The chronology and kinematics of late Palaeozoic deformation in the NW contact metamorphic aureole of the Land's End Granite

Abstract

A structural investigation of coastal exposures between Cape Cornwall and Pendeen Watch, in the NW contact metamorphic aureole of the Land’s End Granite, has confirmed a similar deformation chronology as in a reference section around Porthleven. D1 deformation is represented by an ubiquitous bedding-parallel S1 cleavage although F1 folds have not been recognised. D2 deformation is more localised and characterised by open F2 folds that verge WSW to NW and are associated with an ENE to SE dipping S2 crenulation cleavage. These structures are commonly obscured by later deformation and contact metamorphism and have not been described previously. A set of steeply inclined NNW-SSE trending, and subordinate set of moderately SE dipping, post-D2 metamorphic quartz veins formed coevally during an episode of strike-slip deformation prior to, or during, the early stages of D3 deformation. D3 deformation is widespread and represented by F3 folds and a WNW to NW dipping S3 crenulation cleavage; it has been recorded previously as D2 deformation. Two orders of F3 folds are developed; first order folds have a wavelength of up to 50 m, verge ESE, and result in vertical or steeply inclined bedding and S1 cleavage on their short limbs. Second order folds usually have a wavelength of 1 m or less and usually verge ESE, unless on the short limb of first order folds, where they verge WNW. Previously published data, indicating a dominant NW to WNW vergence of F3 folds on the northern flank of the Land’s End Granite are incorrect. D3 structures are consistent with formation during the extensional reactivation of large-scale thrust faults. Granite emplacement post-dates all three episodes of ductile deformation but granites and their host rocks are deformed by a late brittle expression of D3 deformation. The Land’s End pluton has been accommodated, at the current exposure level, primarily by roof uplift that has resulted in the tilting of D3 and earlier structures to the NW by 40-50º; this may have been accompanied by differential vertical axis rotations of the host rock. The last significant Palaeozoic deformation episode formed F4 folds and S4 cleavage and was a consequence of Mid- to Late Permian ENE-WSW shortening.

Full text

S.P. Hughes, R.J. Stickland, R.K. Shail, N.G. LeBoutillier, A.C. Alexander and M. Thomas
140
THE CHRONOLOGY AND KINEMATICS OF LATE PALAEOZOIC DEFORMATION IN
THE NW CONTACT METAMORPHIC AUREOLE OF THE LAND’SEND GRANITE
SAMUEL P. HUGHES, ROSS J. STICKLAND, ROBIN K. SHAIL, NICHOLAS G. LEBOUTILLIER,
ANDREW C. ALEXANDER AND MARK THOMAS
INTRODUCTION
Late Palaeozoic deformation of the Devonian and
Carboniferous successions in SW England reflects three principal
regional tectonic episodes (e.g. Dearman, 1971; Sanderson,
1973; Leveridge and Hartley, 2006). It is widely accepted that
D1 and D2 deformation occurred during Variscan (late Devonian
to late Carboniferous) plate convergence and collision whereas
D3 deformation relates to a different tectonic regime established
prior to, or during, granite emplacement (Turner, 1968; Rattey
and Sanderson, 1984; Alexander and Shail, 1995, 1996; Leveridge
and Hartley, 2006).
The Land’s End Granite and its host rocks provide a suitable
location to test the chronology of host rock deformation relative
to granite emplacement due to the excellent coastal exposures
of these units and their contacts. Relatively little has been
published on the chronology and kinematics of deformation
within the granite aureole. In part, this may reflect the
challenges posed by a locally intense contact metamorphic
overprint. The deformation chronology indicated within the
aureole on the British Geological Survey Penzance sheet (BGS,
1984), and described in the accompanying memoir (Goode and
Taylor, 1988), differs from that proposed in adjacent areas of the
Gramscatho Basin (e.g. Smith, 1965, 1966; Rattey and Sanderson,
Hughes, S.P., Stickland, R.J., Shail, R.K., LeBoutillier, N.G., Alexander, A.C. and Thomas, M. 2009. The chronology and
kinematics of late Palaeozoic deformation in the NW contact metamorphic aureole of the Land's End Granite. Geoscience in
South-West England,12, 140-152.
A structural investigation of coastal exposures between Cape Cornwall and Pendeen Watch, in the NW contact metamorphic
aureole of the Land’s End Granite, has confirmed a similar deformation chronology as in a reference section around Porthleven.
D1 deformation is represented by an ubiquitous bedding-parallel S1 cleavage although F1 folds have not been recognised.
D2 deformation is more localised and characterised by open F2 folds that verge WSW to NW and are associated with an ENE to
SE dipping S2 crenulation cleavage. These structures are commonly obscured by later deformation and contact metamorphism
and have not been described previously. A set of steeply inclined NNW-SSE trending, and subordinate set of moderately SE
dipping, post-D2 metamorphic quartz veins formed coevally during an episode of strike-slip deformation prior to, or during, the
early stages of D3 deformation. D3 deformation is widespread and represented by F3 folds and a WNW to NW dipping S3
crenulation cleavage; it has been recorded previously as D2 deformation. Two orders of F3 folds are developed; first order folds
have a wavelength of up to 50 m, verge ESE, and result in vertical or steeply inclined bedding and S1 cleavage on their short limbs.
Second order folds usually have a wavelength of 1 m or less and usually verge ESE, unless on the short limb of first order folds,
where they verge WNW. Previously published data, indicating a dominant NW to WNW vergence of F3 folds on the northern flank
of the Land’s End Granite are incorrect. D3 structures are consistent with formation during the extensional reactivation of
large-scale thrust faults. Granite emplacement post-dates all three episodes of ductile deformation but granites and their host rocks
are deformed by a late brittle expression of D3 deformation. The Land’s End pluton has been accommodated, at the current
exposure level, primarily by roof uplift that has resulted in the tilting of D3 and earlier structures to the NW by 40-50º; this may
have been accompanied by differential vertical axis rotations of the host rock. The last significant Palaeozoic deformation episode
formed F4 folds and S4 cleavage and was a consequence of Mid- to Late Permian ENE-WSW shortening.
Camborne School of Mines, College of Engineering, Mathematics and Physical Sciences,
University of Exeter, Cornwall Campus, Penryn, TR10 9EZ, U.K.
(E-mail: R.K.Shail@exeter.ac.uk).
Keywords: Land’s End Granite, Variscan, extensional tectonics, reactivation, granite emplacement.
1984; Alexander and Shail, 1995, 1996). Whilst these latter
authors are in broad agreement on the regional deformation
chronology outside the aureole, they have differing
interpretations of the cause of D3 episode. Rattey and
Sanderson (1984) proposed that D3 structures largely developed
as a response to vertical shortening brought about by granite
emplacement, whilst Alexander and Shail (1995, 1996) proposed
a largely pre-emplacement origin during the extensional
reactivation of Variscan thrusts.
The purpose of this contribution is to demonstrate that: (i) the
regional deformation chronology established by the majority of
previous workers outside the Land’s End Granite aureole can
also be recognized within the NW segment of the aureole.
(ii) Ductile D3 deformation within the aureole pre-dates granite
emplacement and is kinematically equivalent to D3 deformation
outside the aureole. (iii) The accommodation of the Land’s End
Granite at the present exposure level was achieved largely by
post-D3 uplift and tilting of the host rocks. The study is based
upon the comparative structural geology of the contact
metamorphic aureole on the NW margins of the Land’s End
Granite and the section around Porthleven on the south coast
(Figure 1).

