Electronic appendix: Jagoutz et al.
The following section describes the main mineralogy and textures of the dominant
granitoids and does not include the gabbro, dikes and the samples from mingling or
contact zones.
Quartz and feldspar
Quartz grains are anhedral and interstitial in all the samples. With deformation, quartz
shows undulose extinction, subgrain rotation, sutured grain boundaries or polygonization,
indicating dynamic recrystallization. Quartz can be graphically intergrown with epidote
or with orthoclase yielding granophyric textures. Occasionally, subsolidus myrmekites
are present.
Interstitial and anhedral orthoclase grains indicate a late occurrence in the crystallization
sequence. Orthoclase often exhibits perthitic exsolution lamellae. Microcline, which is
abundant in grano diorites and quartz monzodiorites, displays the characteristic tartan
twinning. In grano diorites, orthoclase commonly shows a poikilitic texture and is up to 4
mm in size, enclosing plagioclase, biotite, hornblende and quartz.
Plagioclase grains are subhedral to euhedral, tabular to equant. Polisynthetic twinning
and oscillatory zoning are common. Modal abundance of quartz and feldspars are
illustrated in an IUGS classification diagram (Fig. 6a) after Streckeisen (1973).
Mica
Subhedral to euhedral biotite grains often are associated with hornblende. Apatite, zircon
and opaque minerals are the common inclusions. Titanite either occurs as inclusion or as
chain of small (μm) grains along biotite boundaries, seemingly related to an exsolution of
titanium from biotite. In some samples, biotite is partly retrogressed into chlorite. In most
samples, biotite varies in modal abundance from 10 to 15 %.
Sub-microscopical aggregates of sericite are found as an alteration product occurring in
weathered plagioclase cores. Euhedral muscovite is rarely found in-between feldspar
grains in rocks of grano dioritic composition.
Pyroxene
Ortho- and clinopyroxenes remain as relics (up to 5 modal %) in hornblende in samples
of quartz dioritic, quartz monzodioritic and quartz monzonitic composition. These
pyroxenes, which are early mafic crystallization products, are transformed into
hornblende via a peritectic reaction and obviously are not in textural equilibrium with the
quartzo-feldspatic matrix.
Hornblende
Three main textural relationships can be distinguished: (1) interstitial, (2) poikilitic and
(3) euhedral. Poikilitic and euhedral grains, occasionally, are observed in the same thin
section, and euhedral grains, usually, are absent or less common in samples with
interstitial, anhedral hornblende. Textural relationships between hornblende and
plagioclase point towards two different crystallization sequences. (1) Hornblende
crystallizing after plagioclase: hornblende is interstitial with anhedral to subhedral habit
and up to 2 mm in size. These grains mainly are surrounded by euhedral, tabular
plagioclase and they only rarely contain plagioclase inclusions (Fig. 7a). (2) Hornblende
crystallizing before plagioclase: hornblende in this case is euhedral or poikilitic. Euhedral
hornblende grains vary in size from mm to cm and may occur as inclusion in subhedral to
euhedral plagioclase, which itself can be an inclusion in hornblende grains (Fig. 7b).
Poikilitic hornblende, usually, is up to several millimeters in size and often contains
quartz and feldspar inclusions. Opaque minerals and titanite are other phases found as
inclusions in hornblende. Biotite, in some samples, replaces hornblende by a peritectic
reaction. Some samples are characterized by hornblende, biotite and oxide grains that
occur as nests. In greenschist facies metamorphosed rocks, hornblende is transformed
into actinolite and shows patchy compositional zoning. Amphibole modal abundance
varies between ~30 % in quartz monzodiorite, to ~3 % in the most evolved, hornblendebearing grano diorites. Hornblende compositions are given in Figure 8 and Table 2.
Epidote
In the central, eastern parts and along the western boundary of the Batholith, epidote is
common in all the samples of compositions ranging from quartz diorites to grano diorites.
Four textures can be distinguished: (1) medium in size (2mm) and euhedral, (2) small in
size (<1mm) and subhedral, (3) subhedral to anhedral grains associated with hornblende
and biotite, and (4) within distinct veins or fine grained aggregates. The medium sized (2
mm), euhedral crystals usually are of tabular habit. They occur closely associated with
hornblende and biotite, in contact with biotite, and in the felsic matrix. Some of these
grains are intergrown with quartz (Fig. 9). They may contain allanite cores, which are
anhedral to subhedral. Epidote rarely is twinned and typically is free of inclusions. In
some occasions magnetite is enclosed. Based on these textural relationships, these
epidotes are considered to be of a magmatic origin (Schmidt & Poli 2004).
The small epidote grains (<1mm) usually are anhedral to subhedral and equant. They
often occur associated with biotite and in the felsic matrix. They contain allanite cores,
occasionally show vermicular to myrmekitic intergrowth with the matrix (Fig. 9) and,
thus, are interpreted to be of a magmatic origin also.
Anhedral to subhedral epidote grains, which are in contact with hornblende, in-between
hornblende and biotite in particular, could be late in the crystallization sequence and be
the result of a peritectic reaction such as hornblende + melt = biotite + epidote ± quartz ±
plagioclase (Schmidt & Poli 2004). These grains also can be of a secondary, subsolidus
origin, produced in a similar reaction involving orthoclase instead of a melt. Textural
observations favor a secondary origin for these epidote grains. Subhedral epidote
occurring in micro-cracks and fine grained epidote aggregates of saussuritized
plagioclase are considered to be secondary. Magmatic epidote of the first two types varies
in modal abundance from 2-10 and 1-15 % in grano diorite, tonalite and quartz diorite,
quartz monzodiorite, respectively.
Accessories
Titanite shows two major textures: (1) medium sized (mm), euhedral grains and (2)
chains of small (μm), sub- to euhedral grains associated with biotite (Fig. 6) (see “Mica”
section above). Euhedral titanite of rhombic and tabular habit often occurs associated
with biotite, enclosed in hornblende grains or within the quartzo-feldspatic matrix.
Opaque minerals often are enclosed in mafic phases such as biotite and hornblende, but
may also occur in titanite or feldspars. In general, the abundance of opaques in thin
section decreases with the increasing amount of epidote. Opaque minerals identified by
Raman spectroscopy are ilmenite and magnetite and the modal abundance varies from 1
to 3 % in felsic to more mafic samples, respectively.
Apatite and zircon mainly are enclosed in biotite but also occur in the quartzo-feldspatic
matrix as euhedral grains. Titanite, opaques, apatite and zircon occur in all the rock types
as traces. Titanite amounts to up to 3 modal % in quartz dioritic and quartz monzodioritic
rocks
Figure A1: geological map of Kohsitan showing the sample locations