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N
0 50
kilometers
100
40
35
120
C A S C A D ES &M O D O C
P L AT E AU
K L A M AT HM O U N TA I N S
BA
SIN
& R
AN
GE
SIE
RR
A N
EV
AD
A
SA
LINIA
G
RE
AT
VA
LLE
Y
Zeolite
Lws-Ab-Chl
Blueschist
Franciscan Complexdominant MetamorphicFacies
Other Units
Granitic Plutons
Ophiolitic Rocks
Pre-batholithic rocksof Sierra Nevada
Salinia
Great Valley Sequence
JennerJennerJenner
Ward CreekWard CreekWard Creek
Mount HamiltonMount HamiltonMount Hamilton
San SimeonSan Simeoncoast mélangecoast mélangeSan Simeoncoast mélange
City CollegeCity Collegeshear zoneshear zoneCity Collegeshear zone
Hunters PointHunters Pointshear zoneshear zoneHunters Pointshear zone
South Fork Mountain schistSouth Fork Mountain schist(Tomhead Mtn.)(Tomhead Mtn.)South Fork Mountain schist(Tomhead Mtn.)
Teham
a-C
olu
saTe
ham
a-C
olu
sam
éla
nge
méla
nge
Teham
a-C
olu
sam
éla
nge
Willow SpringsWillow SpringsWillow Springs
Tiburon
Tiburon
mélange
mélange
Tiburon
mélange
E�������� ���������� �� ����-����� ������ �� ��� ����� F��������� ���������� ����
The metamorphic history of high-grade rocks provides invaluable insight into the thermomechanical processes of subduction zones. While subduction in most orogens is terminated by continent collision entailing variably strong overprint of related units, the Franciscan Complex of California allows studying a >150 Myr long subduction history that started at ~175 Ma and ended by transformation into a transform plate boundary (San Andreas fault) without significant metamorphic overprint. The highest grade metamorphic rocks of the Franciscan Complex of California are found as blocks in serpentinite and shale matrix mélanges. They include amphibolites, eclogites, blueschists, and blueschist facies metasediments. These Franciscan mélanges inspired the subduction channel return-flow model, but other processes e.g., buoyancy-driven serpentinite diapirism have been argued to be concordant with our current understanding of their metamorphic history, too.
Introduction
We find: (i) Exhumation from the eclogite-amphibolite facies only occurred at 165–155 Ma with an apparent southward younging trend. (ii) Exhumation of the blocks was uniform and fast in the eclogite-amphibolite facies with rates of 2–8 km/Myr. In the blueschist facies exhumation of the blocks was less uniform and slowed by an order of magnitude. (iii) The age of amphibole in a metasomatic reaction zone indicates that at least one amphibolite was enclosed in a serpentinite matrix at ~155 Ma already. Considering the entire subduction zone system, the high-grade exhumation temporally correlates with a significant pulse of magmatism in the respective magmatic arc (Sierra Nevada) and termination of forearc spreading (Coast Range Ophiolite).Our findings do not support a steady-state process that is continuously exhuming high-grade rocks. Instead the subduction zone system appears to have changed with an eventlike character resulting in exhumation of high-grade rocks enclosed in serpentinite.
Figure 1. Early proposed model of subduction channel return flow (Cloos 1982). Main prediction of this continuous process model: Prograde and retrograde metamorphism occur at all grades at all times.
Study Setup
We sampled high-grade blocks f rom serpentinite and serpentinite-shale mélanges. We focused on eclogite-amphibolites that were previously investigated petrologically and geochronologically (primarily Lu-Hf garnet). We dated amphibole, phengite, and
40 39zircon using the Ar/ Ar and U-Pb systems, respectively.
Figure 4 (↑): Tectonic and metamorphic overview map of northern and central California. Investigated locals in the Franciscan complex are color coded in conjunction with figure 5. Modified from Mulcahy et al. (2018).
Figure 3 (↑): Exemplary high-grade block TIBB in the field (a) and in thin section (b).
500 µm
phengitephengitephengite
hornblendehornblendehornblende
Na-amphiboleNa-amphiboleNa-amphibole
a
b
We investigate a suite of metabasite blocks from serpentinite and shale matrix mélanges of the Califonia Coast Ranges. Our new dataset consists of U-Pb dates of metamorphic zircon and 40Ar/39Ar dates of calcic amphibole and white mica. Combined with published geochronology, particularly prograde Lu-Hf garnet ages we can reconstruct the timing and time scales of prograde and retrograde metamorphism of individual blocks.
