Geological Society of America Special Paper 378 2004 Detecting provenance variations and cooling patterns within the western Alpine orogen through 40Ar/ 39Ar geochronology on detrital sediments: The Tertiary Piedmont Basin, northwest Italy

B. Carrapa* J. Wijbrans* G. Bertotti* Vrije Universiteit Amsterdam, Faculteit der Aardwetenschappen, De Boelelaan 1085, 1081HV Amsterdam, The Netherlands

ABSTRACT

The Tertiary Piedmont Basin is a synorogenic basin located on the internal side of the Western Alps. Because of its key position, the Tertiary Piedmont Basin represents an important record of processes occurring in the Alpine retrowedge for over the last 30 m.y. 40Ar/39Ar geochronology has been applied to detrital white micas as a prov- enance tool and to derive information on cooling and exhumation patterns within the surrounding orogen. The age distribution in the detritus shows that in the Oligocene the clastic sediments were fed mainly from a southern source area (Ligurian Alps) that widely records high pressure (HP) Alpine metamorphism (40–50 Ma) and, in part, Variscan metamorphism (ca. 320 Ma). From the Miocene, the main source area gradually moved from the south to a western Alpine provenance characterized by strong Late Cretaceous (70 Ma) and Early Cretaceous (120 Ma) signals. This enlarge- ment in the source is likely linked to an evolution of the main paleodrainage system into the basin. From the Serravallian, Variscan ages reappear; this is attributed to the exposure of the Argentera Massif as a new source for the Tertiary Piedmont Basin. The lack of thermal overprinting of the main detrital signals through time suggests that the western Alpine orogen has been regulated by episodic fast cooling and exhu- mation events followed by periods of slower erosion. Also, detrital 40Ar/39Ar Creta- ceous signals in Miocene and Present sediments suggest the presence of real Eoalpine events in the Alps.

Keywords: Western Alps, provenance, 40Ar/39Ar geochronology, cooling, exhumation.

INTRODUCTION consequence, clastic sediments are the only remaining direct evidence of the original source rocks outcropping at the time Synorogenic clastic sediments contained in sedimentary of sediment deposition. Therefore, they provide a record of the basins preserve a record of the exhumation kinematics of original setting of mountain belts through time. an orogen. Because of erosional and tectonic processes, the The Tertiary Piedmont Basin, located within the internal original rocks outcropping in the orogen no longer exist. As a western Alpine Arc (retrowedge; Beaumont et al., 1996) in northwest Italy (Fig. 1), contains up to 4 km of clastic sedi- *Present address, Carrapa (corresponding author)—Universität Potsdam, ments (Fig. 2). The Tertiary Piedmont Basin and the western Institut für Geowissenschaften, Postfach 601553, 14415 Potsdam, Germany, Alpine arc formed as a result of the Tertiary European-African [email protected]. E-mails: Wijbrans—[email protected]; Ber- totti—[email protected]. plate collision (e.g., Platt et al., 1989). The Tertiary Piedmont

Carrapa, B., Wijbrans, J., and Bertotti, G., 2004, Detecting provenance variations and cooling patterns within the western Alpine orogen through 40Ar/39Ar geochro- nology on detrital sediments: The Tertiary Piedmont Basin, northwest Italy, in Bernet, M., and Spiegel, C., eds., Detrital thermochronology—Provenance analysis, exhumation, and landscape evolution of mountain belts: Boulder, Colorado, Geological Society of America Special Paper 378, p. 000–000. For permission to copy, contact [email protected]. © 2004 Geological Society of America. 69 70 B. Carrapa, J. Wijbrans, and G. Bertotti

Figure 1. Geological map of the study area; TPB—Tertiary Pied- mont Basin (study area), VG—Vol- tri Group, LA—Ligurian Alps, AGM—Argentera Massif, DM— Dora Maira, GP—Gran Paradiso, SL—Sesia Lanzo.

Basin is well suited for investigation of a substantial part of the of white micas (350–420 °C; e.g., Hames and Bowring, 1994; complex Alpine orogen because it is one of the main sedimen- Kirschner et al., 1996; Kohn et al., 1995; von Blanckenburg et tary basins collecting clastic sediments produced by cooling and al., 1989) is high enough to avoid substantial overprinting due exhumation and erosion of the internal Western Alps (including to short-lived thermal disturbances and sedimentary burial. Also, the Ligurian Alps). The Tertiary Piedmont Basin stratigraphy is 40Ar/39Ar dating of white mica is a well-tested technique that well preserved, exposed, and documented (e.g., Gnaccolini et al., records the time in which the investigated minerals pass through 1998, and references therein; Fig. 2). These data, together with a closure temperature of 350–420 °C (Najman et al., 1997; von paleocurrent directions data (Fig. 3A) on the study area, allowed Eynatten and Wijbrans, 2002; White et al., 2002). a good sample strategy (Fig. 3B). Research in the Himalayas (e.g., Harrison et al., 1993; For the present study, we have applied 40Ar/39Ar geochronol- Najman et al., 2001; White et al., 2002), in the Central Alps ogy to detrital white micas derived from samples selected from (e.g., Bernet et al., 2001; Spiegel et al., 2001; von Eynatten and the entire Tertiary Piedmont Basin stratigraphy (Lower Oligo- Wijbrans, 2002), and in western North America (e.g Heller et cene–Upper Miocene). To extend the covered time interval from al., 1992) has demonstrated the potential of the geochronologi- the oldest Tertiary Piedmont Basin sediments to the present, we cal approach for both provenance and tectonothermal evolution sampled sands from three of the main rivers currently draining studies. In particular, studies on the Central Alpine sedimentary the internal side of the southwestern Alps, which are the main record and on the exhumation of crystalline rocks from the Alpine sources of Tertiary Piedmont Basin sediments (Fig. 3B). orogen have suggested rapid episodic exhumation (e.g., Hurford Detrital mineral thermochronology on present-day river et al., 1991) followed by a relatively steady state of exhumation sands has been largely applied to different tectonic settings to (e.g., Bernet et al., 2001; Schlunegger and Willett, 1999). So far, characterize the present river drainage pattern (e.g., Heller et al., however, little data exist (Carrapa et al., 2003) on the depositional 1992). Dating minerals from present-day river sediments pro- counterpart of the western Alpine erosion. Our data set of over vides new information on the geochronological signal currently 500 individual white mica analyses is well constrained due to recorded at the surface in the southwestern margin of the Dora the proximity of the source to the basin and sheds new light on Massif, the Argentera Massif, and on the Ligurian Alps. the reconstruction of the thermotectonic evolution of the western The major objective of this work is to obtain new informa- Alpine Arc for a time period of over 30 m.y. tion on: (1) Provenance of the clastic sediments; (2) Cooling patterns due to unroofi ng of the original source rocks related to GEOLOGICAL SETTING past denudation and/or tectonic and erosional processes; and (3) potential information on the timing of HP and ultra-high pressure The Tertiary Piedmont Basin is located on the boundary (UHP) metamorphism in the Western Alps. between the internal Alpine domain, consisting of deep crustal White micas are well suited for this geochronological rocks, and the Apennine domain, constituted mainly by upper approach because of their high K content, their widespread Cretaceous–Eocene fl ysch (Fig. 1). The Tertiary Piedmont Basin occurrence in different lithologies, and their resistance against is fl anked to the south by the Ligurian Alps and to the west and mechanical breakdown. Furthermore, the closure temperature north by Plio-Quaternary sediments, which in turn are bounded Detecting provenance variations and cooling patterns 71 to the west by metamorphic units belonging to the internal west- Alps (sensu stricto) to the west. The western Alpine arc contains ern Alpine domain (Fig. 1). HP and UHP rocks that experienced deep burial during the Alpine orogeny and subsequent rapid exhumation, such as the The Orogen Surrounding the Tertiary Piedmont Basin Dora Maira and Gran Paradiso massifs to the west (Hurford et al., 1991; Hurford and Hunziker, 1989; Rubatto and Hermann, 2001) The western Alpine arc surrounding the Tertiary Piedmont and the Voltri Group to the south (Brouwer, 2000). All these Basin includes the Ligurian Alps to the south and the Western rocks constitute potential sources of sediments for the Tertiary Piedmont Basin.

Figure 2. (continued on next page) A: Geological framework of the study area modifi ed after Gnaccolini et al. (1998). 1—Pliocene to Recent deposits; 2—Messinian deposits; 3—Langhian to Tortonian siliciclastic and carbonate shelf to slope deposits; 4—Late Burdigalian to Tortonian mainly turbidite succession (only Burdigalian in the eastern sector of the fi gure); 5—Late Oligocene to Burdigalian turbidite systems and hemi- pelagic mudstones; 6—Late Eocene to Early Oligocene deposits: (a) alluvial to coastal conglomerates, shallow marine sandstones and hemipe- lagic mudstones, (b) slope and base-of-slope, resedimented conglomerates, and (c) mainly turbidites; 7—Late Eocene to Tortonian siliciclastic deposits of the northwestern Apennines–Monferrato–Torino Hill wedge; 8—Alpine and Apennine allochthonous units; 9—depocenter axis of the Plio-Quaternary basins; 10—buried thrust-front of the Torino Hill–Monferrato–northwestern Apennine wedge; 11—buried, southvergent back- thrusts of the Monferrato, active from Messinian onward; 12—buried, pre Burdigalian backthrusts of the Western Alps (as inferred from Roure et al., 1990); 13—faults: SV—Sestri-Voltaggio; VVL—Villalvernia-Varzi line; I: Bagnasco–Ceva–Bastia Mondovì transect; II: Millesimo–Mo- nesiglio–Somano transect; III: Dego–Torre Bormida–Alberetto della Torre transect; IV: Spigno Monferrato–Cessole transect; V: Montechiaro d’Acqui; VI: Cavatore; VII: Visone. The square corresponds to the area of the paleocurrent study of Gnaccolini and Rossi (1994). B: Oligo-Mio- cene depositional sequences (A, B1–B6, C1–C6) in the study area after Gelati et al. (1993). 1—mudstones, locally with thin-bedded turbidites (a); 2—turbidite systems (sand/mud ratio from very high to = 1; locally, conglomerates); 3—resedimented ophiolite breccia; 4—olistolith-bear- ing pebbly mudstones; 5—shallow-water carbonates; 6—alluvial conglomerates, coastal sandstones, and conglomerates, freshwater mudstones (a); 7—Pre-Cenozoic rocks; 8—sequence boundary; 9—fault. The square inset is mainly based on Cazzola et al. (1981), Cazzola and Sgavetti (1984), and Cazzola and Fornaciari (1990). The ages of the unconformities and sequence boundaries are based on planktonic foraminifers and calcareous nannofossils and correlate with the third order global cycles boundaries of Haq et al. (1988). C: Stratigraphic scheme modifi ed after Gelati (1968). 72 B. Carrapa, J. Wijbrans, and G. Bertotti

Figure 2. (continued).

2. The Montenotte Nappe (Piemontese unit), which is The Ligurian Alps derived from the transitional domain between the ocean and the The Ligurian Alps bound the Tertiary Piedmont Basin to paleo-European continental margin (Vanossi et al., 1984). This the south. They consist of a nappe stack (Vanossi et al., 1984), unit experienced HP/low temperature (LT) Alpine metamorphism including the following: with a re-equilibration in blueschist facies (Messiga, 1981). No 1. The meta-ophiolite Voltri Group, which is a remnant of chronological data is available on the age of the metamorphism. the Piedmont-Ligurian ocean and consists of a cover sequence 3. The Briançonnais complex, which is derived from thinned constituted by metasedimentary rocks (calc-schists, mica schists, paleo-European continental crust and includes the Variscan Crys- quartz schists, and metabasalts) and a basement sequence of talline Massifs (e.g., Calizzano–Savona Massifs). These units Mg-gabbros, Fe-Ti–gabbros, and serpentinites (Messiga, 1984). have been affected by Alpine greenschist facies metamorphism The Voltri group experienced a complex retrograde metamor- (e.g., Messiga et al., 1992, and references therein). The Variscan phism ranging from peak eclogitic and blueschist facies toward Crystalline Massifs are characterized by 40Ar/39Ar ages ca. 380– greenschist facies (Cimmino et al., 1981; D’Antonio et al., 1984; 240 Ma (Hunziker et al., 1992; Fig. 4). Zircon fi ssion-track ages Messiga et al., 1989; Messiga and Scambelluri, 1991). Scarse K- on the Briançonnais domain yielded ages between 180–125 and Ar geochronology on white micas from presently outcropping 31 Ma (Vance, 1999). gneisses of the Voltri group give cooling ages of 31–41 Ma (Hun- ziker et al., 1992; Schamel and Hunziker, 1977; Fig. 4). 40Ar/39Ar The Western Alps dating on white mica from the Beigua serpentinite unit (Voltri The Western Alps consist of different domains including Group) gives ages of 45 ± 2 Ma (data cited in Brouwer, 2000). numerous units. In the following, we will consider only those Detecting provenance variations and cooling patterns 73

Alpine units affected by cooling and exhumation during the forma- tion of the Tertiary Piedmont Basin and that therefore constitute a possible source for the Tertiary Piedmont Basin sediments. The Internal Massifs (e.g., Dora Maira, Gran Paradiso; Fig.1) belong to the Penninic units, which represent the European continental basement and form the core of the western Alpine chain. They were affected by Eoalpine HP or UHP metamor- phism during Alpine subduction (e.g., Chopin, 1984; Chopin and Monié, 1984; Compagnoni and Lombardo, 1974; Dal Piaz, 1999; Monié and Chopin, 1991; Paquette et al., 1989; Polino et al., 1990; Scaillet et al., 1992) and subsequent exhumation. The timing and mechanism of the HP metamorphism and kinemat- ics of exhumation of the Internal Massifs are still debated (e.g., Brouwer, 2000; Compagnoni et al., 1995; Hurford et al., 1991; Michard et al., 1993; Rubatto et al., 1999; Rubatto and Hermann, 2001; von Blanckenburg et al., 1989). The Dora Maira Massif is mainly characterized by 40Ar/39Ar age ranges of 45–30 Ma, 85–60 Ma, and ≥120 Ma (Monié and Chopin, 1991; Scaillet et al., 1992; Scaillet et al., 1990; Fig. 4). Determination of cooling and relative exhumation kinematics for the UHP rocks of the Dora Maira has not been totally resolved (Gebauer et al., 1997; Hurford et al., 1991; Michard et al., 1993). One important issue in the Western Alps exhumation evolution is the interpretation of ages ~70–120 Ma. Different geochronom- eters (U-Th-Pb on zircons and monazites, U/Pb on whole rock, and 40Ar/39Ar on white micas) from HP rocks of the Dora Maira record ages ranging between 70–120 Ma (Monié and Chopin,

Figure 3. A: Paleocurrent directions modifi ed after Gnaccolini and Rossi (1994); location given in B. B: Enlargement of the study area with loca- tion of the analyzed samples. The inset area corresponds to the study on paleocurrent directions of Gnaccolini and Rossi (1994) (Fig. 3A). 74 B. Carrapa, J. Wijbrans, and G. Bertotti

Figure 4. Probability distribution diagrams of 40Ar/39Ar ages on white micas (single/total fusion ages) in the Tertiary Piedmont Basin surrounding source areas based on literature data from Stöckhert et al. (1986), Hurford et al. (1991), Hunziker et al. (1992), Scaillet et al. (1992), Ruffet et al. (1997), and Cortiana et al. (1998). For legend, see Figure 1.

