A 3‐D Model of Gas Generation, Migration, and Gas Hydrate Formation at a Young Convergent Margin (Hikurangi Margin, New Zealand). (19th November 2019)

• Record Type: Journal Article
• Authors: Kroeger, K. F.; Crutchley, G. J.; Kellett, R.; Barnes, P. M.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 20:Number 11(2019)
• Page Start: 5126
• Page End: 5147
• Publication Date: 2019-11-19
• Subjects: methane hydrate -- microbial gas generation -- gas hydrate systems -- subduction zones -- petroleum systems -- natural gas resources; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2019GC008275
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: We present a three‐dimensional gas hydrate systems model of the southern Hikurangi subduction margin in eastern New Zealand. The model integrates thermal and microbial gas generation, migration, and hydrate formation. Modeling these processes has improved the understanding of factors controlling hydrate distribution. Three spatial trends of concentrated hydrate occurrence are predicted. The first trend (I) is aligned with the principal deformation front in the overriding Australian plate. Concentrated hydrate deposits are predicted at or near the apexes of anticlines and to be mainly sourced from focused migration and recycling of microbial gas generated beneath the hydrate stability zone. A second predicted trend (II) is related to deformation in the subducting Pacific plate associated with former Mesozoic subduction beneath Gondwana and the modern Pacific‐Australian plate boundary. This trend is enhanced by increased advection of thermogenic gas through permeable layers in the subducting plate and focused migration into the Neogene basin fill above Cretaceous‐Paleogene structures. The third trend (III) follows the northern margin of the Hikurangi Channel and is related to the presence of buried strata of the Hikurangi Channel system. The predicted trends are consistent with pronounced seismic reflection anomalies related to free gas in the pore space and strength of the bottom‐simulating reflection. However, only trend I is also associated with clear and widespread seismic indications of concentrated gas hydrate. Total predicted hydrate masses at the southern Hikurangi Margin are between 52, 800 and 69, 800 Mt. This equates to 3.4–4.5 Mt hydrate/km 2, containing 6.33 × 10 8 –8.38 × 10 8 m 3 /km 2 of methane. Plain Language Summary: Gas hydrates are ice‐like substances of natural gas enclosed in a lattice of water molecules. They are stable under pressure and temperature conditions found beneath the sea‐floor offshore beyond continental shelfs. Gas hydrates house a significant part of the natural gas methane contained in the geosphere and hence are a potential energy resource. However, if methane is released into surface systems through decomposition of gas hydrates, for instance, due to an increase in ocean bottom temperatures, it will contribute to ocean acidification, and may acerbate climate warming. Hence, quantification and a better understanding of controls on formation and distribution of gas hydrates is important. Here we present a basin‐wide study predicting hydrate formation offshore eastern New Zealand, where the Pacific plate is subducted beneath the Australian plate. We explore the implications of deep gas generation and migration patterns in this setting for gas hydrate formation and distribution. Key Points: Gas hydrate system modeling predicts three pronounced spatial trends in gas hydrate distribution along the southern Hikurangi Margin Hydrate distribution is controlled by sources of microbial and thermogenic gas, basin fill architecture, and convergent margin deformation Predicted volumes of gas stored in gas hydrate warrant further exploration as an energy resource in New Zealand