Different Localities of Potassium-Rich Silica-Undersaturated Igneous Rocks and Their Silica-Rich Variants - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 93

4.1.3 Occurence of K-Rich Silica-De cient Rocks

from Turkey

Altherr et al. (2008) have described leucite tephrites from the southern zone of
Eastern Pontides. It is an isolated small outcrop (1.5 km 2 ) occurring in the Asutka
thrust sheet. Field relations constrain the timing of volcanism between Maastrich-
tian and late Paleocene. The leucite tephrites consist of clinopyroxene, analcime
(psudomorph after leucite), Ti-magnetite, plagioclase, sanidine, apatite and acces-
sory biotite. The rocks are represented by three geochemical and petrographic
varieties: Types I and II are mostly blocks within epiclastic debris and type III are
lava flows. All the rocks are considerably altered, whereby leucite is almost totally

analcimized. There are however leucite inclusions within clinopyroxene that occurs
remote from the solution-bearing channels. Furthermore, calcite and chlorite/
smectite also have been formed due to low grade metamorphism. Chemical effects
of alteration are primarily re

ected in an unsystematic variation in the whole-rock

K 2 O/Na 2 O ratios (0.12 1.71) and in the abundance of large-ion lithophile elements,

such as Cs, K, and also Rb. Both the high modal abundance of leucite and the
composition of clinopyroxene, indicate an ultrapotassic nature of the primary rocks.
In primitive mantle-normalized element concentration diagrams, all samples are
characterized by negative anomalies of Nb

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Hf and Ti and a positive
anomaly in Pb, testifying the orogenic nature of the rocks. The rocks cover
restricted ranges in all initial isotopic ratios with Sr 87 /Sr 86 (60 Ma) ranging from
0.70537 to 0.70568, Nd 143 /Nd 144 from 0.512529 to 0.512585, Pb 206 /Pb 204 from
18.65 to 18.83, Pb 207 /Pb 204 from 15.65 to 15.66 and Pb 208 /Pb 204 from 38.64 to
38.88. There is no obvious relationship between the degree of analcimization and
the isotopic composition. Chondrite-normalized rare earth element (REE) patterns
show no signi

Ta, Zr

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cant Eu anomaly, but a strong enrichment of the LREE over the
HREE with (La/Yb) (cn) = 11.6 14.2, whereby normalized concentration of Eu to

Lu are nearly similar. The Everek Hanlan leucite tephrites represent the youngest
products of Cretaceous to Paleocene arc magmatism of the Eastern Pontides, thus
documenting the last stages of the Neotethyan subduction.
Coban and Flower (2006) studied the ultrapotassic rocks in the Bucak area of
Isparta Angle, SW Turkey. These rocks are characterized by low SiO 2 (46.8

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49.2 wt

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%) and relatively high MgO (10.4 11.6 wt%) contents, with lamproitic af nity (K/

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Na, > 2.5; Mg#, 73 75; Al 2 O 3 (9.2 11 wt%), CaO (7.4 10.6 wt%), Cr,

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(525,675 ppm); Ni (442 615 ppm). They are made up by phlogopite (30 40 vol%),

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leucite (25 30 vol%), olivine (5 20 vol%), which rarely contain Cr-spinel, clino-

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pyroxene (5 10 vol%), sanidine (5 vol%) and richterite, with accessory apatite,

magnetite and ilmenite. One sample also include negligible amount of sodalite in the
groundmass, which is an unusual mineral in lamproites. Mineral phase variation and
textures record discrete phases of pre-eruptive crystallization: (1) early appearance
of (Cr-spinel-bearing olivine), Ti poor phlogopite

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± apatite crystallizing at pressures

of 1.0 2.0 GPa, at or close to the lithospheric Mechanical Boundary Layer (MBL),

and (2) later appearance of Ti-rich phlogopite, clinopyroxene, richterite, leucite,

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