Parent Magma Characteristics
of Early Midcontinent Rift
Ultramafic Intrusions
Jim Miller1, Brian Goldner1,2, Dan Foley1,
Pete Hollings3, and Geoff Heggie3,4
1) Department of Geological Sciences, University of Minnesota Duluth
2) Rio Tinto Exploration, Salt Lake City, Utah
3) Department of Geology, Lakehead University
4) Magma Metals, Thunder Bay, Ontario
Early Midcontinent Rift
Ultramafic
Intrusions in
Tamarack
Hele
Disraeli
the Western Lake
Seagull
Kitto
Superior Region
Kitto
Disraeli
Hele
Seagull
Current L.
Ontario
E
Minnesota
Tamarack
BIC
Eagle
Talk Outline
• Textural and chemical characteristics of
chilled margins in Tamarack, BIC, and
Seagull Intrusions
• Estimation and testing of major/minor
element parent magma compositions by
subtracting contributions of Ol phenocrysts
• Trace element compositions of estimated
parent magmas
BODY 02L003)
Cumulate
PHC PHCFO
Type
Tamarack Intrusion
Complete Alteration
cOhcp
Recharge
CHILL-
TAIL (03L004)
fOhc
OCHp
Tamarack Basal Chill
Basal Chill Zone
5 mm
BIC Intrusion
Recharge
Chill
Igneous Stratigraphy of 08BIC-044
Cumulus Min.
Pl+Cpx+Ox
Cpx+Ox±Ol
Cpx+Ol
Ol
Cpx+Ol
Ol
 Chill Zone
Seagull Intrusion
Seagull Basal Zone
Amphibole-Olivine
Pyroxenite
Estimation of EUMI Parent Magmas
Major-Minor Elements
Tamarack Intrusion
Intrusion
Sample
TAMARACK
4-334.2
Ol Correction
Fe+2/Fe+3
Set at QFM,
1200oC
BIC
4-334.2
4-334.2
20%Fo89
30%Fo89
08BIC-044.660
SEAGULL
08BIC-044.660
WM00-01 710
20%Fo86
WM00-01 710
WM00-01 716
20%Fo86
WM00-01 716
HELE
DISRAELI
02TRH091N
03TRH154N
20%Fo86
SiO2
47.5
49.8
51.5
48.1
50.5
48.4
51.0
48.2
50.8
48.8
46.5
TiO2
0.82
1.02
1.17
1.53
1.92
1.27
1.60
1.16
1.47
2.32
1.80
Al2O3
8.7
10.9
12.5
7.8
9.8
7.2
9.0
6.2
7.9
8.4
7.4
Fe2O3
1.20
1.20
1.21
1.35
1.32
1.37
1.39
1.46
1.46
1.22
1.50
Cr2O3
0.49
0.27
0.46
0.20
0.26
0.38
0.47
0.31
0.39
0.10
0.20
FeO
9.7
9.8
9.8
11.0
10.7
11.1
11.2
11.8
11.8
9.9
12.1
MnO
0.17
0.18
0.18
0.18
0.19
0.21
0.23
0.20
0.21
0.18
0.30
MgO
23.2
16.6
12.0
18.4
11.3
19.5
12.6
20.9
14.2
12.0
14.9
CaO
5.63
6.95
7.90
7.88
9.80
5.80
7.23
5.25
6.56
11.67
10.97
Na2O
1.13
1.42
1.63
1.60
2.01
1.99
2.52
2.04
2.58
2.79
1.90
K2O
0.41
0.51
0.58
0.48
0.60
1.12
1.42
1.00
1.27
1.01
0.90
P2O5
0.08
0.10
0.11
0.19
0.24
0.19
0.23
0.16
0.20
0.20
0.22
H2O+
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
Total
100.5
100.3
100.5
100.1
100.1
100.0
100.5
100.3
100.4
100.1
100.2
mg#
80.8
75.1
68.4
74.7
64.9
75.3
66.5
75.8
68.0
68.3
68.4
Q
0
0
1.21
0
0
0
0
0
0
0
0
or
2.34
3
3.47
2.82
3.61
6.53
8.47
5.81
7.54
6.02
5.36
CIPW Norm
ab
9.91
12.7
14.82
14.29
18.4
17.64
22.85
18.02
23.29
19.45
13.81
an
16.96
21.75
25.32
12.68
16.35
7.21
9.28
4.76
6.18
7.53
9.19
ne
0
0
0
0
0
0
0
0
0
3.48
2.04
di
7.77
9.56
10.92
19.99
25.31
15.99
20.35
15.87
20.19
39.62
35.4
hy
29.96
38.14
41.08
21.31
28.64
15.22
20.65
14.51
20.06
0
0
ol
29.43
11.97
0
24.98
3.03
33.83
14.19
37.61
18.72
18.93
29.63
mt
2.35
1.25
1.28
1.41
1.42
1.45
1.47
1.5
1.53
1.29
1.58
il
1.11
1.42
1.65
2.12
2.73
