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Trace element concentrations in plagioclase phenocrysts of Trace element concentrations in plagioclase phenocrysts of Karymsky andesite: Evidence for basalt replenishmentsKarymsky andesite: Evidence for basalt replenishments
Pavel IzbekovPavel Izbekov11, John Eichelberger, John Eichelberger11, , Thomas A. VogelThomas A. Vogel22 and Lina Patino and Lina Patino22
1 Alaska Volcano Observatory, Geophysical Institute University of Alaska Fairbanks
2 Department of Geological Sciences, Michigan State University
Purpose of presentationPurpose of presentation
To discuss the results of comparative study of plagioclase phenocrysts from Karymsky andesites and Academy Nauk basalt, which erupted simultaneously in January 1996
Karymsky, July 1998
Location of Karymsky and Academy NaukLocation of Karymsky and Academy Nauk
Ray Sterner, Johns Hopkins University, Applied Physics Laboratory, 1998
Karymsky volcano, 54003'N 159027' E, is one of the most active volcanoes of the Eastern volca-nic zone of Kamchatka arc, which lies ~220 km inland and parallel to the Kamchatka trench. According to recent geophysical data this corresponds to approximately 120 km above the upper surface of the subducted slab.
Karymsky and Academy NaukKarymsky and Academy Nauk
Academy NaukAcademy NaukAcademy Nauk
Karymsky is a stratovolcano located in the center of a 5-km-diameter caldera, which formed ~6600 years ago as a result of caldera-forming. The active cone of Karymsky was constructed throughout the last 5100 years with a repose period between 2800 and 500 BP. It is mostly composed by andesite of relatively constant composition (59-62% SiO2). However at least twice in its history, 6100-5400 BP and 2800 BP, Karymsky produced andesitic basalt (52-56% SiO2)
Academy Nauk is located ~9 km on the South from Karymsky on the same longitudinally oriented fault. It is a 4-km-diameter caldera formed ~28,000-48,000 years ago. AN produced small volumes of basalt from eruptive centers located within caldera 5500, 4100, 950 BP and in January 1996.
KarymskyKarymskyKarymsky
Karymsky and Karymsky Lake, September 1997
1996 eruption of Karymsky1996 eruption of Karymskyand Academy Naukand Academy Nauk
• Eruptions started simultaneously
• The erupted magmas were considerably different in chemical composition
• Significant extension occurred perpendicular to the fault connecting two eruptive vents
New ventNew vent
Karymsky, view from SWAugust 1999
Academy Nauk eruptive center,view from North, July 1998
Basalt of Academy Nauk and andesite of Karymsky,Basalt of Academy Nauk and andesite of Karymsky,Comparison of mineralogy and chemistryComparison of mineralogy and chemistry
Aca
dem
y N
au
k b
asal
tK
arym
sky
and
esi
te
Ol
Pl
Pl
Pl
CPx
Pl
Basalt AndesiteOlivine 4 NoneMagnetite <0.3 1Matrix glass 59 72Orthopyroxene <0.3 1Plagioclase 30 23Clinopyroxene 6 3Total 100 100
Modal Abandances, vol. %
AcademyNauk basalt
Karymskyandesites
AcademyNauk basalt
Karymskyandesites
SiO2 52.55 62.75 Eu 0.93 1.49 Al2O3 19.21 16.50 Gd 2.75 5.08 TiO2 0.74 0.91 Tb 0.46 0.86
FeO* 7.64 5.83 Dy 2.93 5.45 MnO 0.15 0.15 Ho 0.60 1.14 CaO 10.55 5.35 Er 1.64 3.15 MgO 5.51 1.90 Tm 0.24 0.47 K2O 0.60 1.62 Yb 1.49 2.99
Na2O 2.91 4.72 Lu 0.24 0.48 P2O5 0.14 0.26 Ba 170.96 398.12Total 100 100 Th 0.58 1.61
Ni 28.50 2.46 Nb 1.38 3.24 Cr 82.50 9.00 Y 15.70 30.68
V 206.00 127.08 Hf 1.70 3.93 Zr 73.50 141.92 Ta 0.11 0.25
Cu 63.50 31.54 U 0.31 0.87La 5.40 11.49 Pb 2.63 5.88Ce 12.27 26.25 Rb 7.56 21.41Pr 1.74 3.60 Cs 0.31 0.86Nd 8.37 16.91 Sr 454.09 357.18Sm 2.51 4.86 Sc 31.86 22.71
Chemical composition of basalt and andesite
Variations of melt composition in Karymsky andesiteVariations of melt composition in Karymsky andesite
50
55
60
65
70
75
80
1/1/96 7/19/96 2/4/97 8/23/97 3/11/98
wt.
%
65
67
69
71
73
75
1/1/96 4/10/96Time
SiO
2
Glass ofAN basalt
Composition of volcanic glass from Karymsky tephra produced during 1996-1998 was studied using Cameca SX-50 electron microprobe at University of Alaska, Fairbanks
Analytical conditions:
»15 kV accelerating voltage;
»10 nA beam current;
»10 micron electron beam.
The microprobe study of volcanic glass from Karymsky volcano tephra
supported our hypothesis that the current eruption have been triggered by a
basaltic dike penetrated the crustal portion of the Karymsky magma system.
Types of Plagioclase PhenocrystsTypes of Plagioclase Phenocrysts
Academy Nauk basalt Karymsky andesite
Rimmed
Oscillatory
Analytical methodsAnalytical methods
Composition of plagioclase phenocrysts of Academy Nauk basalts and Karymsky andesites was studied by
• Electron microprobe (major elements) Cameca SX-50 at University of Alaska Fairbanks;
15 kV acceleration voltage;
10 nA beam current;
5 micron beam.
• ICP-MS (Ba and Sr) Micromass Platform ICP- HEX-MS at Michigan State University;
Cetac LSX 200 laser ablation system equipped with UV laser;
30 micron beam.
Results of analysesResults of analyses
Microprobe data ICP-MS data
0
20
40
60
80
100
120
140
160
43 49 55 61 67 73 79 85 91
An, mole %
Fre
quen
cy
KarymskyAN basalt
Examples of individual Plagioclase phenocrystsExamples of individual Plagioclase phenocrysts
Basalt of Academy Nauk
A
BC D
E
F
Sieved texture;
An80-An88;
Low Ba/Ca and Sr/Ca ratios.
Examples of individual Plagioclase phenocrystsExamples of individual Plagioclase phenocrysts
C D
Basalt of Academy Nauk
No melt inclusions in the core;
An77-An90;
Low Ba/Ca and Sr/Ca ratios.
Examples of individual Plagioclase phenocrystsExamples of individual Plagioclase phenocrysts
Karymsky andesite,oscillatory zoned phenocryst
A B
No melt inclusions;
An47-An60;
High Ba/Ca and Sr/Ca ratios.
Examples of individual Plagioclase phenocrystsExamples of individual Plagioclase phenocrysts Karymsky andesite,rimmed phenocryst
Sharp boundary between core and rim;
Rim has the same composition as oscillatory zoned plagioclases, while core has the same composition as plagioclases from Academy Nauk basalt
ConclusionConclusion
Compositional similarity of cores of plagioclase phenocrysts of Karymsky andesites to plagioclase phenocrysts of Academy Nauk basalts suggests that the cores came from the Academy Nauk basaltic source and were introduced to andesite by basalt replenishments of 1996 and/or earlier events.