# New constraints on the Late Miocene-Pliocene deformational and depositional evolution of the Eastern Cordillera and Sub-Andean Zone in Southern Peru

Gabriel Ribeiro Moizinho, Martin Roddaz, S. Brichau, M. Louterbach, E.L. Dantas, R.V. Santos, Germain Bayon, Julien Bailleul, J. Vink, C. Hoorn

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## To cite this version:

Gabriel Ribeiro Moizinho, Martin Roddaz, S. Brichau, M. Louterbach, E.L. Dantas, et al. New constraints on the Late Miocene-Pliocene deformational and depositional evolution of the Eastern Cordillera and Sub-Andean Zone in Southern Peru. Journal of South American Earth Sciences, 2024, 133, 104700 [24 p.]. 10.1016/j.jsames.2023.104700. hal-04452310

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Submitted on 16 Sep 2025

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# New constraints on the Late Miocene-Pliocene deformational and depositional evolution of the Eastern Cordillera and Sub-Andean Zone in Southern Peru

Moizinho G.R. <fnref n="1" />, <fnref n="2" />, <fnref n="3" />, *, Roddaz M. <fnref n="1" />, Brichau S. <fnref n="1" />, Louterbach M. <fnref n="4" />, Dantas E.L. <fnref n="2" />, Santos R.V. <fnref n="2" />, Bayon Germain <fnref n="3" />, Vink J. <fnref n="5" />, Hoorn C. <fnref n="6" />, <fnref n="7" />

## Abstract :

The deformation history of the Eastern Cordillera (EC) and Sub-Andean Zone (SAZ) of southern Peru is critical for understanding the roles that tectonics and climate played in the erosional exhumation of bedrock and the associated sediment flux delivered to the Amazon drainage basin. In this study, we report new field and subsurface data, apatite fission track (AFT) and (U–Th)/He thermochronological ages, U–Pb ages on detrital zircon grains, Sr–Nd isotopic compositions of fine sediments, which combined with previously published data, provide new constraints on the Neogene deformation and deposition history across the southern Peruvian EC and SAZ between 12° and 14°S. Late Miocene-Pliocene deformation is recorded by AFT and AHe ages in both the EC and SAZ and by growth strata geometry in the SAZ. This period is characterized by the development of piggy-back synclines and duplexes in the SAZ, overthrusting of the EC, and input of recycled sedimentary rocks of the SAZ and first cycle sediments from Triassic Plutonic rocks from the EC to the late Miocene-Pleistocene piggy-back syncline sediments. We report a transition from low-energy sand-dominated to high-energy conglomerate-dominated deposits in the Plio-Pleistocene marking an increase in sedimentation rates, indicating that the thrust wedge has continued to propagate. Our data agrees with that of previously published studies and indicate that the Late Miocene-Pliocene was a period of tectonic uplift and deformation in both the EC and SAZ.

<footnote n="1">¹ Géosciences-Environnement Toulouse, Université de Toulouse, Toulouse, France</footnote>

<footnote n="2">² Instituto de Geociências, Universidade de Brasília, Brasília, Brazil</footnote>

<footnote n="3">³ IFREMER, Geo-ocean, Plouzané, France</footnote>

<footnote n="4">⁴ Harvard Graduate School of Design, Department of Landscape Architecture, Cambridge, USA</footnote>

<footnote n="5">⁵ Bassins-Réservoirs-Ressources, Institut Polytechnique Lasalle Beauvais, Beauvais Cedex, France</footnote>

<footnote n="6">⁶ Centre for Biodiscovery School of Biological Sciences Victoria University of Wellington Wellington, New Zealand</footnote>

<footnote n="7">⁷ Institute of Biodiversity and Ecossistem Dynamics, University of Amsterdam, Netherlands</footnote>

<footnote>* Corresponding author : G. R. Moizinho, email address : gabriel.ribeiro-moizinho@univ.tlse3.fr</footnote>
**Highlights**

► Timing of Late Miocene-Pliocene uplift of the Eastern Cordillera and Sub Andean Zone constrained by AFT and AHe data. ► Transition from a low to high energy fluvial system in the Late Miocene-Pliocene.

► Provenance analysis of the Madre de Dios basin indicates Eastern Cordillera denudation and recycling of SAZ sediments.

**Keywords** : Andes, Miocene-Pliocene, Uplift, Thermochronology, Chronostratigraphy, Provenance
## 1. Introduction

The Andes, the longest and second largest continental mountain range on Earth, constitute an important barrier to atmospheric fluxes in the Southern Hemisphere and affect the regional-scale climate by blocking zonal flows, influencing regional wind patterns, and precipitation rates (Figure 1; Lenters and Cook, 1995; Campetella and Vera, 2002; Garreaud et al., 2003; Insel et al., 2010; Espinoza et al., 2020). Hence, the rise of the Andes is thought to have affected the climate in the eastern Pacific Ocean, besides moisture transport, and precipitation patterns in the
adjacent Amazon Basin (Uba et al., 2007; Sepulchre et al., 2009; Insel et al., 2010; Poulsen et al., 2010).

The Eastern Cordillera (EC) and the Sub-Andean Zone (SAZ) define the Eastern Andean Orogenic wedge of Bolivia and Peru and constitute an orographic barrier to the moisture flux from the Amazon (e.g., Bookhagen and Strecker, 2008; Chavez and Takahashi, 2017). Most of the studies indicate that the EC experienced deformation, exhumation, and surface uplift during the Miocene (e.g., Horton, 1999; McQuarrie et al., 2008b; Eude et al., 2015; Sundell et al., 2019). In Bolivia, by comparing the shape of the wedge assimilated to a Coulomb wedge and the present climatic zones, Horton (1999) interpreted precipitation-induced erosion to be responsible for a lesser propagation of the wedge in the north. Similarly, the decrease in width of the northern Bolivian Eastern Orogenic wedge has been interpreted as the result of a wetter climate of northern Bolivia since ca. 19 Ma (McQuarrie et al., 2008b). Alternatively, weakening of the retroarc lithosphere and development of a crustal-scale detachment due to strain accumulation in the Central Andes (13-22°C; Oncken et al., 2012) as well as inherited properties of the retroarc lithosphere or flat slab subduction (Horton et al., 2022) may explain accelerated shortening in the SAZ since the Middle Miocene.