Late Palaeozoic deformation in the Land’s End Granite aureole
141
Figure 1. A simplified geological map of south Cornwall after
Leveridge et al. (1990) showing the location of the study areas in
the NW aureole of the Land’s End Granite (LEG) and the Porthleven
section to the SE of the Tregonning-Godolphin Granite (TGG).
The parautochthonous host rocks to these granites comprises the
Mylor Slate Formation which is located structurally below the
Carrick Thrust (CT), Veryan Thrust (VT) and Lizard Thrust (LT).
PREVIOUS WORK
Stratigraphy
The recognition of a major NNW-directed Variscan thrust
nappe pile in south Cornwall (Leveridge et al., 1984; Holder
and Leveridge, 1986; Leveridge et al., 1990) has greatly
improved the understanding of the stratigraphy and tectonic
evolution of the Gramscatho Basin (Figure 1). The inferred
trace of the Carrick Thrust occurs at the southern end of the
Porthleven section and separates the parautochthonous Mylor
Slate Formation from the Portscatho Formation of the Carrick
Nappe (Leveridge and Holder, 1985; Holder and Leveridge,
1986). The Portscatho Formation comprises deep marine
sandstones and mudstones whilst the Mylor Slate Formation
predominantly comprises thinly bedded deep marine siltstones
and mudstones, along with basaltic pillow lavas and dolerite
sills; its upper part is represented by olistostromes of the
Porthleven Breccia Member (Leveridge and Holder, 1985;
Leveridge et al., 1990). These olistostromes are interpreted
to have been sourced primarily from the south during the
northwards translation and emergence of the Carrick Nappe
(Leveridge and Holder, 1985; Leveridge et al., 1990).
Palynological data indicate both formations are predominantly
Upper Devonian in age, although possibly including some
Tournaisian strata (Turner et al., 1979; Le Gall et al., 1985;
Wilkinson and Knight, 1989). The Tregonning Granite is
a topaz granite that has been dated by the Rb-Sr
whole rock method as 280 ± 4 (2σ) Ma (Darbyshire and
Shepherd, 1987), although a 40Ar/39Ar zinnwaldite cooling age of
281.0 ± 1.3 (2σ) Ma suggests emplacement was probably a
little earlier at 283-284 Ma (Clark et al., 1994). The Land’s End
Granite comprises a variety of textural types of biotite granite
dated by the U-Pb monazite method between 277.1 ± 0.4
(2σ) Ma and 274.4 ± 0.4 (2σ) Ma (Chen et al., 1993; Clark
et al., 1994).
Deformation chronology outside the aureole
Outside the contact metamorphic aureole of the Land’s End
Granite the first detailed investigations of the structural geology
of the Mylor Slate Formation were in the Porthleven area. Stone
(1962, 1966) identified the polyphase nature of deformation and
interpreted the dominant folds as having formed during a
regional D2 event. Although two cleavage generations were
recognized as predating the ‘S2’ cleavage, the earliest cleavage
was related to ‘early (pre-F1) folding’ (Stone, 1966) and not
incorporated into the regional deformation chronology. Smith
(1965, 1966) subsequently identified three principal deforma-
tion events in the area around Godrevy and correlated these
with the structures around Porthleven, re-assigning the D2
structures of Stone (1962, 1966) to the regional D3 event.
Most subsequent studies largely corroborated this tripartite
deformation chronology (D1-D3) for the principal events
(Turner, 1968; Dearman, 1971; Sanderson, 1973; Rattey, 1980;
Rattey and Sanderson, 1984). A more complex deformation
chronology was established further east during remapping
of the Falmouth sheet (Leveridge et al., 1990). It was later
rationalized within the existing D1-D3 scheme by Alexander
and Shail (1995, 1996) who also included the brittle-ductile
detachments and brittle SE dipping listric faults described by
Shail and Wilkinson (1994) within the D3 event. The proposal
by Rattey and Sanderson (1984) of a NW-dipping S2 cleavage
and upright D2 Godrevy Antiform was refuted by Alexander
and Shail (1995) who considered it a consequence of the
misidentification of the NW dipping S3 cleavage as S2.
The consensus, from the above work outside the contact
metamorphic aureole, is that these three deformation episodes
have an expression in the Gramscatho Basin succession as
follows: (1) D1 deformation is ubiquitous and characterised by
isoclinal to tight F1 folds that are recumbent or gently inclined
to the SSE with an axial planar S1 cleavage that is generally
sub-parallel to bedding away from fold hinges. (2) D2
deformation is more partitioned and usually comprises zones of
moderately to steeply SSE inclined F2 folds and an associated
S2 crenulation cleavage. (3) D3 deformation consists of F3
folds of varying geometry and scale that are commonly SSE
verging and have an associated sub-horizontal or NNW dipping
S3 crenulation cleavage that locally transposes earlier fabrics.
Most previous workers additionally identify at least two post-D3
deformation events (D4 and D5) that resulted in the local
development of steeply inclined cleavages and typically upright
folds (e.g. Smith, 1965, 1966; Rattey and Sanderson, 1984;
Alexander and Shail, 1995, 1996).
Deformation chronology inside the aureole
Little detailed work has been published on polyphase
deformation within the contact metamorphic aureole of the
Land’s End Granite and it was not included in the regional
studies of D3 deformation in west Cornwall by Alexander and
Shail (1995, 1996). A large amount of structural data for the NW
aureole, including sketches of cliff-sections between Botallack
and Levant, are contained within the PhD thesis of Jackson
(1976). Larger-scale folds of bedding and S1 cleavage,
associated with a NW dipping cleavage, were assigned to a D2
event and minor coaxial folds on the steep F2 limbs were
assigned to a D3 event. The structural data on the Penzance
sheet (BGS, 1984) indicate the widespread occurrence of D3
folds and cleavage in the coastal sections of Mount’s Bay and
St Ives Bay, including within the contact aureole immediately
east of the Land’s End Granite around Carbis Bay. However,
along the northern and NW aureole of the granite, between
St Ives and Cape Cornwall, the dominant folds shown are F2
and associated with a moderately to steeply NW-dipping S2
cleavage. In the accompanying memoir (Goode and Taylor,
1988), F2 folds are represented as S verging and associated with
a N dipping S2 cleavage, i.e. they have all the characteristics of
F3 folds and S3 cleavage as described by previous workers, and
as shown outside the aureole on the Penzance sheet (BGS,
1984). Similar structures at Porthmeor Cove (Exley and Stone,
1982; Stone and Exley, 1984) and Priest’s Cove (Salmon and
Shail, 1999) have been assigned to the D3 episode. Other
workers have suggested that D3 deformation is widespread
along the whole northern margin of the Land’s End Granite
(Rattey and Sanderson, 1984; LeBoutillier, 2002; Kratinova et al.,
2003). The basis for assigning these structures to the D3
episode is their geometrical similarity with structures outside the
aureole. However, there has been no description of regional D2
structures within the aureole and this may explain the apparently
anomalous assignation of D2 (BGS, 1984; Goode and Taylor,

