Mantle-derived helium in hot springs of the Cordillera Blanca, Peru: Implications for mantle-to-crust fluid transfer in a flat-slab subduction setting

Newell, Dennis L.; Jessup, Micah J.; Hilton, David R.; Shaw, Colin A.; Hughes, Cameron

doi:10.1016/j.chemgeo.2015.10.003

Cited by 42 publications

(46 citation statements)

References 61 publications

(99 reference statements)

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“…The Cordillera Blanca is a massif in the Peruvian flat slab segment (a distinct type of low-angle subduction 47 ) characterized by an absence of active continental arc magmatism and a millions years old undertaking extensional regime 48 . The helium isotopic data from the thermal springs issuing from this region provided direct evidence for circulation of mantle-derived fluids in an amagmatic flat-slab setting 49 . The more southern Pampean flat-slab segment of the Central Andes displays a similar scenario of the Cordillera Blanca, but with minor current extensional tectonics 50 and known degassing activity 15 .…”

Section: Resultsmentioning

confidence: 88%

Global-scale control of extensional tectonics on CO2 earth degassing

et al. 2018

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Earth degassing of CO2-rich fluids has been proven to contribute significantly to the global carbon budget. The presence of ubiquitous outgassing reveals some degree of permeability of the crust that often coincides with seismically active zones. In this study, we took advantage of the most recent global geological datasets to better understand earth degassing and how it correlates with tectonic regimes. Here we use an ad hoc point pattern analysis to show that there is a spatial correlation between CO2 discharges and the presence of active fault systems, in particular with those characterized by a normal slip type. Seismic data demonstrate the existence of a positive spatial correlation between gas discharges and extensional tectonic regimes and confirms that such processes would play a key role in creating pathways for the rising gases at micro- and macro-scales, increasing the rock permeability and connecting the deep crust to the earth surface.

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Section: Resultsmentioning

confidence: 88%

Global-scale control of extensional tectonics on CO2 earth degassing

et al. 2018

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“…The hanging wall comprises Jurassic to Cretaceous sediments, Eocene-Pliocene volcanics, and Miocene-Pliocene sediments of the Lloclla Formation (Cobbing et al, 1981;Petford and Atherton, 1992;Giovanni et al, 2010;Margirier et al, 2015). Hot springs issue along the main detachment system and along steeply dipping faults and inferred synthetic faults proximal to the shear zone (Newell et al, 2015). We present data from samples collected in Quebrada Gatay (Fig.…”

Section: ■ Geologic Background and Sample Descriptionsmentioning

confidence: 98%

Deformation conditions during syn-convergent extension along the Cordillera Blanca shear zone, Peru

et al. 2019

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Strain localization across the brittle-ductile transition is a fundamental process in accommodating tectonic movement in the mid-crust. The tectonically active Cordillera Blanca shear zone (CBSZ), a ∼200-km-long normal-sense shear zone situated within the footwall of a discrete syn-convergent extensional fault in the Peruvian Andes, is an excellent field laboratory to explore this transition. Field and microscopic observations indicate consistent top-down-to-the-southwest sense of shear and a sequence of tectonites ranging from undeformed granodiorite through mylonite and ultimately fault breccia along the detachment.Using microstructural analysis, two-feldspar and Ti-in-quartz (TitaniQ) thermometry, recrystallized quartz paleopiezometry, and analysis of quartz crystallographic preferred orientations, we evaluate the deformation conditions and mechanisms in quartz and feldspar across the CBSZ. Deformation temperatures derived from asymmetric strain-induced myrmekite in a subset of tectonite samples are 410 ± 30 to 470 ± 36 °C, consistent with TitaniQ temperatures of 450 ± 60 to 490 ± 33 °C and temperatures >400 °C estimated from microstructural criteria. Brittle fabrics overprint ductile fabrics within ∼150 m of the detachment that indicate that deformation continued to lower-temperature (∼280–400 °C) and/or higher-strain-rate conditions prior to the onset of pervasive brittle deformation. Initial deformation occurred via high-temperature fracturing and dissolution-precipitation in feldspar. Continued subsolidus deformation resulted in either layering of mylonites into monophase quartz and fine-grained polyphase domains oriented subparallel to macroscopic foliation or the interconnection of recrystallized quartz networks oriented obliquely to macroscopic foliation. The transition to quartz-controlled rheology occurred at temperatures near ∼500 °C and at a differential stress of ∼16.5 MPa. Deformation within the CBSZ occurred predominantly above ∼400 °C and at stresses up to ∼71.4 MPa prior to the onset of brittle deformation.