The SAZ defines the eastern limit of the Central Andes, and it provides an example of an active fold and thrust belt in a retro-arc, non-collisional setting (Figure 2). The onset of the SAZ deformation of the Central Andes and its Neogene history varies. Pliocene thrusting and forward propagation of the deformation has been documented in the SAZ in central and northern Peru (4-12.5 Lat S°, Espurt et al., 2011; Gautheron et al., 2013; Eude et al., 2015). However, in northern Bolivia and southern Peru (12.5-17 Lat S°), the absence of deformation in the EC and a "limited deformation in the Subandes" for the past 4 Ma in northern Bolivia and southern Peru have been used to advocate for a Pliocene climatic control on the exhumation and erosion of the terrain, (Lease and Ehlers, 2013).

In this paper, we revisited the Late Miocene-Pliocene exhumation history of the Amazonian southern Peruvian SAZ based on the correlation of previously published seismic sections (Baby et al., 2018b; Zamora et al., 2019), thermochronology (Mora et al., 2011; Baby et al., 2018b) and biostratigraphic ages (Marivaux et al., 2012; Antoine et al., 2013) with new AFT and AHe ages. Additionally, we report new sedimentological, provenance (Sr-Nd isotopic compositions of fine sediments and U-
Pb ages of detrital zircon in sandstones), biostratigraphic and chronostratigraphic ($^{40}$Ar/$^{39}$Ar in biotite ages) data sets to better understand the basin-fill evolution of the Madre de Dios retroarc foreland basin in response to the forward propagation of the Eastern Andean Orogenic wedge.

## 2. Geological Background

### 2.1 Structural setting

The studied area is located between 12° and 14° S latitudes on the eastern side of the Peruvian Andes, and it comprises the EC and the Madre de Dios Basin. The basin is part of the southern Amazonian foreland basin systems and can be divided into the SAZ and the Madre de Dios foredeep (Gil, 2001; Hermoza, 2004; Roddaz et al., 2005b; Figure 2). The Madre de Dios basin is bounded in the southwest by the Azulmayo thrust, which places pre-Mesozoic rocks of the EC over the Mesozoic sedimentary rocks of the SAZ, north and northeast by the Brazilian Shield, and north and northwest by the Fitzcarrald Arch. The southern Peruvian EC is a double verging thrust wedge consisting, in its inner part, of an SW-verging system of thrust faults and folds of the Central Andean back thrust belt involving Paleozoic and Mesozoic sedimentary strata (McQuarrie and DeCelles, 2001). In its outer part, Permo-Triassic plutons and metamorphosed Precambrian and Paleozoic strata (Dalmayrac et al., 1980; Kontak et al., 1990; Mišković et al., 2009) overthrusting the SAZ. The oldest rocks outcropping in the studied area are the metamorphic rocks of the "Iscaybamba Complex". The exact age of these metamorphic rocks is unknown, but they could be Cambrian or older (Marocco, 1978; Megard, 1978; Dalmayrac et al., 1980; Dalmayrac and Molnar, 1981; Laubacher, Gérard and Megard, 1985). In this section (see location in Figure 3), the EC is interpreted as a large crustal-scale ramp anticline above a footwall ramp. Additional east-verging faults to the west of the anticline are interpreted to repeat the Ordovician section (i.e., Marcapata and Ollachea thrust faults, Figures 2 and 3).

In the Madre de Dios Basin, the SAZ is separated from the EC by the Azulmayo thrust, also known as the "Main thrust" (Perez et al. 2016), and from the foredeep by the Tambopata thrust, which corresponds to the Sub-Andean thrust front (Figures 3 and 4). The SAZ is interpreted as being constituted of a hinterland dipping duplex developed either in the Paleogene sedimentary infill (Figure 4, Baby et al., 2018b; Gil Rodriguez et al., 2001) or in the Ordovician to Cretaceous series (Perez et al., 2016).
On the other hand, Mora et al. (2014) have interpreted it as a thin-skinned passive-roof duplex. This duplex is overthrust by an imbricate system of Cretaceous strata as observed in seismic lines (see Figure 17B in Baby et al., 2018b), and field relationships (see Figure 18 in Baby et al. 2018b and Figure 38 in Louterbach, 2014). The propagation of the deformation towards the Madre de Dios foredeep is partly controlled by the development of the deep duplexes. Their shortening is accommodated at the surface by tectonic imbricates and by the Tambopata frontal thrust (Gil Rodriguez et al., 2001; Baby et al., 2018a), which transported eastwards the Punquiri piggyback syncline consisting of Cenozoic sediments (Baby et al., 2018a). The strata involved in the Punquiri syncline are Paleogene through to Plio-Pleistocene in age, as shown by biostratigraphic evidence (Antoine et al., 2013; Louterbach et al., 2014; this study).

The balanced cross-section published by Baby et al. (2018b) shows that the shortening in the SAZ is kinematically linked to the displacement of the EC over a crustal-scale ramp, linking the development of the EC crustal anticline to the documented shortening in the SAZ. This link has also been recognized in other parts of the eastern Andes (Echavarria et al., 2003; Espurt et al., 2011; Eude et al., 2015). Since this transport of the EC along a crustal ramp implies a tectonic uplift, it follows that it was also contemporary with the deformation of the SAZ.

