Melt inclusions in migmatites
Cesare et al. (2009) have described Ml in a regional anatectic terrane. Appear in many anatectic terranes. Very small, crystallized, "nanogranites".
Melt inclusions in migmatites
Melt inclusions in migmatites
Melt inclusions, definition modified by Césare et al. (2015), to include those present in regional migmatites:
Small droplets of melt that are trapped in minerals during their growth in the presence of a melt phase (Cesare et al. 2009, 2015). NANOGRANITOIDS
Roedder(1979)
Schiano (2003)
Audétat & Lowerstern (2014)
Frezzotti & Ferrando (2015)
Melt inclusions in anatectic enclaves
Grt-Bt-Sil
Cesare et al. (1997), Cesare (2008)
Melt inclusions in anatectic enclaves
Melt inclusions in anatectic enclaves
Melt inclusions in anatectic enclaves
Acosta et al. (2007) Cesare et al. (1997), Cesare (2008)
Melt inclusions in anatectic enclaves
Inclusions in UHP crustal rocks
Inclusions, reported by 2001 in high-grade crustal rocks, taken to mantle depths, i.e. UHP crustal rocks: Melt, polyphase or multiphase inclusions
Stöckhertet al. (2001), Erzgebirge, Germany
St 6102/2 Ll -09
Korsakov & Hermann (2006) Kokchetav, Kazakhstan
Gao et al. (2001) Dabie-Sulu, China
Lang & Gilotti (2007) Caledonian, Greenland
Inclusions in UHP crustal rocks
Inclusions, reported by 2001 in high-grade crustal rocks, taken to mantle depths, i.e. UHP crustal rocks: Melt, polyphase or multiphase inclusions
Stóckhertet al. (2001), Erzgebi
St 6102/2 Ll -09
0.01 mm
10 n 0
Wang etal. (2017)
Korsakov & Hermann (2006) Kokchetav, Kazakhstan
1111111111111111111111111111111111111111111111111111111
500       600       700       800 900
Temperature (°C)
& Gilotti (2007) Ionian, Greenland
Primary vs secondary melt inclusions
Cesare et al. (2015)
See Roedder (1979)
Bartoli etal. (2016)
Stóckhertl et al. (2009)
Melt inclusions in anatectic rocks versus volcanic rocks
Melt inclusions in anatectic rocks represent primary melts produced at the source rocks of crustal granites upon melting
Cesareet al. J Virt Expl (2011) & Bartoli etal. EPSL(2014)
Melt inclusions in anatectic rocks versus volcanic rocks
Melt inclusions in anatectic rocks represent primary melts produced at the source rocks of crustal granites upon melting
1 - Peritectic
Ti
entrapment of melt inclusions
m
-Migmatites, granulites -Enclaves and xenoliths in lavas -Host growth in solid framework -Entrapment during heating -Primary melt composition
suprasolidus ^
2 - Igneous
t
-Intrusive and extrusive rocks -Leucosomes in migmatites -Host growth in magma -Entrapment during cooling -Evolved melt composition
Cesare et al. (2015)
Identifying melt inclusions in migmatites
1. Optical microscope on regular, but well-polished, thin sections
- Regular, crystal-negative shape, brownish color (at least 20x)
- Polycristalline and/or glassy nature, multiple birefringent phases and/or
isotropic
Cesare et al. (2015)
Identifying melt inclusions in migmatites
1. Optical microscope on regular, but well-polished, thin sections
- Regular, crystal-negative shape, brownish color (a
- Polycristalline and/or glassy nature, multiple birefringent phases and/or isotropic
	urn	
		
Cesare et al. (2015)
Barich et al. (2014), Acosta-Vigil et al. (2016)
Characterization of melt inclusions
2. SEM (Field Emission, 5-10 microns Ml)
Cesareetal. (2015)
Characterization of melt inclusions
2. SEM (Field Emission, 5-10 microns Ml)
JU-8, core
Bt (no Ti, Fe>Mg)
1/17/2013    WD    Mag Spol   HV   Det HFW 1 3803 PM 10 0 mm4000x 50 20 0 kV SSD 64 00 urn
low Zn-|
Spl
• 1 »
o/1
PI
(«andesine)
St 6102/2 LI-09
0.01 mm
1/15/2013 WD Mag Spol HV Del HFW 2:01 01 PM 10 0 min 2900X 5 1 20 0 kV SSD 88 28 prr
20 urn
Bt
Barich etal. (2014), Ronda
8.5kV    X3.700      1pm     WD 9.1 mm
Ferrero etal. (2012), Himalaya
Characterization of melt inclusions
Kumdykolite, polymorph of albite Kokchetavite, polymorph of alkali feldspar Cristobilite, polymorph of quartz
Ferrero etal. (2016)
Analysis of melt inclusions
4. Re-homogenization experiments: piston cylinder (pressure)
- Prepare several thin sections from the rock under study (focus on Grt)
- Identify the thin section with the most abundant and best preserved Ml (no offshots!)
