Evolution of the Western Cordillera in the Andes of Ecuador (Late Cretaceous-Paleogene)

Cristian Vallejo Cruz

Research output: Other contribution

Abstract

ABSTRACT
The subduction of ocean floor at a convergent plate boundary can be regarded as approximating
a steady-state process. Interruption or cessation of that process commonly follows the arrival
of a buoyant object. Arcs and continents are the familiar kinds of buoyant objects involved
in collisions. I here provide a detailed analysis of a less familiar kind of collision, that of an
oceanic plateau.
The determination of accurate and precise ages for the timing of collision between oceanic
plateaus and continental crust provides an understanding of how the indenting and buttressing
plates respond to the collisional event. The volcanic basement of the Ecuadorian Western
Cordillera (Pallatanga Formation and San Juan Unit) is made up of mafic and ultramafic rocks
with oceanic plateau geochemical affinities. A SHRIMP crystallization age (zircon) of 87.1±1.66
Ma (2s) and 40Ar/39Ar (hornblende) age of 84.69±2.22 Ma (2s) from an accreted fragment of the
plateau, overlap with an 40Ar/39Ar age of 88±1.6 Ma age obtained for oceanic plateau basement
rocks of the Piñon Formation in coastal Ecuador (Luzieux et al., 2006), and a suite of ~92-88
Ma ages reported for oceanic plateau sequences in Colombia and the Caribbean region. These
results are consistent with the idea that the oceanic plateau rocks of the Western Cordillera and
coastal Ecuador are derived from the Late Cretaceous Caribbean Colombia Oceanic Plateau
(CCOP).
Intraoceanic island arc sequences (Pujilí Granite, Rio Cala Group, Naranjal Unit) overlie
the plateau and yield crystallization ages that range between ~85–72 Ma. The geochemistry
and radiometric ages of lavas associated with the Rio Cala Arc, combined with the age range
and geochemistry of their turbiditic, volcanoclastic products indicate that the arc initiated by
westward subduction beneath the Caribbean Plateau, and are coeval with island arc rocks of
coastal Ecuador (Las Orquideas, San Lorenzo and Cayo formations). These island arc units
may be related to the Late Cretaceous Great Arc of the Caribbean.
Paleomagnetic analyses of volcanic rocks, of the Piñon and San Lorenzo formations of the
southern external forearc (Luzieux, 20067), indicate their pre-collisional extrusion at equatorial
or shallow southern latitudes. Furthermore, paleomagnetic declination data from basement and
sedimentary cover rocks in the coastal region (Luzieux, 2007) indicate 20–50o of clockwise
rotation during the Campanian, which was probably synchronous with the collision of the
oceanic plateau and arc sequence with South America.
The initial collision between the South American Plate and the Caribbean Plateau was
synchronous with accelerated surface uplift and exhumation (>1km/my) within the buttressing
continental margin during the Late Cretaceous (c. 75–65 Ma), in an area extending as far inland
as the Eastern Cordillera. The rapid exhumation coincides with the deposition of continental
siliciclastic material in both the fore- and backarc environments (Yunguilla and Tena formations
respectively).
Collectively, this evidence shows that the initial collision between the Caribbean Plateau
and the Ecuadorian margin occurred during the late Campanian–Maastrichtian (73–70 Ma),
and resulted in plugging of the subduction zone, the termination of island arc magmatism, and
deformation of the continental margin.
Magmatism associated with the Campanian–early Maastrichtian Rio Cala Arc, which
erupted through the Pallatanga Formation, ceased during the Maastrichtian and was followed
by the initiation of east-dipping subduction beneath the accreted oceanic plateau. The new
active margin gave rise to the latest Maastrichtian (ca 65 Ma) Silante volcanic arc, which was
deposited in a terrestrial environment.
During the Palaeocene to Eocene, marine conditions were dominant in the area now occupied
by the Western Cordillera, and volcanic rocks of the Macuchi Unit were deposited, possibly as
a temporal continuation of the Silante volcanic arc. This submarine volcanism was coeval with
the deposition of siliciclastic rocks of the Angamarca Group, and the Saguangal Formation,
which were mainly derived from the emerging Eastern Cordillera.
Finally, no evidence exists to support previous hypotheses that the Macuchi Arc accreted in
the Late Eocene, causing structural inversion of the Angamarca Basin. It is geometrically difficult
to suggest that the Macuchi Block accreted in the Late Eocene, and inserted itself between the
Piñon and Pallatanga blocks, which accreted during the Late Cretaceous. Furthermore, volcanic
rocks of the Macuchi Unit are found to be conformably overlain by turbidites of the Angamarca
Group.
Original languageEnglish
TypePhD Thesis
PublisherETH
Number of pages215
Place of PublicationZürich
DOIs
Publication statusPublished - 2007

