Sedimentation in different tectonic environments of the Middle America Trench, southern Mexico and Guatemala

Abstract

Summary Late Pleistocene to Holocene sediment facies and composition within and bordering the Middle America Trench offshore southern Mexico and Guatemala reflect two distinctly different tectonic provinces. The truncated Mexican margin with crystalline rocks onshore and a narrow shelf exhibits a locally thick sandy trench fill. Sand mineralogy of quartz, feldspar, and biotite matches the onshore source terrane. The Guatemalan margin with a volcanic terrane onshore and a wide forearc basin show smaller amounts of predominantly muddy trench fill. Sand composition of volcanic rock fragments, plagioclase, and heavy minerals accurately reflects the volcanic source. Trench fill in both areas corresponds to submarine canyon location, and extensive bypassing of the slope occurs. The outer shelf contributes little sediment to the Mexican slope and trench, the main source being in the littoral zone and inner shelf. Conversely, most Guatemalan slope and trench sand has come from the shelf. Trench fill correlates best with onshore geology, with similar slope sediments in both areas. The Mexican margin with locally thick trench fill displays clear evidence of accretion, the Guatemalan margin with meagre trench fill apparently has not accreted lower plate sediments recently. Possibly, larger volumes of trench fill encourage accretion.