AVO Logo
Site Map | FAQ |
Alaska Volcano Observatory
 
You are here: Home > Samples > 54-D-27

SAMPLE INFO : 54-D-27
Sample ID:54-D-27
Station ID:54-D-27
Latitude:53.88707
Longitude:-166.93202
Datum:NAD83
Date Sampled:1954-01-01
Sample Type 1:Lava
Sample Type 2:Sill
Field Lithology:Gabbro
Text Description:
Gabbro from the sea cliff 3 miles north-northeast of the southern tip of Cape Aiak. The texture is porphyritic and hypidiomorphic, and the mafic minerals are locally aggregated. Felsic minerals range in abundance from 50 to 70 percent, of which about 1 percent is orthoclase and the rest is plagioclase replaced by 10-15 percent albite and minor sericite. The unaltered plagioclase composition, by extinction angle, is An78 [mean of 26 crystals, standard deviation is 11 percent An, average amount of zoning per individual plagioclase crystal is 3 percent An per crystal] ; by index oils, is An68. Mafic minerals make up 30-50 percent, of which 25-30 percent is stubby euhedral phenocrysts of clinopyroxene, 2-3 percent clinopyroxene or uralite needles (length-to-width ratio is 20:1) grown on the margins of the large pyroxenes rather than altered from them, 0-1 percent biotite(?) now completely altered to antigorite, 8-10 percent magnetite, <1 percent is apatite, and <1 percent serpentine. Discrepancy in plagioclase compositions (above) is probably due to two causes. (1) Low temperature curves were used; using the same angles, high temperature curves give average plagioclase as An67. (2) Alteration to albite lowers normative plagioclase. Presence of 7.10 percent olivine and 0.85 percent nepheline in the norm is unexplained, but other specimens from the Cape Aiak sill contain abundant zeolites through out the groundmass, and if the analyzed sample contained a pocket of these the total rock might be undersaturated in silica.

References:
Geology of Unalaska Island and adjacent insular shelf, Aleutian Islands, Alaska

GEOCHEM DATA
StationIDLatitudeLongitudeGeologistDateVisitedAge InfoVolcanoEruptionLocation DescriptionText DescriptionSample IDMaterialSiO2TiO2Al2O3FeOTMnOMgOCaONa2OK2OP2O5Total-majorsREF majorsMETH majorsFe2O3/Fe203T origFeO/FeOT origVolatiles csvMETH volatilesCsRbBaSrLaCePrNdSmEuGdTbDyHoErTmYbLuYZrNbHfTaPbThUScVCrFeCoNiCuZnGaMoAsNaKRef trace1METH trace1RbBaSrLaCeNdSmEuGdDyErYbLuYZrNbPbThUScTiVCrNiCuZnGaRef trace2METH trace2Light csvHalogen csvother major csvother lile csvother ree csvother hfse csvother hpe csvother tm csvother misc csv
54-D-2753.88707-166.93202Drewes, Harald1954-01-01 MakushinSmall gabbroic intrusive from 3 mi NE of Cape AiakGabbro from the sea cliff 3 miles north-northeast of the southern tip of Cape Aiak. The texture is porphyritic and hypidiomorphic, and the mafic minerals are locally aggregated. Felsic minerals range in abundance from 50 to 70 percent, of which about 1 percent is orthoclase and the rest is plagioclase replaced by 10-15 percent albite and minor sericite. The unaltered plagioclase composition, by extinction angle, is An78 [mean of 26 crystals, standard deviation is 11 percent An, average amount of zoning per individual plagioclase crystal is 3 percent An per crystal] ; by index oils, is An68. Mafic minerals make up 30-50 percent, of which 25-30 percent is stubby euhedral phenocrysts of clinopyroxene, 2-3 percent clinopyroxene or uralite needles (length-to-width ratio is 20:1) grown on the margins of the large pyroxenes rather than altered from them, 0-1 percent biotite(?) now completely altered to antigorite, 8-10 percent magnetite, <1 percent is apatite, and <1 percent serpentine. Discrepancy in plagioclase compositions (above) is probably due to two causes. (1) Low temperature curves were used; using the same angles, high temperature curves give average plagioclase as An67. (2) Alteration to albite lowers normative plagioclase. Presence of 7.10 percent olivine and 0.85 percent nepheline in the norm is unexplained, but other specimens from the Cape Aiak sill contain abundant zeolites through out the groundmass, and if the analyzed sample contained a pocket of these the total rock might be undersaturated in silica.54-D-27Whole Rock 47.7 1.1 17.2 10.8 0.14 4.9 10.9 3.4 0.72 0.23Total not given in table. 100.32315RAPIDA4.36.9H2OM=0.12; H2OP=2.7; CO2=0.05RAPIDAB V=0.005, M=NN, R=315;S V=0.01, M=RAPIDA, R=315;Ba V=0.006, M=NN, R=315;Sr V=0.1, M=NN, R=315;Yb V=0, M=NN, R=315;Y V=0, M=NN, R=315;Zr V=0.004, M=NN, R=315;Pb V=0.002, M=NN, R=315;Co V=0.004, M=NN, R=315;Cr V=0.002, M=NN, R=315;Cu V=0.02, M=NN, R=315;Ga V=0, M=NN, R=315;Mo V=0, M=NN, R=315;Ni V=0.002, M=NN, R=315;Sc V=0.004, M=NN, R=315;V V=0.04, M=NN, R=315;

SAMPLE LOCATION

Contact AVO Privacy Accessibility Information Quality FOIA
URL: www.avo.alaska.edu/samples/sample_info.php
Page modified: July 14, 2014 13:37
Contact Information: AVO Web Team

twitter @alaska_avo
facebook alaska.avo
email Receive volcano updates by email: USGS VNS