- Prepare double polished, >200 micron thick, sections
- Select areas under the microscope rich in Ml, individualize Ml-rich areas.
Ferrero etal. (2012)
Bartolietal. (2016)
Analysis of melt inclusions
4. Re-homogenization experiments: piston cylinder (pressure)
- Prepare several thin sections from the rock under study (focus on Grt)
- Identify the thin section with the most abundant and best preserved Ml (no offshots!)
- Prepare double polished, >200 micron thick, sections
- Select areas under the microscope rich in Ml, individualize Ml-rich areas.
Analysis of melt inclusions
4. Re-homogenization experiments: piston cylinder (P)
Australian National University, Canberra
Analysis of melt inclusions
4. Re-homogenization experiments: piston cylinder (P)
Bartolietal. (2013)
Mb I
Thermocouple
MgO-salt
(0 = 10 mm)
Au capsule
(0 = 3 mm)
Graphite heatei
(0 = 12 mm)
NaCl sleeve
(0 = 22 mm)
Analysis of melt inclusions
4. Re-homogenization experiments: piston cylinder (P)
b
Analysis of melt inclusions
4. Re-homogenization experiments: piston cylinder (P)
✓
WD    Mag Spot   HV    Det HFW I0.0mm5215x 5.2 20.0 kVSSD 49.09 urn
Acosta-Vigil etal. (2016)
Bartolietal. (2013) Cesare etal. (2015)
20 jam
3/21/2014     WD     Mag Spot   HV    Det HFW 12:14:36 PM 10.0 mm 2063x 5.0 20.0 kV SSD 0.12 mm
Analysis of melt inclusions
4. Re-homogenization experiments: piston cylinder (P)
Bartolietal. (2013)_
I   Barich et al. (2014)
Analysis of melt inclusions
5. Electron microprobe analyses (major elements)
Comparison of melt inclusions with leucosomes in migmatites and granites intruded in the upper continental crust
_i_i_i_i_,_i_i_i_i_i_i_i_._
0.8  0.9   1.0   1.1   1.2   1.3   1.4   1.5 1
Cesareetal. (2015)
Analysis of melt inclusions
6. Laser ablation ICP-MS (trace elements)
Australian National University, Canberra smaller beam diameter was 19 microns
Analysis of melt inclusions
6. Laser ablation ICP-MS (trace elements)
Oh
a
c
700
500
Li
O MI in PI
O MI in Grt H Mat gl enclaves I Mat gl dacites
0.0001
0.00001
•	P°
	"      O -
	o
	o _
□ t	ft^Q) -
HO-50A
.................................
Cs Ba Li  B   U Ta Co Nd Zr Eu Gd Y   Yh V  Cu Sc Ni Rb Pb Be Th Nb La Sr  Sm HI Ti  Dy Er Lu Zn Cr Co
10
<s 6
2 0
U/Th	1
- •	-
•o	
o	
	
	REE
1	
50
100
150
1000
100
10
o
c -E
^     0.1 r
0.01
0.001
~1—I—I—r
i—i—i—r
—i—i—i—i—r
Ml in PI
HO-50A
J_I_I_L
J_I_I_I_L
. Ce „ Nd c Ru„,Tb_. Ho ^ Tra „, Lu La     Pr Sin    Gd    Dy     Er Yb
Acosta-Vigil etal. (2010)
Analysis of melt inclusions
7. NanoSIMS (H20)
Information from study of melt inclusions
2. That (part of) a mineral grew in the presence of melt
Platt et al. (2003)
Information from study of melt inclusions
4. Primary melt compositions: mechanisms/nature of anatexis
Problems and pitfalls
From the current available data, it is clear that nanogranitoids represent former melt, but:
a) How representative is the melt composition of the bulk melt in the system at the time of entrapment?
b) How much has the original composition been modified during/after the entrapment process? That is, how representative is the currently measured composition of the original melt at the surface of the growing mineral?
