TY - JOUR
T1 - Structural analysis of syn-depositional hydrothermal veins of the 3.48 Ga Dresser Formation, Pilbara Craton, Australia
AU - Tadbiri, Sahand
AU - Van Kranendonk, Martin J.
N1 - Funding Information:
The authors would like to acknowledge funding support from the Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS), as well as Discovery Grant DP 180103204 to Professor Martin Van Kranendonk. Thanks to Luke Stellar and Tara Djokic for their help and support during the field study, and to Faye and Geoff Myers from the Normay Mine for their hospitality. This is CCFS contribution 1517.
Publisher Copyright:
© 2020 Elsevier B.V.
PY - 2020/9
Y1 - 2020/9
N2 - The lower chert unit of the 3.48 Ga Dresser Formation (Pilbara Craton, Western Australia) hosts Earth's oldest convincing evidence of life in the form of stromatolites in a depositional setting that has been interpreted as either a shallow marine lagoon, an active volcanic caldera, or a basin deposited during regional extension. Understanding the environment where early life thrived is important not only for early life studies on Earth, but in the search for life on Mars, and for understanding the setting for the origin of life. Structural analysis of the extensive network of syn-depositional hydrothermal chert-barite veins that immediately underlies the Dresser was undertaken in order to test if deposition occurred within an evolving caldera system, or during regional extension. Over 190 hydrothermal veins were mapped for their geometry and relative age relationships. Bedding orientations were recorded within nine fault-bounded structural sub-blocks and used for back-rotating the measured veins to their original orientation. The results show that: 1) There are four main vein systems, including three that were emplaced during deposition of the Dresser Formation lower chert unit, and a fourth that was emplaced within syn- to post-depositional listric growth faults; 2) The majority of veins were sub-vertical prior to regional tilting; 3) The first three vein systems show mutually cross-cutting relationships; 4) Vein densities and the number of vein systems vary between sub-blocks; 5) Conjugate vein networks (NE-SW and NW-SE) dominate two middle and northern sub-blocks.These results show that the first three vein systems were emplaced through fracturing under a stress regime with a vertical σ1. Vertical conjugate fractures are consistent with sandbox models of overburden fracturing during emplacement and discharge of a magma chamber in a volcanic caldera. Areas of single vein orientations reflect marginal areas of the caldera system, dominated by radial or by ring faults. The veins in late listric growth faults represent the final period of caldera collapse, which controlled the depositional thicknesses of overlying strata, possibly during subsequent regional extension. These results document an unique setting for earliest life on Earth, within shallow water and terrestrial deposits of an active, low-eruptive caldera setting.
AB - The lower chert unit of the 3.48 Ga Dresser Formation (Pilbara Craton, Western Australia) hosts Earth's oldest convincing evidence of life in the form of stromatolites in a depositional setting that has been interpreted as either a shallow marine lagoon, an active volcanic caldera, or a basin deposited during regional extension. Understanding the environment where early life thrived is important not only for early life studies on Earth, but in the search for life on Mars, and for understanding the setting for the origin of life. Structural analysis of the extensive network of syn-depositional hydrothermal chert-barite veins that immediately underlies the Dresser was undertaken in order to test if deposition occurred within an evolving caldera system, or during regional extension. Over 190 hydrothermal veins were mapped for their geometry and relative age relationships. Bedding orientations were recorded within nine fault-bounded structural sub-blocks and used for back-rotating the measured veins to their original orientation. The results show that: 1) There are four main vein systems, including three that were emplaced during deposition of the Dresser Formation lower chert unit, and a fourth that was emplaced within syn- to post-depositional listric growth faults; 2) The majority of veins were sub-vertical prior to regional tilting; 3) The first three vein systems show mutually cross-cutting relationships; 4) Vein densities and the number of vein systems vary between sub-blocks; 5) Conjugate vein networks (NE-SW and NW-SE) dominate two middle and northern sub-blocks.These results show that the first three vein systems were emplaced through fracturing under a stress regime with a vertical σ1. Vertical conjugate fractures are consistent with sandbox models of overburden fracturing during emplacement and discharge of a magma chamber in a volcanic caldera. Areas of single vein orientations reflect marginal areas of the caldera system, dominated by radial or by ring faults. The veins in late listric growth faults represent the final period of caldera collapse, which controlled the depositional thicknesses of overlying strata, possibly during subsequent regional extension. These results document an unique setting for earliest life on Earth, within shallow water and terrestrial deposits of an active, low-eruptive caldera setting.
KW - Caldera
KW - Dresser Formation
KW - Early Archean
KW - Hydrothermal veins
KW - Pilbara Craton
KW - Structural analysis
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U2 - 10.1016/j.precamres.2020.105844
DO - 10.1016/j.precamres.2020.105844
M3 - Article
AN - SCOPUS:85088022399
SN - 0301-9268
VL - 347
JO - Precambrian Research
JF - Precambrian Research
M1 - 105844
ER -
