美国伍兹霍尔海洋研究所Jian, Hanchao和Canales, J. Pablo报道了，由镁铁质侵入体控制的大洋核杂岩中的热液流动与蛇纹岩化作用。相关论文于2024年5月6日发表于国际顶尖学术期刊《自然—地球科学》杂志上。

据介绍，慢速/超低速扩张洋中脊的深海热液系统通常位于大洋核杂岩的超镁铁质岩石中。这些杂岩含有由于滑脱断裂而掘出的下地壳和地幔部分。这些环境中的热液循环导致了大量的硫化物沉积，海洋岩石圈的水化作用和类似于早期地球生命起源的条件。然而，这些环境中的热液通道与岩浆和地幔岩性、断裂、岩浆作用、蛇纹岩化和蚀变之间的关系尚不清楚。

研究人员提出了中大西洋海脊核复合体及其超镁铁质热液系统的地震模型，该模型来源于可控地震数据的全波形反演和局部地震层析成像。模型和衍生的岩石性质揭示了沿核心杂岩复合体侧翼的蛇纹石化橄榄岩中的高渗透性通道。这些通道在活动热液场和古热液场下汇合，并绕过机械强度大、不渗透的浅镁铁质地层(2-3km宽，约1km厚)，引导热液流出，并在其边缘形成大量硫化物矿床。

这些镁铁质侵入体也起到了盖子的作用，限制了核心杂岩复合体中心的流体向下流动，从而限制蛇纹石化。结果表明，超镁铁质环境下的热液流动受岩性接触控制，镁铁质侵入体调节热液通道和深部地幔蛇纹石化的程度。

附：英文原文

Title: Hydrothermal flow and serpentinization in oceanic core complexes controlled by mafic intrusions

Author: Jian, Hanchao, Canales, J. Pablo, Dunn, Robert, Nedimovi, Mladen R.

Issue&Volume: 2024-05-06

Abstract: Deep-sea hydrothermal systems at slow/ultraslow-spreading mid-ocean ridges are often located within ultramafic rocks that are part of oceanic core complexes. These complexes contain lower-crustal and mantle sections exhumed due to detachment faulting. Hydrothermal circulation in these environments leads to massive sulfide deposits, hydration of oceanic lithosphere and conditions resembling early Earth’s life origin. However, the relationship between hydrothermal pathways in these environments and crustal and mantle lithologies, faulting, magmatism, serpentinization and alteration is poorly understood. Here we present seismic models of a Mid-Atlantic Ridge core complex and its ultramafic-hosted hydrothermal system derived from full waveform inversion of controlled-source seismic data and from local earthquake tomography. The models and derived rock properties reveal high-permeability channels within serpentinized peridotite along the flanks of the core complex. These channels converge beneath active and fossil hydrothermal fields and are diverted around mechanically strong, impermeable shallow mafic intrusions (2–3km wide, ~1km thick), causing hydrothermal outflow and the formation of massive sulfide deposits around the intrusions’ edges. These mafic intrusions also act as lids that limit fluid downflow—and thus serpentinization—in the centre of the core complex. Our results demonstrate that hydrothermal flow in ultramafic settings is controlled by lithology contacts, with mafic intrusions modulating hydrothermal pathways and extent of mantle serpentinization at depth.

DOI: 10.1038/s41561-024-01444-y

Source: https://www.nature.com/articles/s41561-024-01444-y