Through investigation and analysis of melt inclusions in many case studies
se st
c enclaves
Melt inclusions in anatectic metapelitic enclaves from El Hoyazo, S Spain
High-K calc-alkaline and shoshonite rocks
Calc-alkaline rocks Internal Zones (undiferentiated)
5% enclaves 25% phenocrysts 50% glass ASI=1.5
El Hoyazo volcano
Löpez-Ruiz & Rodnguez-Badiola (1980) , Zeck (1992)
Grt-Bt-Sil enclave i.
mm:t
South-Iberian (Subbetic and Prebetic) and Maghrebian Cover
Flysch Trough Units
Alboran Crustal Domain
^^^^^^^^^^^^^^^^^
3 Volcanic Rocks
Neogene sedimentary cover
Lower Miocene to Recent Sediments |   d   | Mud Diapirs South Balearic Basin H Anomalous Crust ? B Oceanic Crust ?
/ IBERIAN FORELANE (-~-- "Sr^Selics Atlantic _ I     l External Z	/ _ O" ^—South l^^^v Balearic \--<^-"---' AFRICAN 14B FORELAND unes        Alboran Domain
	
Petrography, P-T conditions of melting
y*- -
Césare (2008) J
Petrography, P-T conditions of melting
iflfirfl Alvarez-Valero et al. JMG (2007)
Melt inclusions in anatectic enclaves versus anatectic terranes
Pros-cons: quenching, matrix glass vs. decrepitation, abundance
surface
brittle-ductile transition
solidus
Moho
volcano
	
	pluton
	
quenching glassy Ml matrix glass
x
Bartoli et al. EPSL(2014)
crystallization nanogranites leucosomes
Modified after Sawyer et al. Elements (2011)
Melt inclusions under microscope/SEM
4 gg*
Grt
Acosta-Vigil et al. Chem Geol (2007)
Normative composition of glasses
2 cm
Orthoclase
Acosta-Vigil et al. in preparation
Major element composition of glasses
16 15 14 13 12 11 10
Al90
i-1-1-1-r
□
2^3
□
j_I_I_I_i_
66    68    70 72
74    76 78
Si02 (Wt%)
10
66 68
74 76 78 Si02 (Wt%)
66 68
72    74    76 78 Si02 (Wt%)
o MI in PI □ MlinGrt ■ Matrix gl
o
0 12 3
FeO+MgO+Ti02 (wt%) Acosta-Vigil et al. in preparation
1.0 1.5
CaO (wt%)
5 6 7
K20 (wt%)
Processes changing composition of
Ferrero et al. (2011)
Mass balance modeling Ml in Pi-matrix gl
16
15
14
13
12
1 1 1 i 1 1 1 i 1 1 1 i 1 1 1 i 1 1 1 i 1 1 1 i 1 1 1 i 1 ■ 1 i 1 1 1 i
A1203
OMI in PI ■ matrix glass
11
68        70 72 74        76 78
i 1 ■ 1 i 1 1 1 i 1 1 1 i 1 1 1 i
i 1 ■ 1 i 1 1 1 i
1.5
1.0
0.5
CaO 0
o
i1111111111111111
o
o
o o
boundary layers
dissol./crystal. 3 wt% host PI v crystallyzation
20 wt% daugh. Kfs
diffusive loss 4 wt% H2O
O
OQ
o
™ ■ Jrwlr -
o
oo
78 68
; molar Al/Na	1 ■ ■ ■ 1 . . . 1 . . ,
oo	o
o o°o	o «t
	
uo^ o 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1	
	Si02;
-p 2000
§; 1500 |
^ iooo0°°
500 F
68       70        72        74       76        78       68       70        72        74       76 78
o
———
10    20 :
0°ooo0°00oo0°o0
Line 4 I
, ...........,,,,.....-
)     30     40     50     60     70 80
Distance (microns)
Mass balance modeling Ml in Pl-matrix gl
200
150
100
50
Sr
compatible elements
o
2?