S.P. Hughes, R.J. Stickland, R.K. Shail, N.G. LeBoutillier, A.C. Alexander and M. Thomas
142
Figure 2. A model for emplacement-related D3 defor mation after
Rattey and Sanderson (1984, figure 6). The forceful (diapiric)
emplacement of granite plutons creates broad large-scale antiforms.
Vertical shortening during the emplacement process creates
predominantly N verging F3 folds on the northern flank of the
pluton and predominantly S verging F3 folds on the southern flank of
the pluton, together with an approximately horizontal cleavage (S3).
1988), in a locally valid deformation chronology, to structures
that outside the aureole are classified as regional D3.
Kinematics and timing of deformation
relative to granite emplacement
All recent workers agree that regional D1 and D2 structures
in south Cornwall were generated by a top sense-of-shear to
the NNW during Variscan convergence and collision (e.g.
Dearman, 1971; Rattey and Sanderson, 1984; Shail and
Alexander, 1995, 1996; Leveridge and Hartley, 2006). Much of
the research on the kinematics of post-convergence D3
deformation, and its timing relative to granite emplacement, has
been focussed around Porthleven and the Tregonning Granite.
The earliest model was developed by Stone (1962, 1966; his
D2) and Smith (1965, 1966); they concluded that D3 structures
were generated by pre-granite vertical shortening, possibly due
to an increase in super incumbent load following ‘sliding’.
Turner (1968) attributed the vertical shortening to the rise of the
upper surface of the granite batholith, but considered that the
resultant D3 fabrics were post-dated by the emplacement of
individual cupolas. A similar emplacement-related model
was adopted by Rattey (1980) and Rattey and Sanderson (1984)
who suggested that small-scale F3 folds typically verged away
from the granite margins to define a ‘fir tree’ interference
pattern (Figure 2). It was proposed that this resulted from
the superposition of pure shear vertical flattening of the limbs
of large-scale upright open antiforms generated above the
granite plutons during earlier stages of diapiric emplacement
(Figure 2).
An alternative model was proposed by Alexander and Shail
(1995, 1996) whereby D3 deformation resulted from the
reactivation of major Variscan thrusts in a NNW-SSE post-
convergence extensional regime. A top-to-the SSE sense of
simple shear, when superimposed on an end-D2 orogenic
architecture dominated by SSE dipping elements (bedding, S2
cleavage etc.), resulted in the widespread development of SSE
verging folds within the parautochthonous footwall of the
Carrick Nappe. Hence granite generation and emplacement,
instead of being the cause of D3 deformation, was interpreted
as one of its consequences (Shail and Wilkinson, 1994; Shail
et al., 2003). Predominantly ESE to SSE verging D3 folds along
the northern margins of the Land’s End Granite do not appear
compatible with the emplacement-related models of Rattey
(1980) and Rattey and Sanderson (1984) and have also been
interpreted using the extensional reactivation model (Salmon
and Shail, 1999; LeBoutillier, 2002; Kratinova et al., 2003). It has
been suggested that zones of predominantly NW verging F3
folds, such as to the west of the Tregonning Granite, might
be related to vergence reversals during very high strain D3
deformation prior to granite emplacement (Alexander and Shail,
1995, 1996).
FIELD DATA FROM THE PORTHLEVEN SECTION
In order to evaluate the geometry and chronology of
deformation in the NW aureole with that outside the aureole,
a reference data set was collected from the widely investigated
coastal section between Blue Rocks [SW 6489 2333] and
Legereath Zawn [SW 6077 2680], on the south side of the
batholith. The SE end of the section, from Porthleven to Blue
Rocks has not experienced significant contact metamorphism,
but to the NW, from Porthleven to Megiliggar Rocks, slatey
mudrocks exhibit a progressive change to low-pressure
amphibolite facies (biotite-cordierite ± andalusite) hornfels.
D1 structures
D1 deformation occurs throughout the section. The
Portscatho Formation at Blue Rocks [SW 6489 2333] exhibits
NNW verging tight to isoclinal F1 folds on a 1 to 10 m scale
(Figure 3a). S1 is an axial planar spaced cleavage that is
bedding-parallel on the fold limbs; no earlier penetrative fabric
is observed in the fold hinges. Whilst a S1 slatey cleavage is
ubiquitous in the Mylor Slate Formation, few primary folds have
been observed and none in the northern end of the section. D1
orientation data are summarised in Figure 4a. F1 fold axes
exhibit a range of plunge directions, from NE to ESE, that reflect
curvilinear hinges; occasional WSW plunge directions result
from D4 refolding. S1 cleavage dips gently to the SSE.
D2 structures
D2 strain is partitioned throughout the section, so that in
some areas no structures are developed, whereas elsewhere
they may be the dominant element in zones of high D2 strain.
Examples of F2 folds in Portscatho Formation sandstones are
displayed immediately south of Loe Bar [SW 6437 2414]; they
have a shorter wavelength (0.1 – 1 m) than F1 folds, an open
to tight style, and generally verge NNW (Figure 3b). The
associated axial planar S2 cleavage crenulates the S1 fabric and
dips moderately SSE and is commonly associated with a later
‘post-D2’ generation of subparallel quartz veins (Figure 3c). D2
data are summarised in Figure 4b. F2 folds plunge gently to the
ENE and are broadly co-axial with F1 folds; they usually verge
NNW, unless on the shorter overturned limbs of larger scale F2
folds where they verge SSE. Facing is to the NNW where folds
develop on long ‘right way-up’ F1 limbs but SSE on the short
overturned F1 limbs.
Post-D2 quartz veins
Sub-vertical quartz veins, striking NNW-SSE and up to 0.3 m
in width, were observed throughout the section. The mean
orientation of a set of seventeen veins was 151º/84º NE. The
veins post-date D1 and D2 folds and cleavage, but were
buckled during D3 ductile deformation and offset by brittle D3
faults. In the contact aureole, andalusite is often localised in the
blackened wallrock of these veins. Approximately S2 parallel
quartz veins are common and were also deformed during D3
deformation; in appropriately orientated sections these can be
observed to branch from the subvertical NNW-SSE veins.
D3 structures
In the Mylor Slate Formation, zones of ductile D3
deformation are dominant. F3 folds generally verge SSE with
short limbs varying in length from 0.05–0.5 m where localised
in the hangingwall of extensional faults to several metres in
regions of distributed shear (Figure 3d). D3 fold and cleavage
orientation data are summarised in Figure 4c. F3 folds

