8/12/2019 Batolito d La Costa
1/2
The Coastal Batholith,The Coastal Batholith,
Mesozoic PeruMesozoic Peru
Rebecca WilliamsRebecca Williams
OUTLINEOUTLINE
Why Coastal Batholith, Peru?Why Coastal Batholith, Peru?
Geological SettingGeological Setting
Tectonic SettingTectonic Setting
Crustal RockCrustal Rock
StructureStructure
PetrologyPetrology
Contribution to AndesContribution to Andes
InterpretationInterpretation
Relation to Sierra NevadaRelation to Sierra Nevada
WHY COASTAL BATHOLITH?WHY COASTAL BATHOLITH?
CB Major plutonicCB Major plutonic
phase of Mesozoicphase of Mesozoic
magmatism in Peru.magmatism in Peru.
Typical of WesternTypical of Western
American batholiths.American batholiths.
100100--37Ma37Ma
Start of major plutonicStart of major plutonic
activity that continuedactivity that continued
up until 3Ma withup until 3Ma with
Cordillera BlancaCordillera Blanca
BatholithBatholith
GEOLOGICAL SETTINGGEOLOGICAL SETTING
Intruded into rifted continental marginIntruded into rifted
continental marginparallel to todayparallel to todays trench.s
trench.
Albian volcanogenic marginal basin, alongAlbian volcanogenic
marginal basin, alongmajor crustal, extensional lineament.major
crustal, extensional lineament.(1600km long.)(1600km long.)
Basinal systems related to continentalBasinal systems related to
continentalmargin extension which started inmargin extension which
started inJurassic.Jurassic.
Uplifted in Upper Cretaceous and LowerUplifted in Upper
Cretaceous and LowerTertiary.Tertiary.
TECTONIC SETTINGTECTONIC SETTING CRUSTAL ROCKCRUSTAL ROCK
Marginal rifting in Albian marginal basinMarginal rifting in
Albian marginal basin
and crustal dilation.and crustal dilation.
Basin filled in with basaltic lavas, sills,Basin filled in with
basaltic lavas, sills,hyaloclasts, turbidites and gabbros:
densehyaloclasts, turbidites and gabbros: dense
materials.materials.
Basin inverted and batholith intruded.Basin inverted and
batholith intruded.
Shallow melting of Albian basin basaltic fillShallow melting of
Albian basin basaltic fill
produced CB magmasproduced CB magmas-- derived from NEWderived
from NEW
basaltic material.basaltic material.
8/12/2019 Batolito d La Costa
2/2
STRUCTURESTRUCTURE PETROLOGYPETROLOGY
CalkCalk--alkaline suite, dominated by Tonalites. Alsoalkaline
suite, dominated by Tonalites. Alsosome diorites,some diorites,
granograno--diorites, and granites.diorites, and granites.
Grouped into Super Units e.g. Santa RosaGrouped into Super Units
e.g. Santa Rosa
Tonalite: 2/3 of batholith.Tonalite: 2/3 of batholith. Super
units show basicSuper units show basic--acid sequence related
toacid sequence related to
fractionation.fractionation.
Bimodal magmatism characteristic of manyBimodal magmatism
characteristic of manycordilleran batholiths.cordilleran
batholiths.
Zoned tonalite super units typically rich in plag,Zoned tonalite
super units typically rich in plag,cpx and hornblendecpx and
hornblende zircon.zircon.
I type basalts and island arc andesites: wedgeI type basalts and
island arc andesites: wedgederived magmas.derived magmas.
CONTRIBUTION TO ANDESCONTRIBUTION TO ANDES
CB started the plutonic addition stage ofCB started the plutonic
addition stage of
the Andes 100mya that continued passthe Andes 100mya that
continued pass
the CB through the Cordilleran Blancothe CB through the
Cordilleran Blanco
Batholith to 3Ma.Batholith to 3Ma.
Consists of multiple plutons (estimates upConsists of multiple
plutons (estimates up
to 1000), all of a thin, tabular structureto 1000), all of a
thin, tabular structure
that added a thin veneer to the crust.that added a thin veneer
to the crust.
Growth by intrusion and under plating,Growth by intrusion and
under plating,
caused great crustal thickening.caused great crustal
thickening.
INTERPRETATIONINTERPRETATION
I type magmas that show an eastwardI type magmas that show an
eastward
change in composition and isotopicchange in composition and
isotopic
signature, related to increase insignature, related to increase
in
continental crust component.continental crust component.
Increase KIncrease K220 and incompatible element0 and
incompatible element
abundances. Indicates increasinglyabundances. Indicates
increasingly
enriched continental mantle rather thanenriched continental
mantle rather than
depth.depth.
Migration towards the interior of continentMigration towards the
interior of continent
related to subduction direction.related to subduction
direction.
RELATION TO SIERRA NEVADARELATION TO SIERRA NEVADA
SN U. JurassicSN U. Jurassic--
Cretaceous.Cretaceous.
Similar aspect ratios asSimilar aspect ratios as
CB.CB.
Similar processes forSimilar processes for
roomroom--makingmakingin crust forin crust for
intrusions.intrusions.
Extensional processesExtensional processes
more dominant for CB.more dominant for CB.
Similar zoning patternsSimilar zoning patterns
seen in both batholiths.seen in both batholiths.
QUESTIONS? & REFERENCESQUESTIONS? & REFERENCES
Atherton MP, 1990. The Coastal Batholith ofAtherton MP, 1990.
The Coastal Batholith ofPeruPeru--The product of rapid recycling of
new crustThe product of rapid recycling of new crustformed within
rifted continentalformed within rifted
continental--margin.margin.Geological Journal 25(3Geological
Journal 25(3--4) 3374) 337--349.349.
Atherton MP & Petford N, 1996. Plutonism andAtherton MP
& Petford N, 1996. Plutonism andthe growth of the Andean Crust
at 9the growth of the Andean Crust at 9 S fromS from100Ma to 3Ma.
Journal of South American Earth100Ma to 3Ma. Journal of South
American EarthSciences 9 (1/2) 1Sciences 9 (1/2) 1--9.9.
Goeke, 2002.Goeke,
2002.http://snebulos.mit.edu/home/egoeke/lectures/phttp://snebulos.mit.edu/home/egoeke/lectures/pet/chp18et/chp18--2.pdf2.pdf
Haederle M & Atherton MP, 2002. Shape andHaederle M &
Atherton MP, 2002. Shape andintrusion style of the Coastal
Batholith, Peru.intrusion style of the Coastal Batholith,
Peru.Tectonophysics 345 17Tectonophysics 345 17--28.28.
Winter JD, 2001. An introduction to Igneous andWinter JD, 2001.
An introduction to Igneous andMetamorphic Petrology. Prentice
Hall.Metamorphic Petrology. Prentice Hall.
