Tectono-stratigraphic evolution of the Comondú Group from Bahía de La Paz to Loreto, Baja California Sur, Mexico

William R. Drake, Paul J Umhoefer, Alexis Griffiths, Ann Vlad, Lisa Peters, William McIntosh

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

The late Oligocene to mid-Miocene volcanic and volcaniclastic rocks of the Comondú Group are well exposed along the Main Rift Escarpment of Baja California Sur from the Bahía de La Paz region to Bahía Concepción. New mapping and stratigraphic analysis of the Comondú Group from Bahía de La Paz to Loreto reveal facies trends and correlations that form the foundation for a continuous stratigraphic framework for the Comondú Group along a 300km-long transect on the eastern coast of the Baja California peninsula. Broad but distinct lithostratigraphic trends, alluvial fan facies, and volcanic and volcaniclastic facies record an overall coarsening-upwards package that includes ignimbrite deposits within increasingly proximal alluvial fan deposits, both derived from the east. Geochronology of the unit, including 32 isotope ages and 12 previously unpublished 40Ar/39Ar ages, provide the timing of four main increasingly proximal depositional events. Non-marine sandstone, defining the base of the Comondú Group, was first deposited between ~26Ma and ~24Ma. Emplacement of rhyolitic ignimbrites initiated between ~24Ma and ~23Ma and marked a westward expansion of volcanic activity affiliated with the Sierra Madre Occidental ignimbrite sequences in southern Sinaloa, western Durango, and northern Nayarit. A change in volcanism occurred at ~19Ma to ~18Ma with more ignimbrites, increased intermediate compositions, and the appearance of local vents and proximal volcanic facies. A final localized change of volcanism occurred from ~14 to ~12Ma in the Loreto area with an increase of proximal alluvial fan deposits and local volcanoes in the Upper Comondú Group. The bulk of the Upper Comondú Group is absent south of the Loreto area and has either been removed by erosion as a source for the Magdalena Fan in the Pacific Ocean, or was focused primarily in the Loreto area and northward. We use a pre-rift tectonic reconstruction of the Gulf of California to align broad stratigraphic trends along the peninsula, the Gulf conjugate margins, and within the Gulf. The Cascadia arc of Oregon and northern California may be a modern analog for the Comondú Group with a linear volcanic arc formed above shrinking subducting microplates, and a broad backarc region of moderate extension and scattered volcanism.

Original languageEnglish (US)
JournalTectonophysics
DOIs
StateAccepted/In press - Sep 2 2016

Fingerprint

Lower California (Mexico)
ignimbrite
Mexico
alluvial fan
igneous rocks
volcanism
volcanology
fans
tectonic reconstruction
gulfs
deposits
peninsulas
trends
microplate
escarpment
geochronology
island arc
arcs
Oligocene
Gulf of California (Mexico)

Keywords

  • Baja California Sur
  • Comondú Group
  • Geochronology
  • Miocene
  • Stratigraphy
  • Volcanic arc

ASJC Scopus subject areas

  • Geophysics
  • Earth-Surface Processes

Cite this

Tectono-stratigraphic evolution of the Comondú Group from Bahía de La Paz to Loreto, Baja California Sur, Mexico. / Drake, William R.; Umhoefer, Paul J; Griffiths, Alexis; Vlad, Ann; Peters, Lisa; McIntosh, William.

In: Tectonophysics, 02.09.2016.

Research output: Contribution to journalArticle

Drake, William R. ; Umhoefer, Paul J ; Griffiths, Alexis ; Vlad, Ann ; Peters, Lisa ; McIntosh, William. / Tectono-stratigraphic evolution of the Comondú Group from Bahía de La Paz to Loreto, Baja California Sur, Mexico. In: Tectonophysics. 2016.
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abstract = "The late Oligocene to mid-Miocene volcanic and volcaniclastic rocks of the Comond{\'u} Group are well exposed along the Main Rift Escarpment of Baja California Sur from the Bah{\'i}a de La Paz region to Bah{\'i}a Concepci{\'o}n. New mapping and stratigraphic analysis of the Comond{\'u} Group from Bah{\'i}a de La Paz to Loreto reveal facies trends and correlations that form the foundation for a continuous stratigraphic framework for the Comond{\'u} Group along a 300km-long transect on the eastern coast of the Baja California peninsula. Broad but distinct lithostratigraphic trends, alluvial fan facies, and volcanic and volcaniclastic facies record an overall coarsening-upwards package that includes ignimbrite deposits within increasingly proximal alluvial fan deposits, both derived from the east. Geochronology of the unit, including 32 isotope ages and 12 previously unpublished 40Ar/39Ar ages, provide the timing of four main increasingly proximal depositional events. Non-marine sandstone, defining the base of the Comond{\'u} Group, was first deposited between ~26Ma and ~24Ma. Emplacement of rhyolitic ignimbrites initiated between ~24Ma and ~23Ma and marked a westward expansion of volcanic activity affiliated with the Sierra Madre Occidental ignimbrite sequences in southern Sinaloa, western Durango, and northern Nayarit. A change in volcanism occurred at ~19Ma to ~18Ma with more ignimbrites, increased intermediate compositions, and the appearance of local vents and proximal volcanic facies. A final localized change of volcanism occurred from ~14 to ~12Ma in the Loreto area with an increase of proximal alluvial fan deposits and local volcanoes in the Upper Comond{\'u} Group. The bulk of the Upper Comond{\'u} Group is absent south of the Loreto area and has either been removed by erosion as a source for the Magdalena Fan in the Pacific Ocean, or was focused primarily in the Loreto area and northward. We use a pre-rift tectonic reconstruction of the Gulf of California to align broad stratigraphic trends along the peninsula, the Gulf conjugate margins, and within the Gulf. The Cascadia arc of Oregon and northern California may be a modern analog for the Comond{\'u} Group with a linear volcanic arc formed above shrinking subducting microplates, and a broad backarc region of moderate extension and scattered volcanism.",
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