< Back to previous page
Publication
El'gygytgyn impact crater's fireball layer: spherules, impact melts, meteoritic component.
Book Contribution - Book Chapter Conference Contribution
Introduction: The 18 km Ø El'gygytgyn impact crater in
NE Siberia formed 3.6 Ma ago in a target of 83.2 to 89.3 Ma old,
~620 m thick, rhyolitic, andesitic, and dacitic volcanics [1,2]. An
International Continental Drilling Program (ICDP) project recovered
drill cores from an inner-crater continuous section of impactite
deposits that contain scarce, pristine impact melt particles
and glass spherules [3,4]. These deposits allow studying the mixing
of target rock components and the meteoritic projectile.
Samples and methods: Three glassy impact melt rocks that
were collected near the W' rim of the crater and 17 samples from
the ICDP-Lake Drilling Hole D1 were investigated. Powdered
bulk samples were characterized for major and trace element
abundances, including the platinum group elements (PGE), using
ICP-OES and ICP-MS. The compositions of 3 glassy impact
melt rocks, 11 ~mm-size glassy melt particles, and 7 glass spherules
in suevitic rocks of the upper ~10 m of impactite drill core
were determined with electron microprobe X-ray analysis.
Results: Major and trace element concentrations for bulk
rock samples are in good agreement with previously published
data [3,5] and indicate a moderately homogeneous rhyo-dacitic
drill core. A single sample at 391.6 m has a basaltictrachyandesitic
composition and higher than normal concentrations
of Ti, Fe, Mn, Mg, Ca, Sc, V, Cr, Co, Ni and Zn. Although
major and trace elements show typical crustal values and ratios
(e.g., subchondritic Ni/Cr of ~0.30-0.60), PGE abundances revealed
the presence of a meteoritic component (~0.05 wt%) in
three samples. The 11 glassy melt particles and the 3 glassy melt
rocks have rhyolitic compositions. In contrast, 6 spherules range
in composition from rhyolitic, dacitic, trachytic, and andesitic.
Discussion: Scaling laws suggest the depth of the melt zone
at El'gygytgyn was 1.5 to 2.6 km [6]. Nonetheless, the compositions
of glassy melt particles and impact melt rocks indicate
melt-mixtures solely derived from the ~620 m thick volcanic
succession of rhyolites, dacites and andesites [5]. In contrast, 5
of the 6 spherules record contribution from a mafic target component
[7] that is known from regional outcrops and clasts in the
ICDP drill core [3,4]. Thus, the impact melts in suevite deposits
appear homogenized but the spherules that presumably condensed
from the vapor plume record heterogeneities of an extended
target section. A diluted projectile component was detected
in a spherule-bearing drill core sample and two melt rock
samples.
References: [1] Gurov et al. (2007) MAPS 42, 307-319. [2]
Gurov & Gurova (1991) Geological structure and rock composition
of impact structures, Naukova Dumka Press, Kiev, 160 p.
[3] Raschke et al. 2011 LPSC XLII, abstract 1299. [4] Wittmann
et al. (2011) LPSC XLII, abstract # 2792. [5] Gurov et al. (2005)
GSA Spec. Pap. 384, 391-412. [6] Grieve & Cintala (1992) Meteoritics
27, 526-538. [7] Adolph & Deutsch (2009) LPSC XL,
abstract #1116.
NE Siberia formed 3.6 Ma ago in a target of 83.2 to 89.3 Ma old,
~620 m thick, rhyolitic, andesitic, and dacitic volcanics [1,2]. An
International Continental Drilling Program (ICDP) project recovered
drill cores from an inner-crater continuous section of impactite
deposits that contain scarce, pristine impact melt particles
and glass spherules [3,4]. These deposits allow studying the mixing
of target rock components and the meteoritic projectile.
Samples and methods: Three glassy impact melt rocks that
were collected near the W' rim of the crater and 17 samples from
the ICDP-Lake Drilling Hole D1 were investigated. Powdered
bulk samples were characterized for major and trace element
abundances, including the platinum group elements (PGE), using
ICP-OES and ICP-MS. The compositions of 3 glassy impact
melt rocks, 11 ~mm-size glassy melt particles, and 7 glass spherules
in suevitic rocks of the upper ~10 m of impactite drill core
were determined with electron microprobe X-ray analysis.
Results: Major and trace element concentrations for bulk
rock samples are in good agreement with previously published
data [3,5] and indicate a moderately homogeneous rhyo-dacitic
drill core. A single sample at 391.6 m has a basaltictrachyandesitic
composition and higher than normal concentrations
of Ti, Fe, Mn, Mg, Ca, Sc, V, Cr, Co, Ni and Zn. Although
major and trace elements show typical crustal values and ratios
(e.g., subchondritic Ni/Cr of ~0.30-0.60), PGE abundances revealed
the presence of a meteoritic component (~0.05 wt%) in
three samples. The 11 glassy melt particles and the 3 glassy melt
rocks have rhyolitic compositions. In contrast, 6 spherules range
in composition from rhyolitic, dacitic, trachytic, and andesitic.
Discussion: Scaling laws suggest the depth of the melt zone
at El'gygytgyn was 1.5 to 2.6 km [6]. Nonetheless, the compositions
of glassy melt particles and impact melt rocks indicate
melt-mixtures solely derived from the ~620 m thick volcanic
succession of rhyolites, dacites and andesites [5]. In contrast, 5
of the 6 spherules record contribution from a mafic target component
[7] that is known from regional outcrops and clasts in the
ICDP drill core [3,4]. Thus, the impact melts in suevite deposits
appear homogenized but the spherules that presumably condensed
from the vapor plume record heterogeneities of an extended
target section. A diluted projectile component was detected
in a spherule-bearing drill core sample and two melt rock
samples.
References: [1] Gurov et al. (2007) MAPS 42, 307-319. [2]
Gurov & Gurova (1991) Geological structure and rock composition
of impact structures, Naukova Dumka Press, Kiev, 160 p.
[3] Raschke et al. 2011 LPSC XLII, abstract 1299. [4] Wittmann
et al. (2011) LPSC XLII, abstract # 2792. [5] Gurov et al. (2005)
GSA Spec. Pap. 384, 391-412. [6] Grieve & Cintala (1992) Meteoritics
27, 526-538. [7] Adolph & Deutsch (2009) LPSC XL,
abstract #1116.
Book: 74th Annual Meteoritical Society Meeting. Abstract 5338.
Series: 74th Annual Meteoritical Society Meeting. Abstract 5338.
Volume: 74
Publication year:2011
Keywords:impact crater