Geochronology: Science of determining within a specified uncertainty
the absolute age of a geological process
•
Provides the temporal framework for
geological interpretations
•
Major ore forming systems related to
specific temporally brief events
during a favourable period in earth
evolution (metallogenic epoch)
•
Erects a stratigraphy in complex and
polydeformed unfossiliferous rocks
•
Key in placing mineralization within
geodyamic context
•
Provides a vector to mineralization –
if age of host rock, deposit or other
datable event known (e.g. fluid flow),
then this signature can be searched
for
•
Reduces exploration risk
“Greenland U-Pb”
c. 300 documents = conservative estimate of c. 150,000 analyses
With 10 – 20 new papers per year
HUGE RESOURCE!
1968
1993
2013
Australia
UK
Geochronology database – why

Different
nomenclatures for 
(essentially) the same
Different formats
238U/206Pb
± % error (2 sigma)
206Pb/238U ± abs. error (1 sigma)
Migmitization vs. High grade
metamorphism
Inheritance vs. Xenocryst
interpretation
Missing information

e.g. no sample location information
Geographic coordinates non-standard
Captured
Extracted
from
Source
Geochronology database – why
Interpretation and presentation of data in useful formats by transforming raw
data into information.
• Distribution of data and information to the right people at the right time.
• Data preservation.
Different formats
Reduced accessibility of data
Different nomenclatures for
the same interpretation
Requiring a specialist for
rudimentary interpretation
Missing information
Lack of use of geochronology
to address questions (it maybe
uniquely placed to answer)
Geochronology database – why
Interpretation and presentation of data in useful formats by transforming raw
data into information.
• Distribution of data and information to the right people at the right time.
• Data preservation.
Different formats
Consistent format
Different nomenclatures for Consistent nomenclature to
enable ease of searching
the same interpretation
Missing information
Base level of information
consistently populated
Geochronology database – why
Systematic collation and
assessment of
geochronological data best
achieved by means of a
database which holds
information within a
structured and consistent
framework
Permits querying to extract relevant data and minimises
difficulty in cross comparison of age information.
Collate information scattered widely across published
sources making this information vastly more accessible.
Geochronology database – how
Lookup tables:
essential function of helping
maintain data integrity by
enforcing consistent nomenclature
Rock Type
Lithology
Terrane
Formation
Mineral
Technique
U-Pb geochronology table
Sample
GUID (globally unique identifier)
totally unique ID number
impossible to replicate.
ф
Location (lat, long, DMS)
location capture method
Reference
Ages
Statistics
Uncertainty
MSWD
Interpretation
Approach
Geochronology database – how
Geographic and reference
information
Geochronology database – how
Geological information,
including a limited rock type
list to enable ease of
searching
Geochronology database – how
Mineral and the
technique
Geochronology database – how
Pooled ages (e.g. the mean age from
several analyses). Used to defined
the ages of geological events.
Geochronology database – how
Every analysis on a single spot level
is assigned an interpretation
S = detrital
I = magmatic
M = metamorphic
X = inherited
D = rejected
Geochronology database – where are we at?
500 U-Pb samples (70
publications)
10,000 individual analyses
(each coded for interpretation)
X
(inherited)
4%
D (rejected)
2%
M
(metamorphic)
17 %
I (igneous)
32 %
S (detrital)
45 %
Geochronology database – where are we at?
500 U-Pb samples (70 publications)
10,000 individual analyses
(each coded for interpretation)
Baddeleyite
Other
Monazite
Titanite
Zircon
Geochronology database – where are we at?
Total
500 U-Pb samples (70 publications)
10,000 individual analyses
(each coded for interpretation)
(blank)
MS (single fragment/grain)
Electron microprobe
ICPMS
ICP
MS
(few fragments/grains)
Other
Count of Technique
(few fragments/grains)
IonSIMS
microprobe (other than
SHRIMP)
(other than SHRIMP)
TIMS
s/grains)
(multi fragments)
Laser
SIMS
(SHRIMP)
Laser ablation ICP MS
Technique
Electron microprobe
ICP MS (few fragments/g
Ion microprobe (other tha
Laser ablation ICP MS
SHRIMP
TIMS (few fragments/grai
TIMS (single fragment/gra
(blank)
Geochronology database – where are we at?
What is this going to allow
Magmatic Zircon
Detrital Zircon
Age (Ma)
Oldest grain within
analytical
uncertainty of
concordia
3970 Ma
Geochronology database – what can we do with it?
Help refine
stratigraphy.
Place direct
temporal
constraint on
mineralization
and fluid flow.