1991; Paquette et al., 1989; Scaillet et al., 1992; Scaillet et al., Stöckhert et al., 1986) and 70–40 Ma (Cliff et al., 1998; Cortiana 1990), partially reset by a later Eocene-Oligocene greenschist et al., 1998; Rubatto et al., 1999; Fig. 4). A phase of rapid exhu- phase (Chopin and Maluski, 1980; Monié, 1985). A contrasting mation of the Sesia Lanzo zone occurred during the Oligocene view is that cooling of the UHP in the Dora Maira massif occurred (25–30Ma) Insubric phase (Hurford et al., 1991; Schmid et al., at 35–38 Ma (Gebauer et al., 1997; Rubatto and Hermann, 2001) 1989). while 70–120 Ma 40Ar/39Ar ages are ascribed to incorporation of The Argentera Massif is one of the largest external crystal- excess 40Ar (Arnaud and Kelley, 1995; Kelley et al., 1994). line massifs of the Western Alps, and it is the most proximal to The Gran Paradiso massif was affected by HP metamorphism the Tertiary Piedmont Basin. The Argentera Massif is made of during the Alpine orogeny. Rb-Sr dating on white micas yielded Variscan basement overlain by Upper Carboniferous, Permian, ages ca. 34 Ma (Freeman et al., 1997), while zircon fi ssion-track and Triassic series (Menot et al., 1994). The massif was overthrust (ZFT) ages are ca. 30 Ma (Hurford and Hunziker, 1989). Apatite by the Penninic nappes during the Oligocene and exhumed and fi ssion-track (AFT) ages are ca. 20 Ma, indicating that the mas- eroded in Miocene time (Bigot-Cormier et al., 2000). 40Ar/39Ar sif was at a few kilometers depth in the early Miocene (Hurford dating on the Argentera Massif give Variscan ages (e.g., Monié and Hunziker, 1989), possibly constituting a source for Tertiary and Maluski, 1983; Fig. 4) while apatite fi ssion-track ages show Piedmont Basin sediments in late Miocene time. that the Massif was at few kilometers from the surface during the A further potential source for the Tertiary Piedmont Basin is Late Miocene–Pliocene (Bigot-Cormier et al., 2000). the Sesia Lanzo zone and the Argentera Massif. The fi rst belongs to the Austroalpine basement and was part of the Adriatic plate, The Tertiary Piedmont Basin while the second belongs to the Provençal Delphinois domain. The Sesia Lanzo zone was affected by Paleogene-Neogene exhu- Sedimentation in the Tertiary Piedmont Basin started with a mation (Hurford et al., 1991). Timing of HP metamorphism in transgression dated as Late Eocene in the east and as Late Oli- the Sesia Lanzo Zone has been argued to be between 130 Ma gocene in the west (Fravega et al., 1994; Lorenz, 1984; Vannucci (Inger et al., 1996; Oberhänsli et al., 1985; Ruffet et al., 1997; et al., 1997) and continued until Late Miocene (e.g., Gelati and Detecting provenance variations and cooling patterns 75

Formation, Lequio Formation), tabular bodies are formed that can be traced through the whole basin, reaching a thickness of up to 2000 m (Fig. 2B, 2C). This reorganization is also recorded by uniform sandstone composition (Gnaccolini and Rossi, 1994). In particular, rock fragments of Miocene (from the Cortemilia Formation up) sediments mainly comprise quartzite, micashist, orthogneiss, acid metavulcanite, phyllite, carbonatic rock and subordinate metabasic rock, serpentinite, and phyllite, indicat- ing mainly a western Alpine source. Also, a detailed sandstone petrographic study on the Cassinasco Formation by Caprara et al. (1985) shows that sandstones from this formation are very rich in all types of metamorphic lithics and indicates a composite col- lision orogen source (e.g., Dickinson and Suczek, 1979), which could correspond to the Alpine Penninic nappe.

METHODOLOGY

Concepts for the Interpretation of Detrital Minerals Ages

Source rocks, each with characteristic geochronological Figure 5. Sketch showing: A: continuous cooling and exhumation, ero- signals, will result in the contribution of different ages to the sion of the source, and the correspondent geochronological signature 40 39 produced in the clastic infi ll; B: rapid cooling and exhumation fol- basin infi ll. Potentially, mica Ar/ Ar ages from different strati- lowed by slower erosion and the correspondent geochronological sig- graphic levels of the Tertiary Piedmont Basin can be interpreted nature produced in the clastic infi ll. For both scenarios, nappe stacking as recording variations in the original source rock cooling ages. took place at a temperature entirely below ~350 °C. Therefore, 40Ar/39Ar age populations refl ect the contribution in ages present in the original source area surface at the time of sedi- Gnaccolini, 1996; Mutti et al., 1995). Sedimentation continued ment deposition. The major assumption underlying the geochro- until the Plio-Pleistocene in the surrounding Po Plain. Initially, nological approach is that of a short, and therefore negligible, transitional (fl uvial, fan deltas) environments characterized time span between erosion in the belt and deposition of clastic sedimentation with the deposition of a mainly conglomeratic sediments in the correspondent sedimentary basin (Brandon and sequence up to 600 m thick, known as the Molare Formation Vance, 1992; Heller et al., 1992). This assumption is important (Fig. 2B, 2C) (e.g., Gnaccolini et al., 1990; Turco et al., 1994). for the calculation of cooling rates. We argue that this assumption Sediments from the Molare Formation were locally sourced from is justifi ed in the case of the Tertiary Piedmont Basin because of the Ligurian Alps (Gnaccolini et al., 1990; Barbieri et al., 2003). the close proximity of the source and basin. These sediments pass stratigraphically into the Rocchetta and In general, two different end member scenarios can be Monesiglio formations (lower Oligocene pro parte-Aquitanian; envisaged for the potential Tertiary Piedmont Basin source area Gnaccolini et al., 1998, and references therein). These sediments cooling and exhumation pattern and related 40Ar/39Ar ages in consist of transitional facies (Rocchetta Formation) and turbid- the Tertiary Piedmont Basin sediments. The fi rst one involves itic sandstones (Monesiglio Formation) in the lower part and by tectonic nappe stacking taking place entirely at temperatures in pelagic mudstones in the upper part, for a total of up to 1500 m excess of ~350 ºC. In this case, exhumation of the nappe stack (Fig. 2B, 2C). They are indicative of the progressive deepening would create a younging of cooling ages in the sediments (detri- of the Tertiary Piedmont Basin. The Rocchetta Formation in tal ages) due to continuous upward movements of crustal rocks the eastern sector includes a redeposited sandy body known as (e.g., Neubauer et al., 1996; Bernet et al., 2001) (Fig. 5A). In the Cassinelle Sandstones of Rupelian age. Facies characteristics, sedimentary record, this would result in a decreasing of detrital petrographic data, and paleocurrent directions obtained from the ages (age populations or peaks of ages) up-sequence (e.g., “mov- Rocchetta and Monesiglio formations suggest a provenance from ing peaks” of Brandon and Vance, 1992). However, if cooling both southern sectors, mainly the Briançonnais domain of the and exhumation ceased following an initial pulse of rapid cool- Ligurian Alps and the Voltri Group, and western sectors (Gelati et ing, and erosion was insuffi cient to unroof deeper crustal levels al., 1993; Gnaccolini and Rossi, 1994). (recording younger cooling ages), constant cooling ages in the From the Miocene, sedimentation became more homoge- detritus would be detected over a substantial period of time (e.g., neous (Gelati et al., 1993) with paleocurrent directions indicat- “static peaks” of Brandon and Vance, 1992) (Fig. 5B). ing dominant fl ow to the east (Gnaccolini and Rossi, 1994; Fig. The second scenario involves tectonic nappe stacking tak- 3A). From the late Burdigalian (Cortemilia Formation) up to ing place entirely at temperatures less than ~350 ºC. In this case, the Serravallian-Tortonian (Cassinasco Formation, Murazzano exhumation and erosion would produce ages recording old 76 B. Carrapa, J. Wijbrans, and G. Bertotti cooling processes while the time of tectonic nappe stacking after every fi ve unknowns. The unknowns were corrected for the would not be recorded by the Ar system, because it would have interpolated blanks at the time of analysis of the unknown, and occurred at a temperature lower than the closure temperature the 2σ error on the blank was further used for the error calculation (T) of the system (T < ~350 ºC). As we are dealing with the of the unknown. 40Ar intensities for the analyzed samples were in integrated contribution of minerals over a large source area, the order of >100 times the blanks (see Wijbrans et al. [1995] for any combination of the proposed scenarios may occur. Thus, by further details on mass spectrometer sensitivity). The discrimina- looking at changes in the main detrital age populations, we can tion factor was on average equal to 1.006 (see Kuiper [2003] for obtain information on different source rock contributions and on further details on discrimination factor calculation). Note that the different cooling patterns (e.g., Harrison et al., 1993; White et 2σ errors reported in Table A2 do not include the uncertainties in al., 2002; von Eynatten and Wijbrans, 2002). For provenance dis- J and uncertainties related to the age of the standards (the average crimination, we use variations in main detrital age populations. of J-related errors is in the order of 0.3%). The exclusion of the J- related errors in the analytical errors reported in Table A2 enables Analytical Technique a better comparison between samples (Foland, 1983). For further details on the calculation of the ages and related errors reported 40Ar/39Ar geochronology has been applied to detrital phen- in Table A1, refer to Koppers (2002). gites from over 60 samples from selected stratigraphic units of Probability distribution diagrams (Sircombe, 1999; Sir- the Tertiary Piedmont Basin, ranging in age from Oligocene to combe, 2000) have been used to identify the main populations Tortonian and to present-day river sands, with an average of of detrital ages present in different formations of the Tertiary seven samples for each formation and two samples for each river Piedmont Basin clastic infi ll and present-day river sands. The (Tables A1 and A2). Single fusion was applied on ~10 single probability distribution curves are compiled by summing the crystals (ranging between 250–500 µm in size) for each selected Gaussian distribution of each individual measurement, which sample, for a total of over 500 individual experiments. Step heat- is defi ned by the age and its error (e.g., Sircombe, 2000). Some ing was applied to 10 single grains ranging between 500 and formations (e.g., Rocchetta-Cassinelle, Cortemilia-Paroldo, 1000 µm in size, derived from different formations and rivers, to Murazzano-Cassinasco) have been combined because they are check the internal distribution of radiogenic 40Ar in each sample. synchronous and contain similar sedimentological patterns Only experiments concordant within 95% confi dence intervals (similar depositional environment and/or similar petrographic (i.e., MSWD < 2.5) have been used to derive plateau ages. The compositions and paleocurrent directions). As we are using the ages obtained on Tertiary Piedmont Basin clastic phengites are age probability distribution mainly as an indication of prov- interpreted to represent the time of isotopic closure during cool- enance, the major conclusions of this research are independent ing of the crystalline source through 350–420°C, as temperatures of any possible 40Ar excess problems in the source rocks. When reached during the main metamorphic events of the basement addressing the question of differential exhumation and cooling of rocks were generally higher than ~500 °C in the whole source the source rocks, we assess systematic age differences in the mica area (e.g., Messiga and Scambelluri., 1991; Gebauer, 1999). populations at different stratigraphic levels. Biostratigraphic ages The 40Ar/39Ar experiments were carried out with the of the formations indicated in the following paragraphs are given VULKAAN laserprobe at the Isotope Geology Laboratory of using the stratigraphic scheme of Figure 2C and the geological the Vrije Universiteit in Amsterdam, following laser extraction timescale of Berggren et al. (1995). and mass spectrometry methods for the laserprobe described by Wijbrans et al. (1995). The irradiation was carried out in RESULTS the cadmium-lined CLICIT facility of the TRIGA reactor of the Oregon State University Radiation Center. Irradiation times Results from Tertiary Piedmont Basin Clastic Minerals were 7 h for three different irradiations VU32, VU36, VU41. Correction factors for interferences of Ca and K isotopes were The geochronological data set is presented in Figure 6 and 0.000673 for 39Ar/37Ar, 0.000264 for 36Ar/37Ar, and 0.00086 for Tables A1, A2, and A3. The results will be discussed in order of 40Ar/39Ar, respectively. These values were determined using zero stratigraphic succession. The Molare Formation (Oligocene, ca. age K-feldspar and anorthite glass. After irradiation, a J curve 33.7–23.8 Ma) is characterized mainly by 40Ar/39Ar ages cluster- was derived for individual samples by interpolation between fi ve ing ~38–52 Ma with a strong 320 Ma signal and few ages ca. 99 single fusion experiments on every fl ux monitor. As fl ux moni- Ma and 60–75 Ma (Fig. 6). We refer to Barbieri et al. (2003) for tor standards for this project, we used Taylor Creek sanidine (for further details on this formation. VU32) and DRA (Drachenfels trachite [Wijbrans et al., 1995; The Rocchetta Formation (Lower Oligocene pro parte-Aqui- Steenbrink et al., 1999]) sanidine (for VU36-41; Steenbrink et tanian; ca. 30–20.5 Ma) is characterized by a dominant age signal al., 1999), with an age of 28.34 ± 0.16 Ma and 25.26 ± 0.14 Ma, of 40–65 Ma (Fig. 6), which is similar to the main age population respectively. These values are compatible with the set from Renne also found in the Molare Formation. Some ages ranging between et al. (1998), based on biotite GA1550 (at a K/Ar age of 98.79 90 Ma and 150 Ma are present, while the Variscan signal is less ± 0.69 Ma). In the present study, system blanks were determined pronounced than in the Molare Formation. Step heating analy- Detecting provenance variations and cooling patterns 77

