Experimental constraints on mantle metasomatism caused by silicate and carbonate melts
Experimental constraints on mantle metasomatism caused by silicate and carbonate melts
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DOI：
10.1016/j.lithos.2017.03.004
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发表时间：
2017-06
期刊：
影响因子：
3.5
通讯作者：
F. Gervasoni;S. Klemme;A. Rohrbach;T. Grützner;J. Berndt
中科院分区：
文献类型：
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作者：
F. Gervasoni;S. Klemme;A. Rohrbach;T. Grützner;J. Berndt
交代过程是造成上地幔中许多非均质性的原因。为了更好地了解岩石圈地幔中的交代作用，阐明含水硅酸盐和富含碳酸盐的熔融体交代作用的差异，我们进行了多种相互作用实验：(1)在2.2 ~ 2.5 GPa和900 ~ 1000℃条件下，含水榴辉岩衍生的熔融体与橄榄岩的相互作用再现了俯冲带上方地幔楔的交代作用。(2) 2.5 GPa和1050 ~ 1000℃、6 GPa和1200 ~ 1250℃富碳酸盐熔体与橄榄岩的反应模拟了克拉通岩石圈不同区域碳酸盐和超镁铁性硅酸盐-碳酸盐熔体的交代作用。实验结果表明，含水榴辉岩部分熔融生成含水富硅、富铝熔体，与橄榄岩反应形成富铝正辉石和富镁角闪洞双矿物组合。不同组成的富碳酸盐熔体与橄榄岩发生反应，形成新的交代石英矿物组合。富钙碳酸盐熔体引起的交代反应消耗原生橄榄岩，产生大量交代斜辉石；另一方面，由超镁铁性硅酸盐-碳酸盐熔体引起的交代作用产生较少的斜辉石。此外，我们的实验表明，超镁铁性硅酸盐-碳酸盐熔体与橄榄岩发生强烈反应，导致大量交代Fe-Ti氧化物结晶。交代熔体与橄榄岩的反应也改变了熔体的组成。例如，如果碳酸盐熔体在交代反应中没有完全被消耗，其熔体成分可能会发生巨大变化，产生与I型金伯利岩成分相似的富碱碳酸盐硅酸盐熔体。
Metasomatic processes are responsible for many of the heterogeneities found in the upper mantle. To better understand the metasomatism in the lithospheric mantle and to illustrate the differences between metasomatism caused by hydrous silicate and carbonate-rich melts, we performed various interaction experiments: (1) Reactions between hydrous eclogite-derived melts and peridotite at 2.2–2.5 GPa and 900–1000 °C reproduce the metasomatism in the mantle wedge above subduction zones. (2) Reactions between carbonate-rich melts and peridotite at 2.5 GPa and 1050–1000 °C, and at 6 GPa and 1200–1250 °C simulate metasomatism of carbonatite and ultramafic silicate–carbonate melts in different regions of cratonic lithosphere. Our experimental results show that partial melting of hydrous eclogite produces hydrous Si- and Al-rich melts that react with peridotite and form bi-mineralic assemblages of Al-rich orthopyroxene and Mg-rich amphibole. We also found that carbonate-rich melts with different compositions react with peridotite and form new metasomatic wehrlitic mineral assemblages. Metasomatic reactions caused by Ca-rich carbonatite melt consume the primary peridotite and produce large amounts of metasomatic clinopyroxene; on the other hand, metasomatism caused by ultramafic silicate–carbonate melts produces less clinopyroxene. Furthermore, our experiments show that ultramafic silicate–carbonate melts react strongly with peridotite and cause crystallization of large amounts of metasomatic Fe-Ti oxides. The reactions of metasomatic melts with peridotite also change the melt composition. For instance, if the carbonatite melt is not entirely consumed during the metasomatic reactions, its melt composition may change dramatically, generating an alkali-rich carbonated silicate melt that is similar in composition to type I kimberlites.