## 2.2. Neogene Stratigraphic Framework

The Madre de Dios Basin sedimentary infill consists of approximately 3.3km of siliciclastic sediments that overlie the marine Cretaceous Cachiayacu Formation. Its stratigraphic record has been described regarding both the SAZ and foredeep compartments (Gil Rodriguez, 2001; Hermoza, 2004; Roddaz et al, 2010). In the SAZ, three units are recognized: the Paleocene Huayabamba Formation, the Miocene Ipururo Group, and the Plio-Pleistocene Mazuko Formation. In the foredeep, the two older units are also observed, and the Plio-Pleistocene Mazuko Formation absent. These depositional ages are supported by palynological data (Carpenter and Berumen, 1999; Cooperación Técnica Peruana-Alemana, 1982; Gutierrez, 1982; Valdivia, 1974), thermochronological analysis (Apatite to Zircon Inc., 2004; Hermoza, 2004) and radiometry ($^{40}$Ar/$^{39}$Ar on volcanic feldspar and biotite; Campbell et al., 2001; Gil Rodriguez, 2001; Mobil Oil Corporation, 1998).
In the SAZ, the Ipururo Group consists of Miocene deposits divided into three formations: the Bala, Quendeque, and Charqui formations (Roddaz et al., 2010). At first, these formations were thought to be fluvial to alluvial in nature (Gil Rodriguez, 2001; Hermoza, 2004; Roddaz et al., 2010). Alluvial, deltaic, and estuarine coastal plain facies have been reported in the Miocene Bolivian Quendeque Formation (Hovikoski et al., 2007b; Hovikoski et al., 2007c). Miocene tidal-influenced deposits were also described in the Bolivian Beni-Mamoré Basin, which is adjacent to the Madre de Dios Basin (Roddaz et al., 2006).

In the Peruvian foredeep, the Ipururo Group encompasses the Ipururo Formation and Units A and B of the Madre de Dios Formation (Campbell et al., 2001). The Ipururo Formation is thought to be Miocene in age based on stratigraphic correlations (Hermoza, 2004). The Madre de Dios Formation is Late Miocene ($^{40}$Ar/$^{39}$Ar dating on feldspars at 9.01 ± 0.28 Ma, Campbell et al. 2001) and thus considered as a lateral equivalent of the Bolivian Charqui Formation (Roddaz et al., 2010). Overall, the Madre de Dios Formation has been interpreted as formed by tide-dominated estuarine deposits (Hovikoski et al., 2005; Roddaz et al., 2006).

## 3. Sampling and methodologies

### 3.1. Low temperature thermochronology

Eight samples were collected along two vertical profiles in the eastern flank of the EC for Apatite Fission Track (AFT) and Apatite U-Th/He (AHe) analyses: six Permo-Triassic plutonic rocks (MD164, MD169, MD170, MD192, MD194, and MD211) and two metasedimentary rocks belonging to the Paleozoic (Cambrian?) Iscabambay Complex (MD112 and MD216; see Tables 1 and 2). The AFT age of MD216 was previously presented by Baby et al. (2018b) but the dataset was never published. In the SAZ, we provide the full dataset for three AFT ages of three Cretaceous to Paleogene sedimentary rocks (MD30, MD29, and MD28). These AFT ages were reported by Mora et al. (2011) and Baby et al. (2018b) but the dataset was never published. The locations of the samples are shown in Figure 3 and projected onto the cross-section in Figure 4.

