Mid-Pleistocene Acheulean-like Stone Technology of the Bose Basin, South China

available online at http://meteoritics.org Micro-Raman spectroscopic study of fine-grained, shock-metamorphosed rock fragments from the Australasian microtektite layer Abstract-Shock-metamorphosed rock fragments have been found in the Australasian microtektite layer from the South China Sea. Previous X-ray diffraction (XRD) studies indicate that the most abundant crystalline phases in the rock fragments are coesite, quartz, and a 10 Å phase (mica/clay?).In addition, the presence of numerous other phases was suggested by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis. In the present research, ten of the rock fragments, which had previously been studied using SEM/EDX, were studied by micro-Raman spectroscopy. The presence of K-feldspar, plagioclase, rutile, ilmenite, titanite, magnetite, calcite, and dolomite were confirmed. In addition, the high-pressure TiO 2 polymorph with an α-PbO 2 structure (i.e., TiO 2 II) was found in several rock fragments. Two grains previously thought to have been zircon, based on their compositions, were found to have Raman spectra that do not match the Raman spectra of zircon, reidite, or any of the possible decomposition products of zircon or their high-pressure polymorphs. We speculate that the ZrSiO 4 phase might be a previously unknown high-pressure polymorph of zircon or one of its decomposition products (i.e., ZrO 2 or SiO 2 ). The presence of coesite and TiO 2 II, and partial melting and vesiculation suggest that the rock fragments containing the unknown ZrSiO 4 phase must have experienced shock pressures between 45 and 60 GPa. We conclude that micro-Raman spectroscopy, in combination with XRD and SEM/EDX, is a powerful tool for the study of small, fine-grained impact ejecta.

Section: Introductionmentioning

confidence: 99%

Micro‐Raman spectroscopic study of fine‐grained, shock‐metamorphosed rock fragments from the Australasian microtektite layer

Glass

Fries

2008

“…1). Darwin Glass and Australasian tektites have been dated repeatedly using K-Ar and fission track techniques, which yielded a broadly coincident though large range of ages from 720 to 803 ka (Gentner et al, 1969(Gentner et al, , 1973Storzer and Wagner, 1980a,b;Izett and Obradovich, 1992;Kunz et al, 1995;Yamei et al, 2000). This coincidence along with the geographic association led some workers (Fleischer and Price, 1964;Gentner et al, 1969;Storzer and Wagner, 1980a,b) to propose that Darwin Glass and Australasian tektites are genetically related despite the fact that the Darwin Glass has distinct textural, geochemical and oxygen isotopic features from Australasian tektites (Taylor and Solomon, 1964;Taylor and Epstein, 1969;Meisel et al, 1990).…”

Section: Introductionmentioning

confidence: 99%

Laser fusion argon‐40/argon‐39 ages of Darwin impact glass

Howard

Chung

et al. 2002

Abstract-Three samples of Darwin Glass, an impact glass found in Tasmania, Australia at the edge of the Australasian tektite strewn field were dated using the 40Ar/ 39 Ar single-grain laser fusion technique, yielding isochron ages of 796-815 ka with an overall weighted mean of 816 ± 7 ka. These data are statistically indistinguishable from those recently reported for the Australasian tektites from Southeast Asia and Australia (761-816 ka; with a mean weighted age of803 ± 3 ka). However, considering the compositional and textural differences and the disparity from the presumed impact crater area for Australasian tektites, Darwin Glass is more likely to have resulted from a distinct impact during the same period of time.

“…Recent dating of Australasian tektites indicates an age of 803 ± 3 ka for the Australasian tektite event (e.g., Yamei et al 2000). A similar age is obtained for the Australasian microtektite layer based on an age of 789 ± 2.8 ka for the Brunhes/Matuyama (B/M) reversal boundary (SarnaWojcicki et al 2000) and an age difference of ∼14 ka between the Australasian microtektite layer and the B/M reversal boundary, with the Australasian microtektite layer being older (Burns 1989;Schneider et al 1992;Lee and Wei 2000).…”

Section: The Middle Pleistocene Toba Supereruptionmentioning

confidence: 99%

“…These tektites were formed ∼0.8 Ma ago based on 40 Ar/ 39 Ar dating (Izett and Obradovich 1992;Kunz et al 1995;Yamei et al 2000). Geochemical studies suggest that the source rock was a sedimentary deposit or rock, such as a graywacke (e.g., Taylor and Kaye 1969).…”

Section: Introductionmentioning

confidence: 99%

Australasian microtektites and associated impact ejecta in the South China Sea and the Middle Pleistocene supereruption of Toba

Glass

Koeberl

2006

113

Abstract-Australasian microtektites were discovered in Ocean Drilling Program (ODP) Hole 1143A in the central part of the South China Sea. Unmelted ejecta were found associated with the microtektites at this site and with Australasian microtektites in Core SO95-17957-2 and ODP Hole 1144A from the central and northern part of the South China Sea, respectively. A few opaque, irregular, rounded, partly melted particles containing highly fractured mineral inclusions (generally quartz and some K feldspar) and some partially melted mineral grains, in a glassy matrix were also found in the microtektite layer. The unmelted ejecta at all three sites include abundant white, opaque grains consisting of mixtures of quartz, coesite, and stishovite, and abundant rock fragments which also contain coesite and, rarely, stishovite. This is the first time that shock-metamorphosed rock fragments have been found in the Australasian microtektite layer. The rock fragments have major and trace element contents similar to the Australasian microtektites and tektites, except for higher volatile element contents. Assuming that the Australasian tektites and microtektites were formed from the same target material as the rock fragments, the parent material for the Australasian tektites and microtektites appears to have been a fine-grained sedimentary deposit. Hole 1144A has the highest abundance of microtektites (number/cm 2 ) of any known Australasian microtektite-bearing site and may be closer to the source crater than any previously identified Australasian microtektite-bearing site. A source crater in the vicinity of 22° N and 104° E seems to explain geographic variations in abundance of both the microtektites and the unmelted ejecta the best; however, a region extending NW into southern China and SE into the Gulf of Tonkin explains the geographic variation in abundance of microtektites and unmelted ejecta almost as well. The size of the source crater is estimated to be 43 ± 9 km based on estimated thickness of the ejecta layer at each site and distance from the proposed source. A volcanic ash layer occurs just above the Australasian microtektite layer, which some authors suggest is from a supereruption of the Toba caldera complex. We estimate that deposition of the ash occurred ∼800 ka ago and that it is spread over an area of at least 3.7 × 10 7 km 2 .