structure peru02

7/28/2019 Structure Peru02

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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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Aim:

To identify structures that have important geological

significance and tectonic context.


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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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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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Examples

Horst boundary faults at

margins of basement uplifts

Figure from CCOP EPF website


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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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Structures

interpreted from

the shapes of

Precambrian

basement.


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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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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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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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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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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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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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Present day

development of

small intermontane

graben


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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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Paleozoic intrusives

Interpreted faults


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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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Major faults defined where

several interpreted faults

overlap


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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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Porphyry and related deposits

Occur in Tertiary volcanic

arc

Difficult to relate deposits to

individual major structures


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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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projects

Huachocoi and Azulcocha faults

Sami, Sumaq,

Marcia Claims

Josnitoro Claims

S th t R (MISOSA)


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projects

Minaspata and Antay faults may

form major underlying structure

through the Liam JV area

S th t R (MISOSA)


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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

structure peru02

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