Late Palaeozoic deformation in the Land’s End Granite aureole
143
Figure 3. Examples of D1-D3 structures in the Porthleven section: (a) NNW facing F1 fold with axial planar S1 slatey cleavage in
mudstones, Portscatho Formation [SW 6460 2367]; (b) NNW facing and verging F2 fold with SSE dipping axial planar S2 crenulation
cleavage, Portscatho Formation [SW 6457 2374]; (c) SSE dipping S2 crenulation cleavage, Portscatho Formation [SW 6457 2372]; (d) SSE
verging and facing F3 fold, Mylor Slate Formation [SW 6323 2518]; (e) SSE dipping S2 crenulation cleavage folded into small-scale SSE
verging F3 folds in vicinity of detachment fault, Portscatho Formation [SW 6407 2431]; (f) bedding parallel detachment fault (brittle D3)
with breccia and synthetic Riedel R1 faults in footwall consistent with a top sense-of-shear to the SSE, Portscatho Formation [SW 6482 2334].
predominantly plunge to the ENE, but some to the WSW; S3
cleavage varies from gently NW-dipping at Vellin Gluz [SW 6378
2471] to gently SE-dipping at Western Tye [SW 6326 2512] and
sub-horizontal at Megiliggar Rocks [SW 6093 2666]. Further
south, in the Portscatho Formation, complex arrays of bedding
parallel and listric faults are developed. These are sometimes
associated with SSE verging F3 folds and an associated NNW
dipping S3 cleavage in their hangingwall that crenulates the SE
dipping S2 crenulation cleavage (Figure 3e). Similar bedding
parallel fault zones, that have a more brittle expression with
well-developed breccia zones and SE dipping Riedel R1 faults
in their footwall, occur south of Loe Bar (Figure 3f) and

are compatible with a top-sense-of-shear towards the SSE. All of
these structures are post-dated by steeply SSE dipping
extensional or dextral-extensional faults.
D4 structures
A fourth phase of ductile deformation is recognized,
consisting of large scale open folding of the Mylor Slate
Formation at Vellin Gluz and Western Tye, together with small
scale tight folding. The F4 folds verge WSW and plunge SSE.
The S4 cleavage, which dips steeply ENE, was only clearly
discernible at Vellin Gluz (Table 1).
Boundary relations with the Tregonning
Granite
F3 folds and S3 cleavage within the Mylor Slate Formation
are truncated along a stepped sharp boundary with the upper
part of the Tregonning Granite at Legereath Zawn [SW 6077
2680]. There is no evidence of a similar high strain fabric
within the granite. The granite sheets, exposed between there
and Megiliggar Rocks [SW 6093 2666] are hosted by fractures
that are commonly parallel or slightly oblique to the composite
S3/S1 fabric and include host rock fragments displaying F3 folds
and S3 cleavage.
FIELD DATA FROM THE CAPE CORNWALL AREA
Cape Cornwall is situated on the NW margin of the Land’s
End Granite (Figure 1). The adjacent areas of Priest’s Cove
to the south [SW 3520 3165] and Porth Ledden to the north
[SW 3535 3200] are classic locations at which the contact
relationships between the Land’s End Granite and host rock and
the internal textural variations in the Land’s End Granite can be
examined (e.g. Salmon and Shail, 1999; Halls et al., 2001; Müller
et al., 2006 ).
Host rock lithologies and contact
metamorphism
The Mylor Slate Formation comprises metasedimentary rocks
and metabasic igneous rocks (typically as sills <10 m thickness)
and is exposed from Priest’s Cove northwards across
Cape Cornwall to the Porth Ledden foreshore platform. The
metasedimentary rocks indicate low pressure amphibolite facies
(biotite-cordierite ± andalusite) contact metamorphism. The
sedimentary protolith was dominated by thinly bedded
siltstone/very fine-grained sandstone-mudstone couplets in
which the siltstone/very fine sandstone is typically 10-20 mm
thick and usually accounts for <20% of unit thickness. Contact
metamorphism has brought about a grain size inversion,
whereby the quartz-dominated metasiltstones/metasandstones
underwent relatively minor textural modification, but the
growth of biotite and cordierite in the metapelites has resulted
in a mean grain size of 1-5 mm. Despite this, structural fabrics
pre-dating contact metamorphism have been recognised in
metasedimentary rocks across the area.
D1 structures
F1 folds have not been observed. However, a primary
cleavage (S1) is recognised throughout the area, with good
examples in Priest’s Cove to the east of the slipway [SW 3530
3170]. S1 is sub-parallel to bedding, typically dipping between
5° and 20° to the NW at Cape Cornwall and is overprinted by
all subsequent structures.
D2 structures
Localised areas of D2 strain, manifested as F2 folds and S2
crenulation cleavage, were recognised primarily in Priest’s
Cove. F2 folds are open and rounded and have short limb
lengths <1 m (Figure 6a). They plunge gently NNW and verge
to the WSW. The associated axial planar S2 crenulation
cleavage deforms and crosscuts the primary foliation and dips
20-40° to the ENE. These relations are best displayed in the
low-lying cliff immediately east of the Priest’s Cove slipway
[SW 3526 3168] and along the track on the south side of Cape
Cornwall. D2 orientation data are summarised in Figure 7.
S.P. Hughes, R.J. Stickland, R.K. Shail, N.G. LeBoutillier, A.C. Alexander and M. Thomas
144
Figure 4. Equal area lower hemisphere stereograms of cleavage pole (■) and fold hinge (✩) orientation data from the Porthleven section;
D1: S1 (n = 15), F1 (n = 11); D2: S2 (n = 11), F2 (n = 13); D3: S3 (n = 23), F3 (n = 26).).
Table 1. Summary D1-D3 structural data, including mean
orientations, from the Porthleven section.