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“…A trend in increasing CO2/ 3 He ratios is therefore commonly associated with admixture of crustal CO2 and/or degassing in open system (e.g. Crossey et al, 2009;Newell et al, 2015;Ruzié et al, 2013), defined by Rayleigh fractionation. Here, we test both of these possibilities.…”

Section: Radiogenic 4 He Stripping From Enriched Pore-watermentioning

confidence: 99%

“…CO2/ 3 He ratios ranging between 10 9 to 10 14 combined with δ 13 C(CO2) values without an obvious trend towards organic of carbonate end-member is a common observation, commonly interpreted as a result of simple mantle and crustal end-member mixing (Aka et al, 2001;Crossey et al, 2009;Mao et al, 2009). Other workers recognised that simple mixing is not a conclusive interpretation (Italiano et al, 2014) and suggested contribution of a solubility fractionation process (Matthews et al, 1987;Hilton, 2009;Newell et al, 2015). Where open system Rayleigh fractionation is proposed, it is commonly not conclusively supported by evidence from δ 13 C(CO2) values (Ruzié et al, 2013;Bräuer et al, 2016).…”

Section: Radiogenic 4 He Stripping From Enriched Pore-watermentioning

confidence: 99%

“…The 3 He/ 4 He ratio can be modified by dilution with non-CO2 gas (usually methane) with a different He isotopic signature (Sherwood Lollar et al, 1994), radiogenic 4 He accumulation in situ (Newell et al, 2015;Liu et al, 2016) or He stripping from formation water during gas migration through lithological units enriched in 4 He (Sano et al, 1990;Sakamoto et al, 1992). The resulting 3 He/ 4 He ratio can then be overprinted by addition of CO2 from a different source (O'Nions and Oxburgh, 1988) or phase fractionation during degassing (Matthews et al, 1987).…”

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confidence: 99%

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Tracing the migration of mantle CO2 in gas fields and mineral water springs in south-east Australia using noble gas and stable isotopes

Karolytė

Johnson

Gyӧre

et al. 2019

Geochimica et Cosmochimica Acta

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Geochemical monitoring of CO2 storage requires understanding of both innate and introduced fluids in the crust as well as the subsurface processes that can change the geochemical fingerprint of CO2 during injection, storage and any subsequent migration. Here, we analyse a natural analogue of CO2 storage, migration and leakage to the atmosphere, using noble gas and stable isotopes to constrain the effect of these processes on the geochemical fingerprint of the CO2. We present the most comprehensive evidence to date for mantle-sourced CO2 in southeast Australia, including well gas and CO2-rich mineral spring samples from the Otway Basin and Central Victorian Highlands (CVH). 3 He/ 4 He ratios in well gases and CO2 springs range from 1.21 to 3.07 RA and 1.23-3.65 RC/RA, respectively. We present chemical fractionation models to explain the observed range of 3 He/ 4 He ratios, He, Ne, Ar, Kr, Xe concentrations and δ 13 C(CO2) values in the springs and the well gases. The variability of 3 He/ 4 He in the well gases is controlled by the gas residence time in the reservoir and 2 associated radiogenic 4 He accumulation. 3 He/ 4 He in CO2 springs decrease away from the main mantle fluid supply conduit. We identify one main pathway for CO2 supply to the surface in the CVH, located near a major fault zone. Solubility fractionation during phase separation is proposed to explain the range in noble gas concentrations and δ 13 C(CO2) values measured in the mineral spring samples. This process is also responsible for low 3 He concentrations and associated high CO2/ 3 He, which are commonly interpreted as evidence for mixing with crustal CO2. The elevated CO2/ 3 He can be explained solely by solubility fractionation without the need to invoke other CO2 sources. The noble gases in the springs and well gases can be traced back to a single end-member which has suffered varying degrees of radiogenic helium accumulation and late stage degassing. This work shows that combined stable and noble gas isotopes in natural gases provide a robust tool for identifying the migration of injected CO2 to the shallow subsurface.

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Mantle-derived helium in hot springs of the Cordillera Blanca, Peru: Implications for mantle-to-crust fluid transfer in a flat-slab subduction setting

Cited by 42 publications

References 61 publications

Global-scale control of extensional tectonics on CO2 earth degassing

Global-scale control of extensional tectonics on CO2 earth degassing

Deformation conditions during syn-convergent extension along the Cordillera Blanca shear zone, Peru

Tracing the migration of mantle CO2 in gas fields and mineral water springs in south-east Australia using noble gas and stable isotopes

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