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Evolution of continental crust in the Proterozoic : growth and reworking in orogenic systems

Petersson, Andreas LU (2015) In LITHOLUND THESIS DOCTORAL DISSERTATIONS 24.
Abstract (Swedish)
Popular Abstract in Swedish

För att förstå tillväxten av den kontinentala jordskorpan

är det nödvändigt att kunna uppskatta balansen mellan

juvenilt bidrag från manteln, infra-krustal omarbetning

av jordskorpa och transport av krustalt material tillbaka

till manteln. Sedan början av seklet har användandet

av in situ U–Pb, Lu–Hf och O-isotop analyser av

mineralet zirkon som ett verktyg för att adressera dessa

frågor ökat exponentiellt. Många sammanställningar av

ständigt växande databaser, som använder kombinerade

U–Pb-Lu–Hf och/eller U–Pb-Lu–Hf-O isotop-data,

har presenterats tillsammans med modeller som påvisar

globala... (More)
Popular Abstract in Swedish

För att förstå tillväxten av den kontinentala jordskorpan

är det nödvändigt att kunna uppskatta balansen mellan

juvenilt bidrag från manteln, infra-krustal omarbetning

av jordskorpa och transport av krustalt material tillbaka

till manteln. Sedan början av seklet har användandet

av in situ U–Pb, Lu–Hf och O-isotop analyser av

mineralet zirkon som ett verktyg för att adressera dessa

frågor ökat exponentiellt. Många sammanställningar av

ständigt växande databaser, som använder kombinerade

U–Pb-Lu–Hf och/eller U–Pb-Lu–Hf-O isotop-data,

har presenterats tillsammans med modeller som påvisar

globala konsekvenser för den kontinentala jordskorpans

tillväxt. Många av dessa modeller, lider dock av

ett antal antaganden, bland annat inkluderandet av en

homogen mantelreservoar som utarmats linjärt sedan

jordens skapelse.

Användandet av framför allt detritala zirkoner tagna ur

sitt geologiska sammanhang, och tillämpningen av dess

modell-åldrar, försvagar trovärdigheten hos dessa modeller.

För att ta itu med frågan om den kontinentala

jordskorpans tillväxt, med hjälp av kombinerad zirkon

U–Pb-Lu–Hf (-O) isotop-data, måste man ha kontextuell

kontroll och minimera osäkerheterna i de tillämpade

modellerna.

I denna avhandling har ett sådant tillvägagångssätt använts

på tre olika Palaeo- och Meso-Proterozoiska (2500–1000

miljoner år gamla) orogena bälten; i den Fennoskandiska

skölden, i nordamerikanska Grenville provinsen och i den

Birimiska terrängen på den västafrikanska kratonen.

Den östra delen av den Svekonorvegiska provinsen (belägen

i de sydvästra delarna av den Fennoskandiska skölden)

skapades genom sekventiell omarbetning av en reservoar

som bildades genom blandning mellan en 2.1–1.9

miljarder år gammal juvenil komponent samt Arkeisk

skorpa. Från 1.7 till och med 1.4 miljarder år sedan

genererades den kontinentala jordskorpan med liten eller

ingen tillförsel av juvenilt material.

Längre västerut, i Idefjordsterrängen av Svekonorvegiska

provinsen, återfinns 1.65–1.33 miljarder år gammal

berggrund med isotopsignaturer som indikerar omarbetning

av äldre kontinental jordskorpa och sediment.

På det hela taget indikerar dock isotopsignaturerna från

berggrunden i Idefjordsterrängen en ökning av juvenilt

material med tiden. Detta är i linje med en retirerande

öbåge, samtida med avsättning av den lokala sedimentära

bassängen, Stora Le-Marstrand.

Trender i isotopdata från den Grenvilliska orogenen

under Ohio föreslår juvenilt bidrag från manteln för ca.

1.65 miljarder år sedan, följt av sekventiell omarbetning

av denna reservoar med litet eller inget ytterligare bidrag

från manteln.

Den ca. 2.31–2.06 miljarder år gamla Birimiska terrängen

i Ghana, är känd för att till hög grad uppvisa juvenila

signaturer. Men vi kan visa att omarbetad Arkeisk skorpa

bidragit i mycket större utsträckning än tidigare känt,

vilket återigen betonar vikten av infrakrustal omarbetning

under bildandet av kontinental jordskorpa. Vi kan

även påvisa att denna terräng, som normalt beskrivs som

bildad via initialt bidrag från en mantelplym, har granitiska

bergarter som är äldre än de mafiska leden. Detta

påvisar istället en subduktionsrelaterad tillväxt för den

kontinentala krustan i denna terräng.