0.5
OMI in PI ■ matrix gl
Eu
150
100
50
1.5
Sr_
compatible element
1"
o
o o
o
Q o
)
o
I incompatible! element
o
o
oy)o Q
Zr
10
20
30
40
50
Ba    Li    La   Sr   Nd    Eu   Tb   Ho  Lm   Lu Ni Pb    Be   Ce    Pr    Sm   Gd  Dy    Er   Yb Cu
Acosta-Vigil et al. J Petrol (2012)
Trace element composition of glasses
Acosta-Vigil et al. J Petrol (2010)
40
30
20
10
Cs
h o
o
t
oMI in PI • Ml in Grt □ matrix glass ■ dacite glass
B
200
150
100
50
V
V
□
o
□
□
□     o ^
_qg ~o
cP □
8 8
Ti
500      1000m 1500
Ti
2000
100
0   100 200 300 400 500 600 700 800      0 1000       2000       3000 4000
10
U/Th
- O
o.
20 0
CD |
\-1—
50
REE
100
150
Zrn and Mnz saturation Temperatures
900
800
700
600
i-1-1-1-1-1-1-r
Tz
rn
oMI in PI • Ml in Grt □ matrix glass ■ dacite glass
710-81 a °c
670-700 °C
o
□on
□ 700-750 °C
O
Tm
nz
_i_i_i_i_i_i_i_i_i_i_i_i_i_i_
600
700
800
900
Acosta-Vigil et al. J Petrol (2010)
Extent of mineral-melt equilibrium (TE)
microns
Acosta-Vigil et al. J Petrol (2012)
Extent of host PI-MI and Pl-matrix melt equilibrium based on trace elements
Acosta-Vigil et al. J Petrol (2012)
if) O
■ ■■■■■
Co
■E 1000
o
CD
CD O
c
o o
if) if)
03
100 \
10 \
1
0.1
0.01 ;
^0.001
CL
i—I—I—r
o o
o
O
.............8
rEL 700-
8(X)~ »2k-^-750üC 850°C^m
l    I   I r
I    I   I r
O
HO-50 enclave ; <
0 □
0
B □ D 0
n B g ü—[J
a
R 700 U850°C
g □
□ □
o	Ml#5 in PI
o	Rest of Ml in PI
□ 1 1	Matrix glass NC85,EL02
7ÖÖ°C	BW91 at
	T=700°C
......	
□
§ Q H □
ü   rn D
□ □
-□......................
□
J_I_I_L
Plagioclase
I_i_L
Ba    Li    La Nd Tb   Ho  Tm   Lu Ni
Pb Be   Ce   Pr   Sm   Gd Dy   Er   Yb Cu
Extent of host Grt-MI and Grt-matrix melt equilibrium based on trace elements
Acosta-Vigil et al. J Petrol (2012)
O
CO
o
CD
o
c
o o
(/) (/)
O)
5
1000
100 10
1
0.1
0.01 0.001 0.0001
"i—i—i—i—i—i—i—i—i—i—i—i—i—i—r
HO-33 enclave ....................................................• •
f i f i t
i—i—i—i—g
■B
y.ea.n.Mg.y......
8
.a I
□
i—i
I
"D-l-O-
0
0
□
□ ■
□
I   i ? I
1
Garnet
J_I_I_I_I_I_I_L
•	Ml in Grt	
□	Matrix glass	
1 1	RH07 at T=	
	800-850°C	
1 1	.....	
Li   U   Ce Nd  Zr Eu Th La   Pr Sm Hf
Cr Co Zn Sc
Extent of Bt-matrix melt equilibrium based on trace elements
Acosta-Vigil et al. J Petrol (2012)
C/) O
To
o
03
C
0) O
c
o o
CO CO 03
O)
1000 100 10 1
0.001 Ir
0.0001
~l—I—I—I—I—I—I—I—I—I
HO-50 enclave
i—i—i—i—i—i—i—i—r
~i—i—i—r □ □
---------p ■ ■ ■!-----
□
0
□
□
□
□
□
Tj-n
□ Matrix glass
MH83,NC85
IL95 at T= 650-750°C
Biotite
J_I_I_L
J_L
J_I_I_I_I_L
J_I_L
Be       La  Sr  Zr Eu Yb  V  Cu Ni B        Ce Sm Hf Gd  Lu        Cr Co
Extent of equilibrium Ml-matrix minerals, e.g. Bt, based on trace elements
Acosta-Vigil et al. J Petrol (2012)
O
00
o
03
C
CD O
c
o o
(/) c/)
1000
100 10
1
0.1
0.01 0.001 0.0001
~l—I—I—I—I—I—I—I—I—I
HO-50 enclave
i—i—i—r
i C 1   1 1
□
□
Ooo
o
Biotite
J_L
J_L
J_L
o	Ml in PI
•	Ml in Grt
1 1	MH83.NC85
—	IL95 at T=
	650-750°C
1   1  1   1   1   1 1	
Be       La  Sr Zr Eu Yb  V Cu Sc Ni B        Ce Sm Hf Gd Lu Zn Cr Co
Origin of Ml and matrix glass compositionsP
> Primary Ml, glassy, leucogranitic, peraluminous, similar to gl in experiments.