ses on single grains were carried out on four samples from the Rocchetta Formation (Fig. 7). A step heating experiment on D61a produced a discordant age spectrum with a total fusion age of 109.8 ± 1.1 Ma. This spectrum is represented by slightly higher ages at lower temperatures, which might be the result of alteration or excess 40Ar. However, in case of excess 40Ar, a much more disturbed spectrum should be expected (e.g., McDougall and Harrison, 1999). The “plateau-like” region of the spectrum has a weighted mean age of 113.5 ± 7.4 (Fig. 7; Table A3). The analysis on sample D61b gives a plateau age of 108.7 ± 1.0 Ma, suggesting that this signal is undisturbed. The analysis of sample D57 yields a slightly discordant total fusion age of 73.2 ± 3.1 Ma, whereas a plateau age of 51.4 ± 1 Ma was obtained from sample D72, showing that this signal is undisturbed. The Monesiglio Formation (Upper Oligocene–Aquitanian; ca. 28.5–20.5 Ma), laterally interfi ngering with the Rocchetta Formation toward the east, is characterized mainly by ages ca. 50 Ma. The other ages range between 38 Ma and 150 Ma. Step heating analysis on sample D69 produced a slightly discordant age spectrum (e.g., alteration) with a total fusion age of 51.7 ± 0.5 Ma. The “plateau-like” region of the spectrum has a weighted mean age of 51.6 ± 1.3 Ma (Fig. 7; Table A3). The Cortemilia and Paroldo formations (latest Aquitanian– Langhian; ca. 22–14.8 Ma) display a cluster of ages mainly rang- ing between 38 and 70 Ma, with a few ages between 100 and 180 Ma. A minor component shows ages in the range 250–300 Ma. The Cassinasco and Murazzano formations (Langhian-Ser- ravallian; ca. 16.4–11.2 Ma) are characterized by an important contribution of ages ca. 70 Ma (Fig. 6), which is distinctive, because it is older than the dominant age population (ca. 50 Ma) detected in general in the previous formations. A minor signal indicating Variscan provenance is present. These formations are further characterized by an important group of ages between 90 and 150 Ma. Step heating analyses on single grains have been carried out on three samples from the Cassinasco Formation. Samples D40 and D50 give a plateau age of 106 ± 1 Ma and 78 ± 1 Ma, respectively (Fig. 8). The third analysis, on sample D65, produced a slightly discordant age spectrum (e.g., alteration) with a total fusion age of 94.4 ± 0.7 Ma. The “plateau-like” region of the spectrum has a weighted mean age of 94.4 ± 0.7 Ma (Fig. 8; Table A3). The Lequio Formation (Serravallian-Tortonian; ca. 14.8–7.12 Ma) displays two major peaks in its detrital mica ages, one at 50 Ma and the other at 70 Ma, and a strong reappearance of Variscan ages.

Results from Present-Day River Sands

Three samples (average of 20 grains for each sample) com- ing from the main rivers draining the present western Alpine Arc (Tanaro, Maira, and Stura Rivers; Fig. 3) have been analyzed using single fusion analyses. Step heating analyses have been 40 39 Figure 6. Probability distribution diagrams of Ar/ Ar (detrital) ages performed on a single grain from each river sample. for the samples (grouped in formations) investigated in this study. N—number of experiments; gray bars—indicative depositional ages. The headwaters of the Tanaro River are in the Ligurian For further details, see Table A2. Alps. It drains Triassic and Permian formations belonging to the 78 B. Carrapa, J. Wijbrans, and G. Bertotti

Figure 8. Step heating analyses of selected samples from the Cassi- nasco Formation. For further details, see Tables A1 and A2.

Piemontese and Briançonnais domain and, further to the south- west, the Variscan Crystalline Massifs belonging to the Ligurian Alps. The sample was collected at the entrance of the Tanaro River into the Tertiary Piedmont Basin (Fig. 3A). White mica ages range mainly between 270 and 306 Ma, with only one age of 37 Ma (Fig. 9, Table A2). A step heating analysis performed on sample B16 (Fig. 10) gives a plateau age of 314 ± 3 Ma, sug- gesting an homogeneous signal. The Stura River drains mainly the Argentera Massif and partly the Briançonnais domain. The main age population detected falls between 204–302 Ma (Fig. 9). A step heating analysis performed on sample B18 gives a plateau age of 306 ± 2 Ma (Fig. 10, Table A2), suggesting a Variscan signal undisturbed by subsequent Alpine overprinting. The Maira River drains the poly-metamorphic HP-UHP Figure 7. Step heating analyses of selected samples from the Rocchetta units of the southwestern part of the Dora Maira Massif. Detrital and Monesiglio formations. For further details, see Table A3. mica ages range between 39 Ma and 159 Ma (Fig. 9), with a Detecting provenance variations and cooling patterns 79

Figure 9. Probability distribution diagrams of samples coming from present-day river sands. For further details, see Tables A1 and A2.

cluster of ages between 65 and 95 Ma. A step heating analysis Ma, which can be linked to the contribution of detritus from the performed on sample B14 produced a slightly discordant spec- Variscan Crystalline Massifs present in the Ligurian Alps (Barb- trum with a total fusion age of 75.9 ± 0.6 Ma signal (Fig. 10). The ieri et al., 2003). “plateau like” region of the spectrum has a weighted mean age of Within the Rocchetta and Monesiglio formations, deposi- 76.3 ± 0.7 Ma (Fig. 10). tional facies change from transitional to marine with the hemi- pelagic sediments and high to low density turbidity bodies (e.g., PROVENANCE DISCRIMINATION AND INFERENCES Noceto, Mazzurrini, Piantivello; Gelati and Gnaccolini, 1998, FOR SOURCE AREA EVOLUTION and references therein), marking a deepening of the basin. There- fore, more distal sources compared to the Molare Formation can The wide range of ages in the Tertiary Piedmont Basin sam- be expected. The presence of a common (ca. 45–50 Ma) age ples refl ects the diverse provenance of the micas from different population for the Rocchetta and Monesiglio formations could tectonic units of the surrounding belt. Discrimination between have different interpretations: (1) a primary contribution from the different source areas has been attempted using the main detrital southern domain (e.g., Voltri Group), which refl ects the signal of age populations for each formation or group of formations as the crystalline basement that was widely affected by the Eocene distinctive of different source area contribution. Alpine metamorphism; (2) a contribution from western sectors, which also record the same Eocene signal (ca. 45 Ma); (3) a mix Oligocene–Early (Middle) Miocene of these different sources; or (4) partial reworking of sediments from the underlying formations. Oligocene-Aquitanian The fi rst hypothesis is less likely because in case of a pri- The Molare Formation is the fi rst Tertiary Piedmont Basin mary southern source, a stronger Variscan signal might have been clastic infi ll that lies on the crystalline rocks of the Ligurian Alps, expected. mirroring directly the source area outcropping at time of deposi- Ages between 200 and 120 Ma are widely preserved in the tion (Barbieri et al., 2003; Gnaccolini, 1974). Ages range mainly western Alpine domain (e.g., Hunziker et al., 1992; Cortiana et ca. 40–45 Ma, which can be related to the Alpine metamorphic al., 1998) but less so in the Ligurian Alps (Vance, 1999). Ages rocks of the Voltri Group and Montenotte Nappe, and ca. 320 ca. 200 Ma may represent the cooling following the Middle 80 B. Carrapa, J. Wijbrans, and G. Bertotti

in comparison to that feeding the Molare Formation. Therefore, the Rocchetta and Monesiglio ages are interpreted to record the fi rst signal of the erosion of western Alpine sectors.

Latest Aquitanian–Langhian Facies characteristics, petrographic data, and paleocurrent directions in latest Aquitanian–Langhian sediments (Cortemila and Paroldo formations) suggest a change in sedimentary pat- terns with provenance mainly from western sectors (Gelati et al., 1993; Gnaccolini and Rossi, 1994). The detrital signal in the Cortemilia and Paroldo formations spans a broad range of ages, which is interpreted to indicate a wide source area (possibly wider than the one feeding the Rocchetta and Monesiglio for- mations), including mainly western Alpine sectors. The lack of Variscan ages discounts the southern sectors as a possible source area. The main age population (40–50 Ma) could be interpreted partially as a signal coming from the Western Alps, which could potentially also record the Eocene signal or be the result of partial reworking. Other ages, ranging between 50 and 150 Ma, suggest a contribution from the western Alpine domains.

Middle–Late Miocene

This time span is characterized by a change in paleocur- rent directions, sandstone composition, and sedimentary facies (Gelati et al., 1993; Gnaccolini and Rossi, 1994). With the Cas- sinasco and Murazzano formations (Langhian-Serravallian), an important shift in main detrital age population (from 40 to 50 Ma toward 70 Ma) occurs, with a signifi cant cluster of ages at ca. 90–150 Ma. The stronger proportion of 70 Ma ages, which appears to be a dominant age cluster, older than the main age population (ca. 50 Ma), revealed in older formations is not com- patible with a simple scenario in which continuous exhumation and erosion of a fi xed source takes place (Fig. 5A). An evolution Figure 10. Step heating analyses of selected samples from present river of the paleodrainage system, including more western-north- sands. For further details, see Tables A1, A2, A3. western sectors (e.g., Sesia Lanzo), may explain the stronger contribution of the 70 Ma predominant signal. Also, in the cur- rently exposed crystalline units of the Ligurian Alps, there is little Triassic thermal anomaly, which infl uenced the Southern Alps evidence for units that have experienced cooling following a ca. and the Lombardian Basin and which was possibly related to the 70 Ma event, while evidence for an Eocene cooling after HP intrusion of a magmatic body in the lower crust (Bertotti et al., metamorphism is widespread in the western Alpine domain (e.g., 1997, and references therein). Ages ca. 85–100 and 65 Ma can Cortiana et al., 1998; Hunziker et al., 1992; Ruffet et al., 1995; potentially be linked to early exhumed oceanic units (e.g., the Agard et al., 2002, and references therein). Therefore, the shift in Sestri-Voltaggio Unit; no geochronological data are available in the main detrital age is interpreted as an evolution in sedimentary this particular area). pattern and provenance related to an enlargement of the Tertiary The presence of different ages that can potentially be related Piedmont Basin source area toward more western-northwestern to different sources within the same formation (e.g., D57–59, Alpine domains. This enlargement in the main Tertiary Piedmont Noceto system: depositonal lobes as in Mutti and Normark, Basin source area is probably associated with a reorganization of 1987), with paleocurrent directions coming from both southern the paleodrainage system. Reorganization of paleodrainage sys- and western sectors (Fig. 3), suggests mixing of sources within tems has also been recorded for this particular time in the Central the same formation and possibly within the same sample. and Eastern Alps (Carrapa and Di Giulio, 2001; Spiegel et al., The wider range of ages present in the Rocchetta and Mone- 2001; Frisch et al., 1998), suggesting a regional rearrangement siglio formations compared to the Molare Formation suggests a in the erosional pattern of the Alpine chain, probably caused by a wider source area (including both southern and western sectors) period of increased tectonic activity. Detecting provenance variations and cooling patterns 81

The Lequio Formation (Serravallian-Tortonian; 14.8–7.12 southern domain at present (Fig. 4). The same is true for 70–120 Ma) shows a main detrital population ca. 50–70 Ma, which can Ma ages recorded as a strong signal in Langhian-Serravallain still be attributed to a western Alpine domain with a strong reap- sediments and in the present-day sands, which is very similar to pearance of Variscan ages. The Variscan ages are interpreted in 40Ar/39Ar data on present outcropping rocks of the western Alpine this case as a signal coming from the Argentera Massif since domain (e.g., Cortiana et al., 1998; Ruffet et al., 1997; Scaillet et petrographic and paleocurrent data (Gnaccolini and Rossi, 1994) al., 1992; Stöckhert et al., 1986; Agard et al., 2002; Fig. 4). These do not give any support to the hypothesis of a southern source lines of evidence are not supported by a continuous exhumation (Variscan Crystalline Massifs in the Ligurian Alps). This conclu- and erosion pattern of a fi xed source. This shows that a consistent sion is well supported by a Late Miocene cooling and exhuma- amount of crustal rocks with indistinguishable 40Ar/39Ar ages has tion event recorded in the Argentera Massif (Bigot-Cormier et been eroded for a substantial amount of time, suggesting that the al., 2000). Western Alps have been regulated by episodes of fast cooling and exhumation (see also Carrapa et al., 2003). During these epi- Present sodes, enough crustal material with indistinguishable 40Ar/39Ar isotopic ages was formed and then was eroded over long periods The main detrital 40Ar/39Ar age population in the Tanaro of time and at present still sheds the same signals. River clearly mirrors cooling ages of the Variscan Crystalline Also, Cretaceous ages (i.e., 120 Ma, 70 Ma) in Miocene Massifs. Ages ranging between 204 and 302 Ma in the Stura and Present sediments derived from different western Alpine River are representative of the Variscan metamorphic event rocks could be the result of real geological events or the effect recorded at present in the Argentera Massif. Our data agree with of excess 40Ar (Arnaud and Kelley, 1995; Ruffet et al., 1995; the conclusion reached by Monié and Maluski (1983) that the Ruffet et al., 1997). Ages ca. 120 Ma have been originally Alpine peak temperature in the Argentera Massif was <220–250 interpreted as the result of cooling following the peak of high °C and consequently did not overprint the Variscan signal in pressure metamorphism (Monié and Chopin, 1991; Oberhänsli white micas. The signal coming from the Tanaro and the Stura et al., 1985). Some authors have dismissed a Cretaceous thermal Rivers (mainly Variscan ages) could be evidence of either a event for the internal Western Alps and consequently interpret geochronologically homogeneous source or of a low degree of this cluster of ages as due to excess 40Ar (e.g., Arnaud and Kelley, mixing of the present drainage system. 1995; Kelley et al., 1994). Monié and Chopin (1991) have shown The wide range of ages in the Maira River record the het- that 40Ar/39Ar ages ca. 100–110 Ma in the Dora Maira Massif erogeneity of sources mainly characterized by middle-late Creta- are representative of a real signal. One of their major arguments ceous ages and possibly also a good degree of mixing of different was that it was highly unlikely that high pressure phengites from geochronological domains. Rocks outcropping in the present different internal units of the Western Alps (Monte Rosa, Sesia Maira drainage system provide a signal very similar to the one Lanzo, and Dora Maira) could have incorporated equivalent produced by present-day river sands (Figs. 4 and 9). amounts of excess 40Ar leading to the same result. If the signal By combining the age data coming from the three rivers is geologically meaningful, then these ages could potentially be (Fig. 9), we obtain a picture that is remarkably similar to the one linked with a mid-Cretaceous metamorphic event (e.g., Cortiana observed for the Upper Miocene sediments (Lequio Formation; et al., 1998; Monié and Chopin, 1991). Scaillet et al. (1992) show Fig. 6). This suggests that no major paleodrainage reorganiza- that high Mg-phengites from UHP rocks of the Dora Maira often tions occurred at least since the Late Miocene in the western yield Cretaceous ages, while Fe-phengites yield ages ca. 35–40 Alpine catchment area. Ma. It is thus sometimes unnecessary to involve the presence of excess 40Ar to explain Cretaceous ages. Also, it is very unlikely WESTERN ALPINE COOLING EXHUMATION that different rocks all experienced the same amount of excess PATTERNS 40Ar leading to the same ages. Furthermore, because of the widespread occurrence of the same cluster of ages recorded by In theory, a continuous pattern of exhumation of a fi xed different thermochronometers in the Western Alps (Cortiana et source area, represented by crustal rocks, is recorded by moving al., 1998; Inger et al., 1996; Vance, 1999) and Central Alps (e.g., peaks up sequence (younging of the main signal) in the sedimen- Hunziker et al., 1992), we consider the 120–70 Ma signal to be tary infi ll (Brandon and Vance, 1992). Continuous exhumation representative of important geological Eoalpine events(see also through time would create a constant resetting of ages due to Carrapa and Wijbrans, 2003). a steady upward movement of crustal material through the iso- therms. Looking at the main detrital age populations of the Ter- CONCLUSIONS tiary Piedmont Basin sediments (Fig. 6), a lack of moving peaks up sequence is apparent; this is mainly the result of the evolution The general trend in the Tertiary Piedmont Basin sediments of the paleodrainage system through time. The same ca. 45–50 is that the main isotopic age population found in the oldest Ma signal recorded as the main detrital population in Oligocene sediments (ca. 45–50 Ma) gets older toward younger sediments to Aquitanian sediments is very similar to outcropping ages in the (ca. 70 Ma). This trend is interpreted as the result of a gradual 82 B. Carrapa, J. Wijbrans, and G. Bertotti

