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Low-volume magmatism linked to flank deformation on Isla Santa Cruz, Galápagos Archipelago, using cosmogenic 3He exposure and 40Ar/39Ar dating of fault scarps and lavas.

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Title: Low-volume magmatism linked to flank deformation on Isla Santa Cruz, Galápagos Archipelago, using cosmogenic 3He exposure and 40Ar/39Ar dating of fault scarps and lavas.
Authors: Schwartz, D. M.1 (AUTHOR) darinschwartz@boisestate.edu, Harpp, K.2 (AUTHOR), Kurz, M. D.3 (AUTHOR), Wilson, E.4 (AUTHOR), Van Kirk, R.2 (AUTHOR)
Source: Bulletin of Volcanology. 8/1/2022, Vol. 84 Issue 9, p1-17. 17p.
Subject Terms: *Archipelagoes, *Magmatism, *Geological time scales, *Volcanoes, *Calderas, *Lava, *Volcanism
Geographic Terms: Santa Cruz (Calif.)
Abstract: Isla Santa Cruz is a volcanic island located in the central Galápagos Archipelago. The island's northern and southern flanks are deformed by E–W-trending normal faults not observed on the younger Galápagos shields, and Santa Cruz lacks the large summit calderas that characterize those structures. To construct a chronology of volcanism and deformation on Santa Cruz, we employ 40Ar/39Ar geochronology of lavas and 3He exposure dating of fault scarps from across the island. The combination of Ar–Ar dating with in situ-produced cosmogenic exposure age data provides a powerful tool to evaluate fault chronologies. The 40Ar/39Ar ages indicate that the island has been volcanically active since at least 1.62 ± 0.030 Ma (2SD). Volcanism deposited lavas over the entire island until ~ 200 ka, when it became focused along an E–W-trending summit vent system; all dated lavas < 200 ka were emplaced on the southern flank. Structural observations suggest that the island has experienced two major faulting episodes. Crosscutting relationships of lavas indicate that north flank faults formed after 1.16 ± 0.070 Ma, but likely before 416 ± 36 ka, whereas the faults on the southern flank of the island initiated between 201 ± 37 and 32.6 ± 4.6 ka, based on 3He exposure dating of fault surfaces. The data are consistent with a model wherein the northeastern faults are associated with regional extension owing to the young volcano's location closer to the Galápagos Spreading Center at the time. The second phase of volcanism is contemporaneous with the formation of the southern faults. The expression of this younger, low-volume volcanic phase was likely related to the elongate island morphology established during earlier deformation. The complex feedback between tectonic and volcanic processes responsible for southward spreading along the southern flank likely generated persistent E-W-oriented magmatic intrusions. The formation of the Galápagos Transform Fault and sea-level fluctuations may be the primary causes of eruptive and deformational episodes on Santa Cruz. [ABSTRACT FROM AUTHOR]
Database: Energy & Power Source
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  Data: Low-volume magmatism linked to flank deformation on Isla Santa Cruz, Gal&#225;pagos Archipelago, using cosmogenic &lt;superscript&gt;3&lt;/superscript&gt;He exposure and &lt;superscript&gt;40&lt;/superscript&gt;Ar/&lt;superscript&gt;39&lt;/superscript&gt;Ar dating of fault scarps and lavas.
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  Data: &lt;searchLink fieldCode=&quot;JN&quot; term=&quot;%22Bulletin+of+Volcanology%22&quot;&gt;Bulletin of Volcanology&lt;/searchLink&gt;. 8/1/2022, Vol. 84 Issue 9, p1-17. 17p.
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  Data: &lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Santa+Cruz+%28Calif%2E%29%22&quot;&gt;Santa Cruz (Calif.)&lt;/searchLink&gt;
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Isla Santa Cruz is a volcanic island located in the central Gal&#225;pagos Archipelago. The island&#39;s northern and southern flanks are deformed by E–W-trending normal faults not observed on the younger Gal&#225;pagos shields, and Santa Cruz lacks the large summit calderas that characterize those structures. To construct a chronology of volcanism and deformation on Santa Cruz, we employ 40Ar/39Ar geochronology of lavas and 3He exposure dating of fault scarps from across the island. The combination of Ar–Ar dating with in situ-produced cosmogenic exposure age data provides a powerful tool to evaluate fault chronologies. The 40Ar/39Ar ages indicate that the island has been volcanically active since at least 1.62 &#177; 0.030 Ma (2SD). Volcanism deposited lavas over the entire island until ~ 200 ka, when it became focused along an E–W-trending summit vent system; all dated lavas &lt; 200 ka were emplaced on the southern flank. Structural observations suggest that the island has experienced two major faulting episodes. Crosscutting relationships of lavas indicate that north flank faults formed after 1.16 &#177; 0.070 Ma, but likely before 416 &#177; 36 ka, whereas the faults on the southern flank of the island initiated between 201 &#177; 37 and 32.6 &#177; 4.6 ka, based on 3He exposure dating of fault surfaces. The data are consistent with a model wherein the northeastern faults are associated with regional extension owing to the young volcano&#39;s location closer to the Gal&#225;pagos Spreading Center at the time. The second phase of volcanism is contemporaneous with the formation of the southern faults. The expression of this younger, low-volume volcanic phase was likely related to the elongate island morphology established during earlier deformation. The complex feedback between tectonic and volcanic processes responsible for southward spreading along the southern flank likely generated persistent E-W-oriented magmatic intrusions. The formation of the Gal&#225;pagos Transform Fault and sea-level fluctuations may be the primary causes of eruptive and deformational episodes on Santa Cruz. [ABSTRACT FROM AUTHOR]
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RecordInfo BibRecord:
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    Identifiers:
      – Type: doi
        Value: 10.1007/s00445-022-01575-3
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 17
        StartPage: 1
    Subjects:
      – SubjectFull: Archipelagoes
        Type: general
      – SubjectFull: Magmatism
        Type: general
      – SubjectFull: Geological time scales
        Type: general
      – SubjectFull: Volcanoes
        Type: general
      – SubjectFull: Calderas
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      – SubjectFull: Lava
        Type: general
      – SubjectFull: Volcanism
        Type: general
      – SubjectFull: Santa Cruz (Calif.)
        Type: general
    Titles:
      – TitleFull: Low-volume magmatism linked to flank deformation on Isla Santa Cruz, Galápagos Archipelago, using cosmogenic 3He exposure and 40Ar/39Ar dating of fault scarps and lavas.
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            NameFull: Schwartz, D. M.
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            NameFull: Harpp, K.
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            NameFull: Kurz, M. D.
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            NameFull: Wilson, E.
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            NameFull: Van Kirk, R.
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            – D: 01
              M: 09
              Text: 8/1/2022
              Type: published
              Y: 2022
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              Value: 84
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              Value: 9
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            – TitleFull: Bulletin of Volcanology
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