> Gl of each microstructural location: variable, distinctive, non eutectic.
> H20 concentrations indicate H20-undersaturated anatexis.
> Melt inclusions in PI and Grt represent former melt films in contact with crystals, remains of first anatectic melts we have access to for study.
> Ml in PI, most heterogeneous and evolved compositions, lowest Zrn-Mnz saturation T. Matrix melt, more homogeneous and less compositionally evolved, highest Zrn-Mnz saturation T. Ml in Grt, in between both.
> Differences among gl in several locations: not related to syn-, post-entrapment processes, likely reflecting matrix melt compositions at different T.
> Melt inclusions analyzed in several crystals/enclaves: matrix melt with well defined LILE-rich, HFSE- and REE-poor geochemical character. Matrix melt likely at or close to equilibrium with the residue (except Grt).
> Matrix glass: melts produced after Ml, mostly at or close to equilibrium with rims of most minerals (except Grt).
Pedogenesis of crustal anatectic systems from the study of melt inclusions
Pedogenesis of crustal anatectic systems from the study of melt inclusions
Melt inclusions in granulites from the Betic Cordillera Ronda area S Spain
< 5 km
Malaguide complex
<330°C
Jubrique unit
> 650°C
Ronda peridotite Dynamothermal aureole Blanca unit       j q
Jubrique Unit Ron
Metamorphic isograds
Ronda Peridotite d
Grt-Spl Spl tectonite Recrystallization mvlnnitp frnTLf
Estepona
MapbetTa "
Alboran Sea
Barich et al. (2014), Barich PhD (2015)
- ?'        9 ,       ' I v.
■ :'V,'wt: ' y~
Field geology
Petrography
Petrography & SEM
of the melt inclusions
• :'.V<».
p.
Grt
■■t
20 urn
1 flT\»
1/17/2013    WD    Mag Spot   HV    Det HFW 1:38:03 PM 10.0 mm 4000x 5.0 20.0 kVSSD 64.00 urn
SEM of the melt inclusions
Barich et al. (2014)
P-T of host rocks
Barich etal. (2014)
Melt inclusions in granulites from the Betic Cordillera, Bonda area, S Spain Field geology, petrography, SEM
* Melt inclusions are primary based on their distribution in the host garnet. Mostly crystallized.
• They appear from core to rim of large garnets and hence most garnets grew in the presence of melt.
• Melt inclusions were trapped both at peak conditions (12-14 kbar, 800-850°C; Grt cores) and post-peak conditions (5-6 kbar, 750-800°C; Grt rims+Matrix).
* They appear to have granitic mineral compositions (daughter minerals are Qz, Fds, micas).
Experimental remelting: rehomogenizion
Experimental remelting: rehomogenizion
850 °C
4 Experiments
15 Kbar Dry (no added H20) 24h
825 °C
825 °C
800 °C
Barich PhD (2014)
Acosta-Vigil et al. (2016)
Experimental remelting: SEM study
Rehomogenized melt inclusions:
having glass, and also
- Rregular walls,
- No daughter minerals,
- No offshots,
- No host recrystallization,
- No reactions between melt-accidental minerals.