Figure 11. Schematic paleoreconstruction of the study area from Oligocene until post Tortonian times. + indicates uplifting area;– indicates sub- siding area. Data from this work have been combined with literature data on paleogeography and paleocurrents (Gnaccolini, 1970; Lorenz, 1979; Gelati and Gnaccolini 1982; Fannucci, 1986; Dondi and D’Andrea, 1986; Gnaccolini and Rossi, 1994; Clari et al., 1995; Foeken et al., 2003). Detecting provenance variations and cooling patterns 83 enlargement of the catchment area to include tectonic units with the exhumed western Alpine Arc. From Serravallian time, there progressively older isotopic ages (Fig. 11). is evidence of detritus coming from the Argentera Massif, char- Detrital micas from Oligocene until approximately Aqui- acterized by a Variscan signal. The very similar signal shown by tanian time sediments in the Tertiary Piedmont Basin show a present-day river sands and Upper Miocene sediments suggests source area localized in the southern sectors (Ligurian Alps and that the paleodrainage system did not continue to evolve after Voltri Group), which was affected by a major Alpine metamor- Miocene time in this sector of the Alps. Also, our data suggest phic overprint at ca. 40–50 Ma. Since about Aquitanian-Burdi- that regional rapid and episodic Cretaceous and Middle Eocene galian time, ages ca. 120–200 Ma and 70 Ma are widely recorded cooling events in the Western Alps were followed by periods of from detrital micas. This indicates a wider and mixed source area relatively slow erosion, and later Mesoalpine-Neoalpine meta- with contributions from both the Ligurian Alps and the western morphic events did not overprint the main original signals. Alpine domain. Since the Langhian, the main detrital population shifts from 50 Ma toward 70 Ma, indicating an enlargement of the source ACKNOWLEDGMENTS area from southern sectors toward more western-northwestern sectors, which are characterized mainly by Eoalpine signals. This study was supported by the Netherlands Foundation This reorganization of the Tertiary Piedmont Basin source is of Scientifi c Research (NWO). Special thanks to Yani Najman, likely linked to an evolution of the paleodrainage system most an anonymous reviewer, and Glen Murrell for their construc- likely related to vertical tectonic movements in the hinterland. tive advice in the preparation of the manuscript. This is NSG This evidence allows us to conclude that from the Early Miocene (Netherlands School for Sedimentary Geology) publication on, the Tertiary Piedmont Basin starts to record the erosion of number 2003.05.15. 84 B. Carrapa, J. Wijbrans, and G. Bertotti (continued) PS G (UTM, 32T, EU 1950) system, Cazzola and Rigazio, 1982) 452159–492792 TABLE A1. DETAILED INFORMATION OF THE STUDY SAMPLES 4,4 Molare X 99M0140+99M0143 Rupelian (section 12, Mutti et al., 1995) 453834–492276 4,4 Molare X 99M0287 Rupelian (section 12, Mutti et al., 1995) 453834–492276 57-7 Cassinelle Sst. 30-9 37-2 38-3 top Paroldo Marls X base Cortemilia 99m0175 Top Cortemilia Rupelian (d’Atri et al., 1997) X 99m0193+195 X Langhian (Gelati, 1968) 99m0241 X 99m0212 Aquitanian (Gelati, 1968) Langhian (Gelati, 1968) 465454–493862 425280–491956 436475–493307 434343–493702 27-6 Rocchetta X 99m0155 Aquitanian (Gelati, 1968) 424250–491619 24-3 Molare X 99M0183+99j0119 Chattian? (Gelati et al., 1993) 423639–491334 54-4 Molare 25-4 27-6 X top Rocchetta Fm.–base Monesiglio Fm. 99M0144 Rocchetta 2X 99m0301, 99m0300 Rupelian (Gelati et al., 1993) Aquitanian (Gelati, 1968) X 99m0149+99m0186 Aquitanian (section Ceva, Gelati 1968) 465800–493815 424250–491619 424250–491619 10,10 10,10 Rocchetta Rocchetta X 99m0299 X 99m0168 Chattian-Aquitanina (Mioglia system, Cazzola and Rigazio, 1982) Chattian-Aquitanina (Mioglia system, Mutti et al., 1995) 452502–492717 452502–492717 12,12 Rocchetta X 99m0159 Aquitanian (top Mioglia 15-15 20-20 20-20 Rocchetta Monesiglio Monesiglio 61-11 19-19 X 99m0167 31-10 X 99m0370 Cortemilia X Lower Oligocene–Aquitanian (Gelati, 1968) base Murazzano 99m0192+190 Cortemilia Burdigalian (Piantivello body, Gelati and Gnaccolini, 1998) Burdigalian (Piantivello body, Gelati and Gnaccolini, 1998) 443360–493583 443360–493583 X X 445540–423183 99m0255 99m0246 X 99m0247 Langhian (Gelati, 1968) Aquitanian (Gelati, 1968) Burdigalian (Gelati, 1968) 458183–494519 426250–492180 442307–493503 16-16 21-21 18-18 18-18 Rocchetta Rocchetta Rocchetta Rocchetta X 99m0148 X X 99m0197+0199 99m0403 X Aquitanian (Mazzurrini body, Gelati and Gnaccolini, 1998) 99m0185 Lower Oligocene–Aquitanian Chattian (Noceto system, Cazzola and Fornaciari, 1990) 443750–493646 Chattian (Noceto system, Cazzola and Fornaciari, 1990) 44507–4932356 44507–4932356 445238–493171 71 72 74 77 69 70 76 43 47 56 81 48 62 66 42 60 67 80 45 46 52 57 59 61 B B 7 B 10 29-8 23 34-13 B 76-7 20 63-1 Top Monesiglio Monesiglio B Monesiglio B 9 Paroldo Marls 29 32-11 87-18 Murazzano Fm. (Cassinasco) X 00m0064 X 00m0076 X Murazzano 00m0079 X 00m0078 X Burdigalian-Langhian (Gelati, 1968) 00m0074 Aquitanian? (Gelati, 1968) Chattian (N2, Gelati et al., 1996) Burdigalian-Langhian (Gelati, 1968) Langhian-Serravallian (Gelati, 1968) X 00m0082 424170–491830 Serravallian (Gelati, 1968) 414788–491567 426400–492110 433929–492018 421529–492661 427842–493809 B B 1 B 21 B 2,2 33 64-2 B 42 108-9 B 45 72 B 47 83 B 40 90 B 52 77 36 86 Molare Molare 70-1 Molare Molare Molare top Molare Molare Molare Molare X X X 00M0061 00M0070 00M0085 X X 00M0258+01M0258L X Rupelian (Gelati et al., 1993) 01M0029 00M0276 Rupelian (section 12, Mutti et al., 1995) Rupelian (Gelati et al., 1993) X Rupelian (Gelati et al., 1993) 00m0257 X X 00M0277+01M0277 00M0088 Rupelian (Gelati et al., 1993) Rupelian (Gelati et al., 1993) Rupelian (Gelati et al., 1993) Rupelian (Gelati et al., 1993) Chattian (N2, Gelati et al., 1996) 453834–492276 448500–491220 461620–492711 477478–494043 446500–493195 445850–493190 455600–492890 414965–491319 442125–491480 D D D D D D D D D D D D D D D D D D D D D D D D CODE No. Field No. Formation Step H F Total Lab code Depositional time Detecting provenance variations and cooling patterns 85 PS G (UTM, 32T, EU 1950) ) continued Langhian–lower Serravallian (Gelati, 1968) 423854–490674 TABLE A1. DETAILED INFORMATION OF THE STUDY SAMPLES ( Lequio X 01M0368 Serravallian-Tortonian (Gelati, 1968) 408000–491670 39-4 Cassinasco X 99m0210+209 Langhian-Serravallian (Gelati, 1968) 431926–493473 39-4 Cassinasco X 99m0402 Langhian-Serravallian (Gelati, 1968) 431926–493473 62-12 Cassinasco X 99m0404 Langhian-Serravallian (Gelati, 1968) 462191–494965 62-12 Cassinasco X 99m0211 Langhian-Serravallian (Gelati, 1968) 462191–494965 47-12 Cassinasco X 99m0203+0208 Langhian-Serravallian (Gelati, 1968) 423854–490674 47-12 base Cassinasco X 99m0373 upper 45-10 Cassinasco X 99m0122+184 Serravallian (section type of Gelati 1968) 443982–494878 46-11 46-11 Cassinasco Cassinasco X 99m0371 X 99m0200+202 Serravallian (section type of Gelati 1968) Serravallian (section type of Gelati 1968) 44403–4948162 44403–4948162 Mondovi' 65 64 55 54 51 50 49 40 41 : Ps—present-day sands. B B 11 B 24 42-7 B 81-12 27 B 84-15 34 B top Cassinasco-Murazzano 121-7 base 26 A 82-13 30 Serravalle Sandstone (Cassinasco) A 89-20 2 Top Cassinasco A 6 4 80-11 A 83-14 Cassinasco X 5 Maira 00m0072 B 13 X Maira 88-19 00m0087 A 34 Lequio Maira B 14 Tanaro Lequio B 15 Tanaro X A 31 Lequio Tanaro 00m0073 B 16 Lequio Serravallian (Gelati, 1968) – B Langhian-Serravallian (Gelati, 1968) X – A Lequio 17 00m0081 – B 33 Stura – 18 Stura – Stura – X Serravallian (Gelati, 1968) 00m0080 X 00M0067 X 00m0083 01M0387 X X 00M0089 Serravallian (Gelati, 1968) 01M0383 X 00M0068 X X 451790–495200 01M0415 01M0388 X – 01M0044 X Present 419966–492936 – X 01M0416 Present Serravallian (Gelati, 1968) – Present Tortonian (Gelati, 1968) Present Serravallian-Tortonian (Gelati, 1968) Present Serravallian-Tortonian (Gelati, 1968) Present 430993–494386 Serravallian-Tortonian (Gelati, 1968) 429263–493713 X X 00M0069 X 419141–4930859 01M0423 418495–493108 427669–493806 01M0039 422410–493902 424127–493865 Present Present Dronero Present Dronero Dronero Ceva Ceva Ceva Borgo S. Dalmazzo Borgo S. Dalmazzo Borgo S. Dalmazzo D D D D D D D D D Ps Note CODE No. Field No. Formation Step H F Total CODE LAB Depositional time 86 B. Carrapa, J. Wijbrans, and G. Bertotti