Tillsammans understryker dessa studier vikten av infrakrustal

omarbetning i Palaeo- och Meso-Proterozoiska

ackretionsorogener. Dessa studier ger också goda exempel

på tillämpning av kombinerade zirkon U–Pb-Lu–Hf

(-O) isotop- analyser av berggrund med känd affinitet,

där valet av använda modeller kan styrkas. (Less)
Abstract
To understand the growth of continental crust, the

balance between juvenile mantle derived extraction,

infracrustal reworking and crustal recycling, needs to be

estimated. Since the beginning of the century, the use of

coupled in situ zircon U–Pb, Lu–Hf and O isotope analyses

as a tool to address these questions have increased

exponentially. Numerous compilations of ever growing

datasets have been presented, leading to new, and sometimes

contrasting models of continental growth. Many

of theses models, however, suffer from a number of

assumptions, including a mantle reservoir that has been

homogeneously and linearly depleted since the... (More)
To understand the growth of continental crust, the

balance between juvenile mantle derived extraction,

infracrustal reworking and crustal recycling, needs to be

estimated. Since the beginning of the century, the use of

coupled in situ zircon U–Pb, Lu–Hf and O isotope analyses

as a tool to address these questions have increased

exponentially. Numerous compilations of ever growing

datasets have been presented, leading to new, and sometimes

contrasting models of continental growth. Many

of theses models, however, suffer from a number of

assumptions, including a mantle reservoir that has been

homogeneously and linearly depleted since the Hadean.

Further, the use of (mainly) detrital zircon, taken out

of their geological context, and the application of their

depleted model-ages clearly hamper the validity of these

models.

To accurately address the question regarding continental

crustal growth using combined zircon U–Pb-Lu–Hf(-O)

isotope data, one needs to have contextual control and

minimise the uncertainties of the applied models.

In papers included in this thesis such an approach has

been used on three different Palaeo- to Meso-Proterozoic

orogenic belts; in Fennoscandia, in North American

Grenville and in the Birimian terrane of the West African

craton.

The eastern part of the Sveconorwegian Province, located

in the southwestern part of the Fennoscandian Shield, is

made up of granitiod rocks that were emplaced through

sequential tapping of a reservoir that formed through

mixing between a 2.1–1.9 Ga juvenile component and

Archaean crust. Between 1.7 and 1.4 Ga the continental

crust of the Eastern Segment was reworked with little or

no generation of new crust.

Further to the west, in the Idefjorden terrane of the

Sveconorwegian Province, 1.65 to 1.33 Ga rocks have

isotopic signatures that indicate reworking of older

continental crust, including sediments. However, overall

the isotopic signatures in the Idefjorden terrane indicate

an increase in juvenile material with time, consistent with

development of an extensional back-arc rift geotectonic

setting, accommodating deposition of the local metasedimentary

basin, Stora Le-Marstrand.

Isotope data from rocks within the Grenville orogen in

subsurface Ohio suggest a common c. 1.65 Ga juvenile

source to a majority of the sampled bedrock. Emplacement

of this juvenile crustal contribution was followed

by sequential reworking of that reservoir with little or no

additional contribution to the source.

The c. 2.31–2.06 Ga Birimian terrane in Ghana, West

African craton, is a commonly cited example of plume

initiated crustal growth, that is known to have largely

juvenile signatures. However, we can show that reworked

Archaean crust contribute in a much larger extent than

previously known, once again highlighting the importance

of infracrustal reworking during emplacement of

continental crust. Further, the emplacement of felsic

rocks during the Eoeburnean pre-dates suggested plume

related rocks, contradicting a suggested plume initiated

crustal growth.