Acosta-Vigil et al. (2016)
Experimental remelting: EMPA study
ff> 0.6 ^ 0.5 0.4,
toiialite
0.3 Apjw8s
0.1 L        ?ri""N-...A     ^ramre \0.9
'tiondhje _^_
0.9    0.8    0.7   0.6   0.5    0.4    0.3    0.2 0.1
albite
Leucogranitic: plot close to water undersaturated haplogranitic
eutectics Granodioritic to Tonalitic: plot close to Qz-Ab joint
Two main compositions: -Leucogranites -Granodiorites to Tonalites
Acosta-Vigil et al. (2016)
# Haplogramtic eutectics at
0.5-2 GPaandajjjosl -----Cotectic lmes at 0.5 GPa H-,0
j Haplogramte-NaCl-KCl eutectics t} at 0.6 GPa, aH:0 - 0 86-0 35 £j at 1.0 GPa, aH:0- 0.63*34 £j at 1.4 GPa. aH:0-0.74-0.44
0.9    0.8    0.7   0.6   0.5    0.4    0.3    0.2 0.1
albite
Experimental remelting: EMPA study
Peraluminous High Si02
Low FeO+MgO+Ti02
Variable CaO, alkalis and H20
Leucogranitic: Low Ca, H20; high K
Granodioritic to Tonalitic: high Ca, H20; low K
Large Grt Rims
.2 2
CaO
O 800 °C n A 825 °C
□
□ 850 °C
H Cores of large Grt ■ Rims of large Grt
□ Small Grt
f WR mylonilic gneiss <^         WR leucosome
□
a
kO
SiO,
60
65
70
4
75
—1-1-1-1-1-1-1-r
CaO
□
□
ä A# ' • A
J
J_i_I_i_I_i_L
0      12      3 4
Concentration (wt%)
1   1   1   1   1   1   1 1	■   i    i   i i
	-
v •J	-
	
0    12    3 4	5    6 "
K20 i,i,	
5      6 7	
CaO
~i—1—i—1—i—1—i—1—r
b
A
O
8 10
CaO
n—1—i—1—i—1—i—1—i—1—i—1—r
▲ Al
A A
°A
H,0
i.i,_i_i_i_i_i_i_i_
4 8 12
Concentration (wt%)
16
20
Jubrique granulites: Pedogenesis
r iui iiuiu a
akdown me
CD Q_
o e
=5
CO CD
600
700
800
900
1000
Acosta-Vigil et al. (2016)
Temperature (°C)
Jubrique granulites: Pedogenesis
Type II Ml / Grt Rims:
•Trapped in Grt rims P-T •Granodioritic-tonalitic compositions, high H20 ( mean of 10-12 wt%)
•Composition and H20 content similar to melt in H20-present experimental melting of metapelites
•Low F and CI, hence no brines involved
03 Q_
Ě
=5 if) <D
CL 0.4
0.2
i Qz Liq
I Grt Crd Bt Kfi hj^
I PI Sil Mm Qz Liq jy,'
	Grt Crd Ftp Sp i .i. Qz Liq
Grt Cld Kfí P Sp Mm Qz Liq /	
	I
J H 06
J_I_I_I_I_I_I_I_I_I_I_i_I   i r
600
700
800
900
1000
Acosta-Vigil etal. (2016)
Temperature (°C)
Jubrique granulites: Conclusions
Type I melt inclusions are trapped at the cores of large garnets, formed at <850 (800 °C) and 12-14 kbar.
Significance of GJas5 Composition in ih. riamahad JVJJ
Leucogranitic melts in garnet cores were produced by anatexis at low activity of H20. Likely due to fluid absent melting of hydrous minerals (e.g. biotite).
Geodynarnic Setting
Closed-system anatexis at the bottom of a thickened continental crust in a context of a continental collision.
Jubrique granulites: Conclusions
Type II granodioritic-to-tonalitic Ml are trapped at the rims of large garnets formed at -800 9C and 6-8 kbar.
Q) 0.6
Significance of Glass Composition in the JHernelied JVJJ
_1^. 4£__ - .tss
CnCidBIKts Gil Cid Kt» PI \ / Mm
| Sp Mm Qtliq ~/ 1—
800   850 900 s-.
600 700 800 900
Temperature (°C)
1000
Granodioritic-to-tonalitic melts were produced by H20-fluxed (saturated or nearly saturated) melting, likely the entrance of H20-rich fluids into the system.
Geodynarnic Setting
Open-system anatexis at the bottom of a continental crust of regular thickness in a context of a continental extension.
Migmatites of Jubrique underwent two melting events under
contrasting fluid regimes