Transcript Provenance Analysis

Provenance Analysis
Provenance: the lithological (and chemical, isotopic, age) characteristics of
the source region for a sedimentary rock
Composition of sediments (mostly sandstones) can tell you about the location,
tectonic setting, climate, etc. of the source area and the transport mechanism
and pathway
Mechanical weathering
No changes to mineralogical composition
of sediment produced from rock
Chemical weathering
Mineralogical composition of sediment
differs from parent rock
Chemical weathering dominates in warm, wet climates
Mineral stability during weathering follows Bowen’s reaction series
Compositional Maturity: degree to which sediment contains only resistant
grains (quartz and stable heavy minerals like magnetite, apatite, rutile, zircon)
Textural Maturity: based on presence of clay, sorting, and rounding
More transport leads to greater textural maturity
Rock particles can indicate the tectonic setting of the source
QFL diagram plots relative
percentages of quartz,
feldspar, and lithics
If chert or quartzite are abundant,
treat them as lithics and plot
monocrystalline quartz (Qm)
Other ternary plots (QpLvmLsm and LmLvLs) subdivide and plot just the lithic
components for discrimination of tectonic settings
Qp = polycrystalline quartz (chert, quartzite)
Lm = metamorphic lithics
Lvm = volcanic and metavolcanic lithics
Lv = volcanic lithics
Lsm = sedimentary and metased lithics
Ls = sedimentary lithics
Sm/Nd isotopes
Negative εNd values found in continental crust (Nd system has been separated
from Sm “enriched” mantle for long time)
Positive εNd values are commonly found in mantle derived melts
Strontium isotopes (87Sr/86Sr)
Rubidium (87Rb) strongly partitions into
continental magmas and decays to 87Sr
Continental crust is enriched in 87Sr/86Sr
Primitive mantle and magma have low 87Sr/86Sr
Ratio tracks continental influence on source
rocks
Detrital zircon U-Pb
Single-crystal age dates give
age of rocks in source region