Emplacement processes of tuffaceous sandstones at IODP Site C0011B, Nankai Trough, derived from modal analysis

Author(s): Schindlbeck, Julie C.; Kutterolf, Steffen; Freundt, A.
Author Affiliation(s): Primary:
IFM-GEOMAR, Kiel, Germany
Volume Title: AGU 2011 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2011; American Geophysical Union 2011 fall meeting, San Francisco, CA, Dec. 5-9, 2011. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Tuffaceous sandstones are characterized by their high amount (25 to 75%) of pyroclasts in their modal composition. During IODP Expedition 322 three interbeds of tuffaceous sandstones have been found within a moderately lithified and bioturbated silty claystone sequence in the late Miocene (>7.07 to ∼9.0 Ma) upper part of the middle Shikoku Basin facies. Of the three sandstones, units 1 and 2 are single beds whereas unit 3 is composed of three beds. Modal analyses of 29 sandstone thin sections reveal systematic vertical changes within each bed. Generally low-density pyroclasts are enriched at the top (50-60 vol%) of each sandstone bed whereas dense lithic components (25-30 vol%) and minerals (25-30 vol%) are enriched at the bottom. The vertically varying abundance of various types of lithic fragments (sedimentary, volcanoclastic and metamorphic) suggests that these have also been segregated according to their respective densities. The highest amount of fine-grained matrix glass is found in the middle of each bed. Pumice and lithic fragments in the middle and upper parts of the sandstone beds carry ash coatings. For sandstone package 3, in contrast to 1 and 2, core pictures and thin section analyses indicate a subdivision in three units showing the same significant variations in top to bottom enrichment. This suggests three sedimentation events following each other in short time intervals. Glass and mineral chemistry of each sandstone bed show no significant vertical variations. Specifically the matrix glass-shard major element compositions are identical to the pumice clast composition in each tuffaceous sandstone bed. The compositions of amphibole and pyroxene crystals differ only slightly between the sandstone packages. Application of the Ridolfi et al. (2009) thermobarometric calculations to amphiboles of sandstone packages 1 and 2 suggests that each of these was derived from a volcanic system comprising both a deep and a shallow magma reservoir. Thickness and massive density-graded structure, and characteristic glass composition of each sandstone bed as well as as their occurrence ∼ 350 km from mainland Japan, the most likely source region, support emplacement by huge turbidity currents directly derived from major explosive volcanic eruptions, probably involving massive entrance of pyroclastic flows into the ocean. Reference: Ridolfi, F., Renzulli, A., Puerini, M. (2009) Stability and chemical equilibrium of amphibole in calc-alkaline magmas: an overview, new thermobarometric formulations and application to subduction-related volcanoes. Contrib. Mineral Petrol., DOI 10.1007/s00410-009-0465-7
Year of Publication: 2011
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 05 Petrology, Igneous and Metamorphic; Amphibole group; Chain silicates; Chemical composition; Clastic rocks; Emplacement; Geologic barometry; Geologic thermometry; IODP Site C0011; Igneous rocks; Integrated Ocean Drilling Program; Magmas; Mineral composition; Modal analysis; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Ocean floors; Pacific Ocean; Pyroclastics; Sandstone; Sedimentary rocks; Shikoku Basin; Silicates; Tuff; Volcanic rocks; West Pacific
Coordinates: N324944 N324945 E1365256 E1365254
Record ID: 2014095246
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