TABLE A2. 40Ar/39Ar ANALYSES OF THE INVESTIGATED SAMPLES Molare 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) 108-9 (B33) J = 0.002408 1 0.00077 0.00000 0.00045 0.14813 3.48675 99.47 ± 0.95 93.89 2 0.00239 0.00000 0.00138 0.25215 3.13148 53.16 ± 0.50 81.58 3 0.00191 0.00058 0.00265 0.48403 4.84879 43.00 ± 0.28 89.55 4 0.00223 0.00041 0.00243 0.41191 6.69340 69.25 ± 0.35 91.04 5 0.00026 0.00000 0.00122 0.03388 0.43804 55.32 ± 2.35 85.10 6 0.00147 0.00029 0.00050 0.23183 5.44954 99.33 ± 0.54 92.61 7 0.00120 0.00132 0.00115 0.40356 3.70387 39.44 ± 0.65 91.23 8 0.00074 0.00005 0.00097 0.21554 2.23130 44.42 ± 0.48 91.10 9 0.00110 0.00062 0.00058 0.18020 2.73370 64.73 ± 0.47 89.35 10 0.00064 0.00054 0.00094 0.25440 2.46275 41.57 ± 0.33 92.82 54-4 (D80) J=0.001572 1 0.00097 0.00367 0.00005 0.10752 2.00720 52.18 ±1.28 87.51 2 0.00225 0.00214 0.00023 0.15023 2.86248 53.24 ± 1.01 81.17 3 0.00328 0.00492 0.00002 0.21857 5.15828 65.72 ± 0.86 84.19 4 0.00078 0.00592 0.00015 0.23252 4.56705 54.86 ± 0.64 95.18 5 0.00520 0.00000 0.00000 0.23364 11.25886 131.74 ± 1.16 88.00 6 0.00234 0.00000 0.00000 0.15658 2.59343 46.37 ± 1.02 78.95 7 0.00223 0.00000 0.00005 0.24038 4.42829 51.50 ± 0.58 87.05 8 0.00212 0.00078 0.00000 0.15601 2.78566 49.94 ± 1.15 81.61 9 0.00100 0.00197 0.00014 0.22418 3.86636 48.26 ± 0.75 92.88 10 0.00035 0.00000 0.00002 0.22746 4.22014 51.87 ± 0.64 97.64 83 (B45) J=0.002731 1 0.00019 0.00000 0.00032 0.19168 1.61768 41.11 ±1.01 96.65 2 0.00056 0.00000 0.00024 0.21093 2.49216 57.29 ±0.77 93.79 3 0.00183 0.00000 0.00024 0.18591 1.53250 40.16 ±0.90 73.93 4 0.00027 0.00170 0.00022 0.10137 0.82470 39.64 ±1.56 91.09 5 0.00044 0.00000 0.00028 0.10768 1.10118 49.69 ±0.64 89.47 6 0.00076 0.00000 0.00025 0.11037 1.73547 75.85 ±1.17 88.59 7 0.00018 0.00071 0.00033 0.08081 0.65787 39.67 ±1.28 92.49 64-2 (B21) J=0.002799 1 0.00022 0.00009 0.00029 0.15834 1.17533 37.10 ±0.84 94.80 2 0.00036 0.00000 0.00009 0.18868 1.38712 36.75 ±0.65 92.82 3 0.00106 0.00010 0.00059 0.28414 3.38003 59.09 ±0.63 91.50 4 0.00093 0.00014 0.00084 0.33570 3.24415 48.15 ±0.35 92.17 5 0.00024 0.00026 0.00025 0.13796 1.02817 37.25 ±0.86 93.50 6 0.00058 0.00240 0.00012 0.13227 0.92269 34.89 ±0.91 84.41 7 0.00132 0.00020 0.00081 0.26750 3.86682 71.56 ±0.80 90.81 8 0.00106 0.00000 0.00073 0.33650 3.18388 47.16 ±0.45 91.00 9 0.00109 0.00034 0.00068 0.16936 3.15318 91.65 ±1.08 90.73 10 0.00128 0.00159 0.00155 0.42424 4.16294 48.88 ±0.42 91.65 90 (B47) J=0.002678 2 0.00169 0.04557 0.00008 0.19861 1.84413 44.31 ±1.65 78.68 3 0.00271 0.00000 0.00000 0.24007 2.06499 41.08 ±1.21 72.05 5 0.00057 0.00000 0.00000 0.16808 1.32738 37.75 ±1.30 88.73 6 0.00066 0.00000 0.00000 0.23407 1.66177 33.98 ±2.25 89.56 7 0.0011 0.00000 0.00000 0.18693 1.46708 37.52 ±3.06 81.88 9 0.00016 0.00000 0.00030 0.11479 1.25148 51.92 ±3.65 96.26 10 0.00051 0.19015 0.00017 0.17385 1.32305 36.40 ±1.99 89.75 (continued) Detecting provenance variations and cooling patterns 87

TABLE A2. 40Ar/39Ar ANALYSES OF THE INVESTIGATED SAMPLES (continued) Molare 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) 2-2 (B1) J=0.003215 1 0.00066 0.00000 0.00000 0.16856 1.20014 40.83 ±0.68 85.99 2 0.00023 0.00010 0.00004 0.13507 1.02065 43.30 ±0.72 93.84 3 0.00067 0.00103 0.00033 0.65053 4.82774 42.54 ±0.26 96.03 4 0.00466 0.00018 0.00032 0.30100 3.56421 67.40 ±0.61 72.12 5 0.00038 0.00048 0.00033 0.21619 1.74999 46.35 ±0.64 93.90 6 0.00236 0.00380 0.00021 0.46942 3.53200 43.12 ±0.32 83.50 7 0.00201 0.00031 0.00005 0.69248 5.18755 42.94 ±0.34 89.72 8 0.00046 0.00080 0.00023 0.30685 2.25728 42.17 ±0.39 94.32 9 0.00292 0.00045 0.00012 0.42481 4.63050 62.14 ±0.42 84.27 4-4 (D60) J=0.001706 1 0.03911 0.00386 0.00012 0.31927 6.47035 61.32 ± 4.39 35.89 2 0.00473 0.00068 0.00011 0.15344 2.93695 57.97 ± 8.96 67.73 3 0.00324 0.00182 0.00000 0.15559 2.51505 49.08 ± 8.86 72.41 4 0.00225 0.00307 0.00000 0.12354 2.36214 57.91 ± 11.11 78.00 5 0.00313 0.00016 0.00015 0.28898 4.86800 51.11 ± 0.96 84.03 6 0.00111 0.00209 0.00000 0.11441 2.04062 54.08 ± 1.65 86.17 7 0.00226 0.00267 0.00000 0.23445 4.14526 53.61 ± 0.92 86.13 8 0.00195 0.00048 0.00000 0.31822 4.62225 44.16 ± 0.41 88.92 9 0.00057 0.02252 0.00000 0.01891 0.36736 58.81 ± 6.43 68.61 D67 J=0.001653 TFA 54.75 ±1.2 86 (B52) J=0.002556 1 0.00660 0.00757 0.00039 0.09250 1.05371 51.78 ± 2.47 35.08 2 0.00519 0.00344 0.00028 0.25660 2.55979 45.42 ± 0.61 62.55 3 0.00118 0.12389 0.00027 0.19427 1.97718 46.33 ± 1.66 84.99 4 0.00043 0.27901 0.00000 0.04523 0.30707 31.04 ± 9.67 70.91 5 0.00375 0.17358 0.00000 0.19450 1.34596 31.63 ± 1.66 54.82 6 0.00342 0.12384 0.00058 0.21019 2.59312 56.01 ± 2.75 71.97 77 (B40) J=0.002856 1 0.00019 0.00000 0.00017 0.09104 6.02044 312.10 ±1.77 99.08 2 0.00013 0.00000 0.00053 0.15551 10.36692 314.42 ±1.21 99.62 3 0.00025 0.00588 0.00050 0.09195 6.02778 309.60 ±2.1 98.77 4 0.00064 0.00171 0.00012 0.20654 13.36365 305.90 ±0.89 98.61 5 0.00026 0.00000 0.00037 0.17751 11.84916 314.81 ±1.31 99.34 6 0.00053 0.00000 0.00017 0.10201 0.76271 38.12 ±0.97 82.94 7 0.00007 0.00017 0.00000 0.05935 3.91726 311.56 ±2.4 99.49 8 0.00006 0.00507 0.00051 0.06963 4.52877 307.39 ±2.34 99.62 9 0.00012 0.00173 0.00047 0.07406 4.83537 308.47 ±2.11 99.28 72 (B42) J=0.002803 1 0.00159 0.00230 0.00017 0.22628 3.19200 69.96 ±0.55 87.16 2 0.00070 0.00000 0.00017 0.22385 4.58688 100.75 ±0.67 95.68 3 0.00026 0.00046 0.00002 0.12872 1.09381 42.47 ±0.72 93.51 4 0.00025 0.00176 0.00072 0.38301 14.20966 178.48 ±0.66 99.49 5 0.00030 0.00038 0.00061 0.14013 9.24694 306.18 ±1.59 99.06 6 0.00000 0.00000 0.00090 0.19676 13.32092 313.48 ±1.06 100.00 7 0.00028 0.00432 0.00099 0.16624 11.06876 308.72 ±2.81 99.27 8 0.00087 0.02498 0.00067 0.11757 1.66105 70.07 ±5.34 86.61 9 0.00055 0.02422 0.00061 0.13672 8.99463 305.33 ±2.06 98.24 10 0.00075 3.22164 0.00057 0.36739 22.35749 291.34 ±2.6 99.02 (continued) 88 B. Carrapa, J. Wijbrans, and G. Bertotti

TABLE A2. 40Ar/39Ar ANALYSES OF THE INVESTIGATED SAMPLES (continued) Molare 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) 24-3 (D42) J=0.001869 1 0.00723 0.00109 0.00024 0.18314 18.53496 312.55 ± 1.98 89.66 2 0.00348 0.00010 0.00000 0.13772 14.04012 314.64 ± 2.64 93.18 3 0.00648 0.00126 0.00015 0.15039 13.89986 287.47 ± 2.51 87.88 4 0.00949 0.00410 0.00000 0.09100 8.00232 274.51 ± 3.77 74.04 5 0.00532 0.00584 0.00010 0.39962 42.29852 325.66 ± 1.68 96.41 6 0.00981 0.00885 0.00000 0.24440 25.28861 318.96 ± 1.97 89.71 7 0.00155 0.00513 0.00000 0.15737 16.38853 320.85 ± 1.77 97.28 8 0.00164 0.00555 0.00000 0.10112 10.78740 328.01 ± 3.13 95.69 9 0.00121 0.00423 0.00000 0.14297 14.92964 321.64 ± 1.81 97.66 10 0.00063 0.00839 0.00000 0.15980 18.14587 347.22 ± 1.96 98.98 B36 J=0.002252 1 0.00021 0.00000 0.00015 0.02526 0.33070 52.42 ±2.81 84.34 2 0.00038 0.00000 0.00030 0.10552 0.96437 36.75 ± 0.67 89.57 3 0.00013 0.00058 0.00048 0.00787 0.07161 36.58 ± 5.66 65.86 4 0.00098 0.00166 0.00124 0.21061 1.96925 37.59 ± 0.52 87.16 5 0.00088 0.00000 0.00040 0.08001 1.00862 50.50 ± 1.07 79.52 6 0.00023 0.00000 0.00015 0.11442 1.45800 51.04 ± 0.88 95.47 7 0.00029 0.00059 0.00080 0.18568 2.18513 47.19 ± 0.51 96.22 8 0.00016 0.00005 0.00050 0.10812 0.97381 36.22 ± 0.76 95.42 9 0.00039 0.00000 0.00031 0.09101 1.75191 76.56 ± 0.85 93.83 10 0.00036 0.00059 0.00043 0.07294 1.47083 80.12 ± 1.27 93.29

Rocchetta 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) D45 J=0.001844 0.00174 0.00048 0.00001 0.03401 0.57140 55.04 ± 7.78 52.58 0.00012 0.00000 0.00000 0.04303 0.53491 40.89 ± 5.61 93.78 0.00008 0.00000 0.00000 0.03165 0.55752 57.67 ± 7.18 96.11 0.00147 0.00240 0.00000 0.09001 4.24593 150.48 ± 2.51 90.73 0.00065 0.00269 0.00001 0.05566 1.06195 62.38 ± 2.77 84.76 0.00022 0.00929 0.00000 0.06210 1.54303 80.83 ± 3.77 96.00 0.00027 0.00000 0.00000 0.07031 2.55568 117.04 ± 1.29 96.97 0.00044 0.01662 0.00000 0.06639 3.09772 148.91 ± 1.45 95.97 D46 J=0.001836 0.00072 0.00000 0.00024 0.34355 36.86724 324.44 ± 1.38 99.43 0.00110 0.00000 0.00010 0.33466 6.80874 66.16 ± 0.48 95.44 0.00147 0.00000 0.00009 0.29135 8.10839 89.90 ± 0.46 94.92 0.00092 0.00000 0.00000 0.22677 7.29025 103.46 ± 0.73 96.41 0.00055 0.00000 0.00000 0.28963 4.09609 46.25 ± 0.64 96.19 0.00180 0.00178 0.00000 0.35071 23.15138 206.38 ± 1.18 97.75 0.00072 0.00061 0.00044 0.46206 3.18960 22.72 ± 0.41 93.74 0.00073 0.00036 0.00001 0.12361 2.39191 62.98 ± 1.38 91.70 0.00092 0.00000 0.00001 0.10619 1.74434 53.60 ± 1.21 86.52 0.00107 0.00000 0.00000 0.12168 3.68076 97.51 ± 1.61 92.08 Bc 0.00065 0.00663 0.00000 0.17724 2.03207 37.58 ± 1.14 93.20 De 0.00057 0.00220 0.00000 0.17801 3.00839 55.13 ±1.23 96.14 Gh 0.00059 0.00000 0.00020 0.38913 2.69283 22.78 ±0.55 95.69 Il 0.00041 0.00000 0.00011 0.17202 2.11834 40.33 ±1.14 96.85 No 0.00046 0.00067 0.00004 0.16952 4.31976 82.49 ±1.37 97.32 (continued) Detecting provenance variations and cooling patterns 89

