Titanium in Quartz: A Case Study of Sediment Provenance, South Island, New Zealand

Quartz is an essential constituent of siliciclastic sediment that has a wide variety of potential primary and recycled sources. Recent experimental calibrations [1, 2] have shown that titanium (Ti) substitution into quartz is proportional to temperature, pressure, and a(TiO2). We have explored the use of Ti and other trace elements in detrital quartz as a “fingerprint” of sediment provenance in modern rivers and ancient basins of the South Island of New Zealand.

Measurements of low levels of Ti and other trace elements in quartz are done routinely by LA-ICP-MS on grain separates and polished thin sections. Raw intensity data are normalized via analyses of the NIST 610 glass standard to obtain trace element concentrations.

Detrital quartz in Permian-Jurassic greywacke sandstones exhibit uniformly high Ti concentrations that reflect plutonic sources. Regional metamorphism of these rocks has resulted in heterogenous re-equilibration at lowest grade and systematic increases in quartz Ti concentations that accompany recrystallization from medium- to high-grade. The latter provide metamorphic P-T estimates that agree with previous thermobarometry [3].

Quartz in bedload sediment from modern rivers that drain these metasedimentary rocks in the Southern Alps has Ti concentrations that correlate with metamorphic grade of upstream bedrock. Some samples exhibit smooth variation of quartz Ti concentrations with grain size that indicate hydrodynamic fractionation of sediment from heterogeneous sources.

Titanium concentrations in detrital quartz from Cretaceous-Neogene siliciclastic deposits exhibit distinct shifts with age and location. Cretaceous sandstones and conglomerates contain quartz with Ti concentrations that are consistent with derivation from local igneous and metamorphic bedrock. Paleogene sandstones have quartz with higher Ti concentrations that require derivation from distal granitic or greywacke sources during marine transgression. Neogene samples contain quartz with a bimodal distribution of quartz having high and low Ti concentrations that probably reflect reworking of underlying deposits during marine regression.

Taken together, these results demonstrate Ti-in-quartz to be a powerful tool in accessing the provenance of siliciclastic sediment.

[1] Wark & Watson (2006) Contrib. Min. Petrol. 152, 743-754. [2] Thomas et al.
(2010) Contrib. Min. Petrol. 160, 743-759. [3] Mortimer (2001) Int. J. Earth Sci. 89:295-306.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California