1.75
2.25
1.59
2.06
3.26
2.53
ap
0.16
0.21
0.23
0.4
0.51
0.39
0.49
0.33
0.42
0.42
0.46
From Goldner (2011)
Estimation of EUMI Parent Magmas
Testing with PELE Fractional Crystallization Modeling
Ox in
Pl in,Ol out
Cp/Op in
Ol out
Ox in
Op in
Pl in
Cp in
Ol in
Estimation of EUMI Parent Magmas
Testing with PELE Fractional Crystallization Modeling
Ol out Pl in
Ox in
Cp in
Qualitative Phase Equilibrium of
EUMI Parent Magmas
DC PM
(Al2O3 14-17%)
Tamarack PM
(Al2O3 9-12%)
BIC & Seagull PM
(Al2O3 6-9%)
Estimation of EUMI Parent Magmas
Trace Elements
100.0
1000.00
Early
EarlyUltramafic
UltramaficIntrusions
Intrusions
100.00
OIB
EMORB
EMORB
OIB
10.0
Tamarack
Tamarack PM
PM
BIC
BIC PM
PM
Seagull
Seagull PM
PM
10.00
1.0
1.00
Nd La Sm
Gd Hf Sm
Tb EuDyTi Gd
Ho Tb Dy
Er
RbLa Ba Ce
U Th PrNb Ta
Ce Pr Eu
Nd Zr
Yb Tm Lu
Y Tm
Ho Er
Yb Lu
V
Sc
* Sun and McDonough (1989), McDonough and Sun (1995)
Comparison to Early MCR Volcanics
Hele
Seagull
Disraeli
Garnet
Lherzolite
BIC
Tamarack
Spinel
Lherzolite
From Hollings et al., 2007
Comparison to Early MCR Volcanics (mg#>59)
100.0
100.0
Siemens Creek
Mamainse Pt Gp 1
Tamarack PM
BIC PM
Seagull PM
10.0
10.0
1.0
100.0
La
Ce
Pr
Nd Sm Eu Gd Tb Dy Ho
Er Tm Yb
Lu
1.0
100.0
Osler Group
10.0
La
Ce
Pr
Nd Sm Eu Gd Tb
Dy Ho
Er
Tm Yb
Lu
Mamainse Point Gps 2-7
10.0
1.0
La
Ce
Pr Nd Sm Eu Gd Tb Dy Ho
Er Tm Yb Lu
1.0
La
Ce
Pr
Nd Sm Eu Gd Tb
Dy Ho
Er
Tm Yb
Lu
Comparison to Early MCR Volcanics
Disraeli
BIC
Seagull
Hele
Tamarack
From Hollings et al., 2007
Comparison to Early MCR Volcanics (mg#>59)
1000.0
Siemens Creek
1000.0
Mamainse Pt Gp1
Tamarack PM
100.0
100.0
BIC PM
Seagull PM
10.0
1.0
1.0
Rb
Ba
U
Th
Nb
Ta
La
Ce
Pr
Nd
Zr
Hf
Sm
Eu
Ti
Gd
Tb
Dy
Y
Ho
Er
Tm
Yb
Lu
V
Sc
Rb
Ba
U
Th
Nb
Ta
La
Ce
Pr
Nd
Zr
Hf
Sm
Eu
Ti
Gd
Tb
Dy
Y
Ho
Er
Tm
Yb
Lu
V
Sc
10.0
1000.0
1000.0
Mamainse Pt Gps 2-7
Osler Group
100.0
100.0
10.0
10.0
1.0
Rb
Ba
U
Th
Nb
Ta
La
Ce
Pr
Nd
Zr
Hf
Sm
Eu
Ti
Gd
Tb
Dy
Y
Ho
Er
Tm
Yb
Lu
V
Sc
Rb
Ba
U
Th
Nb
Ta
La
Ce
Pr
Nd
Zr
Hf
Sm
Eu
Ti
Gd
Tb
Dy
Y
Ho
Er
Tm
Yb
Lu
V
Sc
1.0
Conclusions
• The marginal zones of the Tamarack, BIC and Seagull intrusions
represent chilled zones of magmas moderately enriched (20-30%) in
olivine phenocyrsts.
• Correcting for excess olivine accumulation, marginal compositions
reflect reasonable approximations of likely parent magma compositions
to these intrusions.
• Parent magma compositions for the Seagull and BIC intrusions are
similar to OIB except for depletion in Nb and Ta (Magma Type 2 of
Nicholson). Seagull is more HREE depleted (=deeper source?)
• Parent magma composition of the Tamarack intrusion are more akin to
EMORB differs by the other intrusions by being higher in Si and Al, less
enriched in IE trace elements, and more depleted in Nb and Ta (=
shallow source? Magma Type 1 or 3 of Nicholson). It is noteworthy that
Tamarack is one of the youngest UM MCR intrusions.
• All magmas were contaminated by S and other volatiles, with
Tamarack also contaminated with Si, U, and Th.