TABLE A2. 40Ar/39Ar ANALYSES OF THE INVESTIGATED SAMPLES (continued) Rocchetta 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) D52 J=0.001774 197ab 0.00317 0.00843 0.00021 0.12764 2.76609 68.06 ±1.86 87.13 197de 0.00077 0.00863 0.00004 0.11714 6.00016 156.91 ±2.05 96.35 197gh 0.00038 0.00149 0.00000 0.09796 2.13885 68.56 ±1.89 97.00 199bc 0.00040 0.00000 0.00000 0.12249 2.65719 68.13 ±1.54 97.06 199ef 0.00069 0.00000 0.00014 0.10031 1.15294 36.42 ±1.74 96.63 199gh 0.00027 0.00000 0.00000 0.13293 1.84397 43.86 ±1.14 99.94 199im 0.00025 0.00000 0.00009 0.10214 1.87681 57.87 ±1.50 95.92 199no 0.00047 0.00062 0.00009 0.05797 0.88098 47.99 ±3.45 97.71 199pq 0.00090 0.00093 0.00007 0.15660 6.64318 130.9 ±1.64 96.26 D57 J=0.00173 TFA 72.69±0.67 D59 J=0.00173 0.00059 0.00000 0.00005 0.25186 4.42508 53.65 ± 0.50 96.17 0.00046 0.00000 0.00013 0.12956 5.13876 118.93 ± 0.98 97.40 0.00115 0.00098 0.00005 0.40920 12.05328 89.06 ± 0.41 97.26 df 0.00081 0.00000 0.00022 0.19057 5.85617 92.81 ± 1.51 96.58 gh 0.00036 0.00000 0.00022 0.19985 2.97448 45.55 ± 0.65 97.34 mn 0.00010 0.00100 0.00005 0.21173 2.95362 42.73 ± 1.02 98.73 op 0.00083 0.00222 0.00002 0.37011 8.72166 71.6 ± 0.65 97.60 qr 0.00090 0.00201 0.00000 0.19990 8.54947 127.91 ± 1.08 97.52 tu 0.00038 0.00126 0.00008 0.09074 2.90255 96.51 ± 2.17 96.66 vz 0.00066 0.00555 0.00000 0.27831 6.46287 70.58 ± 0.83 97.70 D61 J=0.001698 a TFA 109.77 ± 1.06 b TFA 108.61 ± 0.85 D62 J=0.001690 0.00074 0.00393 0.00007 0.12016 2.33856 58.38 ± 2.11 91.44 0.00295 0.00652 0.00013 0.11592 4.93581 125.36 ± 2.58 85.00 0.00248 0.00000 0.00022 0.21685 8.21452 111.95 ± 1.37 91.81 0.00048 0.00384 0.00004 0.02310 0.36439 47.46 ± 10.41 71.85 0.00073 0.00000 0.00011 0.16504 2.95852 53.84 ± 0.75 93.17 0.00166 0.00353 0.00004 0.31000 13.82803 131.12 ± 0.82 96.58 0.00100 0.00000 0.00003 0.19379 5.72020 87.82 ± 0.66 95.06 0.00028 0.00277 0.00009 0.10747 12.69059 328.26 ± 2.15 99.34 0.00036 0.00287 0.00012 0.02341 0.51106 65.36 ± 4.68 82.78 D66 J=0.00166 0.00071 0.00083 0.00000 0.04506 0.73080 47.93 ± 3.26 77.63 0.00035 0.00017 0.00015 0.06933 8.31216 327.47 ± 3.57 98.78 0.00046 0.00082 0.00000 0.02808 0.46379 48.79 ± 3.87 77.33 0.00033 0.00024 0.00010 0.03940 2.44456 176.85 ± 2.88 96.13 0.00029 0.00000 0.00011 0.08697 2.65349 89.13 ± 1.52 96.86 0.00000 0.00000 0.00000 0.00340 0.17823 150.46 ± 11.48 100.00 0.00010 0.00075 0.00012 0.02182 1.02951 136.04 ± 5.52 97.21 0.00011 0.00000 0.00009 0.03744 0.71227 56.09 ± 2.34 95.69 0.00117 0.00076 0.00002 0.05237 0.89784 50.62 ± 2.10 72.14 0.00030 0.00000 0.00017 0.03879 2.16027 159.53 ± 3.68 96.00 (continued) 90 B. Carrapa, J. Wijbrans, and G. Bertotti

TABLE A2. 40Ar/39Ar ANALYSES OF THE INVESTIGATED SAMPLES (continued) Rocchetta 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) D71 J=0.001628 0.00488 0.00000 0.00000 0.42917 7.81591 52.71 ± 0.46 84.41 0.00349 0.00000 0.00000 0.33527 5.70112 49.26 ± 0.69 84.66 0.01692 0.00194 0.00014 0.38987 7.75765 57.52 ± 1.12 60.80 0.00123 0.00000 0.00000 0.27295 3.83528 40.80 ± 0.84 91.34 0.00333 0.00268 0.00005 0.31863 4.74650 43.23 ± 0.61 82.83 0.00126 0.00000 0.00000 0.42892 5.52668 37.45 ± 1.10 93.70 0.02720 0.30870 0.00000 1.51318 23.55381 45.15 ± 1.00 74.55 0.00219 0.00000 0.00006 0.17906 2.94696 47.70 ± 2.89 82.00 0.00411 0.00000 0.00007 0.37903 6.10989 46.73 ± 1.34 83.43 0.00174 0.00000 0.00000 0.18811 2.84659 43.91 ± 2.68 84.72 D72 J=0.001622 TFA 51.48± 1.04 TFA D74 J=0.001609 0.00167 0.00000 0.00000 0.20076 3.87398 55.16 ± 2.48 88.72 0.00178 0.00253 0.00000 0.29605 5.31949 51.42 ± 1.57 91.02 0.00201 0.00199 0.00000 0.27424 5.06714 52.85 ± 1.77 89.51 0.00065 0.00000 0.00000 0.16019 2.84000 50.74 ± 2.90 93.64 0.00206 0.00000 0.00000 0.15599 9.31634 165.54 ± 7.35 93.86 0.00107 0.00157 0.00015 0.11745 2.16014 52.61 ± 1.10 87.25 0.00106 0.00000 0.00000 0.14775 3.83256 73.77 ± 1.37 92.43 0.00117 0.00361 0.00034 0.10436 1.57415 43.26 ± 1.45 82.01 0.00108 0.00389 0.00000 0.11736 2.71234 65.87 ± 1.17 89.44 D77 J=0.001591 0.00643 0.00000 0.00000 0.45155 7.61627 47.77 ± 0.39 80.03 0.00116 0.00000 0.00000 0.02252 0.26661 33.66 ± 5.74 43.85 0.00159 0.00080 0.00012 0.21398 3.70928 49.08 ± 0.51 88.74 0.00295 0.00000 0.00025 0.15895 3.29189 58.49 ± 1.10 79.05 0.00021 0.00000 0.00006 0.00671 0.06570 27.87 ± 18.64 51.40 0.00023 0.00374 0.00011 0.00783 0.11160 40.47 ± 10.17 61.79 0.00110 0.00312 0.00008 0.12994 3.08067 66.80 ± 0.95 90.48 0.00186 0.00349 0.00008 0.12017 2.38736 56.14 ± 1.30 81.28 0 00045 0 00000 0 00007 0 16599 2 19846 37 62 0 69 94 31 Detecting provenance variations and cooling patterns 91

TABLE A2. 40Ar/39Ar ANALYSES OF THE INVESTIGATED SAMPLES (continued) Monesiglio 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) D69 J=0.00164 TFA 51.71±0.51 D70 J=0.001634 190ab 0.00070 0.00051 0.00003 0.35096 5.06897 42.08 ±0.56 98.62 190cd 0.00179 0.00462 0.00012 0.19733 9.23657 133 ±1.32 97.30 192cd 0.00142 0.01403 0.00012 0.22648 6.88137 87.42 ±1.04 95.88 190ef 0.00039 0.00000 0.00000 0.01317 0.21446 47.38 ±17.41 76.23 192eg 0.00077 0.00233 0.00005 0.13103 5.53889 120.5 ±1.68 96.83 190gh 0.00142 0.00082 0.00000 0.22606 4.76486 61.09 ±1.06 96.44 192hi 0.00193 0.00362 0.00017 0.29496 5.46119 53.77 ±0.82 97.75 190lm 0.00102 0.00000 0.00000 0.29135 4.04194 40.44 ±0.52 98.67 192mn 0.00053 0.00000 0.00013 0.11893 3.18736 77.32 ±2.03 95.81 B7 J=0.003126 0.00041 0.00050 0.00026 0.31928 3.52550 61.22 ± 0.56 96.71 0.00051 0.00075 0.00062 0.27863 3.70268 73.43 ± 0.67 96.12 0.00033 0.00000 0.00115 0.56657 3.78065 37.25 ± 0.39 97.48 0.00033 0.00053 0.00133 0.42293 3.77504 49.65 ± 0.58 97.46 0.00181 0.00094 0.00039 0.28101 3.55024 69.88 ± 0.81 86.93 0.00014 0.00000 0.00026 0.16212 1.15266 39.66 ± 0.88 96.62 0.00052 0.00000 0.00000 0.03158 0.85868 147.17 ± 3.45 84.88 0.00062 0.00046 0.00059 0.20097 3.59369 98.13 ± 0.87 95.16 0.00001 0.00000 0.00000 0.02391 0.37080 85.40 ± 2.01 98.96 0.00524 0.03995 0.01113 4.27744 39.96818 51.94 ± 0.27 96.26 B10 J=0.003071 0.00031 0.00090 0.00032 0.26298 1.79600 37.45 ± 0.49 95.09 0.00023 0.00015 0.00074 0.15129 1.34870 48.73 ± 1.11 95.24 0.00056 0.00014 0.00066 0.13347 1.34241 54.88 ± 1.23 89.08 0.00196 0.00345 0.00134 0.30706 2.78001 49.48 ± 0.63 82.76 0.00096 0.00114 0.00130 0.16493 1.91568 63.23 ± 0.78 87.08 0.00005 0.00052 0.00013 0.00462 0.03239 38.41 ± 10.64 69.56 0.00323 0.00287 0.00028 0.08169 0.63954 42.86 ± 3.04 40.14 0.00001 0.00000 0.00000 0.05052 0.53378 57.61 ± 3.73 99.34 0.00058 0.00000 0.00120 0.14688 1.30843 48.69 ± 1.62 88.38 0.00097 0.00000 0.00086 0.11091 3.19119 152.76 ± 2.13 91.79 B23 J=0.002755 0.00043 0.00000 0.00108 0.19302 2.35066 59.53 ± 0.75 94.85 0.00014 0.00000 0.00039 0.06476 1.53669 114.24 ± 1.69 97.46 0.00037 0.00000 0.00150 0.20511 2.60984 62.16 ± 0.78 95.94 0.00068 0.00045 0.00140 0.27721 4.41082 77.40 ± 0.63 95.67 0.00017 0.00067 0.00065 0.08052 1.06947 64.84 ± 1.22 95.50 0.00013 0.00005 0.00017 0.03805 0.48558 62.34 ± 2.26 92.55 0.00008 0.00008 0.00067 0.07865 0.85280 53.10 ± 1.37 97.42 0.00018 0.00023 0.00060 0.08581 0.92044 52.54 ± 1.04 94.47 92 B. Carrapa, J. Wijbrans, and G. Bertotti

TABLE A2. 40Ar/39Ar ANALYSES OF THE INVESTIGATED SAMPLES (continued) Paroldo 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) D76 J=0.001597 193ab 0.00196 0.00000 0.00005 0.20382 7.93566 108.83 ± 1.23 94.12 195ab 0.00069 0.00000 0.00000 0.11167 2.85653 72.23 ± 1.38 96.28 195cd 0.00131 0.00000 0.00000 0.15480 4.04510 73.76 ± 1.23 94.08 195fg 0.00056 0.00000 0.00003 0.01443 0.34248 67.1 ± 13.3 99.04 195hi 0.00034 0.00033 0.00000 0.07709 2.21813 81.08 ±2.36 98.88 195no 0.00046 0.00280 0.00001 0.06776 2.17695 90.26 ±3.91 96.95 195pq 0.00090 0.00488 0.00000 0.10028 2.14321 60.55 ±2.7 92.85 195st 0.00009 0.00038 0.00007 0.05051 1.17246 65.67 ±3.76 93.39 175uv 0.00066 0.00000 0.00004 0.18646 10.03146 148.7 ±1.49 98.57 B20 J=0.002834 0.00031 0.00053 0.00112 0.11904 0.86962 36.97 ± 0.88 90.52 0.00026 0.00019 0.00096 0.10678 0.78993 37.43 ± 0.96 91.19 0.00021 0.00048 0.00068 0.07601 1.06034 69.95 ± 1.37 94.44 0.00009 0.00018 0.00144 0.00997 0.07543 38.26 ± 9.10 74.44 0.00028 0.00000 0.00214 0.01432 0.10813 38.21 ± 7.29 56.87 0.00009 0.00000 0.00039 0.01823 0.28796 79.00 ± 5.34 91.56 0.00037 0.00000 0.00084 0.08275 1.10382 66.94 ± 1.21 90.89

Cortemilia 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) D43 J=0.001861 0.00020 0.01265 0.00000 0.00782 0.09842 41.78 ± 14.43 62.10 0.00062 0.00717 0.00013 0.18707 3.35118 59.16 ± 0.63 94.83 0.00240 0.00874 0.00000 0.13244 7.75815 186.67 ± 1.05 91.64 0.00025 0.00999 0.00007 0.08270 1.25431 50.22 ± 1.33 94.37 0.00073 0.00914 0.00000 0.07755 3.50471 145.69 ± 1.71 94.17 0.00122 0.00621 0.00000 0.17614 3.36993 63.12 ± 0.56 90.37 0.00020 0.00924 0.00000 0.09961 9.53589 295.78 ± 1.87 99.39 0.00003 0.00000 0.00004 0.00726 0.08573 39.23 ± 11.48 90.57 0.00007 0.01756 0.00005 0.09435 1.32626 46.59 ± 1.18 98.41 D47 J=0.001828 0.00062 0.00227 0.00010 0.10519 6.12265 182.41 ± 2.63 97.11 0.00017 0.00061 0.00004 0.13871 2.49623 58.39 ± 0.70 98.00 0.00065 0.00189 0.00022 0.21446 3.45724 52.40 ± 0.60 94.72 0.00023 0.00000 0.00015 0.11885 1.92817 52.73 ± 1.36 96.66 0.00003 0.00000 0.00006 0.05228 1.34853 83.11 ± 2.37 99.39 0.00060 0.00000 0.00006 0.11130 2.58222 74.94 ± 1.21 93.60 0.00015 0.00000 0.00016 0.06984 1.37102 63.61 ± 1.79 96.91 0.00120 0.00645 0.00009 0.14060 8.19261 182.60 ± 1.60 95.85 0.00314 0.00000 0.00016 0.13008 2.97166 73.81 ± 1.31 76.20 0.00008 0.00375 0.00004 0.00402 0.03998 32.50 ± 25.34 62.31 (continued) Detecting provenance variations and cooling patterns 93