We sampled high-grade blocks from serpentinite and serpentinite-shale mélanges. We focused on eclogite-amphibolites that were previously invest igated pet ro log ica l ly and geochronologically (primarily Lu-Hf garnet). We dated amphibole, phengite,
40 39and zircon using the Ar/ Ar and U-Pb systems, respectively.
Study Setup
IntA = 163.16 ± 0.74 MaIntA = 163.16 ± 0.74 Ma
159.34 ± 0.67 Ma159.34 ± 0.67 Ma
Heart rock, HR-2 and HR-3Heart rock, HR-2 and HR-3
100100
120120
140140
160160
180180
200200
IntA(18057-01) = 140.4 ± 1.5 MaIntA(18057-01) = 140.4 ± 1.5 Ma
140.37 ± 0.71 Ma (vein)140.37 ± 0.71 Ma (vein)
IntA(18057-02) = 141.4 ± 1.0 MaIntA(18057-02) = 141.4 ± 1.0 Ma
141.86 ± 0.61 Ma (vein)141.86 ± 0.61 Ma (vein)
IntA(18220-01) = 149.7 ± 1.9 MaIntA(18220-01) = 149.7 ± 1.9 Ma
148.4 ± 1.8 Ma (matrix)148.4 ± 1.8 Ma (matrix)
00
22
44
6060
120120
140140
160160
180180
200200
158.13 ± 0.51 Ma158.13 ± 0.51 Ma159.9 ± 2.0 Ma159.9 ± 2.0 Ma
156.39 ± 0.70 Ma156.39 ± 0.70 Ma
154.8 ± 1.3 Ma154.8 ± 1.3 Ma
00
2020
00
6060
RM-8RM-8
120120
140140
160160
180180
200200
156.1 ± 1.1 Ma156.1 ± 1.1 Ma
IntA(18054-01) = 154.6 ± 1.5 MaIntA(18054-01) = 154.6 ± 1.5 Ma
154.79 ± 0.66 Ma154.79 ± 0.66 Ma
00
2020
00
6060
matrix
vein vein
120120
140140
160160
180180
200200
IntA = 152.9 ± 1.3 MaIntA = 152.9 ± 1.3 Ma
155.3 ± 1.3 Ma155.3 ± 1.3 Ma
5050
00
6060
Sunset boulders Je2 and Je1rSunset boulders Je2 and Je1r
matrix
rind
100100
00
Je3dJe3d
100100
120120
140140
160160
180180
200200
IntA = 137 ± 44 MaIntA = 137 ± 44 Ma
156 ± 17 Ma156 ± 17 Ma
4040
00
6060
IntA(18041-03) = 156.19 ± 0.55 MaIntA(18041-03) = 156.19 ± 0.55 MaIntA(18041-04) = 159.8 ± 2.6 MaIntA(18041-04) = 159.8 ± 2.6 Ma
IntA(18059-01) = 156.6 ± 1.6 MaIntA(18059-01) = 156.6 ± 1.6 MaIntA(18230-03) = 157.4 ± 1.7 MaIntA(18230-03) = 157.4 ± 1.7 Ma
00 0.020.02 0.040.0400
0.50.5
1.01.0
1.51.5
2.02.0
2.52.5
Age = 147.3 ± 3.0 MaAge = 147.3 ± 3.0 Ma40 36Ar/ Ar Int. = 404 ± 9240 36Ar/ Ar Int. = 404 ± 92MSWD = 4.5, n = 10MSWD = 4.5, n = 10
00 0.020.02 0.040.04 0.060.0600
11
22
33
IIA = 157.6 ± 1.6 MaIIA = 157.6 ± 1.6 Ma40 36Ar/ Ar Int. = 313.8 ± 5.040 36Ar/ Ar Int. = 313.8 ± 5.0MSWD = 15, n = 11MSWD = 15, n = 11
PG23/TIBBPG23/TIBB
00 0.020.02 0.040.0400
0.50.5
1.01.0
1.51.5
Age = 149.9 ± 2.9 MaAge = 149.9 ± 2.9 Ma40 36Ar/ Ar Int. = 690 ± 18040 36Ar/ Ar Int. = 690 ± 180MSWD = 2.4, n = 14MSWD = 2.4, n = 14
vein
IntA(18046-13) = 154.0 ± 1.6 Ma
36
40
-3A
r/A
r (1
0)
0
36
40
-3A
r/A
r (1
0)
Appare
ntA
ge
(Ma)
Appare
ntA
ge
(Ma)
40
%A
r*40
%A
r*C
a/K
Ca/K
Appare
ntA
ge
(Ma)
Appare
ntA
ge
(Ma)
40
%A
r*40
%A
r*C
a/K
Ca/K
Jenner
Tiburon Mélange (Ring Mountain)
36
40
-3A
r/A
r (1
0)
39 40Ar / Ar*K
39 40Ar / Ar*K
00 0.20.2 0.40.4 0.60.6 0.80.8 1139cum. Ar releaseK
39cum. Ar releaseK
