Tectonic Summary of Leg 18

Sediment Accumulation Rates of the Lesser Antilles Intraoceanic Island Arc, Deep Sea Drilling Project Leg 78A

“…Detailed sediment accumulation rate calculations have not been routinely made for DSDP active margin sites, with the exception of Leg 66 sites in the Middle American convergent margin off central Mexico (Shephard and McMillen, 1982). The maximum accumulation rates of the Pliocene and Quaternary deposits in lower slope Sites 541 and 542 are at the lower end of the range of values observed at other convergent margin lower slope settings (von Huene and Kulm, 1973;Arthur et al, 1980;von Huene, Aubouin, et al, 1980;Moore, Watkins, et al, 1981;Shephard and McMillen, 1982). This observation reflects the intraoceanic setting of the Lesser Antilles arc, where little terrigenous material is contributed to the Leg 78A area.…”

The Hf–Nd isotopic composition of marine sediments

“…Here we simplify the section, with three main units, from top to bottom: (1) a thick ($275 m.) sequence of diatomaceous silty clay with erratics and ash beds; (2) a thick ($450 m.) sequence of silty clay with sand and silt turbidite beds; and (3) a thin ($50 m) sequence of varicolored claystone interbedded with chalk. This section rests on a basement consisting of olivine basalt with an estimated age of anomaly 20, or 45 Ma (von Heune and Kulm, 1973). Sediment ages assume constant sedimentation rate between tie points at 208, 400, 507, 688, 689, 750 and 769 mbsf (with ages as given in Table 1, based on information in DSDP 178 initial report, von Huene and Kulm, 1973, pp.…”

“…1). The sedimentary section (von Heune and Kulm, 1973) is approximately 780 m thick and broken into 13 different units in the initial reports. Here we simplify the section, with three main units, from top to bottom: (1) a thick ($275 m.) sequence of diatomaceous silty clay with erratics and ash beds; (2) a thick ($450 m.) sequence of silty clay with sand and silt turbidite beds; and (3) a thin ($50 m) sequence of varicolored claystone interbedded with chalk.…”

“…1). The sedimentary section (von Heune and Kulm, 1973) is approximately 900 meters thick and consists of two units separated by a seismic discontinuity. From top to bottom, these include: (1) a thick ($285 m.) sequence of turbidites, with predominantly sandy bases grading upward to silts and silty clays; and (2) a thick ($600 m.) sequence of turbidites, consisting of thin-bedded, fissile clays with graded basal silts.…”

Geology of the Willamette Pass area, Cascade Range, Oregon

“…Other northwesterly faults and shears appear to be minor features principally related to nearby volcanic vents respect to the original depositional environment (e.g., Byrne and others, 1966;von Huene and Kulm, 1973), 4) the heat flow patterns of Western Oregon and Washington are typical of volcanic arcs (Blackwell and others, 1982 (Thirukaval and others, 1970;Couch and others, 1982a). The continental crust is a similar or slightly thinner thickness to the east (Thirukaval and others, 1970;Couch and others, 1982a).…”