Orogenic paleofluid flow recorded by discordant detrital
zircons in the Caledonian foreland basin of northern Greenland
C B
A
D
Caledonian Orogenic Front
The Neoproterozoic to Paleozoic evolution of northern Greenland records the
development of a continental margin after Rodinia breakup.
The sedimentary succession consists of Cambrian to Silurian deep-water slope
and trough megasequences formed by major turbidite systems.
Orogenic paleofluid flow recorded by discordant detrital
zircons in the Caledonian foreland basin of northern Greenland
•
•
•
•
Oscillatory zoned magmatic
Homogeneous metamorphic
Altered and strongly discordant
Altered but concordant
D
C
B
A
Orogenic paleofluid flow recorded by discordant detrital
zircons in the Caledonian foreland basin of northern Greenland
18
16
0.38
14
12
Number
3600
Pb
8
6
0.26
4
3200
2
0.22
0
2400
2800
0.18
2600
2800
3000
3200
3400
3600
3800
A single time of Pb loss
Age (Ma)
Recent
2400
0.14
2000
0.10
0.5
1.5
2.5
3.5
238
206
U/
4.5
5.5
Pb
18
16
14
Relative probability
12
Number
206
Pb/
10
Discordant population derived from a
similar geological province with similar
zircon age structure to the concordant
zircon population.
0.30
207
Relative probability
Assumptions:
0.34
10
8
6
4
2
0
2300
2500
2700
2900
3100
Age (Ma)
3300
3500
3700
3900
Model the age of the discordant
population, assuming Pb loss at
different times, and statistically
compare the model age spectra to
that of the concordant population.
Orogenic paleofluid flow recorded by discordant detrital
zircons in the Caledonian foreland basin of northern Greenland
Concordant
Probability
380 Ma
Age of Pb loss (Ma)
Discordant: upper intercept
Modelled Pb loss at 380 Ma
Age (Ma)
Statistically closest similarity between
concordant and discordant populations is
observed at ca. 380–390 Ma
Geochronology database – what can we do with it?
Answer some fundamental geochronology questions.
Change in chronometric power – e.g. when one isotopic ratio is
better to use over the other
500
450
238U/206Pb* age error
207Pb*/206Pb* age error
Linear (207Pb*/206Pb* age error)
Linear (238U/206Pb* age error)
400
Error
Age Error (Ma)
350
1600-1700 Ma
300
250
200
150
100
50
0
0
500
1000
1500
2000
Age (Ma)
Age (Ma)
2500
3000
3500
4000
Geochronology database
A convenient source of Earth history data, normalized to
a consistent standard - including expert opinion.
A resource for understanding the geological history of
Greenland.
Able to address questions on: stratigraphy,
age of rocks, deposits, thermal and fluid events (to
mention just a few uses!)
A work in progress! “Front end” set to be developed
shortly to allow graphic querying and display of data
How do we get the information?
Comparison of U-Th-Pb techniques
EMPA: 4 analyses per hour
$25 per analysis
>2% accuracy
No loss of sample; high spatial
resolution
SIMS: 4 analyses per hour
$25 per analysis
10-35 micron spot; 1 micron
depth
c. 1 % accuracy
Excellent spatial resolution
ID-TIMS: 1 analysis per hour (plus
a lot of lab work!)
$100-$300 per analysis
0.1-0.3% accuracy from crystal (or
fragments)
Best precision and accuracy
LA-ICPMS: 40 analyses per
hour
$4-$8 per analysis
5-50 micron spot; 10 micron
depth
1-2% accuracy
Highest efficiency
Geochronology database – where are we at?
Pangea
Superia/Sciavia
Rodinia
Gondwana
Columbia
Geochronology database – where are we at?
3225-2900 Ma:
Akia terrane
gneisses (west
Greenland)
c. 3800 - 3600 Ma:
oldest gneissses in
the Nuuk region
Geochronology database – where are we at?
c. 2800-2500
Ma: Archean
gneisses (North
Atlantic Craton
& Rae Craton)
2900 - 2800 Ma:
Mesoarchean
granites and
gneisses in west
Greenland
Geochronology database – where are we at?
c. 1950 - 1840 Ma
Paleoproterozoic orogenesis (Rae
Craton & Nagssugtoqidian
Orogen)
c. 1900-1700 Ma:
Ketilidian Orogeny
c. 1700-1600
Ma:
Independence
Fjord Group
Geochronology database – where are we at?
c. 61-55 Ma: Paleogene basaltic
magmatic province - central west and
east Greenland
c. 450-400 Ma
Caledonian uplift
and magmatism
c. 950-900 Ma
Caledonian
granites