Mathematics – Logic
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28r.383k&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 383
Mathematics
Logic
Breccia, Polymict, Impact Craters, Impact Melting
Scientific paper
Although the Manson impact structure (35 km in diameter) in Iowa is of general interest because its age coincides with the end of the Cretaceous Period [1,2], it also provides an opportunity to study systematically the effects of a single, moderate-sized impact in a setting where the preimpact geology is reasonably well understood. We are interested in the extent of compositional uniformity in melt produced in large impacts and the causes of any compositional variation among different small samples of crystalline melt breccia. This understanding is useful for interpretation of data from lunar impact-melt breccias, for which we have less geologic control. We have obtained concentrations of ~30 elements in samples from the M-1 core taken on the flank of the central peak of the Manson impact structure in Iowa [3-6]. The sample set consists of 49 representative samples of breccia matrix determined (by visual inspection) to contain minimal mineralized vugs, fractures, or large or altered clasts [5]. The core consists of three principal units [3]: sedimentary clast breccia (SCB), 54-106-m depth; crystalline clast breccia, melt matrix (CCB-M), 106- 147-m depth; and crystalline clast breccia, sandy matrix (CCB-S), 163-214-m depth; there is an ~16-m "transition zone" between CCB-M and CCB-S. The sandy- matrix breccias, which are believed to be "in-situ brecciated basement with injected melt and shale fragments" [4], may be the equivalent of lunar "fragmental breccias" [e.g., 7]. They contain large clasts, some bigger than the core diameter, and, consequently, are variable in composition at the sample mass studied here (1-4 g). Samples of the overlying melt-matrix breccias (CCB-M) are more uniform in composition. However, the concentrations of some elements (Na, Ca, Sc, Cr, Fe, and Co) generally increase with depth through CCB-M (unit 1 of [4]), while other elements decrease (K, Sb, Cs, La, Hf, and Ta). These trends continue through the transition zone to the CCB-S. Thus, the CCB-M is not a simple melt of the underlying CCB-S. The lithologic components of the two breccias may be the same, but if so, their proportions must differ. CCB-M is enriched relative to CCB-S in one or more lithologies with high K and heavy REE and low Na, Sc, Cr, and Fe. Among target lithologies studied by [8], that designated as MA-11 ("Unit E," upper red clastics) is a likely candidate. The systematic compositional variations with depth in the CCB-M unit may be related in part to the increasing abundance of clasts with depth [4]. For some elements there is a distinct "break" in slope of the profiles between the bottom of CCB-M and the top of the transition zone. This is consistent with the suggestion that CCB-M consists of "transported" basement materials and that the transition zone is a mixing zone [4]. Similarly, for most elements (most notably Na, K, Ca, Sc, As, Sb) there is a major discontinuity in the profiles between the top of the CCB-M and the overlying SCB. This is consistent with the interpretation of SCB as a debris flow [3] and that Paleozoic and younger sediments are a minor component of the melt [1]. References: [1] Anderson R. R. and Hartung J. B. (1992) Proc. LPS, Vol. 22, 101-110. [2] Kunk M. J. et al. (1993) LPS XXIV, 835-836. [3] Anderson R. R. et al. (1993) LPS XXIV, 35-36. [4] Bell M. S. et al. (1993) LPS XXIV, 87-88. [5] Crossey L. J. and McCarville P. (1993) LPS XXIV, 351-352. [6] Koeberl C. et al. (1993) LPS XXIV, 811-812. [7] Stoffler D. et al. (1980) Proc. Conf. Lunar Highlands Crust (J. J. Papike and R. B. Merrill, eds.), 51-70, LPI, Houston. [8] Koeberl C. and Hartung J. B. (1992) Proc. LPS, Vol. 22, 111-126.
Crossey Laura J.
Haskin Larry A.
Jolliff Brad L.
Korotev Randy L.
Rockow Kaylynn M.
No associations
LandOfFree
A Preliminary Geochemical Study of Crystalline Melt from the Manson Impact Structure does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with A Preliminary Geochemical Study of Crystalline Melt from the Manson Impact Structure, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A Preliminary Geochemical Study of Crystalline Melt from the Manson Impact Structure will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1073033