Skip to Main Content
Skip Nav Destination
GEOREF RECORD

Detrital record of the early Central American magmatic arc; petrography of intraoceanic forearc sandstones, Nicoya Peninsula, Costa Rica

Neil Lundberg
Detrital record of the early Central American magmatic arc; petrography of intraoceanic forearc sandstones, Nicoya Peninsula, Costa Rica
Geological Society of America Bulletin (July 1991) 103 (7): 905-915

Abstract

The framework compositions of sand-stones from the Costa Rican forearc provide a compositional norm for detrital modes from basins associated with intraoceanic arcs, a poorly documented tectonic setting. Nicoya Peninsula sandstones are made up of mainly volcanic lithic fragments, plagioclase, sedimentary lithic fragments, and mafic accessory minerals. Modal point counts of 70 samples average Q (sub 3) F (sub 32) L (sub 65) , Qm (sub 2) F (sub 32) Lt (sub 66) , Qp (sub 1) Lvm (sub 72) Lsm (sub 27) , and Qm (sub 6) P (sub 94) K (sub 0) , defining these sand-stones as less quartzose than sandstones from most other tectonic settings and less lithic than most quartz-poor sandstones from intraplate oceanic islands.Four newly defined modal parameters quantify temporal changes in composition. These parameters are (1) Vi/V', the ratio of volcanic fragments with microlitic or felsitic textures to those with lathwork, microlitic, or felsitic textures; (2) Mh/M, the ratio of hydrous to total mafic silicate mineral grains; (3) Po/P, the ratio of oscillatory-zoned to total plagioclase grains; and (4) Sc/S, the ratio of reworked carbonate detritus to total sedimentary lithic fragments. All four parameters increase from negligible values in the basement unit to moderate or high values in cover units. These increases are followed by generally low values in the youngest (Miocene) sandstones. Significant temporal changes are not revealed by previously defined modal parameters that are commonly used to analyze sandstone composition.Petrography of these sandstones provides strong evidence for the initial construction of an andesitic arc edifice by Campanian time (Late Cretaceous). Increases in Vi/V', Mh/M, and Po/P ratios through most of the section record increased detrital input from evolved volcanic sources. A parallel increase in Sc/S ratios reflects the progressive construction and erosion of a carbonate-rich sedimentary are apron. The Miocene reversal of these trends reflects subaerial erosion of up-lifted basement rocks at the forearc structural high. Miocene sandstones also contain minor plutonic detritus that includes potassium feldspar, signaling incipient unroofing of the arc. Sandstones of the Nicoya Peninsula thus preserve a relatively complete record of the evolution and erosion of the Upper Cretaceous through Miocene intraoceanic arc of southern Central America.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 103
Serial Issue: 7
Title: Detrital record of the early Central American magmatic arc; petrography of intraoceanic forearc sandstones, Nicoya Peninsula, Costa Rica
Author(s): Lundberg, Neil
Affiliation: Princeton Univ., Dep. Geol. and Geophys. Sci., Princeton, NJ, United States
Pages: 905-915
Published: 199107
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 77
Accession Number: 1991-035929
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, sect., sketch maps
N09°30'00" - N10°15'00", W85°45'00" - W84°52'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 1991
Close Modal

or Create an Account

Close Modal
Close Modal