Fingerprint

cordillera
Paleogene
plateau
Cretaceous
island arc
collision
Maastrichtian
Eocene
subduction
exhumation
rock
magmatism
volcanic rock
crystallization
terrestrial environment
Campanian
extrusion
plate boundary
hornblende
Paleocene

Keywords

  • lithostratigraphy
  • cretaceous
  • stratigraphy
  • palaeogene
  • provenance of sedimentary particles
  • sedimentary environment
  • heavy minerals
  • mineralogy
  • palaeotectonics
  • geology
  • absolute geological age determination
  • subduction zones
  • Suedamerika, Republic of Ecuador
  • Ecuador Andes
  • S. american mountains

Cite this

Evolution of the Western Cordillera in the Andes of Ecuador (Late Cretaceous-Paleogene). / Vallejo Cruz, Cristian.

215 p. Zürich : ETH. 2007, PhD Thesis.

Research output: Other contribution

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abstract = "ABSTRACT The subduction of ocean floor at a convergent plate boundary can be regarded as approximating a steady-state process. Interruption or cessation of that process commonly follows the arrival of a buoyant object. Arcs and continents are the familiar kinds of buoyant objects involved in collisions. I here provide a detailed analysis of a less familiar kind of collision, that of an oceanic plateau. The determination of accurate and precise ages for the timing of collision between oceanic plateaus and continental crust provides an understanding of how the indenting and buttressing plates respond to the collisional event. The volcanic basement of the Ecuadorian Western Cordillera (Pallatanga Formation and San Juan Unit) is made up of mafic and ultramafic rocks with oceanic plateau geochemical affinities. A SHRIMP crystallization age (zircon) of 87.1±1.66 Ma (2s) and 40Ar/39Ar (hornblende) age of 84.69±2.22 Ma (2s) from an accreted fragment of the plateau, overlap with an 40Ar/39Ar age of 88±1.6 Ma age obtained for oceanic plateau basement rocks of the Pi{\~n}on Formation in coastal Ecuador (Luzieux et al., 2006), and a suite of ~92-88 Ma ages reported for oceanic plateau sequences in Colombia and the Caribbean region. These results are consistent with the idea that the oceanic plateau rocks of the Western Cordillera and coastal Ecuador are derived from the Late Cretaceous Caribbean Colombia Oceanic Plateau (CCOP). Intraoceanic island arc sequences (Pujil{\'i} Granite, Rio Cala Group, Naranjal Unit) overlie the plateau and yield crystallization ages that range between ~85–72 Ma. The geochemistry and radiometric ages of lavas associated with the Rio Cala Arc, combined with the age range and geochemistry of their turbiditic, volcanoclastic products indicate that the arc initiated by westward subduction beneath the Caribbean Plateau, and are coeval with island arc rocks of coastal Ecuador (Las Orquideas, San Lorenzo and Cayo formations). These island arc units may be related to the Late Cretaceous Great Arc of the Caribbean. Paleomagnetic