Download Lithium Isotopes TIMS and MC

Lithium Isotopes
Standard: NIST L-SVEC Li (SRM 8545)
TIMS and MC-ICPMS
Lithium – a trace alkali element
(Li+, Na+, K+, Rb+).
Conservative in Seawater.
Residence time (τ) ~ 1.2 Ma
Two stable isotopes: 6Li & 7Li
~17% difference in mass
~92.4% 7Li and 7.6% 6Li
Teng et al., 2007, 2008
Tracing weathering processes
Schematic illustration of Li isotope systematics in the hydrological
cycle, modified from Elliott et al. (2004).
Tracing crust/mantle recycling
Schematic illustration of Li isotope systematics in a subductionzone setting, modified from Zack et al. (2003)
Variation of Li concentrations vs. Li isotopic ratios. Teng et al., 2007
100 Ma Climate Control – Urey’s Tectonic Cycle
Uplift  Erosion  Weathering  CO2 Drawdown  Cooling
Subduction  Volcanism  Elevated CO2  Warming
CO2
H2O
Weathering
Continental Run Off
Ca2+ + Si(OH)4
Continental
Plate
Ca2+ + 2HCO3- →
CaCO3 + CO2 + H2O
CO2
H2O
Sedimentation
Subduction
CaCO3 + SiO2 ↔ CaSiO3 + CO2
Si(OH)4 → SiO2 + 2H2O
Sedimentation
MOR
Post-Urey: HT Fluxes
& Low Temp. Authigenic
Aluminosilicate Formation:
“Reverse Weathering”
Cations+Al+Si  2o-Clays
Cenozoic
Climate:
CO2 and
weathering
feedbacks
Zachos et al., 2001
Benthic Foraminifera
Seawater
Strontium
Isotopes
Interpretation:
Mixing of continental
Sr (silicate weathering
> 0.720) with basalt
Sr (MORB = 0.703)
sources to ocean.
Seawater cation
composition becomes
more “continental”
after 40 Ma.
Himalayan
Orogeny
Urey’s Tectonic Cycle - Where does Li fit in?
Accepted Value 31.0 ‰ ± 0.5 ‰
Contrast: Almost all igneous rocks on Earth are between 0 and 4‰, so seawater Li is
very heavy
FLi in 109 Moles/yr
Weathering
Lithium Geochemistry is Lithophilic
Lithium cycle is virtually all in silicate rocks and
aluminosilicate clays – none in carbonates
CO2
H2O
Continental Run Off
FRiver = 10
δ7LiRiver = 23‰
[Li]UCC= 24 ppm
δ7LiUCC=1.7‰
[Li]Silicate >>
[Li]Carbonate
Li → 2º Clays
Authigenic Clay Formation
And
Low temperature
δ7LiHT= 8.3‰
FReFlx= 6
Basalt Alteration
δ7LiReFlx= 15‰
FHT=
13
Subduction
MOR
[Li]MORB= 6 ppm
δ7LiMORB=3.4‰
Seawater
Lithium
Isotope
Composition
[Li]sw = 26 µM
Accepted Value
31.0 ‰ ± 0.5 ‰
Tomascak et al. (2004)
and Millot et al. (2004)
-------------Contrast: Almost all
igneous rocks on Earth
are between 0 and 4 ‰,
so seawater Li is
very heavy
Misra & Froelich, Science, 2012
Lithium in Seawater - Present
River Water
At Steady State; Li Input = Li Output
δ7LiRiver = 23‰
[Li]River = 265 nM
δ7LiUCC = 1.7‰, [Li]UCC = 24 ppm
Seawater
[Li] = 26 µM
δ7LiSW = 31‰
τ ≈ 1.2 Ma
Hydrothermal Fluid
δ7LiHT = 8.3‰
[Li]HT = 840 µM
δ7Li
MORB = 3.7‰, [Li]MORB = 6 ppm
∆SW-SED = δSeawater - δSediment = 16‰
Subduction Refluxed
Lithium
δ7LiReFlx = 15‰
δ7LiReFlx = δ7LiSediment
Silicate Reverse Weathering
Low Temperature Basalt Alteration and
Sediment Diagenesis
δ7LiSediment = 15‰
δ7LiSediment = δ7LiSeawater - ∆SED
Planktonic Forams & Bulk Forams
Orbulina universa
N. dutertrei
Globigerina venezuelana
Globigerina cryptomphala
Globigerina eocaena
Globigerina inequispira spp
Marginotruncana spp.