00 0.20.2 0.40.4 0.60.6 0.80.8 1139cum. Ar releaseK
39cum. Ar releaseK
00 0.20.2 0.40.4 0.60.6 0.80.8 1139cum. Ar releaseK
39cum. Ar releaseK
00 0.20.2 0.40.4 0.60.6 0.80.8 1139cum. Ar releaseK
39cum. Ar releaseK
00 0.20.2 0.40.4 0.60.6 0.80.8 1139cum. Ar releaseK
39cum. Ar releaseK
Appare
ntA
ge
(Ma)
Appare
ntA
ge
(Ma)
40
%A
r*40
%A
r*C
a/K
Ca/K
40 39Figure x: Ar/ Ar geochronology results. Apparent age spectra with weighted mean ages and integrated gas ages
(K-Ar equivalent) are reported for all samples and aided by inverse isochron plots for samples with complex 40 36Ar/ Ar composition. Results from amphibole and white mica are in red and green tones, respectively. Uncertainties
are plotted at the 1σ level, but calculated results are at the 2σ level for ease of comparability with other methods.
Further analytical detail in Table x and Table Sx.
2020
MH-3MH-3
100100
120120
140140
160160
180180
200200
IntA(18216-01) = 144.0 ± 2.6 MaIntA(18216-01) = 144.0 ± 2.6 Ma
151.4 ± 2.2 Ma151.4 ± 2.2 Ma
IntA(18216-02) = 141.9 ± 2.5 MaIntA(18216-02) = 141.9 ± 2.5 Ma
153.6 ± 2.2 Ma153.6 ± 2.2 Ma
IntA(18217-01) = 148.3 ± 1.8 MaIntA(18217-01) = 148.3 ± 1.8 Ma
148.2 ± 1.7 Ma148.2 ± 1.7 Ma
1010
00
6060
00
Mount Hamilton
00 0.20.2 0.40.4 0.60.6 0.80.8 1139cum. Ar releaseK
39cum. Ar releaseK
40
%A
r*40
%A
r*C
a/K
Ca/K
Appare
ntA
ge
(Ma)
Appare
ntA
ge
(Ma)
39 40Ar / Ar*K
BH-32BH-32
100100
120120
140140
160160
180180
200200
Appare
ntA
ge
(Ma)
Appare
ntA
ge
(Ma)
IntA(18044-14) = 159.3 ± 2.0 MaIntA(18044-14) = 159.3 ± 2.0 Ma
159.4 ± 1.2 Ma159.4 ± 1.2 Ma
IntA (18056-01) = 145.5 ± 1.5 MaIntA (18056-01) = 145.5 ± 1.5 Ma
145.69 ± 0.68 Ma145.69 ± 0.68 Ma
00
2020
00
6060
BR-5BR-5
100100
120120
140140
160160
180180
200200
IntA = 150.6 ± 1.5 MaIntA = 150.6 ± 1.5 Ma
149.90 ± 0.75 Ma149.90 ± 0.75 Ma
00
22
6060
100100
120120
140140
160160
180180
200200
IntA(18222-01) = 158.5 ± 3.9 MaIntA(18222-01) = 158.5 ± 3.9 Ma
158.1 ± 2.6 Ma158.1 ± 2.6 Ma
IntA(18222-02) = 160.4 ± 3.5 MaIntA(18222-02) = 160.4 ± 3.5 Ma
160.0 ± 2.2 Ma160.0 ± 2.2 Ma
IntA (18223-01) = 147.2 ± 1.9 MaIntA (18223-01) = 147.2 ± 1.9 Ma
146.6 ± 1.8 Ma146.6 ± 1.8 Ma
00
2020
4040
6060
PG14PG14
100100
120120
140140
160160
180180
200200
Appare
ntA
ge
(Ma)
Appare
ntA
ge
(Ma)
IntA(18045-01) = 147.2 ± 3.1 MaIntA(18045-01) = 147.2 ± 3.1 Ma
154.1 ± 1.5 Ma154.1 ± 1.5 Ma
IntA(18045-02) = 147.12 ± 0.59 MaIntA(18045-02) = 147.12 ± 0.59 Ma
00
2020
4040
00
6060
Ca/K
Ca/K
Ca/K
Ca/K
00 0.020.02 0.040.04 0.060.0600
0.50.5
1.01.0
1.51.5
2.02.0 IIA = 148.0 ± 1.4 MaIIA = 148.0 ± 1.4 Ma40 36Ar/ Ar Int. = 495 ± 8840 36Ar/ Ar Int. = 495 ± 88
MSWD= 1.3, n = 13MSWD= 1.3, n = 13
DRM-1DRM-1
00 0.020.02 0.040.0400
0.50.5
1.01.0
1.51.5
2.02.0
2.52.5
IIA = 146.3 ± 2.3 MaIIA = 146.3 ± 2.3 Ma40 36Ar/ Ar Int. = 357 ± 7440 36Ar/ Ar Int. = 357 ± 74MSWD = 4.2, n = 11MSWD = 4.2, n = 11
