英国剑桥大学Sally Gibson团队报道了碳酸岩的分布与产生。这一研究成果发表在2024年6月17日出版的国际学术期刊《地质学》上。

据了解，产生碳酸岩以及最终形成相关稀土元素矿床的物理—化学框架仍存在争议。这主要反映了碳酸岩形成的不同构造环境：大火成岩省、大陆裂谷和主要的伸展地体、碰撞前后的构造环境或海洋岛屿。然而，一个广泛的共识是，碳酸岩(或它们的母体熔体)起源于地幔。这些奇异的熔体体积小，使它们成为探测其潜在源区条件的理想探测器。

研究将碳酸岩的位置与地震层析成像得到的全球岩石圈厚度图结合起来，以解释后—新元古代碳酸岩优先出现在厚的克拉通岩石圈边缘之上(例如，邻近南大西洋和印度洋或北美、格陵兰岛和亚洲)，以及曾经厚的岩石圈经历拉伸的地方(例如，东亚)。热模拟显示，裂谷克拉通边缘的横向和垂直热传导，或克拉通岩石圈的快速拉伸，可以在形成形成原生碳酸岩或其母体碱性硅酸盐熔体，所需的温度(950-1250°C)和压力(2-3GPa)下活化碳化橄榄岩。

重要的是，模型表明，裂谷克拉通边缘上涌地幔柱或周围地幔的热传导，可能足以改变岩石圈地幔的温度，以促进碳酸化橄榄岩的熔融，从而解决了长期以来关于裂谷和加热在碳酸岩生成中作用的争论。

附：英文原文

Title: The distribution and generation of carbonatites

Author: Sally Gibson, Dan McKenzie, Sergei Lebedev

Issue&Volume: 2024-06-17

Abstract: The physio-chemical framework that generates carbonatites and, ultimately, the associated rare earth element deposits remains contentious. This primarily reflects the diverse tectonic settings in which carbonatites occur: large igneous provinces, continental rifts and major extensional terranes, syn- to post-collisional settings, or ocean islands. There is, however, a broad consensus that carbonatites (or their parental melts) originate in the mantle. These exotic melts have small volumes that make them ideal probes of conditions in their underlying source regions. We combine the carbonatite locations with global maps of lithospheric thickness, derived from seismic tomography, and show that post-Neoproterozoic carbonatites occur preferentially above the margins of thick cratonic lithosphere (e.g., adjacent to the South Atlantic and Indian Oceans or in North America, Greenland, and Asia) and where once thick lithosphere has undergone stretching (e.g., eastern Asia). Our thermal modeling reveals that lateral and vertical heat conduction on rifted craton margins, or rapid stretching of cratonic lithosphere, can mobilize carbonated peridotite at the temperatures (950-1250 °C) and pressures (2-3 GPa) required to form primary carbonatites or their parental alkali silicate melts. Importantly, our models show that heat conduction from upwelling mantle plumes or ambient mantle on rifted cratonic margins may sufficiently modify the temperature of the lithospheric mantle to cause melting of carbonated peridotite, settling the long-standing debate on the role of rifting and heating in the generation of carbonatites.

DOI: 10.1130/G52141.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G52141.1/645002/The-distribution-and-generation-of-carbonatitesredirectedFrom=fulltext