The AFT analysis of the SAZ was carried out by Apatite to Zircon Inc. (former Donnelick Analytical LabAFT analyses). Sample preparation and the rest of the AFT
and AHe analyses were performed at Geoscience Environment Toulouse (GET, 193 France) and Caltech (USA), respectively, following the methodology described in Eude 194 et al. (2015). Detailed analytical procedures can be found in the supplementary data 195 material. 196
197
<table><caption>**Table 1:** Fission track data. Abbreviations are as follows: EC: Eastern Cordillera; SAZ Subandean Zone; PC: Pongo de Coneq; IN: Inambari; ps, spontaneous track density (×10⁶ tracks per cm²); Ns, number of spontaneous tracks counted in apatite grains; pi, induced track density in external detector (muscovite)(×10⁶ tracks per cm²); Ni, number of induced tracks counted in micas; pd, density of tracks on the neutron monitor; Nd, number of tracks counted in the dosimeter; Pχ² (%), probability of obtaining χ² value for</caption><thead><tr><th>Area</th><th>Sample Name</th><th>Age</th><th>Lithology</th><th>Longitude</th><th>Latitude</th><th>Elevation (m)</th><th>pS</th><th>Ns</th><th>pi</th><th>Ni</th><th>pd</th><th>Nd</th><th>P(x²) (%)</th></tr></thead><tbody><tr><td rowspan="8">EC</td><td>MD 170</td><td>Permo-Triassic</td><td>Plutonic rock</td><td>-7,049,500</td><td>-1,384,040</td><td>3213</td><td>231600</td><td>114</td><td>6134000</td><td>3124</td><td>1423000</td><td>41768</td><td>99,43</td></tr><tr><td>MD 192</td><td>Permo-Triassic</td><td>Plutonic rock</td><td>-7,098,110</td><td>-1,359,570</td><td>3000</td><td>45540</td><td>39</td><td>1433000</td><td>1234</td><td>1367000</td><td>13741</td><td>92,44</td></tr><tr><td>MD 194</td><td>Permo-Triassic</td><td>Plutonic rock</td><td>-7,091,780</td><td>-1,356,870</td><td>2385</td><td>82870</td><td>70</td><td>4796000</td><td>4283</td><td>1367000</td><td>13741</td><td>99,52</td></tr><tr><td>MD 164</td><td>Permo-Triassic</td><td>Plutonic rock</td><td>-7,046,680</td><td>-1,368,790</td><td>1883</td><td>394400</td><td>186</td><td>9080000</td><td>4115</td><td>1406000</td><td>13542</td><td>81,83</td></tr><tr><td>MD 211</td><td>Permo-Triassic</td><td>Plutonic rock</td><td>-7,047,750</td><td>-1,366,790</td><td>1733</td><td>180712</td><td>107</td><td>7281816</td><td>4364</td><td>1438300</td><td>14485</td><td>99,94</td></tr><tr><td>MD 216</td><td>Paleozoic (Cambrian?)</td><td>Metasediment</td><td>-7,086,083</td><td>-1,334,566</td><td>986</td><td>89265</td><td>37</td><td>3508563</td><td>1403</td><td>1377758</td><td>13741</td><td>75,39</td></tr><tr><td>MD 30</td><td>Late Cretaceous</td><td>Sandstone</td><td>-7,038,383</td><td>-1,318,562</td><td>382</td><td>15000</td><td>51</td><td>3085000</td><td>1051</td><td>3122000</td><td>5154</td><td>1,4</td></tr><tr><td>MD 29</td><td>Late Cretaceous</td><td>Sandstone</td><td>-7,040,074</td><td>-1,314,935</td><td>371</td><td>265000</td><td>131</td><td>3787000</td><td>1875</td><td>3124000</td><td>5154</td><td>0,0</td></tr><tr><td>MD 28</td><td>Miocene</td><td>Sandstone</td><td>-7,039,736</td><td>-1,312,999</td><td>366</td><td>266000</td><td>126</td><td>2413000</td><td>1142</td><td>3126000</td><td>5154</td><td>0</td></tr><tr><th>Area</th><th>Sample Name</th><th>Mean U (ppm)</th><th>Central Age (Ma)</th><th>Pooled age (Ma)</th><th>Mean Age (Ma)</th><th>P1 (Ma)</th><th>P2 (Ma)</th><th>Ng</th><th>TL</th><th>of Tracks</th><th>Dpar (µm)</th><th>Std (µm)</th><th>Analysts</th></tr><tr><td rowspan="8">SAZ</td><td>MD 170</td><td>53,9</td><td>7.9±0.8</td><td><strong>7.9±0.8</strong></td><td>8.1±1.3</td><td></td><td></td><td>28</td><td>11.03±0.5</td><td>50</td><td>2,03</td><td>1,95</td><td>ML</td></tr><tr><td>MD 192</td><td>13,1</td><td>6.5±1.1</td><td><strong>6.5±1.1</strong></td><td>6.1±0.9</td><td></td><td></td><td>19</td><td>12,8</td><td>1</td><td>NO</td><td>NO</td><td>ML</td></tr><tr><td>MD 194</td><td>43,9</td><td>3.4±0.4</td><td><strong>3.4±0.4</strong></td><td>3.4±0.4</td><td></td><td></td><td>26</td><td>11.15±0.6</td><td>26</td><td>2,48</td><td>1,84</td><td>ML</td></tr><tr><td>MD 164</td><td>80,8</td><td>9.6±0.7</td><td><strong>9.6±0.7</strong></td><td>9.0±0.6</td><td></td><td></td><td>20</td><td>11.45±0.2</td><td>80</td><td>1,77</td><td>1,54</td><td>ML</td></tr><tr><td>MD 211</td><td>63,3</td><td>5.3±0.5</td><td><strong>5.3±0.5</strong></td><td>5.4±0.3</td><td></td><td></td><td>20</td><td>11.37±0.2</td><td>103</td><td>2,17</td><td>1,8</td><td>ML</td></tr><tr><td>MD 216</td><td>31,8</td><td>5.5±0.9</td><td><strong>5.5±0.9</strong></td><td>5.5±1.0</td><td></td><td></td><td>19</td><td>10.62±0.87</td><td>4</td><td>2,43</td><td>1,74</td><td>ML</td></tr><tr><td>MD 30</td><td></td><td></td><td><strong>7.91±1.16</strong></td><td>13.9±3.8</td><td><strong>2.6±1.1 (5)</strong></td><td>1.6±2.0</td><td>17</td><td>13.96±0.22</td><td>21</td><td>1,84</td><td>0,99</td><td>D</td></tr><tr><td>MD 29</td><td></td><td></td><td><strong>11.4±1.1</strong></td><td>11.4±1.1</td><td><strong>4.5±1.0 (16)</strong></td><td>1.9±2.1</td><td>26</td><td>13.96±0.21</td><td>53</td><td>1,69</td><td>1,51</td><td>D</td></tr><tr><td>MD 28</td><td></td><td></td><td><strong>18.0±1.8</strong></td><td>13.4±3.0</td><td><strong>5.5±1.5 (15)</strong></td><td>1.6±3.5</td><td>25</td><td>13.67±0.34</td><td>18</td><td>1,8</td><td>0</td><td>D</td></tr></tbody></table>

198

199

200

201

202
n degrees of freedom (where n=number of crystals - 1): if the probability is less than 5%, it is likely that the grains counted represent a mixed age population and in this case the best-fit peak age (P1-P2) were determined with BINOMFIT (Brandon 1996,2002) and are given in Ma ± 1SE; TL, mean length of measured confined tracks; ML: Mélanie Louterbach; D: Donelick; SB: Stéphanie Brichau. See supplementary material for detail in analytical procedures.