Late Palaeozoic deformation in the Land’s End Granite aureole
145
Figure 5. Summary geological map of the NW aureole of the
Land’s End Granite showing lithostratigraphical and boundary
information (BGS, 1984) and summary structural data from Cape
Cornwall, Botallack and Pendeen Watch.
Post-D2 quartz veins
Post-D2 quartz veins, variably deformed by D3, are present
throughout the area. They are very well displayed at the cliff
and foreshore platform at the southern end of the Porth Ledden
where they strike NNW-SSE and the adjacent wallrock is
blackened and commonly contains andalusite.
D3 structures
A third episode of ductile deformation is recognised
throughout the Cape Cornwall area. Primary (S1) and secondary
(S2) cleavages are refolded by F3 folds and the E dipping S2
crenulation cleavage is cut and deformed by the NW-dipping S3
cleavage (Figure 6b-d). These relationships are also best
demonstrated east of the Priest’s Cove slipway; a fine example
of an ESE verging F3 fold with an axial planar S3 cleavage
occurs immediately adjacent to the slipway and includes a
boudinaged metabasalt (Figure 6b). Elsewhere, at the western
end of Priest’s Cove [SW 3480 3175], an east verging F3 fold is
defined by a metadolerite sill. Fold geometry varies, although
most are open to tight and overturned, with typical wavelengths
of 0.1 to 1 m. The folds usually verge ESE and have gently NNE
plunging hinges; the axial planar S3 cleavage is widespread
(Figure 6c), dipping on average 30-40° to the WSW (Figure 7c).
The axial surface of a larger first order F3 fold crops out to the
west of the Priest’s Cove slipway; WNW verging second order
F3 folds are developed on its steeply inclined short limb.
The D3 structures are sometimes localised adjacent to bedding-
parallel faults but there are insufficient data to independently
constrain their kinematics.
Boundary relations with the Land’s End
Granite
In Priest’s Cove the southern boundary of the host rock with
the granite is an ESE-trending high angle fault zone that hosts
Saveall’s Lode, marked by a 0.35 m thick quartz-hematite vein
defining the hanging wall of the stoped ground in the cliff.
The fault zone can be traced to the low water mark where it
intersects and offsets a moderately WSW dipping intrusive
boundary between host rock and granite that continues just
below low water to the SSE (inferred from the presence of
unidirectional solidification textures in the granite). Most of the
intrusive boundary between the granite and host rock at Porth
Ledden is approximately parallel to the S3 cleavage, dipping
20-30º NW; the northern boundary of the granite is formed by
an ESE-trending steeply-dipping mineralized fault. Moderate to
steeply dipping granite and aplite sheets – typically <1 m in
thickness with a weak modal ENE-WSW strike, crop out in both
Priest’s Cove and Porth Ledden; they cut across the S3 cleavage
and F3 folds and are undeformed by this episode.
FIELD DATA FROM THE BOTALLACK AREA
The Mylor Slate Formation in the vicinity of the Crowns
Engine Houses at Botallack [SW 3626 3351] comprises
approximately equal proportions of metasedimentary and
metabasic igneous rocks; in some areas the latter have been
metasomatically altered to produce garnetiferous skarns (e.g.
van Marcke de Lummen, 1985). Polyphase deformation has
been observed in the coastal exposures adjacent to the engine
houses and as far north as Stamps an Jowl Zawn [SW 3622
3400].
D1 structures
A primary foliation (S1) that is parallel to bedding exists
throughout the area. No F1 folds have been observed. The
combined bedding and foliation S1-S0 fabric has a mean dip of
33º to the NW (Figure 7b).
D2 structures
A second phase of deformation is sporadically observed; it
is commonly obscured or modified by the F3 folds and S3
cleavage (Figure 6e). F2 folds are open to tight and overturned,
plunge N or NNE, and verge W or WNW; wavelengths are
typically around 1 m. An axial planar S2 cleavage dips on
average 56° E, with slight variation in proximity to D3 structures
(Figure 7b).
D3 structures
D3 structures are dominant throughout the area. First order
structures have a wavelength of approximately 50 m and verge
to the ESE; they result in localised areas of steeply inclined or
vertical bedding and primary foliation, and the reorientation
of D2 structures. Second order F3 folds are usually tight and
overturned with a wavelength of <1 m; they plunge to the NNE
and verge ESE on the long limbs, and WNW on the short steep
limbs, of first order F3 folds. The SE dipping S2 crenulation
cleavage is locally refolded into a NW dipping cleavage around
F3 fold hinges. The S3 cleavage is axial planar to F3 folds, dips
moderately WNW, and crenulates the S2 fabric (Figure 6e).
FIELD DATA FROM PENDEEN WATCH
Coastal exposures between SW 3790 3565 and SW 3835 3595
are exclusively metasedimentary rocks and more distant from
the granite contact than previous sites.
D1 structures
A primary bedding-parallel foliation (S1), similar to that
elsewhere in the aureole is present and has a mean dip of 23°
to the NNW (Figure 7c), although it is locally re-orientated by
later structures; no F1 folds were observed.

S.P. Hughes, R.J. Stickland, R.K. Shail, N.G. LeBoutillier, A.C. Alexander and M. Thomas
146
Figure 6. Examples of D1-D3 structures in the Mylor Slate Formation of the NW contact aureole: (a) W verging F2 fold with E dipping
axial planar S2 crenulation cleavage, Priest’s Cove; (b) SE verging F3 fold, Priest’s Cove; (c) NW dipping S3 crenulation cleavage cutting
horizontal composite S1-S0 fabric; contact metamorphism has caused grain size inversion so that the original mudstones are now coarser
grained than the subordinate very thinly bedded siltstones (pencil tip is 20 mm long), Priest’s Cove; (d) WNW dipping S3 crenulation
cleavage cuts ESE dipping S2 crenulation cleavage, Priest’s Cove; (e) ESE dipping S2 crenulation cleavage folded by ESE verging F3 folds
(pencil tip is 40 mm long), Botallack Head [SW 3618 3384]; (f) Gently SE dipping S2 crenulation cleavage preserved on NW limb of F3 fold
with steeply NW dipping axial planar S3 crenulation cleavage, Pendeen Watch [SW 3791 3576].