00 0.020.02 0.040.04 0.060.0600
0.50.5
1.01.0
1.51.5
2.02.0
2.52.5
IIA = 144 ± 10 MaIIA = 144 ± 10 Ma40 36Ar/ Ar Int. = 355 ± 8940 36Ar/ Ar Int. = 355 ± 89MSWD = 7, n = 13MSWD = 7, n = 13
IIA = 133 ± 21 MaIIA = 133 ± 21 Ma40 36Ar/ Ar Int. = 480 ± 26040 36Ar/ Ar Int. = 480 ± 260MSWD = 200, n = 8MSWD = 200, n = 8
36
40
-3A
r/A
r (1
0)
0
36
40
-3A
r/A
r (1
0)
36
40
-3A
r/A
r (1
0)
39 40Ar / Ar*K
39 40Ar / Ar*K39 40Ar / Ar*K
39 40Ar / Ar*K
39 40Ar / Ar*K
40
%A
r*40
%A
r*C
a/K
Ca/K
00 0.20.2 0.40.4 0.60.6 0.80.8 1139cum. Ar releaseK
39cum. Ar releaseK
000 0.20.2 0.40.4 0.60.6 0.80.8 11
39cum. Ar releaseK
39cum. Ar releaseK
00 0.20.2 0.40.4 0.60.6 0.80.8 1139cum. Ar releaseK
39cum. Ar releaseK
00 0.20.2 0.40.4 0.60.6 0.80.8 1139
cum. Ar releaseK
39cum. Ar releaseK
40
%A
r*40
%A
r*
Appare
ntA
ge
(Ma)
Appare
ntA
ge
(Ma)
40
%A
r*40
%A
r*C
a/K
Ca/K
Appare
ntA
ge
(Ma)
Appare
ntA
ge
(Ma)
40
%A
r*40
%A
r*
207
206
Pb/
Pb
48
14
65
72
74
70
64
66
63
67
71
79
68
76
0.05
0.06
0.07
0.08
33 35 37 39 41
207
206
Pb/
Pb
238 206U/ Pb
6
70.1
0.2
30
40
52
12_5
3
28
1
35
21
4755
16
15 51
18
19
38
0.05
0.06
0.07
0.08
0.09
160 Ma160 Ma160 Ma
170 Ma170 Ma170 Ma
180 Ma180 Ma180 Ma
190 Ma190 Ma190 Ma
160 Ma160 Ma160 Ma170 Ma170 Ma170 Ma180 Ma180 Ma180 Ma190 Ma190 Ma190 Ma
rim and core analyses:7CA range 154±4.7 - 168.1±4.7 Manon-anchored discordia intercepts:
154.4 ± 5.6 Ma & 3255± 740MSWD = 2.9
PG23/TIBB
BH-32
rims:7CA range 168.1±4.7 - 154±4.7 Ma
discordia intercepts:157.6 ± 2.4 Ma & 4640± 260
MSWD = 1.3
cores:7CA range 175.0±5.0 - 160.5±4.6 Ma
discordia intercepts:163.7±2.7 Ma & 3218± 630
MSWD = 1.6
anchored: 159.9±2.9 MaMSWD = 4.3
anchored: 166.7±1.6 MaMSWD = 1.9
cores
rims
cores
rims
130 140 150 160 170 180
white micagarnet
hornblende zircon
Lawsonite
progressionretrogressionPg31; eclogite; A2004
Je1r&Je2; grt-amphibolite; this study
Je3; amphibolite-blueschist-eclogite; this study
WC-1; grt-laws-blueschist/eclogite; M2014
BR-5; grt-blueschist, hbl relics; M2014, this study
T-90-3AG&AB; eclogite; CS2003
T-90-2; grt-amphibolite; CS2003
PG23, TIBB, TIBBvein; eclogite/grt-amphibolite; A2004, this study
RM-8; grt-epi-amphibolite; M2014, this study
Turtle Rock; lws-blueschist; M2009
RR-1; lws-blueschist; M2014
EA, DRM-1; grt-amphibolite; M2018, this study
PG14; grt-amphibolite; A2004, this study
BH-32; grt-amphibolite; M2018, this study
MP-1; epi-amphibolite; WD2007
HPSZ Meta; grt-amphibolite; WD2007
MH-90-01, MH-3, eclogite/grt-amphibolite; CS2007, this study
PnP; hornblendite block, P2014
KA3839; amphibolite; S2011
AldSp1; amphibolite; S2011
WbSp; amphibolite; S2011
04-EU-SS-45; blueschist; U2012
04-EU-SS-48; blueschist; U2012
04-EU-SS-49; blueschist; U2012
