Two groups of olivine LPO were distinguished in the
ultramafic xenoliths of Lanzarote. Group I (10 samples)
is represented by fabrics intermediate between the single
crystal and the [100] fiber textures, whereas group II
(2 samples) is approximated by the [010] fiber texture.
These LPOs are typical of the upper mantle and have
been widely reported in the literature (e.g. Brothers and
Rodgers, 1969; Nicolas et al., 1973; Mercier and
Nicolas, 1975; Christensen and Salisbury, 1979; Chris-
tensen, 1984; Mainprice and Silver, 1993; Ji et al., 1994;
Ben Ismal and Mainprice, 1998; Mainprice et al.,
2000). It is currently admitted that simple shear or a
combination of simple and pure shear is the dominant
deformation regime in the oceanic upper mantle
(Nicolas, 1976). Generally, a simple shear component
is indicated by a more or less pronounced obliquity of
olivine [100] and [010] axes relative to the X and Z
structural directions, respectively (Zhang and Karato,
1995). This characteristic is a common feature of the
LPO in Lanzarote xenoliths. If we refer to the
experimental deformation experiments of Tommasi et
al. (1999) for polycrystalline olivine samples, the
predominance of the single crystal and [100] fiber
textures (group I) tends to indicate that low strain rate
simple shear, with a possible tensional component
(transtension), is the prevalent deformation regime for
the source region of most of the Lanzarote xenoliths.
These textures are consistent with the activation of the
(010)[100] and (0kl)[100] slip systems at high to
moderate operating temperatures (Raleigh, 1968; Carter
and Av¨| Lallemant, 1970), in good agreement with the
geothermometric determinations of Neumann et al.
(1995). On the other hand, the occurrence of the [010]
fiber texture (group II) is less common in the upper
mantle. According to Tommasi et al. (1999), axial [010]
LPO patterns with strong clustering of the [010] poles
result either from widening¨Cthinning shear (transpres-
sion) or axial shortening, the former being more likely in
our xenoliths, due to the slight obliquity of the pole
maxima. Whatever the scenario, the simultaneous
occurrence of [100] and [010] fiber textures indicate
that at least two deformation regimes operated at
different locations in the upper mantle beneath Lanzar-
ote, suggesting a different source location or depth for
the xenoliths of groups I and II.
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