<table><caption>**Table 2.** (U-Th)/He ages were performed by laser heating for He extraction and ICP-MS for U-Th determinations at Caltech. The estimated analytical uncertainty for He ages is about 15% (2σ) due to multi-grain aliquots. Standard deviation on ages is used as error when higher than the analytical uncertainty. n = number of grains per aliquot. Multiple grain aliquots have been used due to young ages and consequently low He concentration. C\*probably affected by implantation see AHe ages vs eU and Th/U</caption><thead><tr><th></th><th>Sample no.</th><th>Aliquot name</th><th>Mineral</th><th>n</th><th>Rs (µm)</th><th>weight (µg)</th><th>F<sub>T</sub></th><th>He nmol/g</th><th>U (ppm)</th><th>Th (ppm)</th><th>Sm (ppm)</th><th>eU (ppm)</th><th>Th/U</th><th>He raw age (Ma)</th><th>He corr. age (Ma)</th><th>error</th><th>Std dev</th><th>Longitude (Decimal degrees)</th><th>Latitude (Decimal degrees)</th><th>Elevation (m)</th></tr></thead><tbody><tr><td rowspan="10">EC<br/>INAMBARI</td><td rowspan="2">MD112<br/>mean</td><td>A</td><td>Apatite</td><td>2</td><td>55,2</td><td>7,48</td><td>0,77</td><td>0,76</td><td>54,35</td><td>9,72</td><td>162,39</td><td>57,46</td><td>0,18</td><td>2,4</td><td>3,2</td><td>0,5</td><td></td><td>-70,842</td><td>-13,324</td><td>843</td></tr><tr><td>B</td><td>Apatite</td><td>2</td><td>41</td><td>2,89</td><td>0,68<br/>0,72</td><td>0,48<br/>0,62</td><td>48,40<br/>51,38</td><td>7,98<br/>8,85</td><td>128,00<br/>145,20</td><td>50,93<br/>54,19</td><td>0,16<br/>0,17</td><td>1,8<br/>2,1</td><td>2,6<br/>2,9</td><td>0,4<br/>0,3</td><td>0,4</td><td>0,4</td><td>0,3</td><td>0,4</td></tr><tr><td rowspan="3">MD164<br/>mean</td><td>A</td><td>Apatite</td><td>3</td><td>35,6</td><td>3,3</td><td>0,64</td><td>2,63</td><td>69,22</td><td>5,66</td><td>200,95</td><td>71,52</td><td>0,08</td><td>6,8</td><td>10,7</td><td>1,6</td><td></td><td>-70,466</td><td>-13,687</td><td>1883</td></tr><tr><td>B</td><td>Apatite</td><td>3</td><td>40,4</td><td>4,33</td><td>0,71</td><td>2,52</td><td>72,12</td><td>3,47</td><td>212,23</td><td>73,94</td><td>0,05</td><td>6,3</td><td>9,0</td><td>1,3</td><td></td><td></td><td></td><td></td></tr><tr><td>C</td><td>Apatite</td><td>2</td><td>45,5</td><td>4,54</td><td>0,72<br/>0,69</td><td>2,48<br/>2,54</td><td>100,44<br/>80,60</td><td>3,83<br/>4,32</td><td>240,85<br/>218,01</td><td>102,48<br/>82,65</td><td>0,04<br/>0,06</td><td>4,5<br/>5,9</td><td>6,2<br/>8,6</td><td>0,9<br/>0,8</td><td>0,3</td><td>2,3</td><td>0,3</td><td>0,4</td></tr><tr><td rowspan="3">MD169<br/>mean</td><td>A</td><td>Apatite</td><td>4</td><td>68,7</td><td>20,31</td><td>0,78</td><td>0,93</td><td>34,95</td><td>1035,75</td><td>472,39</td><td>288,81</td><td>29,64</td><td>0,6</td><td>0,8</td><td>0,12</td><td></td><td>-70,486</td><td>-13,827</td><td>2994</td></tr><tr><td>B</td><td>Apatite</td><td>4</td><td>42,5</td><td>4,07</td><td>0,64</td><td>0,91</td><td>43,68</td><td>1996,70</td><td>666,90</td><td>531,95</td><td>45,71</td><td>0,3</td><td>0,5</td><td>0,08</td><td></td><td></td><td></td><td></td></tr><tr><td>C</td><td>Apatite</td><td>4</td><td>67,5</td><td>15,25</td><td>0,77<br/>0,73</td><td>0,25<br/>0,69</td><td>7,43<br/>28,69</td><td>257,34<br/>1096,60</td><td>92,49<br/>410,59</td><td>70,39<br/>297,05</td><td>34,64<br/>36,66</td><td>0,7<br/>0,5</td><td>0,9<br/>0,7</td><td>0,13<br/>0,06</td><td>0,2</td><td>0,2</td><td>0,2</td><td>0,2</td></tr><tr><td rowspan="3">MD170<br/>mean</td><td>A</td><td>Apatite</td><td>3</td><td>34,6</td><td>2,8</td><td>0,60</td><td>1,04</td><td>57,21</td><td>356,86</td><td>328,09</td><td>145,43</td><td>6,24</td><td>1,4</td><td>2,3</td><td>0,3</td><td></td><td>-70,495</td><td>-13,840</td><td>3213</td></tr><tr><td>B</td><td>Apatite</td><td>3</td><td>34,3</td><td>2,95</td><td>0,59</td><td>1,01</td><td>46,11</td><td>264,82</td><td>283,42</td><td>111,76</td><td>5,74</td><td>1,7</td><td>2,9</td><td>0,4</td><td></td><td></td><td></td><td></td></tr><tr><td>C</td><td>Apatite</td><td>3</td><td>42,6</td><td>5,15</td><td>0,67<br/>0,62</td><td>0,96<br/>1,00</td><td>42,12<br/>48,48</td><td>217,25<br/>279,64</td><td>299,77<br/>303,76</td><td>96,29<br/>117,83</td><td>5,16<br/>5,71</td><td>1,9<br/>1,6</td><td>2,8<br/>2,7</td><td>0,4<br/>0,2</td><td>0,2</td><td>0,3</td><td>0,3</td><td>0,2</td></tr><tr><td rowspan="3">MD194<br/>mean</td><td>A</td><td>Apatite</td><td>3</td><td>45,8</td><td>8,45</td><td>0,72</td><td>0,24</td><td>46,38</td><td>27,01</td><td>115,96</td><td>53,48</td><td>0,58</td><td>0,8</td><td>1,1</td><td>0,2</td><td></td><td>-70,917</td><td>-13,568</td><td>2385</td></tr><tr><td>B</td><td>Apatite</td><td>3</td><td>54,8</td><td>13,53</td><td>0,76</td><td>0,15</td><td>37,91</td><td>33,19</td><td>134,75</td><td>46,60</td><td>0,88</td><td>0,6</td><td>0,8</td><td>0,1</td><td></td><td></td><td></td><td></td></tr><tr><td>C</td><td>Apatite</td><td>3</td><td>35,9</td><td>2,98</td><td>0,71<br/>0,73</td><td>0,16<br/>0,18</td><td>28,02<br/>37,44</td><td>39,21<br/>33,14</td><td>126,31<br/>125,67</td><td>38,13<br/>46,07</td><td>1,40<br/>0,95</td><td>0,8<br/>0,7</td><td>1,1<br/>1,0</td><td>0,2<br/>0,09</td><td>0,2</td><td>0,2</td><td>0,2</td><td>0,2</td></tr><tr><td rowspan="3">MD211<br/>mean</td><td>A</td><td>Apatite</td><td>3</td><td>32,5</td><td>2,69</td><td>0,62</td><td>1,08</td><td>82,51</td><td>23,13</td><td>194,71</td><td>89,02</td><td>0,28</td><td>2,3</td><td>3,6</td><td>0,5</td><td></td><td>-70,477</td><td>-13,667</td><td>1733</td></tr><tr><td>B</td><td>Apatite</td><td>4</td><td>36,4</td><td>4,92</td><td>0,68</td><td>0,79</td><td>79,45</td><td>30,41</td><td>260,81</td><td>88,04</td><td>0,38</td><td>1,7</td><td>2,5</td><td>0,4</td><td></td><td></td><td></td><td></td></tr><tr><td>C</td><td>Apatite</td><td>4</td><td>34,5</td><td>3,76</td><td>0,66<br/>0,65</td><td>0,43<br/>0,77</td><td>47,67<br/>69,87</td><td>13,49<br/>22,34</td><td>255,86<br/>237,13</td><td>52,12<br/>76,39</td><td>0,28<br/>0,32</td><td>1,5<br/>1,8</td><td>2,3<br/>2,8</td><td>0,3<br/>0,2</td><td>0,7</td><td>0,7</td><td>0,7</td><td>0,7</td></tr><tr><td rowspan="2">MD216<br/>mean</td><td>A</td><td>Apatite</td><td>3</td><td>39,4</td><td>4,21</td><td>0,62</td><td>0,53</td><td>17,50</td><td>531,40</td><td>249,32</td><td>147,78</td><td>30,36</td><td>0,7</td><td>1,1</td><td>0,2</td><td></td><td>-70,860</td><td>-13,345</td><td>986</td></tr><tr><td>C</td><td>Apatite</td><td>4</td><td>28,3</td><td>2,23</td><td>0,52<br/>0,57</td><td>0,16<br/>0,35</td><td>10,14<br/>13,82</td><td>26,37<br/>278,89</td><td>89,46<br/>169,39</td><td>16,96<br/>82,37</td><td>2,60<br/>16,48</td><td>1,8<br/>1,3</td><td>3,5<br/>2,3</td><td>0,5<br/>0,3</td><td>0,2<br/>0,3</td><td>1,7</td><td>0,2</td><td>0,3</td></tr></tbody></table>