Hedbergella spp
G. truncatulinoides
G. triloba
Foram (calcite) Cleaning Method
Reductive - Oxidative - Reductive
(hydrazine) (H2O2) (hydrazine)
(R-O-R) Cleaned (monitor Ca Na
Li Mg Ba Mn Sr….in cleaning sol)
Boyle & Keigwin, 1985
Rosenthal et al., 1997
Globigerina triloba
Li/Ca & δ7Li
of Core-top
& Tow
Forams
Misra & Froelich, JAAS, 2009
[Li/Ca]SW = 26 µM/10.53 mM
= 2.47 x 10-3 mM/M
[Li/Ca]Forams = 10.5 x 10-6 µM/M
(present day)
KD = [Li/Ca]Foram/[Li/Ca]SW
= 4.25 x 10-3
[Li]Forams = 1 ppm
DSDP & ODP Sampling Sites
δ7Li of
Cenozoic
Seawater
Species
and
Bulk
Specific
Foram
Samples
δ7Li
Evolution
of Cenozoic
Seawater
Five-Point
Running Mean
± 2σ
Misra & Froelich, Science, 2012
δ7Li
Evolution
of Cenozoic
Seawater
18
δ O
vs.
δ7Li
Li, Sr, and Os
Isotope Records
of Cenozoic
Seawater
Os isotopes from
Peucker-Ehrenbrink
& Ravizza, GTS (2012)
The Weathering Story
Interpretations
• Seawater δ7Li rose by 8-9 ‰ over the Cenozoic (60 Ma
 today)
• This rise in δ7LiSW requires, all else held constant, a
decrease in [Li]INPUT and increase in δ7LiOUTPUT to the
ocean driven by:
(a) ~ 20‰ rise in δ7LiRiv (from 3‰ at 60 Ma to 23‰ today)
(b) ~ increase / decrease in only Li river flux cannot cause this
rise in δ7LiSW
(c) ~ 80% drop in Li hydrothermal flux over the Cenozoic
(d) ~ 5‰ increase in ∆SW-Sediement (from 11‰ at 60 Ma to 16‰
today)
The early Cenozoic climatic optimum was a result of increased
supply of carbon dioxide to the ocean-atmosphere system as well
as diminished removal of carbon dioxide from the atmosphere
through weathering of silicate rocks. The scarcity of newly
uplifted, fresh, weatherable rocks in the hothouse climate led
to a slowdown of the negative feedback mechanism of the UreyWalker-Berner cycle and promoted a temporary runaway
increase in the CO2 concentrations of the ocean-atmosphere
system on the post-KPg Earth. The absence of evidence from
seawater 87/86Sr and δ7Li records to support increased
continental weathering rates in this high-CO2 hothouse world
indicates that the limiting ingredient was igneous silicates
undergoing weathering. despite global high temperatures, high
CO2, and high rainfall in the tropics (all of which should
accelerate silicate weathering and promote removal of CO2), the
physical and chemical weathering rates of the continents were
subdued because of low uplift rates.
High atmospheric CO2 concentration, rapid global
warming and marine anoxia and euxinia. Enhanced
biological productivity and recovery after ~400kyrs
Pogge et al., 2013
lightest values of the Li isotope ratio (7Li) during OAE2,
indicating high levels of weathering—and therefore
atmospheric CO2 removal.
modelling the observed Li and Sr isotope excursions
requires a 4 Myr 20% increase in the hydrothermal flux and a
200 kyr pulse of enhanced riverine Li flux from basaltic rocks
coupled with very light (river 7Li 2-4‰) fluvial isotope ratios
Lithium in Seawater – 60 Ma
River Water
At Steady State; Li Input = Li Output
δ7LiRiver ~ 3‰
[Li]River = 265 nM (?)
δ7LiUCC = 1.7‰, [Li]UCC = 24 ppm
∆SW-SED = δSeawater - δSediment = 16‰
Seawater
[Li] = 26 µM (?)
δ7LiSW = 22‰
τ ≈ 1.2 Ma (?)
Hydrothermal Fluid
δ7Li
= 8.3‰
[Li]HT = 840 µM
δ7Li
MORB = 3.7‰, [Li]MORB = 6 ppm
HT
Subduction Refluxed
Lithium
δ7LiReFlx = 6‰
δ7LiReFlx = δ7LiSediment
Silicate Reverse Weathering
Low Temperature Basalt Alteration and
Sediment Diagenesis
δ7LiSediment = 6‰
δ7LiSediment = δ7LiSeawater - ∆SED
δ7Li Crash
Across
K-Pg (KT)
Boundary
• Across K-Pg (KT)
boundary δ7LiSW
dropped ~ 4 ‰ in < 0.7
Ma - Almost
Impossible! - NOT
bolide, NOT LIPs
(Deccan Traps).
Something important
changed – what?
Interpretations
• Across K-Pg (KT) boundary δ7LiSW dropped ~ 4 ‰ in < 0.7 Ma Almost Impossible! - NOT bolide,
Something important changed – what?
NOT LIPs (Deccan Traps).
Osmium Isotopes
6 stable isotopes: 184Os, 187Os, 188Os, 189Os, 190Os, and
(most abundant) 192Os. The other natural isotope, 186Os,
has an extremely long half-life (2×1015 years) and for
practical purposes can be considered to be stable as
well. 187Os is the daughter of 187Re (half-life 4.56×1010
years) and is most often measured in an 187Os/188Os ratio.