analyses of volcanic rocks, of the Pi{\~n}on and San Lorenzo formations of the southern external forearc (Luzieux, 20067), indicate their pre-collisional extrusion at equatorial or shallow southern latitudes. Furthermore, paleomagnetic declination data from basement and sedimentary cover rocks in the coastal region (Luzieux, 2007) indicate 20–50o of clockwise rotation during the Campanian, which was probably synchronous with the collision of the oceanic plateau and arc sequence with South America. The initial collision between the South American Plate and the Caribbean Plateau was synchronous with accelerated surface uplift and exhumation (>1km/my) within the buttressing continental margin during the Late Cretaceous (c. 75–65 Ma), in an area extending as far inland as the Eastern Cordillera. The rapid exhumation coincides with the deposition of continental siliciclastic material in both the fore- and backarc environments (Yunguilla and Tena formations respectively). Collectively, this evidence shows that the initial collision between the Caribbean Plateau and the Ecuadorian margin occurred during the late Campanian–Maastrichtian (73–70 Ma), and resulted in plugging of the subduction zone, the termination of island arc magmatism, and deformation of the continental margin. Magmatism associated with the Campanian–early Maastrichtian Rio Cala Arc, which erupted through the Pallatanga Formation, ceased during the Maastrichtian and was followed by the initiation of east-dipping subduction beneath the accreted oceanic plateau. The new active margin gave rise to the latest Maastrichtian (ca 65 Ma) Silante volcanic arc, which was deposited in a terrestrial environment. During the Palaeocene to Eocene, marine conditions were dominant in the area now occupied by the Western Cordillera, and volcanic rocks of the Macuchi Unit were deposited, possibly as a temporal continuation of the Silante volcanic arc. This submarine volcanism was coeval with the deposition of siliciclastic rocks of the Angamarca Group, and the Saguangal Formation, which were mainly derived from the emerging Eastern Cordillera. Finally, no evidence exists to support previous hypotheses that the Macuchi Arc accreted in the Late Eocene, causing structural inversion of the Angamarca Basin. It is geometrically difficult to suggest that the Macuchi Block accreted in the Late Eocene, and inserted itself between the Pi{\~n}on and Pallatanga blocks, which accreted during the Late Cretaceous. Furthermore, volcanic rocks of the Macuchi Unit are found to be conformably overlain by turbidites of the Angamarca Group.",
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author = "{Vallejo Cruz}, Cristian",
year = "2007",
doi = "10.3929/ethz-a-005416411",
language = "English",
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TY - GEN

T1 - Evolution of the Western Cordillera in the Andes of Ecuador (Late Cretaceous-Paleogene)

