Petrology and reflectance spectroscopy of lunar meteorite Yamato 981031: Implications for the source region of the meteorite and remote-sensing spectroscopy

Combined mineralogy and reflectance spectroscopy of lunar meteorite Yamato (Y) 981031 were investigated to determine its possible source region. Mineralogical observations indicate that Y981031 is a mixture of mafic mare and feldspathic highland components. Y981031 has abundant mineral fragments and lithic clasts in a comminuted matrix. Although the most of the lithic clasts are pyroxene-dominant basaltic clasts, some plagioclase-rich lithic fragments are also present. High- and low-Ca pyroxene grains with wide compositional variations are included in the breccia. Since high-Ca pyroxene (Wo43En40Fs17 to Wo29En23Fs48) and a part of Fe-rich low-Ca pyroxene are found in pyroxene-dominant basaltic clasts, they were derived from mare materials. In contrast, abundant Mg-rich low-Ca pyroxene (approximately Wo10En63Fs27) is of highland origin because their chemical compositions resemble highland low-Ca pyroxene. Fusion crust glass compositions (TiO2=0.50-0.77wt and FeO=11.7-15.4wt) suggest that source mafic components of Y981031 have very low-Ti (VLT) affinity. In comparison with global remote-sensing data, the above TiO2 and FeO concentrations resemble those of the VLT affinity in Mare Frigoris and adjacent maria. Thus, we propose that Y981031 was launched from this area. Modified gaussian model analysis of reflectance spectrum shows absorption features of high-Ca pyroxene (mare-origin) and Mg-rich low-Ca pyroxene (highland-origin), and enables us to observe separately mineralogical characteristics of each end member of Y981031 as the soil mixture

Indian Monsoonal Variations During the Past 80 Kyr Recorded in NGHP-02 Hole 19B, Western Bay of Bengal: Implications From Chemical and Mineral Properties

金沢大学理工研究域地球社会基盤学系Detailed reconstruction of Indian summer monsoons is necessary to better understand the late Quaternary climate history of the Bay of Bengal and Indian peninsula. We established a chronostratigraphy for a sediment core from Hole 19B in the western Bay of Bengal, extending to approximately 80 kyr BP and examined major and trace element compositions and clay mineral components of the sediments. Higher δ 18 O values, lower TiO 2 contents, and weaker weathering in the sediment source area during marine isotope stages (MIS) 2 and 4 compared to MIS 1, 3, and 5 are explained by increased Indian summer monsoonal precipitation and river discharge around the western Bay of Bengal. Clay mineral and chemical components indicate a felsic sediment source, suggesting the Precambrian gneissic complex of the eastern Indian peninsula as the dominant sediment source at this site since 80 kyr. Trace element ratios (Cr/Th, Th/Sc, Th/Co, La/Cr, and Eu/Eu*) indicate increased sediment contributions from mafic rocks during MIS 2 and 4. We interpret these results as reflecting the changing influences of the eastern and western branches of the Indian summer monsoon and a greater decrease in rainfall in the eastern and northeastern parts of the Indian peninsula than in the western part during MIS 2 and 4. © 2018. American Geophysical Union. All Rights Reserved

In-situ mechanical weakness of subducting sediments beneath a plate boundary décollement in the Nankai Trough

© 2018, The Author(s). The study investigates the in-situ strength of sediments across a plate boundary décollement using drilling parameters recorded when a 1180-m-deep borehole was established during International Ocean Discovery Program (IODP) Expedition 370, Temperature-Limit of the Deep Biosphere off Muroto (T-Limit). Information of the in-situ strength of the shallow portion in/around a plate boundary fault zone is critical for understanding the development of accretionary prisms and of the décollement itself. Studies using seismic reflection surveys and scientific ocean drillings have recently revealed the existence of high pore pressure zones around frontal accretionary prisms, which may reduce the effective strength of the sediments. A direct measurement of in-situ strength by experiments, however, has not been executed due to the difficulty in estimating in-situ stress conditions. In this study, we derived a depth profile for the in-situ strength of a frontal accretionary prism across a décollement from drilling parameters using the recently established equivalent strength (EST) method. At site C0023, the toe of the accretionary prism area off Cape Muroto, Japan, the EST gradually increases with depth but undergoes a sudden change at ~ 800 mbsf, corresponding to the top of the subducting sediment. At this depth, directly below the décollement zone, the EST decreases from ~ 10 to 2 MPa, with a change in the baseline. This mechanically weak zone in the subducting sediments extends over 250 m (~ 800–1050 mbsf), corresponding to the zone where the fluid influx was discovered, and high-fluid pressure was suggested by previous seismic imaging observations. Although the origin of the fluids or absolute values of the strength remain unclear, our investigations support previous studies suggesting that elevated pore pressure beneath the décollement weakens the subducting sediments. [Figure not available: see fulltext.]