Smit Matthijs A, Kooijman Ellen
Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia Canada.
Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden.
Nat Geosci. 2024;17(10):1053-1058. doi: 10.1038/s41561-024-01538-7. Epub 2024 Sep 19.
Hotspot lavas exhibit chemical heterogeneity, much of which is ascribed to heterogeneous deep mantle sources that contain various components with distinct composition, origin and age. However, characterizing primary melt compositions and mantle heterogeneity directly is challenging. Here we investigate a global dataset of hotspot lavas to constrain the incompatible-element composition of their parental melts and sources. Trace-element ratios indicate that the compositional heterogeneity of global hotspot lavas is not primary, but reflects processes that hotspot melts undergo as they ascend to the surface. We find the parental melts of these lavas, as well as of kimberlites and basalts from large igneous provinces, to be uniform in their elemental, and radiogenic and noble-gas isotope, composition. We suggest that the parental melts to all of these lavas derive from a depleted and outgassed mantle reservoir that was replenished with incompatible element-enriched material during the Archaean. This interpretation explains the elemental, radiogenic and noble-gas isotope compositions of hotspot lavas without requiring a heterogeneous lower mantle or the long-term survival of undegassed relics from a primordial Earth.
热点火山岩表现出化学不均一性，其中大部分归因于不均一的深部地幔源区，这些源区包含具有不同成分、起源和年龄的各种组分。然而，直接表征原生熔体成分和地幔不均一性具有挑战性。在此，我们研究了一个全球热点火山岩数据集，以限制其母熔体和源区的不相容元素组成。微量元素比值表明，全球热点火山岩的成分不均一性并非原生的，而是反映了热点熔体上升至地表过程中所经历的过程。我们发现这些火山岩以及大火成岩省的金伯利岩和玄武岩的母熔体在元素、放射性和稀有气体同位素组成上是均匀的。我们认为，所有这些火山岩的母熔体都源自一个亏损且脱气的地幔储库，该储库在太古宙期间被富含不相容元素的物质所补充。这种解释说明了热点火山岩的元素、放射性和稀有气体同位素组成，而无需不均一的下地幔或原始地球未脱气遗迹的长期留存。
