Chlorine Isotope Composition of Apatite from the >3.7 Ga Isua Supracrustal Belt, SW Greenland

The study of the oldest surviving rock suites is crucial for understanding the processes that shaped the early Earth and formed an environment suitable for life. The metasedimentary and metavolcanic rocks of the early Archean Isua supracrustal belt contain abundant apatite, the geochemical signature...

Full description

Bibliographic Details
Published in:Minerals
Main Authors: Alicja Wudarska, Ewa Słaby, Michael Wiedenbeck, Łukasz Birski, Richard Wirth, Jens Götze, Aivo Lepland, Christof Kusebauch, Izabela Kocjan
Format: Article in Journal/Newspaper
Language:English
Published: MDPI AG 2019
Subjects:
chlorine isotopes
apatite
isua
archean
sims
tem
cathodoluminescence
geochemistry
Mineralogy
QE351-399.2
Greenland
Online Access:https://doi.org/10.3390/min10010027
https://doaj.org/article/112d1e65750944a58a419d68866ab8af
Description
Summary:The study of the oldest surviving rock suites is crucial for understanding the processes that shaped the early Earth and formed an environment suitable for life. The metasedimentary and metavolcanic rocks of the early Archean Isua supracrustal belt contain abundant apatite, the geochemical signatures of which may help decipher ancient environmental conditions. However, previous research has shown that secondary processes, including amphibolite-facies metamorphism, have reset the original hydrogen isotope composition (δD) of apatite from the Isua belt; therefore, δD values are not indicative of primary conditions in the Archean. Here, we report the first in situ chlorine isotope (δ 37 Cl) analyses by Secondary Ion Mass Spectrometry (SIMS) from Isua apatite, which we combine with information from transmission electron microscopy, cathodoluminescence imaging, and spectroscopy, documenting the micron-scale internal features of apatite crystals. The determined δ 37 Cl SMOC values (chlorine isotope ratios vs. standard mean ocean chloride) fall within a range from −0.8‱ to 1.6‱, with the most extreme values recorded by two banded iron formation samples. Our results show that δ 37 Cl values cannot uniquely document primary signatures of apatite crystals, but the results are nonetheless helpful for assessing the extent of secondary overprint.

Similar Items