TABLE A2. 40Ar/39Ar ANALYSES OF THE INVESTIGATED SAMPLES (continued) Cortemilia 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) D56 J=0.001739 0.00030 0.00000 0.00006 0.08945 8.95995 289.69 ± 2.83 99.01 0.00038 0.00000 0.00000 0.14283 5.97093 126.60 ± 1.26 98.16 0.00013 0.00332 0.00005 0.00718 0.11389 49.10 ± 15.89 74.55 0.00093 0.00000 0.00000 0.14432 7.66076 159.28 ± 1.60 96.53 0.00024 0.00290 0.00000 0.16771 6.51132 117.87 ± 0.83 98.93 0.00038 0.01412 0.00000 0.00874 0.10131 36.00 ± 10.50 47.21 0.00012 0.00987 0.00000 0.09659 2.68299 85.11 ± 0.92 98.66 0.00010 0.00000 0.00000 0.00545 0.09623 54.60 ± 11.66 75.67 0.00016 0.01165 0.00000 0.16664 3.07933 57.06 ± 0.76 98.53 0.00038 0.00498 0.00019 0.10225 1.79978 54.39 ± 0.87 94.10 D81 J=0.001565 0.00001 0.00000 0.00000 0.03974 0.63077 44.26 ± 1.51 99.32 0.00047 0.00451 0.00010 0.08033 4.17747 141.16 ± 1.49 96.77 0.00028 0.00000 0.00007 0.05417 2.48371 125.03 ± 1.11 96.80 0.00044 0.00000 0.00000 0.05065 0.80757 44.46 ± 1.73 86.26 0.00012 0.00082 0.00000 0.06914 9.39602 347.90 ± 2.87 99.62 0.00359 0.01538 0.00004 0.22468 4.07134 50.45 ± 0.51 79.35 0.00019 0.01589 0.00007 0.01972 0.75874 105.49 ± 5.15 93.25 0.00036 0.02986 0.00002 0.04994 2.30631 125.89 ± 3.09 95.59 0.00022 0.01898 0.00008 0.07171 9.12178 327.51 ± 4.80 99.30 0.00032 0.02256 0.00020 0.04780 1.58515 91.29 ± 2.64 94.30 0.00064 0.00254 0.00003 0.09834 2.78768 78.31 ± 1.43 93.62 0.00278 0.00929 0.00007 0.14245 3.76182 73.06 ± 0.95 82.06 0.00115 0.03604 0.00006 0.09937 10.08616 265.98 ± 4.46 96.75

Murazzano 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) D48 J=0.001821 0.00102 0.00893 0.00011 0.21132 7.73155 116.36 ± 0.97 96.25 0.00101 0.00393 0.00007 0.09568 3.44312 114.50 ± 1.73 92.01 0.00044 0.01544 0.00001 0.09710 2.93672 96.71 ± 1.45 95.74 0.00081 0.00000 0.00000 0.07976 1.83752 74.15 ± 2.70 88.48 0.00016 0.00000 0.00004 0.14764 2.07513 45.59 ± 1.36 97.73 0.00023 0.00000 0.00000 0.09301 1.07176 37.46 ± 2.13 94.05 0.00221 0.00000 0.00007 0.16599 3.24008 63.01 ± 1.28 83.23 0.00127 0.00000 0.00001 0.09918 3.89857 124.72 ± 2.28 91.23 0.00037 0.00633 0.00003 0.12614 13.66040 324.71 ± 1.88 99.21 0.00029 0.01158 0.00005 0.05420 1.73843 102.41 ± 2.52 95.26 0.00018 0.00090 0.00004 0.03259 0.97916 96.10 ± 3.92 94.95 B9 J=0.003089 0.00013 0.00082 0.00023 0.22652 1.77568 43.16 ± 0.40 97.81 0.00073 0.00056 0.00025 0.41089 5.18311 68.96 ± 0.29 95.99 0.00027 0.00034 0.00000 0.05148 0.61004 64.85 ± 2.74 88.43 0.00006 0.00063 0.00044 0.01312 0.58978 234.51 ± 12.35 96.96 0.00032 0.00145 0.00193 0.26553 2.30684 47.78 ± 0.72 96.06 0.00060 0.00081 0.00132 0.20445 2.62401 70.14 ± 1.00 93.65 0.00097 0.00063 0.00089 0.10989 2.71549 132.71 ± 1.57 90.49 0.00044 0.00075 0.00032 0.07600 0.97370 70.02 ± 2.16 88.21 0.00029 0.00000 0.00217 0.20004 1.36717 37.69 ± 1.93 94.13 0.00006 0.00000 0.00098 0.00594 0.05043 46.70 ± 33.13 73.39 0.00028 0.00000 0.00095 0.11300 0.78456 38.28 ± 2.09 90.48 (continued) 94 B. Carrapa, J. Wijbrans, and G. Bertotti

TABLE A2. 40Ar/39Ar ANALYSES OF THE INVESTIGATED SAMPLES (continued) Murazzano 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2Ma 40Ar(%) 39Ar(%) B29 J=0.002577 0.00044 0.00067 0.00053 0.13158 2.07542 71.88 ± 1.04 94.15 10.17 0.00108 0.00092 0.00182 0.17130 4.17635 109.93 ± 0.66 92.92 13.23 0.00059 0.00075 0.00168 0.20913 3.44964 75.10 ± 0.59 95.20 16.16 0.00073 0.00201 0.00109 0.11981 3.32769 124.72 ± 1.03 93.93 9.26 0.00036 0.00047 0.00088 0.11041 2.70065 110.27 ± 1.19 96.16 8.53 0.00025 0.00000 0.00075 0.09706 1.22990 57.97 ± 1.67 94.42 7.50 0.00039 0.00024 0.00051 0.05818 1.55052 119.82 ± 2.81 93.02 4.50 0.00061 0.00000 0.00076 0.12014 1.63738 62.28 ± 1.26 90.02 9.28 0.00006 0.00051 0.00082 0.14348 1.17065 37.54 ± 1.10 98.40 11.09 0.00115 0.00341 0.00037 0.13319 5.28963 175.79 ± 1.28 93.98 10.29

Cassinasco 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) 39Ar(%) D40 J=0.001888 TFA 105.7±1.92 D41 J=0.001878 200ab 0.00120 0.00130 0.00011 0.38048 10.69314 92.79 ±0.69 98.66 74.55 200cd 0.00104 0.00445 0.00011 0.17019 4.77855 92.71 ±1.02 95.63 76.30 200fg 0.00067 0.00000 0.00003 0.41259 4.79422 38.95 ±0.43 99.26 97.80 200hi 0.00291 0.00000 0.00000 0.57131 20.05338 115.2 ±0.71 97.01 97.14 200no 0.00053 0.00304 0.00001 0.15647 6.13619 128.2 ±1.73 97.89 95.05 200pq 0.00062 0.00000 0.00000 0.21670 2.76107 42.66 ±1.16 95.77 15.67 200st 0.00465 0.03999 0.00022 0.70260 13.90670 65.84 ±1.27 95.53 98.48 202bc 0.00073 0.00124 0.00018 0.24561 11.44977 151.4 ±1.11 98.16 77.13 D49 J=0.001803 122 0.00918 0.00000 0.00000 0.21078 3.46377 52.68 ± 2.10 56.08 27.63 0.00918 0.00158 0.00000 0.27920 14.05690 156.75 ± 1.49 83.82 36.59 0.00918 0.00135 0.00000 0.09199 1.10806 38.76 ± 4.10 29.00 12.06 0.00918 0.00000 0.00000 0.17047 2.21011 41.69 ± 2.54 44.90 22.34 0.01558 0.00041 0.00005 0.01056 0.23810 71.91 ± 43.70 4.92 1.38 184 0.00126 0.00099 0.00017 0.15295 5.67705 116.87 ± 1.78 93.83 14.25 0.00206 0.00085 0.00018 0.24627 8.51992 109.16 ± 0.95 93.33 22.94 0.00620 0.00061 0.00000 0.28746 11.73730 128.15 ± 0.75 86.49 26.77 0.00164 0.00286 0.00000 0.24125 8.56335 111.91 ± 0.98 94.65 22.47 0.00178 0.00000 0.00000 0.14569 2.83263 62.16 ± 1.76 84.32 13.57 D50 J=0.001793 77.71 ± 0.76 TFA D51 J=0.001783 203ab 0.00056 0.00000 0.00015 0.36421 6.02308 52.43 ±0.49 98.79 75.92 203ce 0.00059 0.00042 0.00011 0.39867 8.72783 69.08 ±0.71 98.68 92.40 203fg 0.00065 0.00280 0.00014 0.23056 5.22240 71.43 ±1.29 98.93 75.86 203hi 0.00073 0.00391 0.00023 0.33995 11.59065 106.5 ±10.5 98.52 80.44 203pq 0.00226 0.06519 0.00022 0.70990 26.09092 114.5 ±1.6 98.58 93.20 203st 0.00133 0.05905 0.00032 0.40403 9.53687 74.37 ±2.63 94.43 21.60 203uv 0.00149 0.05709 0.00042 0.49672 10.15882 64.62 ±2.15 97.55 96.58 208ab 0.00144 0.01706 0.00024 0.41071 8.94133 68.7 ±0.62 98.07 59.34 208cd 0.00044 0.01006 0.00005 0.05389 1.26140 73.77 ±2.4 92.42 30.96 (continued) Detecting provenance variations and cooling patterns 95

TABLE A2. 40Ar/39Ar ANALYSES OF THE INVESTIGATED SAMPLES (continued) Cassinasco 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) D54 J=0.001755 TFA 94.01±0.7 D55 J=0.001747 209b 0.00057 0.00571 0.00000 0.09919 3.92317 120.54 ±1.81 95.91 209cd 0.00096 0.00897 0.00008 0.02650 0.47750 55.92 ±7.63 90.15 209ef 0.00096 0.00856 0.00000 0.27605 7.55033 84.21 ±0.85 96.62 209jl 0.00271 0.01210 0.00007 0.21435 8.15645 116.11 ±1.18 91.60 209no 0.00028 0.01050 0.00013 0.10606 1.96222 57.39 ±1.14 91.88 210bc 0.00072 0.00000 0.00000 0.19157 5.54382 88.98 ±0.98 96.84 210de 0.00264 0.00000 0.00009 0.35575 28.48430 236.19 ±1.39 98.03 210gh 0.00261 0.00000 0.00000 0.20928 10.17397 147.06 ±1.31 94.46 210il 0.00125 0.01584 0.00000 0.15479 4.38469 87.14 ±0.98 92.72 D64 J=0.001675 0.00056 0.00000 0.00000 0.19138 6.36258 97.76 ± 0.95 97.47 0.00088 0.00000 0.00000 0.17509 9.19408 152.08 ± 1.10 97.26 0.00112 0.00000 0.00032 0.30675 9.99170 95.84 ± 0.59 96.79 0.00088 0.00000 0.00000 0.30453 8.79460 85.22 ± 0.52 97.12 0.00009 0.00000 0.00011 0.04558 1.08187 70.34 ± 3.51 97.59 0.00027 0.00000 0.00001 0.04860 1.26108 76.75 ± 5.80 94.01 0.00043 0.00000 0.00002 0.11816 4.22067 104.83 ± 2.45 97.06 0.00065 0.00000 0.00000 0.13516 3.63828 79.56 ± 2.19 94.99 0.00008 0.00000 0.00000 0.00672 0.17773 78.18 ± 43.07 88.35 D65 J=0.001668 TFA 94.44 ± 0.69 B11 J=0.003052 0.00068 0.00000 0.00029 0.38029 4.22907 60.22 ± 0.36 95.44 0.00041 0.00017 0.00076 0.47620 4.45147 50.75 ± 0.27 97.34 0.00066 0.00000 0.00055 0.12623 3.55487 148.76 ± 0.97 94.80 0.00038 0.00000 0.00036 0.14264 1.56721 59.50 ± 0.75 93.27 0.00041 0.00000 0.00013 0.09471 0.85465 49.01 ± 1.01 87.68 0.00029 0.00000 0.00029 0.18471 1.65350 48.63 ± 0.58 95.01 0.00052 0.00020 0.00039 0.11761 2.00304 91.42 ± 1.05 92.83 0.00021 0.00046 0.00011 0.14548 9.17756 317.66 ± 1.01 99.34 0.00024 0.00000 0.00005 0.10353 1.19749 62.59 ± 1.07 94.50 0.00054 0.00054 0.00057 0.15385 1.85755 65.28 ± 0.83 92.04 B24 J=0.002712 0.00077 0.00038 0.00034 0.18185 2.55486 67.46 ± 0.90 91.82 0.00032 0.00000 0.00000 0.15674 2.09977 64.38 ± 0.73 95.68 0.00016 0.00000 0.00006 0.08506 0.78331 44.50 ± 1.19 94.19 0.00039 0.00000 0.00014 0.17311 10.12281 265.56 ± 1.03 98.88 0.00044 0.00037 0.00044 0.09283 1.77921 91.41 ± 1.16 93.13 0.00018 0.00000 0.00004 0.09199 0.71223 37.49 ± 0.79 93.14 0.00018 0.00000 0.00020 0.41221 14.23411 161.50 ± 0.41 99.62 0.00049 0.00000 0.00114 0.21974 1.74031 38.34 ± 0.56 92.37 0.00062 0.00000 0.00082 0.18277 3.12162 81.68 ± 0.78 94.42 0.00064 0.00000 0.00091 0.31646 3.16821 48.33 ± 0.37 94.39 (continued) 96 B. Carrapa, J. Wijbrans, and G. Bertotti

TABLE A2. 40Ar/39Ar ANALYSES OF THE INVESTIGATED SAMPLES (continued) Cassinasco 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) B27 J=0.002634 0.00026 0.00097 0.00254 0.01820 0.12682 32.82 ± 9.57 62.56 0.00020 0.00037 0.00089 0.09403 2.04448 100.48 ± 1.78 97.22 0.00046 0.00027 0.00188 0.23393 3.29560 65.73 ± 0.76 96.06 0.00061 0.00031 0.00103 0.13414 2.93910 101.22 ± 1.35 94.22 0.00019 0.00074 0.00210 0.02167 0.19339 41.91 ± 8.00 77.94 0.00031 0.00018 0.00101 0.23263 2.37194 47.81 ± 0.48 96.31 0.00041 0.00038 0.00261 0.48812 5.12074 49.18 ± 0.25 97.68 0.00037 0.00048 0.00080 0.17393 3.89705 103.45 ± 0.54 97.30 0.00016 0.00077 0.00084 0.16999 1.55097 42.84 ± 0.40 97.04 0.00376 0.00099 0.00250 0.50528 9.21999 84.69 ± 0.62 89.23 B34 J=0.002361 0.00023 0.00015 0.00022 0.07622 1.18007 64.77 ± 1.65 94.61 0.00024 0.00034 0.00081 0.18670 4.31110 95.77 ± 0.66 98.35 0.00061 0.00022 0.00109 0.24472 3.33059 57.06 ± 0.55 94.84 0.00098 0.00083 0.00121 0.17421 3.62077 86.42 ± 0.94 92.56 0.00019 0.00095 0.00100 0.17702 2.79856 66.11 ± 0.69 98.03 0.00003 0.00000 0.00000 0.04397 0.83430 79.07 ± 2.51 98.89 0.00027 0.00000 0.00028 0.14661 2.20300 62.89 ± 0.73 96.51 0.00034 0.00000 0.00075 0.17543 4.09649 96.82 ± 0.83 97.60 0.00015 0.00000 0.00107 0.21101 3.34448 66.28 ± 0.60 98.66 0.00017 0.00131 0.00102 0.19072 3.04255 66.70 ± 0.66 98.34

