This document summarizes research using amphibole thermometry to compare crystallization temperatures in plutonic and volcanic systems. Analysis of 106 amphibole grains found that 25 showed thermal zoning, with normal zoning (cooling from core to rim) most common. Grain sizes varied between systems, with the largest grains in granitoids. Results provide evidence that recharge of magma occurred in plutons, causing reheating of grains. Future work will further examine relationships between zoning and rock units to better understand magma mixing processes.
1. Amphibole Thermometry and a Comparison of Results from Plutonic and Volcanic Systems
Introduction
New calibrations are used (Putirka 2016 (Am Min, in press)) to estimate amphibole
(hornblende) crystallization temperatures within plutonic and volcanic systems. Results of
these systems are compared so as to test ideas of recharge of magma within plutons, and the
extent of thermal re-equilibration after mixing.
Amphibole compositions are obtained from EMPA for 106 individual grains. Thermometers
are used to reconstruct temperatures at successive phases of growth within each grain and
represent thermal zoning. These T-transects show trends of either heating or cooling from
core to rim, stable thermal conditions (constant T) throughout a grain, or no T-distance
correlation, with much scatter; variation exists between volcanic and plutonic systems in
crystallization temperature and grain size.
The three systems are examined:
• Lassen Peak (Northern California)
• Guadalupe Igneous Complex (GIC; Central Sierra Nevada foothills)
• Pine Flat Intrusive Complex (PFIC; Southern Sierra Nevada).
Trent Sherman (1); Keith Putirka (1); Alyssa De Los Reyes (1) Alexandra Pytlak (1); Barbara Ratschbacher (2)
(1) California State University, Fresno Dept. Earth & Env. Sciences 2576 E. San Ramon Ave. M/S ST90 93740; tsherman91@mail.fresnostate.edu
(2) University of Southern California Department of Earth Sciences 3651 Trousdale Pkwy Los Angeles, CA, 90089
Figure 1: FS2B-A, Grouping 27; Data Points #116-125
800
820
840
860
880
900
920
940
960
980
1000
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450
Temperature(C)
Rim-core-rim distance across grain (μm)
Cross-Sectional Temperature Gradient
Good Data Bad Data
Centerofgrain
Grainboundary
Grainboundary
Figure 2: PF-G-090; Grouping 63; Data Points #183-192
700
710
720
730
740
750
760
770
780
790
800
810
820
0 25 50 75 100 125 150 175 200 225 250 275
Temperature(C)
Rim-core-rim distance across grain (μm)
Cross-Sectional Temperature Gradient:
GIC gabbro amphibole
Figure 3: 843CPX; Grouping 4; Data Points #208-213
860
870
880
890
900
910
920
930
940
950
960
970
980
0 10 20 30 40 50 60 70 80 90 100
Temperature(C)
Rim-core-rim distance across grain (microns)
Grainboundary
Above: cross-sectional temperature gradient showing the points of a hornblende grain
measured by electron microprobe. The transect starts (at zero microns) at the rim of the
crystal, works progressively through the center (around 125 microns) and to the rim at the far
end (near 250 microns). The grain preserves a record of reverse zoning; initially (during
growth of core) the surrounding temperature was relatively low, then temperatures increased
at least until the grain stopped growing. Although it appears that temperature rose quickly
then plateaued, nothing can be said about relative rates of increased temperature because it
is just as plausible that the grain experienced different growth rates; however, no information
can be constrained about growth kinetics here.
Above: granitic amphibole core-to-rim cross-section. Blue points show data that was
trustworthy, while orange points were returned with low weight percent totals (<95%).
Orange points were included to illustrate the size of the grain being measured (grain ending at
430 microns. A cooling trend is observed at the rims (normal zoning). This amphibole came
from a granitic intrusion near Pine Flat Lake, Ca.
Above: Volcanic amphibole cross-sectional temperature gradient. Vertical dashed line at 92
microns marks the end of the grain, where a reliable temperature estimation could not be
constrained with EMPA due to low major oxide weight percent total.
Trend shows either: 1) an asymmetrical growth pattern of the grain 2) oblique viewing angle of
cross section 3) a system that is relatively temperature stable and only reflects “noise” in the
temperature calculation as judged by the error bars.
Conclusion
• This is a viable method to determine thermal zoning trends within amphibole crystals
• Plutonic and volcanic amphibole grains can reveal cross-sectional temperature trends that
reflect how temperature conditions changed throughout the growth of those minerals.
