水合玻璃中的超贫化氢同位素记录了南极洲晚白垩世的冰川作用。

Ultra-depleted hydrogen isotopes in hydrated glass record Late Cretaceous glaciation in Antarctica.

作者信息

Nelson Demian A, Cottle John M, Bindeman Ilya N, Camacho Alfredo

机构信息

Department of Earth Science, University of California, Santa Barbara, CA, USA.

Department of Earth Sciences, University of Oregon, Eugene, OR, USA.

出版信息

Nat Commun. 2022 Sep 7;13(1):5209. doi: 10.1038/s41467-022-32736-9.

DOI:10.1038/s41467-022-32736-9

PMID:36071035

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC9452555/

Abstract

The Early Jurassic Butcher Ridge Igneous Complex (BRIC) in the Transantarctic Mountains contains abundant and variably hydrated silicic glass which has the potential to preserve a rich paleoclimate record. Here we present Fourier Transform Infrared Spectroscopic data that indicates BRIC glasses contain up to ~8 wt.% molecular water (HO), and low (<0.8 wt.%) hydroxyl (OH) component, interpreted as evidence for secondary hydration by meteoric water. BRIC glasses contain the most depleted hydrogen isotopes yet measured in terrestrial rocks, down to δD = -325 ‰. In situ Ar/Ar geochronology of hydrated glasses with ultra-depleted δD values yield ages from 105 Ma to 72 Ma with a peak at c. 91.4 Ma. Combined, these data suggest hydration of BRIC glasses by polar glacial ice and melt water during the Late Cretaceous, contradicting paleoclimate reconstructions of this period that suggest Antarctica was ice-free and part of a global hot greenhouse.

摘要

横贯南极山脉的早侏罗世布彻岭火成杂岩（BRIC）含有大量且水化程度各异的硅质玻璃，这些玻璃有潜力保存丰富的古气候记录。在此，我们展示了傅里叶变换红外光谱数据，该数据表明BRIC玻璃含有高达约8重量%的分子水（HO），以及低含量（<0.8重量%）的羟基（OH）成分，这被解释为大气降水二次水化的证据。BRIC玻璃含有迄今在陆地岩石中测得的最贫化的氢同位素，低至δD = -325‰。对具有超贫化δD值的水化玻璃进行原位氩-氩年代测定，得出的年龄范围为1.05亿年至7200万年，峰值约在9140万年。综合这些数据表明，在晚白垩世期间，BRIC玻璃被极地冰川冰和融水所水化，这与该时期的古气候重建结果相矛盾，后者表明南极洲无冰，是全球热温室的一部分。