Late Palaeozoic deformation in the Land’s End Granite aureole
147
Figure 7. Equal area lower hemisphere stereograms of cleavage pole (■) and fold hinge (✩) orientation data from the NW contact
aureole: (a) Cape Cornwall, D1: S1-So composite fabric (n = 109); D2: S2 (n = 7), F2 (n = 15); D3: S3 (n = 29), F3 (n = 60); (b) Botallack,
D1: S1-So composite fabric (n = 12); D2: S2 (n = 16), F2 (n = 15); D3: S3 (n = 20), F3 (n = 28); (c) Pendeen Watch, D1: S1-So composite
fabric (n = 18); D2: S2 (n = 17), F2 (n = 12); D3: S3 (n =21), F3 (n = 14).

S.P. Hughes, R.J. Stickland, R.K. Shail, N.G. LeBoutillier, A.C. Alexander and M. Thomas
148
Table 2. Summary D1-D3 structural data, including mean orientations, from the NW aureole of the Land’s End Granite.
D2 structures
D2 deformation occurs in localised high strain zones in the
low-lying cliff immediately to the north of the lighthouse. Open
F2 folds that plunge to the NE and verge to the NW have a
wavelength of approximately 0.2 m to 0.5 m; they have an axial
planar S2 crenulation cleavage that dips moderately to the SE
(Figure 7c).
D3 structures
Much of the area has a strong D3 overprint, with close
to tight F3 folds that plunge to the NE and verge to the SE;
the associated axial planar S3 crenulation cleavage dips
approximately 52° NW and crenulates both S1 and S2 (Figure 7c).
In exposures below the lighthouse, SE verging F3 folds
develop on F2 fold limbs and refold the S2 cleavage (Figure 6f).
PORTHMEOR COVE
Porthmeor Cove [SW 4250 3750] is situated 5 km ENE of
Pendeen Watch, towards the western end of the northern
contact aureole; the NW and N aureole segments are separated
by approximately 3.5 km of granite coastline where no host
rocks crop out (Figure 1). This location is well-known due to
the small, easily accessible, granite cupola and cross-cutting
granite sheets (Stone and Exley, 1984). Data was collected
from Porthmeor Point [SW 4255 3790] in the east, to Great Zawn
[SW 4210 3735] in the west so that a comparison could be made
with the sections in the NW aureole and because of previous
brief descriptions of structures assigned to D3 (Exley and Stone,
1982; Stone and Exley, 1984).
D1 and D2 structures
A primary bedding-parallel cleavage (S1) occurs throughout
and has a mean dip of 20° NW. F1 folds and D2 structures were
not observed.
D3 structures
D3 structures are developed in metasedimentary rocks
throughout the area; F3 folds are best observed in the cliff
exposures above the Porthmeor cupola [SW 4255 3765].
Typically, F3 folds are tight and overturned and have a
wavelength <0.5 m; they verge to the SE and have a mean
plunge of 9°/025°. The folds are associated with a NW-dipping
axial planar S3 cleavage that crenulates S1 in the hinge areas of
F3 folds. Small SE dipping extensional faults (trace lengths
<1 m) and SE verging F3 folds above the same bedding-
parallel surfaces indicates the development of D3 detachment
faults similar to those south of Porthleven (Bar Lodge).
DISCUSSION
Regional deformation chronology
Table 1 summarises the geometry and relative chronology of
regional deformation recognised in the Porthleven coastal
section. These data are consistent with previous studies that
established and refined the D1-D3 deformation chronology
(Smith, 1965; Turner, 1968; Rattey and Sanderson, 1984;
Alexander and Shail, 1996). Table 2 summarises the geometry
and relative chronology of regional deformation established
within the NW contact metamorphic aureole of the Land’s End
Granite and at Porthmeor Cove.
D1 deformation is represented by a ubiquitous bedding-
parallel S1 cleavage. F1 folds have not been recognised in the
aureole, but the presence of isoclinal folds is implied by the
bedding-cleavage relationship and would be consistent with the
D1 deformation style outside the aureole (Table 1, see also
Smith, 1965; Rattey and Sanderson, 1984). The identification of
F1 fold hinges is no doubt hindered by the locally intense D2
and D3 overprint; such deformation, together with textural
effects of contact metamorphism, also minimises the occurrence
of unambiguous younging criteria that might additionally be
used to infer fold axial surfaces.
D2 deformation has been positively identified at Cape
Cornwall, Botallack and Pendeen Watch on the basis of
refolding relationships between F3, F2 and S1, and cleavage
overprinting relationships between S3, S2 and S1. The sections
east of the Priest’s Cove slipway and around Botallack Head
and Pendeen are important locations where D2 structures and
their relative chronology with respect to D1 and D3 structures
can be established. D2 structures were not identified at Porth
Ledden or Porthmeor Cove and this may reflect either the
absence of D2 deformation in these areas, due to its partitioned
nature, or its obfuscation by D3 deformation and contact
metamorphism. F2 folds vary from NNW to NE plunging, WSW
to NW verging, and are associated with a moderately ENE to SE
dipping S2 crenulation cleavage. ENE to SE verging parasitic F2
folds might be anticipated on the overturned limbs of larger
scale F2 folds but have not been observed; it may be that
larger scale folds were not generated. However, any such