• T changes may reflect magmatic mixing processes, such that 1) immobile grains are heated
by pulses of recharge magma, or 2) grains are pushed (or fall?) into different magma types
• This method seems best suited in estimating intrusive systems
• volcanic trends mostly lie within the margin of error
• Many plutonic crystals show symmetric zoning
Methods
1) EMPA: field samples were made into thin sections and analyzed by electron microprobe.
Individual grains were analyzed for composition along core-rim transects.
2) Filtering: criteria were applied to filter unreliable data points collected by EMP. Data were
determined to be reliable if weight percent totals were ≥95% and had hornblende composition
39.0% ≤ SiO2 ≥ 50.0%
0.5% ≤ Al2O3 ≥ 18.0%
9.0% ≤ CaO ≥ 13.0%
3) Temperature Plots:
T(oC) = 1781 – 132.74[Siamph] + 116.6[Tiamph] – 69.41[Fet
amph] + 101.62[Naamph]
Temperatures were graphed according to their relative position in the grain as indicated by the
rim-core-rim transect. Successive distances along the transect were normalized to the first
point measured at a rim (using the Pythagorean Theorem).
4) Qualitative Assessment: Plots were assessed for 1) thermal zoning and 2) trends between
volcanic and plutonic systems
Results
• Of 106 grains analyzed, 25 show thermal zoning; all others show no correlation
• Normal zoning (core-rim T decrease) was the dominant trend observed in all samples
• The average size of grains depends on the system it came from:
• Lassen volcanics averaged 199.6 µm across the short axis (27 grains; stdev=277 µm)
• GIC gabbros 428.8 µm (68 grains; stdev= 465 µm)
• Pine Flat Reservoir granitoids 842.7 µm across short axis (11 grains; stdev=235 µm)
Next Steps
• Analyze thermal zoning in context of the rock unit they were found in
• Determine if zoning corresponds to grain mobility between cold felsic magmas and hot
mafic magmas.
• Find extent of thermal re-equilibration after magma mixing
Grainboundary
Graincenter
Grainboundary
Graincenter?
Right: amphibole crystallization
T distribution of the Pine Flat
Intrusive Complex.
• High T limb corresponds to
granitoid outcrop at 1200 ft
elevation
• Low T corresponds to a
mafic/felsic mingling zone at
outcrop elevation 3950 ft
• Temperature difference may
result from difference in
crystallization depth within
pluton
V23B-3112
Granitoid
Mafic
Cross-Sectional Temperature Gradient: Lassen Volcanics
![Amphibole Thermometry and a Comparison of Results from Plutonic and Volcanic Systems
Introduction
New calibrations are used (Putirka 2016 (Am Min, in press)) to estimate amphibole
(hornblende) crystallization temperatures within plutonic and volcanic systems. Results of
these systems are compared so as to test ideas of recharge of magma within plutons, and the
extent of thermal re-equilibration after mixing.
Amphibole compositions are obtained from EMPA for 106 individual grains. Thermometers
are used to reconstruct temperatures at successive phases of growth within each grain and
represent thermal zoning. These T-transects show trends of either heating or cooling from
core to rim, stable thermal conditions (constant T) throughout a grain, or no T-distance
correlation, with much scatter; variation exists between volcanic and plutonic systems in
crystallization temperature and grain size.
The three systems are examined:
• Lassen Peak (Northern California)
• Guadalupe Igneous Complex (GIC; Central Sierra Nevada foothills)
• Pine Flat Intrusive Complex (PFIC; Southern Sierra Nevada).
Trent Sherman (1); Keith Putirka (1); Alyssa De Los Reyes (1) Alexandra Pytlak (1); Barbara Ratschbacher (2)
(1) California State University, Fresno Dept. Earth & Env. Sciences 2576 E. San Ramon Ave. M/S ST90 93740; tsherman91@mail.fresnostate.edu
(2) University of Southern California Department of Earth Sciences 3651 Trousdale Pkwy Los Angeles, CA, 90089
Figure 1: FS2B-A, Grouping 27; Data Points #116-125
800
820
840
860
880
900
920
940
960
980
1000
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450
Temperature(C)
Rim-core-rim distance across grain (μm)
Cross-Sectional Temperature Gradient
Good Data Bad Data
Centerofgrain
Grainboundary
Grainboundary
Figure 2: PF-G-090; Grouping 63; Data Points #183-192
700
710
720
730
740
750
760
770
780
790
800
810
820
0 25 50 75 100 125 150 175 200 225 250 275
Temperature(C)
Rim-core-rim distance across grain (μm)
Cross-Sectional Temperature Gradient:
GIC gabbro amphibole
Figure 3: 843CPX; Grouping 4; Data Points #208-213
860
870
880
890
900
910
920
930
940
950
960
970
980
0 10 20 30 40 50 60 70 80 90 100
Temperature(C)
Rim-core-rim distance across grain (microns)
Grainboundary
Above: cross-sectional temperature gradient showing the points of a hornblende grain
measured by electron microprobe. The transect starts (at zero microns) at the rim of the
crystal, works progressively through the center (around 125 microns) and to the rim at the far
end (near 250 microns). The grain preserves a record of reverse zoning; initially (during
growth of core) the surrounding temperature was relatively low, then temperatures increased
at least until the grain stopped growing. Although it appears that temperature rose quickly
then plateaued, nothing can be said about relative rates of increased temperature because it
is just as plausible that the grain experienced different growth rates; however, no information
can be constrained about growth kinetics here.