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214 3.1.1. Thermal Modeling

215 To understand the significance of the results, thermal histories need to be
216 extracted from the data. This process requires modeling software that incorporates
217 numerical descriptions of thermal resetting in both the FT and (U-Th)/He systems. For
218 this study, sample thermal histories were obtained using the modelling package HeFTy
219 v2.0.9.85 of Ketcham (2005), which includes the multi-compositional AFT annealing
220 algorithm of Ketcham et al. (2007). HeFTy software excels in reverse modeling of both
221 AFT and AHe data. It uses a Monte Carlo approach to seek optimal cooling paths,
222 governed by user-specified t–T boundaries. The software predicts thermal histories
223 that align closely with the actual data collected. The modeling of each sample
224 considers various input parameters, such as central AFT ages, track length
225 distribution, Dpar values, and average AHe dates. When available, grain sizes and
226 chemical attributes are also included (Table 1). The annealing multi-kinetic model of
227 Ketcham et al. (2007) has been used for the AFT data and the radiation damage
228 accumulation model of Gautheron et al. (2009) for the AHe data. Comprehensive
229 results from the thermal modeling are available in the supplementary dataset.

230 Initial constraints used for sedimentary samples are the estimated stratigraphic
231 deposit age (Paleogene for MD28, and Cretaceous for MD29, and 30; Louterbach,
232 2014) and a large box from 40°C to 200°C from the older stratigraphic age to the actual
233 to leave maximum freedom to the software to find solutions and because of the lack of
234 geological constraints. For the crystalline samples (MD112, 164, 169, 170, 194, 211,
235 and 216), initial parameters were established within a temperature range of 0°C to
236 200°C. This range begins from an age marginally older than the previously recorded
237 thermochronological age and concludes between 10 and 20 Ma, based on the specific
238 thermochronological ages. This approach was chosen since the available geological
239 data doesn't provide sufficient detail to pinpoint the thermal history prior to acquiring
240 its AFT ages. For each sample, we tested between 10,000 and 20,000 paths. The
241 model either continued until it found 50 suitable paths or stopped if identifying these
242 paths proved easy for the software. Pink shading highlights the group of 50 optimal
243 cooling paths (based on a 0.5 criterion) derived from a broader set of Monte Carlo trials
244 (usually exceeding 1,000). The green shading indicates the range of "acceptable"
245 paths (more than 30) within the same set, determined by a more relaxed goodness-of-
246 fit criterion of 0.05.

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## 3.2. Facies analyses

In the studied area Neogene deposits outcrop almost continuously along the Inambari River, from the south-western flank of the Punquiri syncline towards the Madre de Dios foredeep. Three stratigraphic sections were studied at locations I, II, and III (Figure 2). These sections were reported in Louterbach (2014, http://thesesups.ups-tlse.fr/2530/) but have never been published. The sedimentary logs corresponding to the studied stratigraphic sections have been measured at 1:500m scale during several field works between 2010 and 2012 following the methodology of Miall (1996).

## 3.3. Chronostratigraphy: $^{40}$Ar/$^{39}$Ar step heating method

We collected a sample in a tuffaceous level dated by Gil Rodriguez (2001) at 3.23 ± 0.3 Ma (by Ar/Ar dating on biotite) and 2.96 ± 0.34 Ma (Ar/Ar dating on plagioclase). This sample (sample MD 157; longitude: -70.409 and latitude -13.1115) is stratigraphically located at ~ 2.5 km to the top of the exposed Plio-Pleistocene series between seismic horizons T3 and T4 (Louterbach, 2014). In the studied area, the tuff and enclosing layers are significantly deformed with steeply dipping beds N90E, 84 (Figure S8).