04-EU-SS-60; blueschist; U2012
WC-1; metachert; WD2007
Tomhead Mtn. samples ; terrane; DW2007, D2010
120110
PG80, PP13, PP1; Hermes Block/Antelope Creek slab; grt-amphibolite; RS1988, A2004, this study
95Diab-107, PG76; eclogite; C2011; WD2007
95Diab-41; epi-blueschist; WD2007
PG73, glaucophane schist; WD2007
Ap
tian
Ba
rre
mia
n
Ha
ute
rivi
an
Va
lan
gin
ian
Be
rria
sia
n
Tith
on
ian
Kim
me
rid
gia
n
Oxf
ord
ian
Ca
llovi
an
Ba
tho
nia
nB
ajo
cia
n
Aa
len
ian
Tehama-Colusa mélange
Ward Creekslab
Jenner
Tiburon mélange(Ring Mountain,Berkeley Hills,and Big Rock
Ridge)
Hunters Pointshear zoneCity Collegeshear zone
Mount Hamilton
San Simeoncoast mélange
North (strike-slip restored)
South (strike-slip restored)
HR2/3; Jenner blueschist; this study
Willow Springsimbrication
To
arc
ian
Alb
ian
0
South ForkMountain schist
retrogression
retrogression
hydrothermal
matrixvein
matrixvein
40 39Ar/ Ar
Lu-Hf
U-Pb
rims cores
ocean floor formation
sedimentation
2nd phase plutonism
volcanopelagicsedimentation
?
in garnetin matrix
matrixrind
matrixrind
BH-1; grt-blueschist; M2014
matrixrind
43
(1
0 k
m/M
yr)
2
3
1
Sierra Nevada magmatism
Coast Range ophiolite
Great Valley group
magma addition rate (PD2015)
JurassicCretaceousSymbology
>/< minimum/maximum age
*>
*>
ac�nolithe * low-confidence
blueschist facies grt
blueschist facies grt
(H2008)
Franciscan Complex sedimentary units
coherent unit
coherent unit
< 131 Ma det. zrc.coherent unit
onset of accretion (D2010)
PG23, TIBB, TIBBvein; eclogite/grt-amphibolite; A2004, this study
Results 1 - Timescales of Metamorphism
40 39Figure 6 (→): Published and new Ar/ Ar amphibole and white mica ages from high-grade blocks and eclogite-amphibolite facies coherent units displayed in histograms, probability density functions (line), and kernel-density estimate curves (area).
Figure 5 (↑). Summary of geochronologic data for Franciscan high-grade bocks and coherent units and comparison with chronology of accretion of Franciscan Complex sedimentary units, Coast Range ophiolite genesis, Great Valley group sedimentation, and Sierra Nevada magmatism. Samples described in black font experienced eclogite-amphibolite facies and variable blueschist facies overprint while those in blue font experienced only blueschist facies metamorphism. Abbreviations: A2004 - (Anczkiewicz et al., 2004); CS2007 - (Catlos & Sorensen, 2003); C2011 - (Cooper et al., 2011); D2010 - (Dumitru et al., 2010); H2008 - (Hopson et al., 2008); M2009 - (Mulcahy et al., 2009); M2014 - (Mulcahy et al., 2014); M2018 - (Mulcahy et al., 2018); P2014 - (Page et al., 2014); PD2015 - (Paterson & Ducea, 2015); RS1988 - (Ross & Sharp, 1988); S2011 - (Shervais et al., 2011); U2012 - (Ukar et al., 2012); WD2007 - (Wakabayashi & Dumitru, 2007).