Thus this is a radiogenic isotope system (like 87/86Sr).
190
α
18 6
Pt
Half-life ­
450
( Walker et
Os
billion years
al. 1 9 9 7 )
Plat inum Isot ope
Abundances
­ 0.01%
190
192
194
195
196
Mass Number
Osmium Isot ope
Abundances
184
185
186
187
188
189
Mass Number
190
191
192
198
Normalization
• Early work reported 187Os/186Os
• Now common convention is to report
187Os/188Os
• This is what is actually measured most
commonly & 190Pt decay caused SUBTLE
variation in 186Os abundance
• Rule of thumb: 187Os/188Os = 0.12 *
187Os/186Os
Like Ir, Os is highly siderophile so...
Most of t he Eart h's Os & Ir reside
in it s core
EARTH'S CRUST
SOLID & LIQIUD
0 .0 0 1 %
CORE 9 9 %
DEEP SILICATE
EARTH 1 %
strong Os enrichment and low
187Os/188Os in extraterrestrial
material and mantle rocks
compared to crustal rocks.
Re (ppb)
Os (ppb)
187Re/188Os
187Os/188Os
Chondrites
40
500
0.42
0.127
Ultramafic Rocks
0.4
5
0.42
0.127
Old Crustal Rocks
0.5
.05
50
1.32
Seawater
.008
.00001
4000
1.06
Organic-rich Sed.
30
0.2
800
1.06
Oxic pelagic clay
0.05
0.2
1.2
1.06
The
Marine
Osmium
System
The Marine Osmium Isotope
Reservoirs - Sources - Sinks
System
Sources and Sinks
Extraterrestrial Impact and Deccan
Volcanism at the Cretaceous-Tertiary
Boundary
Terminal Cretaceous Environmental Events
Charles B. Officer & Charles L. Drake, Science 227, 8 March 1985, 1161-1166.
Original area: ~1 Million km2 (1.5% of land surface).
Original volume: 2-4 Million km3.
Effusion rate: ~10% of the average MORB production rate.
Cover mostly Precambrian shield area.
Nickel-sulfide fire assay to
pre-concentrate PGE
Advantages:
Low blanks (e.g., 0.5 pg Os/g)
Large samples (up to 0.5 kg)
Robust chemistry
Fairly quick sample preparation
Does not require a clean lab
Suitable for most matrices
Os IC and [PGE] on same split
Disadvantages:
High blank (e.g., 0.5 pg Os/g)
Not suitable for Re
Anomalously high platinum group
element concentrations have
previously been reported for Upper
Triassic deep-sea sediments, which
are interpreted to be derived from an
extraterrestrial impact event. Os
isotope data exhibit a marked
negative excursion from an initial Os
isotope ratio. This is synchronous
with the ~215Ma Manicouagan
impact event.
Conclusions
The main phase of Deccan volcanism predates the K/T boundary
impact.
The ~10 kyr residence time of Os in seawater decreases the
likelihood of missing a large impact signal due to an incomplete
sediment record.
The seawater record of Os recovers quickly (<100 kyr) from the
impact event.
Diesel Use and Os Isotopes
Environmental Pathways
Automobile
This image cannot currently be displayed.
Particle
s
Greenland ice
Peat bog
Soil
Roa
d
dust Runof
f
River water
Sediments
Upper Mystic Lake, N. Boston
Aberjona Watershed
- residential area
76,000 inhab.
- industrial area
(Superfund site)
65,000 cars per day,
major roads (I93, I95)
Coring location
Depth 25 meter
Sediment cores
2 cm sections
Dried 105oC
Dated
(210Pb, laminations, As and Cr)
MW digestion
Q-ICP-MS
Isotopic dilution
NiS fire assay
HR-ICP-MS
Pt Concentration (ng g -1)
Pt concentration profile
Upper Mystic Lake, MA
70
60
Core 1
Core 2
50
Core 3
Core 4
40
Core 1
30
20
10
0
1880
1900
1920
1940
1960
Calendar Year
ES&T 2003, 37, 3283 and ES&T 2004, 38, 396
1980
2000
Pt Concentration (ng g -1 )
Pt concentrations in Greenland ice
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1880
Introduction of
catalytic converters
1900
1920
1940
1960
8000BP 6000BP
Calendar Year
Barbante et al. (2001) ES&T 35, 835839
1980
2000
Summary
• Catalytic converters are important sources of PGE to
the environment.
• Anthropogenic PGE are regionally dispersed.
• Distal dispersal (i.e., Greenland ice) seems to require
fractionation of PGE during transport.
• Alternatively, observed enrichment in Greenland ice
is caused by other industrial sources (smelters) or
natural sources (dust, volcanic aerosols).
The 187Os/188Os ratios of
these samples are relatively
low (0.16–0.48), and fall
along a 2-component mixing
line natural & anthropogenic
Anthropogenic osmium in rain and snow reveals
global-scale atmospheric contamination. Chen et al., 2008