INVESTIGADORES
UMAZANO aldo Martin
artículos
Título:
Sedimentary record of a Late Cretaceous volcanic arc in central Patagonia: petrogrpahy, geochemistry and provenance of fluvial volcaniclastic deposits of the Bajo Barreal Formation, San Jorge Basin, Argentina
Autor/es:
UMAZANO, A.M.; BELLOSI, E.S.; VISCONTI, G.; JALFIN, G.; MELCHOR, R.N.
Revista:
CRETACEOUS RESEARCH (PRINT)
Editorial:
Elsevier
Referencias:
Año: 2009 p. 746 - 766
ISSN:
0195-6671
Resumen:
The Upper Cretaceous Bajo Barreal Formation (San Jorge Basin, Argentina) is a fluvial succession mostly
composed of channel sandstones interbedded with thicker floodplain deposits dominated by tuffaceous
strata. The goal of this contribution is to infer the provenance of the unit through combined
petrographical and geochemical data of channel sandstones, primary tuffs and tuffo-psammites
(reworked, no-mixed tuffs). Channel sandstones are dominantly litharenites and feldspathic litharenites
with abundant participation of volcanic lithic fragments with different textures (porphyritic, eutaxitic,
felsitic, pilotaxitic, trachytic and vitric-vitrophyric), pumice and plagioclase. K-feldspar, quartz and
sedimentary rock fragments are scarce. QFLu diagram and several provenance indicators including
dominance and textural types of rock fragments, K-feldspar/plagioclase ratio and inclusion-free quartz
grains indicate a provenance from felsic to intermediate, pyroclastic-rich, arc-related volcanic rocks. This
interpretation agrees with the values of various elemental ratios of trace elements such as La/Sc, Th/Sc,
Cr/Th, Eu/Eu* and (La/Lu)N and discriminant functions based on major elements.
Pyroclastic floodplain strata are commonly pumice-rich, occasionally glass shard-rich, vitric tuffs
suggesting an origin from plinian-like eruptions. Subordinate components include volcanic lithic
fragments, quartz, orthoclase and plagioclase. Zr/Ti versus Nb/Y and SiO2 versus K2O diagrams, as well as
a multi-element diagram of selected trace elements shows that the pyroclastic rocks were originated
from medium-K content, intermediate, arc related magmatic source.
Considering the palaeoflow direction towards the east and south-east and presence of subduction
processes along the western margin of Patagonia during the Late Cretaceous, it is interpreted that Bajo
Barreal Formation constitutes the sedimentary record (distal facies of volcano-flanking fan or apron) of
this coeval volcanic arc. Channel sandstones probably were mostly derived from the Divisadero
Formation volcanic rocks because of similar petrographical features and REE pattern. In contrast,
pyroclastic tuffaceous floodplain deposits would be derived from vents located over the actual outcrops
of the Patagonian Batholith.
* and (La/Lu)N and discriminant functions based on major elements.
Pyroclastic floodplain strata are commonly pumice-rich, occasionally glass shard-rich, vitric tuffs
suggesting an origin from plinian-like eruptions. Subordinate components include volcanic lithic
fragments, quartz, orthoclase and plagioclase. Zr/Ti versus Nb/Y and SiO2 versus K2O diagrams, as well as
a multi-element diagram of selected trace elements shows that the pyroclastic rocks were originated
from medium-K content, intermediate, arc related magmatic source.
Considering the palaeoflow direction towards the east and south-east and presence of subduction
processes along the western margin of Patagonia during the Late Cretaceous, it is interpreted that Bajo
Barreal Formation constitutes the sedimentary record (distal facies of volcano-flanking fan or apron) of
this coeval volcanic arc. Channel sandstones probably were mostly derived from the Divisadero
Formation volcanic rocks because of similar petrographical features and REE pattern. In contrast,
pyroclastic tuffaceous floodplain deposits would be derived from vents located over the actual outcrops
of the Patagonian Batholith.
2 versus K2O diagrams, as well as
a multi-element diagram of selected trace elements shows that the pyroclastic rocks were originated
from medium-K content, intermediate, arc related magmatic source.
Considering the palaeoflow direction towards the east and south-east and presence of subduction
processes along the western margin of Patagonia during the Late Cretaceous, it is interpreted that Bajo
Barreal Formation constitutes the sedimentary record (distal facies of volcano-flanking fan or apron) of
this coeval volcanic arc. Channel sandstones probably were mostly derived from the Divisadero
Formation volcanic rocks because of similar petrographical features and REE pattern. In contrast,
pyroclastic tuffaceous floodplain deposits would be derived from vents located over the actual outcrops
of the Patagonian Batholith.