Collectively, these studies highlight the importance of

infracrustal reworking in Palaeo- to Meso-Proterozoic

accretionary orogens. These studies also provide good

examples of combined zircon U–Pb-Lu–Hf-(O) isotope

analyses on rocks and rock suites with known affinity

where the validity of chosen models can be justified. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Hawkesworth, Chris, University of St Andrews
organization
publishing date
type
Thesis
publication status
published
subject
keywords
crustal reworking, Proterozoic, O-isotopes, Lu–Hf, U–Pb, zircon, Crustal growth
in
LITHOLUND THESIS DOCTORAL DISSERTATIONS
volume
24
pages
171 pages
publisher
Department of Geology, Lund University
defense location
Dept. of Geology, Lund University, Sölvegatan 12, 223 62, Lund, Sweden
defense date
2015-10-02 13:15
ISSN
1651-6648
ISBN
978-91-87847-06-6 (pdf)
978-91-87847-05-9 (print)
language
English
LU publication?
yes
id
bb33da18-045c-4ea2-9f3e-816e3742b681 (old id 7853963)
date added to LUP
2015-09-15 16:59:43
date last changed
2016-09-19 08:44:46
@phdthesis{bb33da18-045c-4ea2-9f3e-816e3742b681,
  abstract     = {To understand the growth of continental crust, the<br/><br>
balance between juvenile mantle derived extraction,<br/><br>
infracrustal reworking and crustal recycling, needs to be<br/><br>
estimated. Since the beginning of the century, the use of<br/><br>
coupled in situ zircon U–Pb, Lu–Hf and O isotope analyses<br/><br>
as a tool to address these questions have increased<br/><br>
exponentially. Numerous compilations of ever growing<br/><br>
datasets have been presented, leading to new, and sometimes<br/><br>
contrasting models of continental growth. Many<br/><br>
of theses models, however, suffer from a number of<br/><br>
assumptions, including a mantle reservoir that has been<br/><br>
homogeneously and linearly depleted since the Hadean.<br/><br>
Further, the use of (mainly) detrital zircon, taken out<br/><br>
of their geological context, and the application of their<br/><br>
depleted model-ages clearly hamper the validity of these<br/><br>
models.<br/><br>
To accurately address the question regarding continental<br/><br>
crustal growth using combined zircon U–Pb-Lu–Hf(-O)<br/><br>
isotope data, one needs to have contextual control and<br/><br>
minimise the uncertainties of the applied models.<br/><br>
In papers included in this thesis such an approach has<br/><br>
been used on three different Palaeo- to Meso-Proterozoic<br/><br>
orogenic belts; in Fennoscandia, in North American<br/><br>
Grenville and in the Birimian terrane of the West African<br/><br>
craton.<br/><br>
The eastern part of the Sveconorwegian Province, located<br/><br>
in the southwestern part of the Fennoscandian Shield, is<br/><br>
made up of granitiod rocks that were emplaced through<br/><br>
sequential tapping of a reservoir that formed through<br/><br>
mixing between a 2.1–1.9 Ga juvenile component and<br/><br>
Archaean crust. Between 1.7 and 1.4 Ga the continental<br/><br>
crust of the Eastern Segment was reworked with little or<br/><br>
no generation of new crust.<br/><br>
Further to the west, in the Idefjorden terrane of the<br/><br>
Sveconorwegian Province, 1.65 to 1.33 Ga rocks have<br/><br>
isotopic signatures that indicate reworking of older<br/><br>
continental crust, including sediments. However, overall<br/><br>
the isotopic signatures in the Idefjorden terrane indicate<br/><br>
an increase in juvenile material with time, consistent with<br/><br>
development of an extensional back-arc rift geotectonic<br/><br>
setting, accommodating deposition of the local metasedimentary<br/><br>
basin, Stora Le-Marstrand.<br/><br>
Isotope data from rocks within the Grenville orogen in<br/><br>
subsurface Ohio suggest a common c. 1.65 Ga juvenile<br/><br>
source to a majority of the sampled bedrock. Emplacement<br/><br>
of this juvenile crustal contribution was followed<br/><br>
by sequential reworking of that reservoir with little or no<br/><br>
additional contribution to the source.<br/><br>
The c. 2.31–2.06 Ga Birimian terrane in Ghana, West<br/><br>
African craton, is a commonly cited example of plume<br/><br>
initiated crustal growth, that is known to have largely<br/><br>
juvenile signatures. However, we can show that reworked<br/><br>
Archaean crust contribute in a much larger extent than<br/><br>
previously known, once again highlighting the importance<br/><br>
of infracrustal reworking during emplacement of<br/><br>
continental crust. Further, the emplacement of felsic<br/><br>
rocks during the Eoeburnean pre-dates suggested plume<br/><br>
related rocks, contradicting a suggested plume initiated<br/><br>
crustal growth.<br/><br>
Collectively, these studies highlight the importance of<br/><br>
infracrustal reworking in Palaeo- to Meso-Proterozoic<br/><br>
accretionary orogens. These studies also provide good<br/><br>
examples of combined zircon U–Pb-Lu–Hf-(O) isotope<br/><br>
analyses on rocks and rock suites with known affinity<br/><br>
where the validity of chosen models can be justified.},
  author       = {Petersson, Andreas},
  isbn         = {978-91-87847-06-6 (pdf)},
  issn         = {1651-6648},
  keyword      = {crustal reworking,Proterozoic,O-isotopes,Lu–Hf,U–Pb,zircon,Crustal growth},
  language     = {eng},
  pages        = {171},
  publisher    = {Department of Geology, Lund University},
  school       = {Lund University},
  series       = {LITHOLUND THESIS DOCTORAL DISSERTATIONS},
  title        = {Evolution of continental crust in the Proterozoic : growth and reworking in orogenic systems},
  volume       = {24},
  year         = {2015},
}