The selected sample was crushed, sieved and single grains of biotite were handpicked under binocular microscope and cleaned in an ultrasonic bath using acetone and distilled water. The minerals were packaged in aluminum foils and irradiated for 50 hours in the core of the Triga Mark II nuclear reactor of Pavia (Italia) with several aliquots of the Taylor Creek sanidine standard (28.34 ± 0.10 Ma) as flux monitor. Argon isotopic interferences on K and Ca were determined by irradiation of KF and CaF₂ pure salts from which the following correction factors were obtained: ($^{40}$Ar/$^{39}$Ar) K = 0.00969 ± 0.00038, ($^{38}$Ar/$^{39}$Ar) K = 0.01297 ± 0.00045, ($^{39}$Ar/$^{37}$Ar)Ca = 0.0007474 ± 0.000021 and ($^{36}$Ar/$^{37}$Ar)Ca = 0.000288 ± 0.000016. Argon analyses were performed at Geosciences Montpellier (France) with an analytical system that consists of: (a) an IR-CO2 laser of 100 kHz used at 5-15% during 30 sec for step-heating experiments, (b) a lenses system for beam focusing, (c) a steel sample chamber, maintained at 10-8 - 10-9 bar, with a drilled copper plate and samples on, (d) an inlet line for purification of gases including two Zr-Al getters, (e) a multi-collector mass spectrometer (Argus VI from Thermo-Fisher). Custom-made software controls the laser intensity, the timing of extraction/purification and the data acquisition. To
measure the argon background within the system, one blank analysis was performed every three sample analyses. The ArArCalc software© v2.5.2 was used for data reduction and plotting. The one-sigma errors reported on plateau, isochron and total gas ages include the error on the irradiation factor J. Atmospheric $^{40}$Ar was estimated using a value of the initial $^{40}$Ar/$^{36}$Ar of 295.5. Results are summarized in Table S1.

## 3.5. Biostratigraphy

We provide two new biostratigraphic constraints from samples MD199 and MD202, collected along the Inambari River. Chunks (approximately 1 kg) of clay were collected and transported in plastic bags. For the preparation a standard procedure (dense liquid separation) of the University of Amsterdam was followed (see (Hoorn, 1993). With a knife, small blocks of approximately 1cm³ were cut from the middle part of the clay. This sample was sieved at 212 µm. The samples were then treated with a 10% sodium pyrophosphate solution ($Na_4P_2O_7 \cdot 10H_2O$). Bromoform was used to separate the inorganic/organic layers. Glycerin was used to stick the grains on the slide and paraffin was used to seal it.

Pollen and spores were counted for a maximum of two slides if the sum was less than 200, and only one slide if it contained more than 200 palynomorphs. Photographs were taken of each of the different pollen and spore types with a Optikam B5- microscope camera at a magnification of 1000x and were identified with a palynological database (Jaramillo and Rueda 2008) and several books (da Silva-Caminha et al., 2010; Germeraad et al., 1968; Hoorn, 1993; Lorente, 1986). Additional determinations were provided by Millerlandy Romero-Baez or were listed as an unknown type. The samples were dated based on the presence of biostratigraphic markers dated and using the stratigraphical zonations from Venezuela and Colombia (Jaramillo et al., 2011). Present day family and genus associations were determined from literature (Jaramillo and Rueda, 2008).

## 3.6. 2-D Seismic Data

The two-dimensional seismic section Mob-97-109, acquired and processed by the Hunt Oil Exploration and Production Company of Peru and their partner Repsol Exploration Company (2009-2010), was used for stratigraphic correlation and structural interpretation in the SAZ (Figure 8). We used the software Move® to project
315 the seismic lines, the biostratigraphic and thermochronological ages, and our field data
316 onto the section.

317
318 3.7. Provenance analyses

319 3.7.1. Sr-Nd Isotopes
320 The Nd-Sr isotopic compositions were measured at Geosciences Environment
321 Toulouse (GET) and were incorporated in the Master thesis of Caroline Sanchez
322 (Sanchez, 2012). The analysed samples were first digested in hydrogen peroxide for
323 24 hours at ambient temperature and then digested in HNO₃ for 24 hours at 80°C
324 followed by HF- HNO₃ for 24 hours at 80°C, and finally HCl+HNO₃ for 24 hours at
325 115°C. Blank tests were performed to estimate the level of contamination induced by
326 the acid digestion, but it was found to be negligible. Aliquots containing about 1000 ng
327 of Sr and Nd were loaded into the ion exchange columns. Sr and Nd were separated
328 using the Sr-SPEC, TRU-SPEC and LN-SPEC resins (Eichrom). Nd and Sr isotopic
329 ratios were measured using a Finnigan Mat 261 thermal ionization mass spectrometer
330 in dynamic mode. During the Nd run, the ¹⁴⁶Nd/¹⁴⁴Nd (=0.7219) was used to correct
331 the signal for mass fractionation. For each sample, checks were made for the absence
332 of samarium (Sm). The accuracy of the measurements was estimated on the Rennes
333 University standard for Nd (=0.511961± 14). This value was calibrated relative to the
334 La Jolla standard by the Brest, Toulouse, and Rennes laboratories (Lacan, 2002).
335 During the Sr run, ⁸⁶Sr/⁸⁸Sr (= 0.1194) was used to correct the signal for mass
336 fractionation. The accuracy of the measurements was checked against the NBS 987
337 standard (=0.710240). The average values fall within the range given for these
338 standards so that no instrumental bias needs to be considered. The repeatability on
339 these standards is around 15 ppm. This value is adopted for the overall uncertainty of
340 all measurements, even if some individual samples yield results with a lower internal
341 precision. Total blanks (acid digestion plus column chemistry) for Nd and Sr were
342 checked by ICP-MS and found to be negligible compared to the Nd and Sr amounts
343 loaded onto the columns.

