QFL diagrams
Encyclopedia
A QFL diagram or QFL triangle is a type of ternary diagram
that shows compositional data from sandstones and modern sands
, point counted using the Gazzi-Dickinson method
. The abbreviations used are as follows:
In general, the most contentious item counted is chert
, which is usually counted as a lithic fragment, but is sometimes better suited in the Q pole. When this happens, the pole is renamed 'Qt' instead of Q.
The importance of a QFL triangle is mainly demonstrated in tectonic exercises. As first demonstrated in the 1979 paper by Bill Dickinson and Chris Suczek, the composition and provenance
of a sandstone is directly related to its tectonic environment of formation.
Ternary plot
A ternary plot, ternary graph, triangle plot, simplex plot, or de Finetti diagram is a barycentric plot on three variables which sum to a constant. It graphically depicts the ratios of the three variables as positions in an equilateral triangle...
that shows compositional data from sandstones and modern sands
Sands
-Buildings:*Sands Casino Resort Bethlehem, a newly-opened casino resort in Bethlehem, Pennsylvania*Sands Hotel, a closed hotel/casino in Las Vegas, Nevada**Sands Atlantic City, a closed hotel/casino in Atlantic City, New Jersey...
, point counted using the Gazzi-Dickinson method
Gazzi-Dickinson Method
The Gazzi-Dickinson method is a point-counting technique used in geology to statistically measure the components of a sedimentary rock, chiefly sandstone. The main focus part of the technique is counting all sand-sized components as separate grains, regardless of what they are connected to...
. The abbreviations used are as follows:
- Q - quartzQuartzQuartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
- F - feldsparFeldsparFeldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
- L - lithic fragmentsLithic fragment (geology)Lithic fragments, or lithics, are pieces of other rocks that have been eroded down to sand size and now are sand grains in a sedimentary rock. They were first described and named by Bill Dickinson in 1970. Lithic fragments can be derived from sedimentary, igneous or metamorphic rocks)...
In general, the most contentious item counted is chert
Chert
Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...
, which is usually counted as a lithic fragment, but is sometimes better suited in the Q pole. When this happens, the pole is renamed 'Qt' instead of Q.
The importance of a QFL triangle is mainly demonstrated in tectonic exercises. As first demonstrated in the 1979 paper by Bill Dickinson and Chris Suczek, the composition and provenance
Provenance
Provenance, from the French provenir, "to come from", refers to the chronology of the ownership or location of an historical object. The term was originally mostly used for works of art, but is now used in similar senses in a wide range of fields, including science and computing...
of a sandstone is directly related to its tectonic environment of formation.
- CratonCratonA craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...
sands are clustered near the Q pole. As sandstones, these are known as quartz arenites.
- Transitional continental sands are along the QF line. As sandstones, these are known as arkoseArkoseArkose is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose....
s.
- Basement upliftTectonic upliftTectonic uplift is a geological process most often caused by plate tectonics which increases elevation. The opposite of uplift is subsidence, which results in a decrease in elevation. Uplift may be orogenic or isostatic.-Orogenic uplift:...
sands are near the F pole. This includes "thick-skinned tectonics." As sandstones, these are known as arkoseArkoseArkose is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose....
s.
- Recycled orogen sands plot near the Q pole, but with significant F and L components. This includes "thin-skinned tectonics" common in subduction back-arc thrusting. As sandstones, these are known as lithic sandstoneLithic sandstoneLithic sandstones, or lithic arenites, or litharenites, are sandstones with a significant component of lithic fragments, though quartz and feldspar are usually present as well, along with some clayey matrix...
s.
- ArcVolcanic arcA volcanic arc is a chain of volcanoes positioned in an arc shape as seen from above. Offshore volcanoes form islands, resulting in a volcanic island arc. Generally they result from the subduction of an oceanic tectonic plate under another tectonic plate, and often parallel an oceanic trench...
sands plot along the F and L line, with sometimes significant Q components. Clustering near the F pole indicates a dissected arc, and clustering near the L pole indicates an undissected, or new arc. As sandstones, these are known as arkoseArkoseArkose is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose....
s and/or lithic sandstoneLithic sandstoneLithic sandstones, or lithic arenites, or litharenites, are sandstones with a significant component of lithic fragments, though quartz and feldspar are usually present as well, along with some clayey matrix...
s.