Classification of quartz textures in crustal rocks derived from time

Crystallographic preferred orientation and properties of quartz: a neutron
diffraction study of Earth's crust rocks
R.N. Vasin1, A.N. Nikitin1, T.I. Ivankina1, K. Ullemeyer2
Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research,
Dubna, Russia
Institut für Geowissenschaften, Universität Kiel, Germany
Quartz is one of the most widespread minerals in the Earth’s crust. In
polycrystalline form it is a constituent of many rocks and possesses a variety of
preferred orientations. The study of those is necessary to understand the evolution
of the Earth’s lithosphere, and also provides information for interpretation of
seismic data on the Earth’s structure.
Textures (crystallographic preferred orientations) of quartz in a large
collection of rocks from various sample locations and with different composition
were studied. Measurements were performed at the SKAT diffractometer located at
channel 7A of the IBR-2 reactor at the Frank Laboratory of Neutron Physics
(Dubna, Russia). Orientation distribution functions (ODFs) were reconstructed
applying WIMV method, and characterized using texture index as well as “ODFspectra”. The {0001}, {11-20}, as well as the {10-11} {01-11} pole figures were
recalculated from the ODFs. Four types of quartz textures were derived using these
pole figures. It is shown that observed texture types are independent from location,
depth, mineral composition etc. We conclude that the texture evolution is
controlled mainly by temperature, symmetry of the stress field and the deformation
rate. Moreover, preferred orientations of some of the samples are characterized by
similar patterns of positive and negative rhombs. Our interpretation is that such
preferred orientations developed in the stability field of β-quartz, and that after
transition to the α-phase the rocks were not exposed to high tectonic stresses. Each
of the four texture types we define may be described either by a single peak
component or by a single fibre component. Hence, observed texture types allow
conclusions on the main mechanisms controlling texture formation in crustal rocks.