似陨石的矿物方钠石，因此它可能为这个陨石群以前没有记录过的星云或母体过程提供了有价值的证据。MET 01075由含水蚀变球粒和富含钙和铝的夹杂物（CAI）组成，其基质主要由富含蛇纹石和托基林石的颗粒组成。陨石球粒已被冲击压扁，并确定了叶理岩组。方钠石以0.6 mm大小的CAI存在，其还含有尖晶石、钙钛矿和透辉石以及富铁页硅酸盐和方解石。通过与CV和CO碳质碳酸盐中的含钾长石的CAIs类比，方钠石被解释为在母体环境中碱卤交代期间通过黄长石或钙长石的置换形成。虽然CAI可能在前体母体中被交代，然后被挖掘并结合到MET 01075母体中，但原位交代是有利的模式。相对高温的水-岩相互作用的短暂插曲是由放射成因或冲击加热驱动的，并且大部分交代作用的证据被随后的低温水蚀变所消除。MET 01075在对经历早期碱-卤素交代并保留其产物之一的CM母体区域进行采样时非常罕见。
Meteorite Hills (MET) 01075 is unique among the CM carbonaceous chondrites in containing the feldspathoid mineral sodalite, and hence it may provide valuable evidence for a nebular or parent body process that has not been previously recorded by this meteorite group. MET 01075 is composed of aqueously altered chondrules and calcium‐ and aluminum‐rich inclusions (CAIs) in a matrix that is predominantly made of serpentine‐ and tochilinite‐rich particles. The chondrules have been impact flattened and define a foliation petrofabric. Sodalite occurs in a 0.6 mm size CAI that also contains spinel, perovskite, and diopside together with Fe‐rich phyllosilicate and calcite. By analogy with feldspathoid‐bearing CAIs in the CV and CO carbonaceous chondrites, the sodalite is interpreted to have formed by replacement of melilite or anorthite during alkali‐halogen metasomatism in a parent body environment. While it is possible that the CAI was metasomatized in a precursor parent body, then excavated and incorporated into the MET 01075 parent body, in situ metasomatism is the favored model. The brief episode of relatively high temperature water–rock interaction was driven by radiogenic or impact heating, and most of the evidence for metasomatism was erased by subsequent lower temperature aqueous alteration. MET 01075 is very unusual in sampling a CM parent body region that underwent early alkali‐halogen metasomatism and has retained one of its products.