structure peru02
TRANSCRIPT
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Structure and Tectonics of the Peruvian
Andes:
Regional Geological Data and Implications for
Exploration
Russell Mason
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Data
Geological data
captured from 1:100000
maps. Polygons labeled
according to age and
basic rock type
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Data
Mineral deposit data - location, type Geochronology data - location, age, rock type
Remote sensing - Landsat
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Interpretation of Structures from Data
Assumptions:
that linear shaped margins or contacts of tectono-
stratigraphic units are fault controlled
Structures that influence the shapes and locations of
tectono-stratigraphic units are likely to be important
structures (as a subset of lineaments)
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Interpretation of Structures from Data
Aim:
To identify structures that have important geological
significance and tectonic context.
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Interpretation of Structures from Data
Lineament analysis (Butler 2007) - approx 20 000 objects
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Interpretation of Structures from Data:
Examples
Fault controlled basins
influence areal distribution of
sediments and volcanics
Major basin boundary
faults can be very large
structures
Segmented basins
indicate transfer structures
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Interpretation of Structures from Data:
Examples
Basement uplift along regionally
significant structures
Inverted basin margin faults
Figure from Vaughan Stagpoole, Andy Nicol, RobFunnell, Richard Cook GNS website (New
Zealand)
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Interpretation of Structures from Data:
Examples
Horst boundary faults at
margins of basement uplifts
Figure from CCOP EPF website
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Interpretation of Structures from Data:
Summary
The shape and distribution of many tectono-stratigraphic units
indicates that their contacts are controlled by faults.
It is anticipated that such structures may have been extensional during
basin formation but have been reactivated during contractionaldeformation.
This interpretation is specifically concerned with those structures that
affect the tectono-stratigraphy
it is assumed that these will be large and potentially long-lived structures
and whose definition using other datasets may not be obvious. It is also postulated that large, long-lived structures have the potential
to localise magma and associated mineralising fluids and therefore
influence the location of mineral deposits
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Tectonics Peru - Pre-Cambrian
Distribution of
Precambrian outcrops
in Peru and their likelyextent under shallow
cover.
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Tectonics Peru - Pre-Cambrian
Structures
interpreted from
the shapes of
Precambrian
basement.
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Tectonics Peru - Pre-Cambrian
Coastal block separate to main areas of pre-
Cambrian outcrops
Differing Paleozoic stratigraphy on the coastal Pre-
Cambrian basement to that of the main Pre-
Cambrian basement suggests different Paleozoic
histories
Main Pre-Cambrian (Maranon Rise) form(ed) a
contiguous part of the Amazonian craton whilecoastal block (Arequipa Block) was accreted to the
margin pre-Mesozoic
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Tectonics Peru - Paleozoic
Paleozoic and
Pre-Cambrian
rocks with
structures
interpreted fromthe distribution of
Paleozoic rocks.
Paleozoic rocksare partly
contiguous with
Pre-Cambrian
rocks.
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Tectonics Peru - Paleozoic
End Paleozoic commonly marked by hiatus
Paleozoic essentially passive margin to Amazonian
craton or back arc to subduction zones that accreted
terranes through the Paleozoic.
Volcanics at base of Ordovician may reflect the
presence of an outboard arc at this time perhaps
associated with the accretion of the Arequipa Block.
Proto-Andean margin essentially in place at end
Paleozoic
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Tectonics Peru - Mesozoic
Development of Marianas-type subduction zone with
back arc extension
Significant development of back-arc rifts and basins
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Tectonics Peru - Mesozoic
Jurassic
Shelf carbonates central and
west
Volcanics in north and south
but absent in central part
Late Jurassic continental
sediments due to uplift of
shallow marine shelf
Structure
Shallow marine basins (shelf
env) controlled by back-arc
extensional faults
Volcanics location - shape of
arc?
Late Jurassic inversion
(Vicusian Orogeny) ?increased
convergence rate?
Inversion caused erosion of
carbonates to form continental
deposits
Late Jurassic continental sediments
Mid Jurassic marine sediments
Triassicearly Jurassic marine sediments
Early Jurassic volcanics
Interpreted faults
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Tectonics Peru - Mesozoic
Cretaceous
Cretaceous sedimentation
coincident with earlier Jurassic
sedimentation
East of Maranon high continued
continental sedimentation to early
Cretaceous
Cretaceous rocks in
shades of green
Maranon high
Jurassic to
Cretaceous back-arc
sea
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Tectonics Peru - Mesozoic
Mid-Cretaceous
Deposition of >6km Cretaceous
volcanics in the Huarmey-Canete
trough, a back-arc rift.
Otherwise Creatceous
sedimentation dominated by shallow
marine conditions.
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Tectonics Peru - Cenozoic
Cenozoic characterized by current day continental
Andean-type margin as distinct from the Mesozoic
Marianas-type subduction zone
Arc and back-arc in compression
Cordillera becomes emergent
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Tectonics Peru - Cenozoic
Tertiary Volcanics
Single elongate arc
Significantly wider in the
vicinity of and south of the
Abancay Deflection
Due to migration of flat slab
geometry during Tertiary
(James and Sacks, 1999).