Hypothesis 1: Continuous Subduction Channel Return Flow (Cloos 1982)
(n=10+3)
(n=24)
40 39Ar/ Ar amphibole
num
ber
num
ber
40 39Ar/ Ar white mica
130 135 140 145 150 155 160 165 170 175
0
1
2
3
4
5
6
7
0
1
2
3
4
5 (n=10)
Teha
ma-
Colus
a m
élan
ge
Teha
ma-
Colus
a m
élan
ge
(Nor
ther
n Califo
rnia)
(Nor
ther
n Califo
rnia)
Teha
ma-
Colus
a m
élan
ge
(Nor
ther
n Califo
rnia)
Cen
tral C
alifo
rnia
Cen
tral C
alifo
rnia
Cen
tral C
alifo
rnia
Cen
tral C
alifo
rnia
Cen
tral C
alifo
rnia
Cen
tral C
alifo
rnia
(n=3)
Age (Ma)
Initiation (Anczkiewicz et al., 2004)Hypothesis 2: Cooling of the Subduction Zone after Subduction
Figure 2. Geothermometric estimates vs. age diagram for analyzed samples. Slope of the regression line suggests ca. 15 °C/Ma cooling rate for the Franciscan subduction (Anczkiewicz et al., 2004).
Lu-Hf garnet
Results 2 - Thermokinetic Evolution of the Subduction zone
Undifferentiated
800
700
600
500
400
300
peak-
T (
°C)
0
10
20
30
40
50
60
70
80~160 Ma (PG23/TIBB)
~158 Ma (PG31)
~121 Ma (SFMS)
blockscoherent
0
0.5
1
1.5
2
2.5
200 300 400 500 600 700
~147 Ma (PG73/WSs)
~158 Ma (PG76/WSs)
depth
(km
)
pre
ssu
re (
GP
a)
125 135 145 155 165 175
800
~169 Ma (PG80/ACs)
max
max
~163 Ma (PG14)
max
14°C/km
7°C/k
m
Ring Mountain
Berkeley Hills
Jenner
temperature (°C)
age (Ma)
white micagarnethornblende
zircon
Lawsonite40 39Ar/ Ar Lu-Hf
U-Pb
Symbology
ac�nolithe
Figure 7. (a) Tt diagram showing dates of geochronometers of individual blocks as a function of the peak-T determined for the block.(b) PT diagram showing peak-PT data of blocks and coherent units along with the approximate age of peak metamorphism, estimated between prograde Lu-Hf garnet
40 39or U-Pb zrc and retrograde Ar/ Ar hornblende or phengite dates. The arrows indicate maximum pressure estimates.
Ÿ Geothermal gradients ranged 7-14°C/km.
Key Findings:
Ÿ Younger metamorphism was rather hotter than cooler.
Key Findings:Ÿ Prograde metamorphism appears temporally variable, but geochronometers may date
variable PT conditions40 39
Ÿ Ar/ Ar amphibole ages cluster at 165-159 Ma with a N-S younging trend
became more variable
- high-T retrograde metamorphism of eclogite-amphibolite was fast and uniform
- Exhumation rates of eclocite-amphibolite slowed in the blueschist facies and
40 39Ÿ Duration between Ar/ Ar amphibole and white mica dates ranges 2–14 Myr
1,2,3 4 5 1,2Daniel Rutte , Joshua Garber , Andrew Kylander-Clark , Paul R. Renne1 Earth and Planetary Science, University of California, Berkeley2 Berkeley Geochronology Center
5 Department of Earth Science, University of California, Santa Barbara
3 University of Bonn4 Penn State University
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References
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Catlos, E. J., & Sorensen, S. S. (2003). Phengite-based chronology of K- and Ba-rich fluid flow in two paleosubduction zones. Science (New York, N.Y.), 299(January), 92–95. https://doi.org/10.1126/science.1076977
a
b
peak
-T
(not substantied in this study)(not substantied in this study)(not substantied in this study)
(not substantied in this study)(not substantied in this study)(not substantied in this study)
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