Chemical Composition of Amphiboles found in veins and host
rocks of Cretaceous plutons of the Northern Cascades
College of Earth, Ocean and Atmospheric Sciences
By Austin George
Results
Introduction
-Possible relationship between
hornblendite and hornblende-pyroxene
rich veins and Cretaceous host plutonic
rocks?
Discussion
Calcic Amphibole Classifica on for AKCP-16a
1
Pargasite
Edenite
Mg/(Mg+Fe)
(Al>Fe)
-Compare the chemical compositions
and petrographic features of
hornblende and pyroxene from veins
and from the surrounding host plutonic
rocks.
AKCP-16a host
rock
Magnesiosdanagaite
AKCP-12 host
rock
Magnesiohas ngsite
(Al<Fe)
0.5
Ferropargasite
AKCP-16a in-vein
(Al>Fe)
Sadangaite
Ferro-edenite
AKCP-407 host
rock
AKCP-12 in-vein
Has ngsite
0
7.5
6.5
5.5
4.5
Si in formula
Figure 1: Classification of hornblende found in
Mount Stuart and Black Peak Batholiths
-Hornblendite and hornblendepyroxene rich veins crystallized from
same magma source as host rock.
Petrographic Model
-Crystallization of of pyroxene and
hornblende from plutonic magma
-Accumulation of settling
hornblende and pyroxenes at
bottom of magma chamber
Methods
-Injections of new magma carries up
the cumulate crystals forming veins.
-Sample AKCP-407 was collected from Mount
Stuart Batholith
Conclusion
-Samples AKCP-12 and AKCP-16a were collected
from Black Peak Pluton
-Hornblende and pyroxene crystals were
analyzed for major elements using the Cameca
SX-100 electron microprobe at Oregon State
University.
-No observable textural differences or
reaction rims
AKCP-407 in-vein
(Al<Fe)
-Investigating the differences in
chemical composition and mineral
textures between crystals and veins that
intersect them will help determine
whether vein minerals form from the
same magma as the surrounding pluton,
or relate to the intrusion of a different
composition magma.
-Hornblende found inside veins are of
similar chemical composition then those
found in host rock.
Figure 2: Classification of pyroxenes found in
Sample AKCP-407
Figure 3: Graph of the relationship
between wt. % Al2O3 and wt. %
SiO2
-Settling of cumulate crystals at the
bottom of chamber which get
injected back into the host rock.
-80 different hornblendes and 35 pyroxenes were
analyzed
Figure 4: Photograph taken of sample
AKCP-12. Note the microcrystalline reaction
rim on plagioclase possibly due to
deformation.
-Hornblendite and hornblendepyroxene rich veins formed from
same magma as surrounding
pluton
Figure 6: Hornblendite zones within the Mount Stuart
Batholith
Figure 5: Photograph of sample AKCP-407
outside the vein. Shows a euhedral
clinopyroxene with exsolution lamella
surrounded by euhedral plagioclase,
anhedral hornblend and iodmorphic
orthopyroxene.
Acknowledgements
-Special thanks to Professor Adam Kent for
mentoring me over the course of the project.