Determinación de la Concentración de Hemoglobina

1.300+20 Ma@ 120±20°C 2.250+30 Ma @ 20±20 °C 3 .150±30 Ma @ 90±30 °C 4 . 10±10M a@ 60±60°C 5.0M a@ 10±10°C T(°C) l e n g t h a g e n o n e 4 7 3 2 1 1 2 l e n g t h + a g e 272 204 196 Time (Me) TTC) L e n g t h a n d A g e P(L ) > - O b e > P |A ) P (L ),P (A ) < O b s P (L ),P (A ) > - O b s P (L ) < O b s < - P (A ) 0 20 40 60 60 100 120 68 940 272 204 196 0 Time (Me)

Fig. 5.17. Input data and length and age fit simulations for the modelling experiment recent uplift 1. Colours for all simulations plot is as in 5.14.

Asturia 1

Laslett Durango

Time - T em perature points 1.250±30M a@ 20±20°C 2 . 115±20 Ma @ 60+60 °C 4.40±10M a@ 60±60°C 5.0M a@ 10±10°C T(»C) L e n g t h a n d A g e P(L) > - O b s > P (A ) P(L ),P{A ) < O b s P (L ),P (A ) > - O b s P ( L ) < O b e < - P ( A ) 100 120 910 186 124 62 0 Time (Me)

Fig. 5.18. Input data and length and age fit simulations for the modelling experiment Asturia

1.

2 0 0 sim ulations failed to predict the m easured age and length values, again sh o w in g th a t this rep resen ts an un lik ely scenario. The p red ic te d age d istribution cannot be confidently com pared to observed d ata because the u ran iu m density w as too low to pro d u ce en o u g h confined tracks w ith which to accumulate a sufficiently precise data set.

T im e tem p.

1 250±30 20+20

2 115+20 40+40

3 40+10 40+40

4 0 10+10

Table 5.10 T-t values w ith bounds for A sturia 3.

5.5 Summary and discussion.

The apatite fission track data presented in this thesis pro v id e a new insight into the hitherto poorly understood post-V ariscan evolution of the A rm orican and H esperian Massifs. Geological evidence com plem ented b y c o m p u ter m o d ellin g sim u la tio n s p ro v id e a h isto ry of P e rm ia n u n ro o fin g , follow ed by b u rial d u rin g the M esozoic an d su b seq u e n t exhum ation, revealing the massifs as observed at the present day.

The m odel slow cool 1 predicted tw o possible scenarios b o th of

w hich p ro v id ed reasonably good fits to the data. The first involved a m o notonie slow cooling scenario w hich sh o u ld be d isc o u n te d on a geological basis, as there is evidence that the Variscan belt w as eroded dow n to a p en ep lain in the Lower Perm ian (Smith et al., 1974). The second scenario allow ed the m assifs to be exhum ed in the Perm ian, an d then b u ried d u rin g the Mesozoic, to be re-exhum ed in the later M esozoic and Tertiary.

Slow cool 2 constrained the m odel to fit a therm al history w hich

involves a Perm ian exhum ation, and the sim ulations predicted a situation w h e re in e n s u in g M esozoic b u ria l o c c u rre d to te m p e r a tu re s of approxim ately 90°C. Similar situations w ere p red icted from the m odels devised to predict the appearance of the younger ages observed.

The m odel recent u p lift w as devised in an attem p t to im prove

p red ic tio n s of track len g th d istrib u tio n s to o bserved d istrib u tio n s. A situ atio n sim ilar to th at predicted in the p relim in ary fo rw ard m odel F, predicted good fits to the observed age and length data. C onsequently this ap p ears to be the m ost likely therm al h isto ry for the ev o lu tio n of the Variscan Massifs from the end of the Variscan Orogeny to the present day.

The relationship of the presented interpretation of the data to the know n geology is as follows. Firstly, the fission track data accom m odates deep d en u d atio n of the A rm orican m assif occurring d u rin g the Perm ian.

H ow ever, g rad u al m onotonie cooling from the end-C arboniferous to the present can be discounted as an unviable therm al history. It is also unlikely th at the rocks rem ained at the surface throughout the Mesozoic after initial exhum ation d u rin g the Permo-Trias. The accepted view th at the A rm orican and H esperian Massifs have rem ained as upstan d in g terrestrial blocks since the Perm ian is contested here as the apatite fission track data show clear evidence of b u rial d u rin g the Mesozoic. As a resu lt of these m odelling experim ents, a proposed therm al history of the A rm orican and H esperian Massifs is illustrated in Figure 5.19. Assum ing a geotherm al gradient of 30°C k m ”l, Perm ian exhum ation w as followed by burial to depths of 3 to 3.5 km (90-100°C), attaining these m axim um depths in the m id Jurassic. This w as follow ed by gradual exhum ation during the U pper Jurassic to m id Miocene to the u p p er limit of the PAZ (60°C) at a rate of -12 m Ma"l. D uring the late M iocene, the rate of u p lift ap p aren tly increased significantly to rates approaching -130 m Ma“l.

The anom alously young Eocene ages determ ined in the A sturian Arc have proved m ore complicated to explain. How ever, the m odels predict th at the innerm ost A sturian Arc has undergone burial to the low er regions of the PAZ (but not to resetting tem peratures) and has only been exhum ed since the Neogene. Alternatively, these young ages could exist as a result of resetting by hot fluids m oving along the m any faults, fractures and thrusts of this region. This view is supported by the rem agnetisation data of Schott an d Peres (1987). Such fluids w ere possibly generated d u e to P yrenean collision. A lthough not readily explicable, a strong case can be m ade for the influence of hot fluids on the anom alously young age of VEND 16, existing as it does in the region w here the oldest ages are found.

The geographical relationships of the data show a generalised tren d of increasing age aw ay from the N o rth A tlantic rift axis and are a p p aren tly u n related , save in their obvious spatial d istrib u tio n , to the riftin g and opening of the Bay of Biscay. The d ata fu rth er u p h o ld the passive n atu re of this particular rift w hen com pared to m ajor continental breakup, such as that of the Atlantic Ocean.

ü o H

C P

Tr

K

Q

Fig. 5.19. The proposed regional thermal history of the continental margins of the Bay of Biscay deduced from geological controls and data-driven computer modelling.

Chapter 6.

The Mesozoic and Cenozoic evolution of the