Above: granitic amphibole core-to-rim cross-section. Blue points show data that was
trustworthy, while orange points were returned with low weight percent totals (<95%).
Orange points were included to illustrate the size of the grain being measured (grain ending at
430 microns. A cooling trend is observed at the rims (normal zoning). This amphibole came
from a granitic intrusion near Pine Flat Lake, Ca.
Above: Volcanic amphibole cross-sectional temperature gradient. Vertical dashed line at 92
microns marks the end of the grain, where a reliable temperature estimation could not be
constrained with EMPA due to low major oxide weight percent total.
Trend shows either: 1) an asymmetrical growth pattern of the grain 2) oblique viewing angle of
cross section 3) a system that is relatively temperature stable and only reflects “noise” in the
temperature calculation as judged by the error bars.
Conclusion
• This is a viable method to determine thermal zoning trends within amphibole crystals
• Plutonic and volcanic amphibole grains can reveal cross-sectional temperature trends that
reflect how temperature conditions changed throughout the growth of those minerals.
• T changes may reflect magmatic mixing processes, such that 1) immobile grains are heated
by pulses of recharge magma, or 2) grains are pushed (or fall?) into different magma types
• This method seems best suited in estimating intrusive systems
• volcanic trends mostly lie within the margin of error
• Many plutonic crystals show symmetric zoning
Methods
1) EMPA: field samples were made into thin sections and analyzed by electron microprobe.
Individual grains were analyzed for composition along core-rim transects.
2) Filtering: criteria were applied to filter unreliable data points collected by EMP. Data were
determined to be reliable if weight percent totals were ≥95% and had hornblende composition
39.0% ≤ SiO2 ≥ 50.0%
0.5% ≤ Al2O3 ≥ 18.0%
9.0% ≤ CaO ≥ 13.0%
3) Temperature Plots:
T(oC) = 1781 – 132.74[Siamph] + 116.6[Tiamph] – 69.41[Fet
amph] + 101.62[Naamph]
Temperatures were graphed according to their relative position in the grain as indicated by the
rim-core-rim transect. Successive distances along the transect were normalized to the first
point measured at a rim (using the Pythagorean Theorem).
4) Qualitative Assessment: Plots were assessed for 1) thermal zoning and 2) trends between
volcanic and plutonic systems
Results
• Of 106 grains analyzed, 25 show thermal zoning; all others show no correlation
• Normal zoning (core-rim T decrease) was the dominant trend observed in all samples
• The average size of grains depends on the system it came from:
• Lassen volcanics averaged 199.6 µm across the short axis (27 grains; stdev=277 µm)
• GIC gabbros 428.8 µm (68 grains; stdev= 465 µm)
• Pine Flat Reservoir granitoids 842.7 µm across short axis (11 grains; stdev=235 µm)
Next Steps
• Analyze thermal zoning in context of the rock unit they were found in
• Determine if zoning corresponds to grain mobility between cold felsic magmas and hot
mafic magmas.
• Find extent of thermal re-equilibration after magma mixing
Grainboundary
Graincenter
Grainboundary
Graincenter?
Right: amphibole crystallization
T distribution of the Pine Flat
Intrusive Complex.
• High T limb corresponds to
granitoid outcrop at 1200 ft
elevation
• Low T corresponds to a
mafic/felsic mingling zone at
outcrop elevation 3950 ft
• Temperature difference may
result from difference in
crystallization depth within
pluton
V23B-3112
Granitoid
Mafic
Cross-Sectional Temperature Gradient: Lassen Volcanics](https://image.slidesharecdn.com/3f0ac769-4c39-436f-ad7a-971f93792037-160916203225/85/AGU_Poster-Trent-1-320.jpg)