AU - Vallejo Cruz, Cristian

PY - 2007

Y1 - 2007

N2 - ABSTRACT The subduction of ocean floor at a convergent plate boundary can be regarded as approximating a steady-state process. Interruption or cessation of that process commonly follows the arrival of a buoyant object. Arcs and continents are the familiar kinds of buoyant objects involved in collisions. I here provide a detailed analysis of a less familiar kind of collision, that of an oceanic plateau. The determination of accurate and precise ages for the timing of collision between oceanic plateaus and continental crust provides an understanding of how the indenting and buttressing plates respond to the collisional event. The volcanic basement of the Ecuadorian Western Cordillera (Pallatanga Formation and San Juan Unit) is made up of mafic and ultramafic rocks with oceanic plateau geochemical affinities. A SHRIMP crystallization age (zircon) of 87.1±1.66 Ma (2s) and 40Ar/39Ar (hornblende) age of 84.69±2.22 Ma (2s) from an accreted fragment of the plateau, overlap with an 40Ar/39Ar age of 88±1.6 Ma age obtained for oceanic plateau basement rocks of the Piñon Formation in coastal Ecuador (Luzieux et al., 2006), and a suite of ~92-88 Ma ages reported for oceanic plateau sequences in Colombia and the Caribbean region. These results are consistent with the idea that the oceanic plateau rocks of the Western Cordillera and coastal Ecuador are derived from the Late Cretaceous Caribbean Colombia Oceanic Plateau (CCOP). Intraoceanic island arc sequences (Pujilí Granite, Rio Cala Group, Naranjal Unit) overlie the plateau and yield crystallization ages that range between ~85–72 Ma. The geochemistry and radiometric ages of lavas associated with the Rio Cala Arc, combined with the age range and geochemistry of their turbiditic, volcanoclastic products indicate that the arc initiated by westward subduction beneath the Caribbean Plateau, and are coeval with island arc rocks of coastal Ecuador (Las Orquideas, San Lorenzo and Cayo formations). These island arc units may be related to the Late Cretaceous Great Arc of the Caribbean. Paleomagnetic analyses of volcanic rocks, of the Piñon and San Lorenzo formations of the southern external forearc (Luzieux, 20067), indicate their pre-collisional extrusion at equatorial or shallow southern latitudes. Furthermore, paleomagnetic declination data from basement and sedimentary cover rocks in the coastal region (Luzieux, 2007) indicate 20–50o of clockwise rotation during the Campanian, which was probably synchronous with the collision of the oceanic plateau and arc sequence with South America. The initial collision between the South American Plate and the Caribbean Plateau was synchronous with accelerated surface uplift and exhumation (>1km/my) within the buttressing continental margin during the Late Cretaceous (c. 75–65 Ma), in an area extending as far inland as the Eastern Cordillera. The rapid exhumation coincides with the deposition of continental siliciclastic material in both the fore- and backarc environments (Yunguilla and Tena formations respectively). Collectively, this evidence shows that the initial collision between the Caribbean Plateau and the Ecuadorian margin occurred during the late Campanian–Maastrichtian (73–70 Ma), and resulted in plugging of the subduction zone, the termination of island arc magmatism, and deformation of the continental margin. Magmatism associated with the Campanian–early Maastrichtian Rio Cala Arc, which erupted through the Pallatanga Formation, ceased during the Maastrichtian and was followed by the initiation of east-dipping subduction beneath the accreted oceanic plateau. The new active margin gave rise to the latest Maastrichtian (ca 65 Ma) Silante volcanic arc, which was deposited in a terrestrial environment. During the Palaeocene to Eocene, marine conditions were dominant in the area now occupied by the Western Cordillera, and volcanic rocks of the Macuchi Unit were deposited, possibly as a temporal continuation of the Silante volcanic arc. This submarine volcanism was coeval with the deposition of siliciclastic rocks of the Angamarca Group, and the Saguangal Formation, which were mainly derived from the emerging Eastern Cordillera. Finally, no evidence exists to support previous hypotheses that the Macuchi Arc accreted in the Late Eocene, causing structural inversion of the Angamarca Basin. It is geometrically difficult to suggest that the Macuchi Block accreted in the Late Eocene, and inserted itself between the Piñon and Pallatanga blocks, which accreted during the Late Cretaceous. Furthermore, volcanic rocks of the Macuchi Unit are found to be conformably overlain by turbidites of the Angamarca Group.

