中国科学技术大学黄方教授研究组取得一项新进展。他们报道了花岗岩岩浆演化中结晶-熔体分离过程中稳定锶同位素的分馏。相关论文于2025年1月8日发表在《地球化学学报》杂志上。

据了解，稳定Sr同位素组成（δ⁸⁸/⁸⁶Sr）可用于研究岩浆过程，但其在岩浆演化过程中的分馏机制尚不清楚。

为了了解岩浆活动中稳定Sr同位素的分馏行为，研究团队对Huili花岗岩岩体的δ⁸⁸/⁸⁶Sr值进行了测定，数据显示，该岩体经历了强烈的结晶-熔体分离。Huili岩体由钾长石花岗岩和演化较早的钠长石花岗岩组成，钠长石花岗岩的δ⁸⁸/⁸⁶Sr值（+0.36‰至+0.52‰）明显高于钾长石花岗岩（+0.11‰至+0.25‰）。钾长石的δ⁸⁸/⁸⁶Sr值（-0.01‰至+0.17‰）略低于整个岩体，占钾长石花岗岩Sr收支的大部分。

Huili花岗岩的δ⁸⁸/⁸⁶Sr变化可以用熔体与钾长石为主的晶体分离来解释，因为钾长石结晶会导致萃取的间隙熔体的重Sr同位素的构成。Huili花岗岩中Sr和Ba同位素稳定比值向重质方向高度耦合，反映了晶体钾长石与熔体之间，相似的元素分配和同位素分选行为。研究表明，熔融萃取在花岗质岩浆演化过程中起着关键作用。

附：英文原文

Title: Stable strontium isotope fractionation during crystal-melt separation in granitic magma evolution

Author: Chen, Xuqi, Deng, Gengxin, Jiang, Dingsheng, Nan, Xiaoyun, Huang, Fang

Issue&Volume: 2025-01-08

Abstract: Stable Sr isotopic composition (δ⁸⁸/⁸⁶Sr) can be used to study magmatic processes, but their fractionation mechanism during magmatic evolution remains unclear. To understand the fractionation behaviors of the stable Sr isotopes during magmatism, we report the δ88/86Sr values of the Huili granitic pluton, which was subjected to intensive crystal-melt separation. The Huili pluton consists of K-feldspar granite and more evolved albite granite, and the albite granite exhibits significantly higher δ⁸⁸/⁸⁶Sr values (+0.36‰ to+0.52‰) than that of K-feldspar granite (+0.11‰ to+0.25‰). K-feldspar, which contributes most of the Sr budget of the K-feldspar granite, has slightly lower δ⁸⁸/⁸⁶Sr values (0.01‰ to+0.17‰) than the whole rock. The δ⁸⁸/⁸⁶Sr variation of the Huili granites can be explained by separation of melt from K-feldspar-dominated crystals, because crystallization of K-feldspar can result in heavy Sr isotopic composition of the extracted interstitial melt. Stable Sr and Ba isotopic ratios in the Huili granites are highly coupled toward the heavy direction, reflecting their similar element partitioning and isotope fractionation behaviors between the crystalline K-feldspar and melt. This study indicates that melt extraction plays a key role in granitic magma evolution.

DOI: 10.1007/s11631-024-00752-9

Source: https://link.springer.com/article/10.1007/s11631-024-00752-9