Late Palaeozoic deformation in the Land’s End Granite aureole
149
Table 3. Summary regional deformation chronology and style for
the Porthleven section and Land’s End contact metamorphic
aureole (this study), compared with that of the second edition
Land’s End sheet (BGS, 1984) and memoir (Goode and Taylor, 1988).
parasitic E to SE verging F2 folds would be optimally orientated
for further tightening during D3 deformation, and could have
developed into composite F2/F3 SE verging folds in which the
S2 cleavage was transposed by the S3 cleavage.
The NNW-SSE and NE-SW trending post-D2 quartz veins
described from the Porthleven section are present throughout
the NW aureole and are best displayed at the southern end of
Porth Ledden. They are variably deformed by D3; depending
upon their orientation, and must have formed prior to, or
during the early stages of D3 deformation. Several sub-types
were recognized in the Porthleven area and assigned to the D3
episode by Wilkinson (1990).
Ductile D3 deformation is widely observed throughout the
aureole and in many areas constitutes the dominant expression
of deformation. F3 folds plunge gently NNE, are tight and
predominantly verge ESE, unless on the overturned limbs of
first order F3 folds. The associated axial planar S3 cleavage
dips gently to moderately WSW. D3 deformation appears
localized in some areas adjacent to bedding-parallel fault zones.
The data presented confirm previous inferences that the
predominant folds and cleavages observed within the Land’s
End Granite aureole formed during the regional D3 event (e.g.
Exley and Stone, 1982; Rattey and Sanderson, 1984; Stone and
Exley, 1984; Salmon and Shail, 1999; LeBoutillier, 2002;
Kratinova et al., 2003). These suggestions were based on the
geometrical similarity with D3 structures outside the aureole.
However, this study has additionally demonstrated that regional
D2 structures are present, albeit commonly overprinted and
obscured by D3 and textural changes accompanying contact
metamorphism. The deformation chronology and style at
Porthleven and in the NW aureole, based on data presented
here, are compared with that shown on the Penzance sheet and
summarised in the memoir (BGS, 1984; Goode and Taylor,
1988) in Table 3. The SE verging folds and NW dipping
cleavage shown in the Land’s End aureole and assigned to D2
(BGS, 1984; Goode and Taylor, 1988) are here re-assigned to
the regional D3 deformation event in the same manner as for
the section between Perranporth and St Ives (Alexander and
Shail, 1995). The N verging F3 folds described by Goode and
Taylor (1988) were not recognized in this study and their D4
deformation, associated with a subhorizontal cleavage and
equivalent to the D3 of Jackson (1976), is interpreted as a high
strain manifestation of the regional D3 episode (cf. Alexander
and Shail, 1995). The regional D4 episode of deformation,
associated with NNW-SSE steeply inclined cleavages (e.g. Smith,
1965, 1966; Rattey and Sanderson, 1984), is confirmed.
Timing of deformation relative to granite
emplacement
The main body of the Land’s End Granite truncates D3 folds
and cleavage in the host rock, and includes arrested xenoliths
containing D3 folds and cleavage, at Porth Ledden and
Porthmeor Cove (all locations). Minor granite / microgranite
intrusive sheets occur widely in the aureole and invariably cut
D3 structures and are not folded by D3. Similar relations occur
in the aureole of the Tregonning Granite (Stone, 1975;
Alexander and Shail, 1996). Granite emplacement post-dated
ductile D3 deformation. The steeply inclined NNW-SSE S4
cleavage crenulates contact metamorphic biotites in the aureole
of the Tregonning Granite.
Kinematics
Regional D1 and D2 structures are interpreted to have
formed during Variscan convergence associated with a
dominant top sense-of-shear to the NNW (e.g. Rattey and
Sanderson, 1984; Alexander and Shail, 1995, 1996; Leveridge
and Hartley, 2006). Kinematic data are not available for D1
structures in the aureole, but the F2 folds have a vergence
varying from WSW to NW that is broadly consistent with these
studies. Nevertheless, D2 structures within the aureole vary in
orientation between each location (Table 2 and Figure 7). D2
structures at Pendeen Watch are closest in orientation to those
at Porthleven; there is counterclockwise change in the plunge
direction of F2 and dip direction of S2 moving SW from
Pendeen Watch to Botallack (~40º) and Cape Cornwall (~55º).
Insufficient data have been collected to fully characterise the
kinematics of post-D2 quartz veins. The thicker, steeply
inclined NNW-SSE veins have been interpreted by Wilkinson
(1990) to have formed in strike-slip shear zones. These thicker
veins commonly have thinner moderately SE dipping branches
that appear approximately parallel to S2 cleavage in section
view (e.g. Figure 3b), but transect S2 cleavage in a counter-
clockwise manner by 10-20º in plan view. A tensile origin for
these NE-SW striking veins would be possible during dextral
movement across the NNW-SSE shear zones as inferred by
Wilkinson (1990). Both the NNW-SSE and NE-SW veins were
subsequently deformed during D3 and hence must have formed
in either a discrete post-D2 regional strike-slip regime that
occurred prior to D3, or in a localized strike-slip regime during
the early stages of D3. The thicker veins are associated with
blackened wall rock hosting andalusite within the contact
metamorphic aureoles of the Land’s End and Tregonning-
Godolphin granites. This association appears anomalous as the
veins predate most or all of the D3 deformation and hence
granite emplacement and contact metamorphism (see below).
The blackened wall rock and andalusite result from a contact
metamorphic overprint of a wall rock altered by the migration
of high temperature metamorphic fluids during the post-D2
strike-slip event. These metamorphic fluids may reflect peak
convergence-related metamorphic conditions at depth;
reduction of the Si/Al ratio in the mudrocks of the Mylor
Slate Formation predisposed them to localized andalusite
formation during later contact metamorphism following granite
emplacement.
D3 structures in the aureole are characterised by an NW to
WNW dipping S3 cleavage and first order F3 folds that verge E
to SE, as do all second order folds on the long limbs of first
order structures. The predominance of E to SE verging F3 folds,
local vergence reversals being restricted to the short overturned
limbs of first order F3 folds, contrasts with the NW verging
summary F3 data for the NW and N aureole shown in figure 4
of Rattey and Sanderson (1984). These data invalidate their
‘fir tree’ model of fold vergence about the Land’s End Granite,
i.e. small scale F3 structures could not have been superimposed
upon pre-existing large-scale antiforms around the granites.
The formation of predominantly E to SE verging F3 folds
from SE dipping elements is kinematically consistent with either