AB - ABSTRACT The subduction of ocean floor at a convergent plate boundary can be regarded as approximating a steady-state process. Interruption or cessation of that process commonly follows the arrival of a buoyant object. Arcs and continents are the familiar kinds of buoyant objects involved in collisions. I here provide a detailed analysis of a less familiar kind of collision, that of an oceanic plateau. The determination of accurate and precise ages for the timing of collision between oceanic plateaus and continental crust provides an understanding of how the indenting and buttressing plates respond to the collisional event. The volcanic basement of the Ecuadorian Western Cordillera (Pallatanga Formation and San Juan Unit) is made up of mafic and ultramafic rocks with oceanic plateau geochemical affinities. A SHRIMP crystallization age (zircon) of 87.1±1.66 Ma (2s) and 40Ar/39Ar (hornblende) age of 84.69±2.22 Ma (2s) from an accreted fragment of the plateau, overlap with an 40Ar/39Ar age of 88±1.6 Ma age obtained for oceanic plateau basement rocks of the Piñon Formation in coastal Ecuador (Luzieux et al., 2006), and a suite of ~92-88 Ma ages reported for oceanic plateau sequences in Colombia and the Caribbean region. These results are consistent with the idea that the oceanic plateau rocks of the Western Cordillera and coastal Ecuador are derived from the Late Cretaceous Caribbean Colombia Oceanic Plateau (CCOP). Intraoceanic island arc sequences (Pujilí Granite, Rio Cala Group, Naranjal Unit) overlie the plateau and yield crystallization ages that range between ~85–72 Ma. The geochemistry and radiometric ages of lavas associated with the Rio Cala Arc, combined with the age range and geochemistry of their turbiditic, volcanoclastic products indicate that the arc initiated by westward subduction beneath the Caribbean Plateau, and are coeval with island arc rocks of coastal Ecuador (Las Orquideas, San Lorenzo and Cayo formations). These island arc units may be related to the Late Cretaceous Great Arc of the Caribbean. Paleomagnetic analyses of volcanic rocks, of the Piñon and San Lorenzo formations of the southern external forearc (Luzieux, 20067), indicate their pre-collisional extrusion at equatorial or shallow southern latitudes. Furthermore, paleomagnetic declination data from basement and sedimentary cover rocks in the coastal region (Luzieux, 2007) indicate 20–50o of clockwise rotation during the Campanian, which was probably synchronous with the collision of the oceanic plateau and arc sequence with South America. The initial collision between the South American Plate and the Caribbean Plateau was synchronous with accelerated surface uplift and exhumation (>1km/my) within the buttressing continental margin during the Late Cretaceous (c. 75–65 Ma), in an area extending as far inland as the Eastern Cordillera. The rapid exhumation coincides with the deposition of continental siliciclastic material in both the fore- and backarc environments (Yunguilla and Tena formations respectively). Collectively, this evidence shows that the initial collision between the Caribbean Plateau and the Ecuadorian margin occurred during the late Campanian–Maastrichtian (73–70 Ma), and resulted in plugging of the subduction zone, the termination of island arc magmatism, and deformation of the continental margin. Magmatism associated with the Campanian–early Maastrichtian Rio Cala Arc, which erupted through the Pallatanga Formation, ceased during the Maastrichtian and was followed by the initiation of east-dipping subduction beneath the accreted oceanic plateau. The new active margin gave rise to the latest Maastrichtian (ca 65 Ma) Silante volcanic arc, which was deposited in a terrestrial environment. During the Palaeocene to Eocene, marine conditions were dominant in the area now occupied by the Western Cordillera, and volcanic rocks of the Macuchi Unit were deposited, possibly as a temporal continuation of the Silante volcanic arc. This submarine volcanism was coeval with the deposition of siliciclastic rocks of the Angamarca Group, and the Saguangal Formation, which were mainly derived from the emerging Eastern Cordillera. Finally, no evidence exists to support previous hypotheses that the Macuchi Arc accreted in the Late Eocene, causing structural inversion of the Angamarca Basin. It is geometrically difficult to suggest that the Macuchi Block accreted in the Late Eocene, and inserted itself between the Piñon and Pallatanga blocks, which accreted during the Late Cretaceous. Furthermore, volcanic rocks of the Macuchi Unit are found to be conformably overlain by turbidites of the Angamarca Group.

KW - lithostratigraphy

KW - cretaceous

KW - stratigraphy

KW - palaeogene

KW - provenance of sedimentary particles

KW - sedimentary environment

KW - heavy minerals

KW - mineralogy

KW - palaeotectonics

KW - geology

KW - absolute geological age determination

KW - subduction zones

KW - Suedamerika, Republic of Ecuador

KW - Ecuador Andes

KW - S. american mountains

U2 - 10.3929/ethz-a-005416411

DO - 10.3929/ethz-a-005416411

M3 - Other contribution

PB - ETH

CY - Zürich

ER -