Lequio 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) B26 J=0.002674 0.00042 0.00025 0.00096 0.21149 3.17208 70.94 ± 0.53 96.22 0.00034 0.00000 0.00087 0.11740 5.45333 211.22 ± 1.27 98.19 0.00019 0.00000 0.00058 0.10173 7.00051 304.72 ± 1.55 99.21 0.00019 0.00029 0.00086 0.21642 14.04228 288.63 ± 1.23 99.59 0.00017 0.00030 0.00127 0.09677 0.96833 47.64 ± 1.05 94.95 0.00013 0.00000 0.00104 0.14888 1.21692 39.01 ± 0.76 96.94 0.00012 0.00000 0.00110 0.15639 9.64211 275.31 ± 1.01 99.64 0.00016 0.00000 0.00105 0.13109 1.20167 43.69 ± 0.90 96.26 0.00017 0.00000 0.00089 0.08509 1.02352 57.11 ± 1.45 95.19 0.00003 0.00000 0.00048 0.05112 3.57944 309.61 ± 3.17 99.75 B30 J=0.002534 0.00066 0.00078 0.00130 0.30676 3.27013 48.09 ± 0.47 94.39 0.00029 0.00023 0.00069 0.13268 1.12180 38.24 ± 0.52 92.83 0.00010 0.00000 0.00022 0.04477 1.07362 106.43 ± 1.93 97.28 0.00011 0.00072 0.00012 0.23841 14.25421 254.50 ± 0.76 99.76 0.00009 0.00006 0.00056 0.08686 6.05692 293.55 ± 1.54 99.58 0.00001 0.00089 0.00003 0.12644 9.42874 312.25 ± 1.03 99.96 0.00101 0.00055 0.00069 0.09900 1.94140 87.49 ± 1.10 86.68 0.00009 0.00099 0.00039 0.14771 10.06651 287.39 ± 1.84 99.75 0.00013 0.00000 0.00044 0.23068 15.92031 290.76 ± 0.55 99.76 0.00042 0.00000 0.00067 0.06847 2.54216 162.21 ± 1.64 95.33 (continued) Detecting provenance variations and cooling patterns 97

TABLE A2. 40Ar/39Ar ANALYSES OF THE INVESTIGATED SAMPLES (continued) Lequio 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) A2 J=0.001894 0.00075 0.03312 0.00020 0.17065 3.69348 72.48 ± 4.79 94.36 0.00119 0.03149 0.00015 0.21709 4.09104 63.27 ± 3.82 92.10 0.00091 0.03233 0.00020 0.16490 2.82484 57.61 ± 4.93 91.28 0.00109 0.03318 0.00038 0.13319 4.67569 116.13 ± 5.93 93.56 0.00160 0.02648 0.00059 0.14182 3.63433 85.51 ± 5.88 88.51 0.00312 0.00126 0.00044 0.20966 7.80716 122.95 ± 1.51 89.45 0.00033 0.00080 0.00045 0.18840 2.35081 42.14 ± 1.53 96.00 0.00059 0.00000 0.00006 0.12655 2.49137 66.04 ± 3.96 93.42 0.00127 0.00075 0.00011 0.21678 3.27260 50.86 ± 2.48 89.73 0.00046 0.00000 0.00019 0.12004 1.88143 52.78 ± 4.34 93.27 A4 J=0.001892 0.00029 0.00105 0.00001 0.05553 1.20649 72.68 ± 6.56 93.43 0.00028 0.00400 0.00018 0.06457 6.78426 327.11 ± 6.83 98.79 0.00021 0.00351 0.00026 0.06035 6.09445 315.42 ± 6.06 98.97 0.00052 0.00214 0.00012 0.10711 2.15708 67.46 ± 3.77 93.32 0.00036 0.00022 0.00000 0.06691 1.18909 59.66 ± 5.06 91.82 0.00006 0.00000 0.00035 0.07782 7.98449 320.06 ± 6.42 99.78 0.00024 0.00314 0.00000 0.03796 0.92680 81.48 ± 10.73 92.99 0.00001 0.00064 0.00000 0.00475 0.07099 50.36 ± 82.80 96.17 0.00016 0.00052 0.00016 0.04992 1.14729 76.78 ± 7.43 96.04 0.00001 0.00000 0.00051 0.08422 8.64381 320.17 ± 5.15 99.95 A5 J=0.001891 0.00085 0.00000 0.00022 0.11662 2.95591 84.46 ± 2.25 92.18 0.00067 0.00089 0.00025 0.18403 4.15946 75.50 ± 1.86 95.44 0.00074 0.00000 0.00032 0.16509 3.25583 66.06 ± 1.61 93.72 0.00084 0.00000 0.00027 0.16146 3.04381 63.19 ± 1.71 92.49 0.00061 0.00000 0.00053 0.10538 2.84253 89.75 ± 2.50 94.00 0.00024 0.00000 0.00015 0.04134 0.89234 72.17 ± 6.14 92.70 0.00030 0.00000 0.00008 0.00577 0.03726 21.91 ± 41.50 29.38 0.00057 0.00000 0.00000 0.16197 3.34630 69.14 ± 1.26 95.24 0.00072 0.00121 0.00015 0.13745 1.89997 46.55 ± 1.78 89.88 0.00022 0.00535 0.00060 0.09118 8.51274 293.31 ± 3.21 99.24 A6 J=0.001890 0.00111 0.00000 0.00025 0.28128 8.60685 101.43 ± 0.77 96.34 0.00008 0.00310 0.00000 0.17956 18.38102 319.09 ± 2.08 99.88 0.00063 0.00242 0.00048 0.20909 3.79445 60.84 ± 1.78 95.29 0.00043 0.00244 0.00010 0.19090 6.33614 109.76 ± 1.66 98.04 0.00035 0.00543 0.00000 0.26135 25.61371 306.58 ± 1.18 99.59 0.00028 0.00183 0.00004 0.11697 4.55877 128.22 ± 2.74 98.24 0.00151 0.00667 0.00000 0.16865 11.78144 223.73 ± 2.56 96.36 0.00074 0.00087 0.00033 0.12450 2.78421 74.69 ± 2.19 92.67 0.00011 0.00229 0.00000 0.10152 9.80241 302.40 ± 3.44 99.68 0 00027 0 00366 0 00032 0 13407 13 39523 312 06 2 76 99 40 98 B. Carrapa, J. Wijbrans, and G. Bertotti

TABLE A2. 40Ar/39Ar ANALYSES OF THE INVESTIGATED SAMPLES (continued) Present sands 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) Tanaro B15 J=0.002958 0.00025 0.00000 0.00000 0.27447 16.49710 295.22 ± 1.33 99.56 0.00015 0.00041 0.00026 0.21008 12.82995 299.59 ± 1.15 99.65 0.00042 0.00115 0.00009 0.21213 13.50218 311.21 ± 1.34 99.08 0.00074 0.00082 0.00070 0.21769 13.36759 301.10 ± 1.15 98.39 0.00013 0.00049 0.00029 0.17809 11.09515 305.14 ± 1.23 99.64 0.00067 0.00198 0.00000 0.24664 14.90981 296.79 ± 1.16 98.69 0.00042 0.00011 0.00009 0.42222 26.47683 306.98 ± 0.87 99.53 0.00045 0.00075 0.00046 0.29752 17.85984 294.87 ± 1.43 99.25 0.00020 0.00086 0.00055 0.24714 1.76190 37.65 ± 0.68 96.72 A31 J=0.001870 0.00000 0.00000 0.00021 0.08279 8.55896 318.86 ± 2.39 100.00 0.00065 0.00289 0.00000 0.17393 5.98778 112.56 ± 1.36 96.87 0.00013 0.00313 0.00000 0.10144 9.22355 283.30 ± 3.16 99.60 0.00031 0.00128 0.00010 0.11995 11.37688 294.57 ± 3.29 99.20 0.00015 0.00030 0.00000 0.16233 1.73807 35.76 ± 1.47 97.54 0.00049 0.00312 0.00000 0.19347 16.77586 271.10 ± 2.25 99.15 0.00029 0.00160 0.00000 0.10937 11.10519 313.64 ± 3.22 99.22 0.00023 0.00556 0.00038 0.16347 15.59394 296.13 ± 2.25 99.57 0.00037 0.00143 0.00000 0.08356 8.72244 321.70 ± 4.82 98.75 0.00081 0.00588 0.00032 0.30906 30.54794 305.97 ± 1.55 99.22 B16 J=0.002934 TFA 314.7 ±2.64

Stura B17 J=0.002910 0.00029 0.00416 0.00000 0.74567 43.77489 284.53 ± 0.63 99.81 0.00094 0.00000 0.00121 0.64183 39.15587 294.82 ± 0.85 99.30 0.00024 0.00000 0.00107 0.48989 30.12441 296.98 ± 1.41 99.76 0.00022 0.00000 0.00091 0.44144 26.80567 293.56 ± 0.98 99.75 0.00028 0.00078 0.00084 0.42577 26.06749 295.79 ± 0.84 99.68 0.00012 0.00035 0.00000 0.20521 12.63738 297.38 ± 1.55 99.72 0.00026 0.00084 0.00010 0.15220 9.55720 302.77 ± 1.39 99.20 0.00010 0.00105 0.00008 0.45785 28.69089 302.20 ± 1.07 99.90 0.00025 0.00048 0.00181 0.35343 21.13772 289.47 ± 1.34 99.65 A33 J=0.001868 0.00015 0.00259 0.00049 0.35855 21.87660 294.86 ± 0.91 99.80 0.00018 0.00008 0.00035 0.16345 16.17064 305.93 ± 3.12 99.66 0.00036 0.00178 0.00028 0.32403 32.69575 311.53 ± 1.84 99.67 0.00052 0.00399 0.00040 0.09496 9.55715 310.80 ± 4.40 98.41 0.00030 0.00449 0.00035 0.10051 10.66317 326.17 ± 4.50 99.17 0.00122 0.00451 0.00052 0.21609 21.01410 301.13 ± 2.93 98.31 0.00013 0.00161 0.00002 0.13643 14.38491 324.34 ± 3.23 99.73 0.00108 0.00000 0.00000 0.14197 13.96509 304.32 ± 3.34 97.76 0.00050 0.00119 0.00004 0.13416 13.65997 314.12 ± 3.52 98.92 0.00070 0.00111 0.00000 0.20369 18.75177 286.28 ± 2.71 98.91 B18 J=0.002879 TFA 305.87 ±1.85 (continued) Detecting provenance variations and cooling patterns 99

TABLE A2. 40Ar/39Ar ANALYSES OF THE INVESTIGATED SAMPLES (continued) Present sands 36Ar(a) 37Ar(Ca) 38Ar(Cl) 39Ar(K) 40Ar(r) Age 2 Ma 40Ar(%) Maira B13 J=0.003012 0.00242 0.00078 0.00044 0.74100 11.98409 85.81 ± 0.45 94.37 0.00171 0.00116 0.00095 0.53839 16.48979 159.19 ± 0.59 97.02 0.00158 0.00113 0.00113 0.26651 4.23196 84.28 ± 0.79 90.07 0.00124 0.00001 0.00134 0.21017 3.74044 94.21 ± 0.87 91.07 0.00119 0.00033 0.00082 0.29666 4.15063 74.47 ± 0.44 92.17 0.00104 0.00000 0.00062 0.12663 0.93653 39.75 ± 1.35 75.27 0.00037 0.00001 0.00040 0.26605 3.02743 60.80 ± 0.58 96.46 0.00048 0.00043 0.00062 0.33386 3.85268 61.64 ± 0.44 96.44 0.00124 0.00071 0.00116 0.37491 6.85901 96.77 ± 17.96 94.93 0.00063 0.00071 0.00086 0.26613 6.12037 120.83 ± 0.62 97.05 A34 J=0.001867 0.00088 0.00559 0.00007 0.42525 7.80664 60.80 ± 1.14 96.77 0.00098 0.00459 0.00029 0.35456 6.16508 57.64 ± 1.21 95.52 0.00441 0.00651 0.00000 0.43850 9.90354 74.51 ± 1.03 88.37 0.00104 0.00407 0.00000 0.29468 5.44614 61.20 ± 1.49 94.64 0.00106 0.00497 0.00058 0.16429 2.70191 54.56 ± 3.12 89.59 0.00199 0.00093 0.00039 0.21428 5.00788 77.05 ± 0.95 89.49 0.00351 0.00502 0.00002 0.39586 8.27521 69.07 ± 0.59 88.85 0.00114 0.00454 0.00005 0.41556 7.94239 63.25 ± 0.49 95.94 0.00277 0.00000 0.00000 0.42950 8.64451 66.55 ± 0.58 91.35 0.00060 0.00315 0.00021 0.33274 5.57909 55.61 ± 0.65 96.93 B14 J=0.002985 TFA 75.9 ±0.6 Note: The Molare data are part of the paper of Barbieri et al. (2003). The values (mols. and %) listed for the 40Ar/39Ar experiments are 36Ar(a): atmospheric component in 36Ar; 37Ar(Ca): calcium-derived 37Ar; 38Ar(Cl): chlorine-derived component 38Ar; 39Ar(K): potassium-derived component in 39Ar; 40Ar(r): radiogenic 40Ar; Age (Ma) with related 2errors; 40Ar(%): percentage radiogenic component in Ar. Note that 37Ar in the experiments was low and indistinguishable from the blank. This could have been the result of sample preparation, which included a leaching step with nitric acid to dissolve the carbonate fraction and enable better mica separation. Time between sample irradiation and the analyses 37 of reported data was never more than 4 months (T1/2 Ar = 35.1 days). D—VU32; B—VU36; A—VU41. TFA—total fusion ages (see Table A3).

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