LCZO -- Geology, Regolith Survey -- Regolith weathering -- Bisley and Icacos -- (2015)

OVERVIEW

Description/Abstract

Lithologic differences give rise to the differential weatherability of the Earth’s surface and globally variable silicate weathering fluxes, which provide an important negative feedback on climate over geologic timescales. To isolate the influence of lithology on weathering rates and mechanisms, we compare two nearby catchments in the Luquillo Critical Zone Observatory in Puerto Rico, which have similar climate history, relief and vegetation, but differ in bedrock lithology. Regolith and pore water samples with depth were collected from two ridgetops and at three sites along a slope transect in the volcaniclastic Bisley catchment and compared to existing data from the granitic Río Icacos catchment. The depth variations of solid-state and pore water chemistry and quantitative mineralogy were used to calculate mass transfer (tau) and weathering solute profiles, which in turn were used to determine weathering mechanisms and to estimate weathering rates.

Regolith formed on both lithologies is highly leached of most labile elements, although Mg and K are less depleted in the granitic than in the volcaniclastic profiles, reflecting residual biotite in the granitic regolith not present in the volcaniclastics. Profiles of both lithologies that terminate at bedrock corestones are less weathered at depth, near the rock-regolith interfaces. Mg fluxes in the volcaniclastics derive primarily from dissolution of chlorite near the rock-regolith interface and from dissolution of illite and secondary phases in the upper regolith, whereas in the granitic profile, Mg and K fluxes derive from biotite dissolution. Long-term mineral dissolution rates and weathering fluxes were determined by integrating mass losses over the thickness of solid-state weathering fronts, and are therefore averages over the timescale of regolith development. Resulting long-term dissolution rates for minerals in the volcaniclastic regolith include chlorite: 8.9 × 10−14 mol m−2 s−1, illite: 2.1 × 10−14 mol m−2 s−1 and kaolinite: 4.0 × 10−14 mol m−2 s−1. Long-term weathering fluxes are several orders of magnitude lower in the granitic regolith than in the volcaniclastic, despite higher abundances of several elements in the granitic regolith. Contemporary weathering fluxes were determined from net (rain-corrected) solute profiles and thus represent rates over the residence time of water in the regolith. Contemporary weathering fluxes within the granitic regolith are similar to the long-term fluxes. In contrast, the long-term fluxes are faster than the contemporary fluxes in the volcaniclastic regolith. Contemporary fluxes in the granitic regolith are generally also slightly faster than in the volcaniclastic. The differences in weathering fluxes over space and time between these two watersheds indicate significant lithologic control of chemical weathering mechanisms and rates.

Creator/Author

Buss,Heather L.;Chapela Lara, Maria|Moore, Oliver W.|Kurtz, Andrew C.|Schulz, Marjorie S.| White, Art F.

CZOs

Luquillo

Contact

Miguel Leon, Miguel.Leon@unh.edu

Subtitle

Lithological influences on contemporary and long-term regolith weathering at the Luquillo Critical Zone Observatory

SUBJECTS

Disciplines

Geochemistry / Mineralogy|Hydrology

Topics

Geology|Regolith Survey

Subtopic

Regolith weathering

Keywords

Chemical weathering|Critical zone|Regolith|Saprolite|Soil formation

Variables

aluminium oxide|calcium oxide|ferrous oxide|potassium oxide|magnesium oxide|sodium oxide|silicon dioxide|titanium dioxide Niobium|Strontium|Zinc|Zirconium|Aluminium|Calcium|Potassium|Magnesium|Sodium|Strontium|Kaolinite|Chlorite|Quartz|Pyroxene|Amphibole|Calcite|Epidote|Prehnite|Illite|Hematite|Goethite

Variables ODM2

Aluminum|Strontium, dissolved|Zinc, dissolved|Zirconium|Calcium|Potassium, dissolved|Magnesium|Sodium, dissolved|Clay|Quartz|Amphibole|Goethite

TEMPORAL

Date Start

2015-05-01

Date End

2015-09-01

SPATIAL

Field Areas

Bisley|Rio Icacos

Location

Bisley and Icacos

North latitude

18.324044

South latitude

18.323332999999998

West longitude

-65.818056

East longitude

-65.815128

REFERENCE

Citation

Buss, H. L., M. C. Lara, O. W. Moore, A. C. Kurtz, M. S. Schulz, A. F.White (2019). LCZO- Geology, Regolith Survey, Lithological influences on contemporary and long-term regolith weathering at the Luquillo Critical Zone Observatory - Bisley and Icacos (2015-2017), HydroShare, http://www.hydroshare.org/resource/70d6eeb63e154f8197467e1f7c91f55b

Publications using this data

Buss, H.L., Lara Chapela M., Moore, O.W., Kurtz A.C., Schulz, M.S., White A.F. (2017). Lithological Influences on Contemporary and Long-Term Regolith Weathering at the Luquillo Critical Zone Observatory. Geochimica et Cosmochimica Acta http://dx.doi.org/10.1016/j.gca.2016.09.038

CZO ID

7162