About NavDat

What is NavDat?

The NavDat project compiled existing age, chemical and isotopic data from Late Cretaceous to Holocene extrusive and intrusive igneous rocks of the western United States, British Columbia and northern Mexico into a web-accessible database. The goal was a comprehensive database of a continent-sized area that lets anyone look at time-space-composition patterns of magmatism and how they relate to tectonic events and geologic hazards, instead of ad hoc datasets that disappear when a project ends.

Data entry for the western United States began in 2002. The content has been static since 2014. NavDat data are also available through the EarthChem Portal.

NavDat is free for everyone. No account is needed to search, map, plot or download.

Using the site

• Search by area (box, drawn polygon, state or province, named volcanic field), age, rock type and name, chemistry ranges, data available, and reference.
• Every search is a link: bookmark or share the results page to come back to the same search.
• From the results you can open a map, make plots (TAS, Harker, any x vs y, AFM, REE, age) and download the data as CSV, tab delimited text or KML, or the references as a text file.
• The glossary lists curated named regions (Snake River Plain, Basin and Range, San Juan volcanic field, ...) that open as ready-made searches.

Database format

The NavDat structure is a modification of the relational structure of the PetDB project, adapted for samples collected on land rather than from the ocean floor. Data are attributed with metadata: reference, material analysed, analytical method and data quality.

NavDat is complementary to PetDB (oceanic igneous rocks) and GEOROC (a global igneous geochemical database).

Rock type and rock name

Each sample is named at four levels:

1. Material: the highest level, usually igneous, but also sedimentary, metamorphic, xenolith, vein, ore or alteration.
2. Rock type: for igneous rocks, volcanic or plutonic.
3. Composition: a basic chemical class (felsic, intermediate, mafic, ultramafic, exotic).
4. Rock name: the name used in the source (basalt, granite, ...).

The TAS classification offered in the search is different: it is calculated from each sample's major element analysis on the total alkali vs. silica diagram (Le Bas et al., 1986).

How ages are calculated

Sources report ages in many ways, so NavDat stores a calculated age with a calculated minimum and maximum for every sample. These were computed when data were entered, from up to six reported items (geological age, its minimum and maximum, and numeric age with its minimum and maximum):

1. Geological age only: minimum and maximum from the geological time table below, age = their average.
2. Minimum and maximum geological ages only: limits from the time table, age = their average.
3. Numeric age only: minimum and maximum = age minus and plus 10%.
4. Age and maximum: minimum = age minus (maximum minus age), not below zero.
5. Age and minimum: maximum = age plus (age minus minimum).
6. Minimum and maximum only: age = their average.

A tight age search uses the calculated age. A loose search also returns samples whose minimum to maximum range overlaps the requested range.

Normalized major elements

Downloads and plots can use major elements recalculated to 100% on a volatile-free basis with total iron as FeO (columns starting n_feo_), as Fe2O3 (n_fe2o3_), or as reported plus H2O (n_plus_). The TAS, Harker and AFM plots use the FeO-total normalization by default; untick "normalized" to plot values as reported.

For teachers and students

NavDat data can be used in undergraduate and graduate petrology and geochemistry classes. Exercises built on NavDat are at SERC: NavDat exercises and mafic rocks exercise; see also Teaching Petrology at Carleton College.