美国自然历史博物馆Ekaterina S. Kiseeva及其团队人员,报道了由西格陵兰岛Majuagaa金伯利岩中异剥橄榄岩捕掳体所证实的,克拉通地幔中的碱性-碳酸盐熔体。该项研究成果发表在2024年10月9日出版的《地质学》上。
据了解,碳酸盐熔体对深部碳循环、地幔熔融、氧化还原反应和高度不相容元素的迁移至关重要。从实验研究、交代转化和捕掳体、金伯利岩和金刚石中的熔体/流体包裹体推断,克拉通地幔中存在碳酸盐岩熔体。然而,由于这种熔体的短暂性和高度反应性,人们很难确定其确切成分。该熔体一旦形成,就会远离源区迁移出去,并与硅酸盐地幔矿物,特别是斜方辉石,发生反应,引发地幔交代作用。异剥橄榄岩是碳酸盐岩熔体与橄榄岩地幔相互作用的产物之一,是碳酸盐岩熔体原位定位的理想候选物。
研究人员报道了西格陵兰岛Majuagaa金伯利岩脉中,石榴子异剥橄榄岩捕掳体的岩石学、地球化学和熔体包裹体数据。捕虏体在4.5GPa和1000℃时与地幔达到平衡,含有丰富的由白云石、方解石、蛇纹石、尖晶石、磷灰石和金云母组成的熔化池。尽管原始岩浆矿物学在很大程度上被低温蚀变破坏,但碳酸盐岩熔体的结晶残余物,作为原生熔体包裹体保存在Ti-Mg-Fe尖晶石液相线中。
这些熔融包裹体由碳酸盐、碱性碳酸盐、方镁石/水镁石以及少量卤化物、钾硫化物、磷灰石和金云母组成,是深克拉通地幔中原位碱性-碳酸盐原位熔融的第一个直接证据。在成分上,它们与实验中发现的原生钠-白云石熔体和金刚石内部的流体包裹体非常相似。
附:英文原文
Title: Alkali-carbonate melts in the cratonic mantle evidenced by a wehrlite xenolith from the Majuagaa kimberlite, West Greenland
Author: Ekaterina S. Kiseeva, Vadim S. Kamenetsky, Ivan F. Chayka, Roland Maas, Troels F.D. Nielsen
Issue&Volume: 2024-10-09
Abstract: Carbonate melts are critically important for the deep carbon cycle, mantle melting, redox reactions, and transport of highly incompatible elements. The presence of carbonate melts in the cratonic mantle has been inferred from experimental studies, metasomatic transformations, and melt/fluid inclusions in xenoliths, kimberlites, and diamonds. However, the exact composition of such melts is difficult to determine due to their ephemeral nature and highly reactive properties. Once formed, they migrate away from the source and react with silicate mantle minerals, especially orthopyroxene, causing mantle metasomatism. Wehrlite is one of the products of interaction between the carbonate melt and peridotitic mantle and hence is an excellent candidate for locating in situ carbonate melts. Here, we report petrological, geochemical, and melt inclusion data for a garnet wehrlite xenolith in the Majuagaa kimberlite dike, West Greenland. The xenolith, which last equilibrated with the mantle at 4.5 GPa and 1000 °C, contains abundant melt pools composed of dolomite, calcite, serpentine, spinel, apatite, and phlogopite. Although the original magmatic mineralogy was largely destroyed by low-temperature alteration, remnants of the crystallized carbonatitic melt are preserved as primary melt inclusions in the liquidus Ti-Mg-Fe spinel. These melt inclusions, composed of carbonates, alkali carbonates, periclase/brucite, and minor halides, K-sulfide, apatite, and phlogopite, are the first direct evidence for in situ alkali-carbonate melt in the deep cratonic mantle. Compositionally, they are very similar to primary Na-dolomite melt found in experiments and in fluid inclusions within diamonds.
DOI: 10.1130/G52274.1
Geology:《地质学》,创刊于1973年。隶属于美国地质学会,最新IF:6.324
官方网址:https://pubs.geoscienceworld.org/geology
投稿链接:https://geology.msubmit.net/cgi-bin/main.plex