pure shear vertical shortening (e.g. Stone, 1962, 1966; Smith,
1965, 1966) or by a top-sense-of-shear to the E or SE (Alexander
and Shail, 1995, 1996) prior to any post-D3 tilting/rotation.
Distinguishing between these models is more challenging in
the aureole as independent kinematic indicators for bedding-
parallel detachment faults, such as those around Loe Bar, are
usually absent. Nevertheless, D3 structures in the aureole are
commonly localised in the vicinity of bedding-parallel faults,
albeit usually kinematically unconstrained. Some examples,
such as at Porthmeor Cove, indicate a complex association of
small-scale SE-dipping extensional (Riedel R1) faults and F3
folds / S3 cleavage above bedding parallel faults and are
consistent with similar structures outside the aureole and a
simple shear rather than vertical shortening origin. Variations
in the attitude of S3 cleavage and the inter-limb angles of
associated F3 folds, on a metre to decametre scale at a single
location, can also be best explained by changes in the intensity
of D3 strain generated during a top sense-of-shear to the E to
SE. Variations in strain intensity associated with idealised pure
shear vertical shortening would modify F3 inter-limb angles but
not the cleavage orientation (effects of post-D3 tilting/rotation
are minimal at outcrop scale).
Although overprinted by contact metamorphic textural
changes the D3 structural styles in the aureole, comprising
zones of distributed shear and more localized detachment-
related deformation, are similar to those in the Porthleven
section. A similar origin involving the development of a top-to-the
SSE sense-of-shear during the extensional reactivation of thrust
faults that, given contact relations between the granite and host
rock, must have occurred prior to granite emplacement (e.g.
Alexander and Shail, 1995, 1996). Whilst the Land’s End
Granite post-dates ductile D3 fabrics, the persistence of a NNW-
SSE extensional regime throughout much of its emplacement
history is consistent with magmatic state fabrics (Kratinova et al.,
2003, in press) and the ENE-WSW trend of the earliest steeply
inclined brittle extensional faults and veins (Shail and
Wilkinson, 1994; Alexander and Shail, 1995). The absence of a
clear ductile expression of this ongoing deformation probably
reflects the exhumation and cooling of the host rocks prior to
granite emplacement and increasing strain accommodation by
brittle faulting. As thin granite / microgranite sheets are also
undeformed by ductile D3, the rheological influence of aureole
contact metamorphism appears to have been limited.
D3 structures within the aureole vary in orientation between
location in a broadly similar manner to D2 structures (Table 2
and Figure 7). F3 hinges at Pendeen Watch are similar in
orientation to those at Porthleven; but there is a counter
clockwise change in F3 plunge direction between Pendeen
Watch and Cape Cornwall (~40º), Botallack (~50º) and
Porthmeor Cove (~35º). S3 cleavage in the aureole typically
dips ~40-50º NNW to WNW and is markedly different to that at
Porthleven. Restoration of this aureole S3 cleavage to the
modal horizontal orientation at Porthleven would therefore
require a 40-50º tilt to the SE about a horizontal ENE to NNE
axis. A similar tilt applied to the aureole S2 cleavage cannot
restore all D2 structures to the orientation around Porthleven.
One reason for this is the presence of apparent differential
vertical axis rotations between locations, described above, of up
to 55º. Other factors might include folding of S2 during D3
and the possibility that the S2 in the NW aureole might
have developed with a steeper attitude, reflecting lower strain,
than at Porthleven. The regional D4 deformation represents
an episode of ENE-WSW shortening during the Mid- to Late
Permian (Alexander and Shail, 1996; Shail and Alexander,
1997).
Accommodation of the Land’s End Granite
Ductile D3 deformation of the host rocks has been shown to
predate the emplacement of the Land’s End Granite and plays
no substantive role in its accommodation. The most obvious
consequence of granite emplacement is the NNW to WNW
tilting of the S1-S0 and S3 fabrics by ~40-50º relative to those at
Porthleven, suggesting that roof uplift during construction or
inflation of the pluton was an important mechanism (Figure 8);
see also Taylor (2007). Although segmented by higher angle
faults, many of the contacts between the granite and the host
rocks in the NW aureole are approximately parallel to the
S1-S0 and/or S3 fabric and are consistent with such an origin.
The vertical axis orientations between aureole locations might
be in part related to large-scale open folding accompanying
roof uplift and emplacement and that are reflected in the strike
variations of the aureole metabasic rocks (Figure 5). Other
possibilities include differential block rotations across NW-SE
faults prior to granite emplacement, as has been demonstrated
elsewhere in the region (e.g. Leveridge and Hartley, 2006), but
testing this would require further mapping.
CONCLUSIONS
The regional deformation chronology can be recognised in
the NW contact metamorphic aureole of the Land’s End Granite.
Regional D2 structures, comprising an ENE to SE dipping S2
crenulation cleavage and WSW to NW verging F2 folds
have been described for the first time and are consistent with
development during a top-sense-of-shear to the NW during
Variscan convergence. These structures are commonly obscured
by later deformation and the textural effects of contact
metamorphism. The ‘local’ D2 structures, comprising a NW
dipping S2 cleavage and SE verging F2 folds, shown in the NW
and N aureole in the Land’s End sheet and memoir (BGS, 1984;
Goode and Taylor, 1988) have been re-assigned here to the
regional D3 deformation episode. A set of post-D2 quartz veins,
comprising steeply inclined NNW-SSE trending segments up to
0.5 m thick, with thinner moderately SE dipping segments,
developed during a discrete episode of post-D2 strike-slip
deformation or in the early stages of D3 deformation. Wall rock
alteration caused by the migration of metamorphic fluids during
that episode may have exerted a favourable compositional
influence on the formation of andalusite during later contact
metamorphism.
S.P. Hughes, R.J. Stickland, R.K. Shail, N.G. LeBoutillier, A.C. Alexander and M. Thomas
150
Figure 8. Summary sketch section summarising the geometry of D3 structures in relation to the granite batholith from the NW aureole
and around Porthleven. F3 folds predominantly verge SE on both flanks of the granite but D3 and earlier structures in the NW aureole
have been tilted to the NW by roof uplift during granite emplacement.

Late Palaeozoic deformation in the Land’s End Granite aureole
151
D3 structures comprise first order E to SE verging F3 folds
and a NW to WNW dipping S3 crenulation cleavage. Some F3
folds may have developed in the vicinity of bedding parallel
detachment zones. Overall there is a similarity with the style
of D3 structures observed in the Porthleven section. Local
vergence reversals of second order folds occur on the steep
overturned limbs of these first order structures, but the
predominant vergence across the NW aureole is to the E or SE.
The suggestion of a dominant NW vergence for F3 folds (Rattey
and Sanderson, 1984) along the NW and northern aureole of
the Land’s End Granite is rejected. Ductile D3 deformation
predates granite emplacement and is consistent with formation
during a top-to-the SE sense of simple shear developed during
the extensional reactivation of large scale thrust faults, although
the possibility of a component of pure shear vertical shortening
cannot be excluded. The most obvious mechanism for the
accommodation of the Land’s End Granite was by roof uplift
that brought about a NNW to WNW tilting of host rock by
~40-50º. Differential apparent vertical axis rotations between
locations in the NW and N aureole may be related to large-scale
open folding accompanying granite emplacement and/or
pre-granite movements on NW-SE strike-slip faults. Regional
D4 deformation, is represented by a steeply dipping NNW-SSE
trending F4 folds and S4 cleavage; it postdates the contact
metamorphism around the Tregonning Granite and is probably
Mid- to Late-Permian and hence marks the latter stages of
Palaeozoic deformation.
ACKNOWLEDGEMENTS
Andrew Alexander and Nick LeBoutillier are grateful to the
University of Exeter for financial support during their PhD studies.
Referee comments from Brian Leveridge and Graeme Taylor are
appreciated.
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