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Tectonics Peru - Cenozoic
Tertiary Volcanics
Faults interpreted have an
approximate conjugate
arrangement
High level brittle structures
developed
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Structure - Fold Belts
Interpreted fold axes
from map data
Two main fold belts: Incaic
and sub-Andean
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Structure - Fold Belts
Interpreted fold axes
from map data
Faults interpreted from
fold axis segmentation
post-folding offset of fold
axes
Syn-folding strain
accommodation structures
Pre-folding basement
structure influenced fold
development.
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Structure - Abancay Deflection
Paleozoic rocks
and interpreted
fold axes in the
vicinity of the
Abancay deflection
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Structure - Abancay Deflection
Interpreted extent of
Pre-Cambrian
basement
Pre-Cambrian
basement structure(ie. Re-entrant) may
be responsible for the
deflection
Nazca ridge
influence?Flat slab geometry
to north
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Structure - Intermontane Basins
Tertiary continental
sediments highlight a
zone of intermontane
basins.
Fault bounded
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Structure - Intermontane Basins
Present day
development of
small intermontane
graben
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Structure - Intermontane Basins
Intermontane basin
observed in
Landsat image
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Structure - Forearc Basins
Fore-arc basin developed
during Tertiary are
onshore with continental
sedimentation in the
south.
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Structure - Forearc Basins
Fore-arc basins also
developed offshore during
the Tertiary in northern
Peru (?turbidite filled)
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Landsat interpreted structure
Despite the common assertion
that Landsat interpreted
features (linear and circular) are
associated with mineral
deposits - difficult to observe
here.
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Aster data
Structures interpreted (by
Mayor, 2007) from aster data
Structures smaller scale than
those interpreted in this study.
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Structure from intrusive rocks
The Coastal Batholith
Intruded mainly during
Cretaceous
Geochron 100Ma - 55Ma
(some workers to 30Ma)
Geochron suggests
younging to the north
Represents zone of
focussed crustal extension
during emplacement
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Structure from intrusive rocks
Paleozoic intrusives
Interpreted faults
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Structure from intrusive rocks
Tertiary intrusives
Interpreted faults
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Definition of major structures
All interpreted structured colour
coded for age from which
tectono-stratigraphic unit they
were interpreted
Highlights zones of long-
lived structural activity
(overlapping structures)Tertiary intermontane
and fore-arc basins faults
Tertiary volcanics faults
Cretaceous faults
Jurassic faults
Triassic Jurassic marine sediments faults
Paleozoic intrusives faults
Paleozoic faults
Precambrian faults
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Definition of major structures
Major faults defined where
several interpreted faults
overlap
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Definition of major structures
Major faults defined where
several interpreted faults
overlap
Major faults from Mesozoic
and Tertiary only units
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Mineral deposits and major structures
Mineral deposits, without regard totheir type or age, have a distributionthat can be described as:
- Forming in zones of different
frequency that are bounded byinterpreted major structures,or
- Occur in zones that are sub-linear and are on or near, butsimilarly oriented to,interpreted major structures,
and- Generally do not occur where
there are no major structures.
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Mineral deposits and major structures
Porphyry and related deposits
Occur in Tertiary volcanic
arc
Difficult to relate deposits to
individual major structures
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Mineral deposits and major structures
Porphyry and related deposits
Show better spatial
relationship to Tertiary aged
structures
S th t R (MISOSA)
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Southwestern Resources (MISOSA)
projects
Tintaya and Antay faults
S th t R (MISOSA)
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Southwestern Resources (MISOSA)
projects
Huachocoi and Azulcocha faults
Sami, Sumaq,
Marcia Claims
Josnitoro Claims
S th t R (MISOSA)
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Southwestern Resources (MISOSA)
projects
Minaspata and Antay faults may
form major underlying structure
through the Liam JV area
S th t R (MISOSA)
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Southwestern Resources (MISOSA)
projects
Canta claims adjacent to
Santander major fault
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ConclusionsThe conclusions of this study can be summarised as follows:
- Structures can be interpreted from regional geological data.- Regional structures can be related to the tectonic evolution of the Peruvian
Andes.
- Major structures are those where data indicates they have been active overextended periods of geological time.
- Many major structures are spatially related to mineral deposits and should beconsidered prospective unless determined otherwise.
- The Antay area comprises several major faults and their intersections and isconsidered highly prospective for porphyry and porphyry-related deposits.
- The Liam JV area is notable for its lack of major structures although this isthought to be due to thick successions of Tertiary volcanics that obscureearlier-formed structures. Major structures may exist in the area and fieldworkmay help quantify the relationship between locally developed and regional
structures.- Several other Minera del Suroeste SAC project areas are considered
prospective from a structural point of view. These include Condorama, Kim,groups of claims on or near the Tintaya Fault, the Sami, Sumaq and Marciaareas and the Josnitoro areas.
- Because major faults interpreted here are considered prospective formineralisation they should be considered as part of exploration area selection