344 The measured ¹⁴³Nd/¹⁴⁴Nd ratios are expressed as the fractional deviation in
345 parts per 10⁴ (units) from ¹⁴³Nd/¹⁴⁴Nd in a Chondritic Uniform Reservoir (CHUR) as
346 measured at the present day:

347 $\mathcal{E}Nd(0) = ((^{143}Nd/^{144}Nd)S / \text{ICHUR}(0) - 1) * 10^4$
348

where (143Nd/144Nd)S is the present-day ratio measured in the sample and ICHUR(0) is the 143Nd/144Nd in the CHUR reference reservoir at the present (ICHUR(0)=0.512638 (Jacobsen and Wasserburg. 1980).

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### 3.7.2. Detrital zircon

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#### 3.7.2.1. U-Pb geochronology

354

10 Neogene sandstones samples were collected on river outcrops along the Punquiri syncline. Figures S4-S7 show their stratigraphic position and Figures S9-S13 the outcrops where the samples were collected. Zircon grain separation and U-Pb analysis were conducted at the University of Brasília, Brazil. For each sample, about 7 kg of sedimentary rocks were first processed in a rock crusher, producing chips roughly 3–5 cm in size. We used a SELFRAG with a voltage of 130 kV and a frequency of 3 Hz to defragment the samples liberating the mineral phases. Heavy minerals were concentrated by panning and the magnetic fraction was removed using a FRANZ isodynamic magnetic separator. After randomly hand-picked, mounted in epoxy resin mounts and polished, back-scattered electron (BSE) images of the detrital zircon grains were obtained using a FEI QUANTA 450 Scanning Electron Microscope (SEM). The BSE images were used to identify the growth areas and zoning in zircon grains, to select suitable areas for U-Pb analysis, and to perform qualitative morphological analysis of detrital zircon grains (Figure S14). The mounts were then cleaned with 3% nitric acid before ICP-MS analysis.

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About 150-200 grains were analyzed per sample with a 25µm beam using a Teledyne Iridia ablation system coupled to a Thermo Finnigan Element XR SF-ICP-MS (See Supplementary Table S3 for details). Analyses were carried out with the standard-sample bracketing method (Albarède et al., 2004). To calibrate downhole fractionation and instrument drift, zircon GJ1 (608 ± 1; Jackson et al., 2004) was used as primary reference material, and zircons 91500 (1065.4 ± 0.3 Ma; Wiedenbeck et al., 1995) and Plešovice (337 ± 0.37 Ma; Sláma et al. 2008) as secondary/validation. Data processing and correction of laser-induced fractionation (LIEF) were performed using IOLITE v4.0 (Paton et al., 2011) and VizualAge (Petrus and Kamber, 2012).

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In general, measured U-Pb ages were filtered considering the quality of individual grain analysis, eliminating zircon grains with the following features: (1) high individual $^{204}$Pb value; (2) high individual errors for isotopic ratios (>3%); (3)

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381 discordances higher than 10%. For clarity, all the generated data is presented in 382 Supplementary Table 3. Finally, the “best age” for a given zircon grain was chosen 383 using $ ^{206}\text{Pb}/^{238}\text{U} $ for zircons younger than 1.5 Ga and $ ^{206}\text{Pb}/^{207}\text{Pb} $ ages were provided 384 for grains older than 1.5 Ga (Spencer et al. 2016). Detrital zircon age data is visualized 385 and compared qualitatively using kernel density estimations (KDE) diagrams and 386 probability density plots (PDP) 387

387 To quantify the degree of dissimilarity between the detrital age distributions of 388 the analyzed samples and investigate the contribution of recycled sedimentary units, 389 we used the standard statistical technique called multidimensional scaling (MDS) 390 popularized by Vermeesch (2013). The MDS method is a superset of principal 391 component analysis that, given a table of pairwise 'dissimilarities' between samples, 392 produces a 'map' of points on which 'similar' samples cluster closely together, and 393 'dissimilar' samples plot far apart (Vermeesch, 2013). Following the latest 394 recommandations by Vermeesch (2018), we used the Kolmogorov-Smirnov test to 395 produce an MDS map comparing the analyzed samples. The closest and second 396 closest neighbors are linked by solid and dashed lines, respectively, and the goodness 397 of fit was evaluated using the "stress" value of the configuration (0.2 = poor; 0.1 = fair; 398 0.05 = good; Vermeesch, 2013). The MDS maps were produced using the provenance 399 package of Vermeesch et al. (2016). 400

### 3.7.2.2. Morphology

401 In this study, we adopted the roundness and elongation classifications proposed 402 by Augustsson et al. (2018). This method applies solely to intact grains that display 403 consistent U-Pb ages. For roundness, we utilized a streamlined version of Powers 404 (1953) framework, categorizing grains as euhedral, subangular to subrounded, or 405 rounded. As for elongation, we used the length-to-width ratios to distinguish between 406 round (below 1.3), oval (ranging from 1.3 to 1.8), and elongated (exceeding 1.8) 407 crystals. 408
413

# 4. Deformation, Exhumation, and Erosion of the Southern Peruvian EC and SAZ

414

## 4.1. Eastern Cordillera

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All EC AFT ages passed the χ2 test (P(χ2)>5%) indicating that they have concordant grain age distributions (Table 1). The AFT central ages range from 3.4 ± 0.4 to 9.6 ± 0.7 Ma with MTL ranging from 10.62 ± 0.9 to 12.8 µm. AHe ages range from 0.8 ± 0.2 to 8.8 ± 2.3 Ma (Table 2). Overall, the AHe ages are younger or like their associated AFT ages. When comparing the AHe and AFT ages with elevation (Figure 5), two trends can be observed. The AFT and AHe ages increase from elevations of 986 ± 10 to 1883 ± 15 meters above sea level (m.a.s.l.). Our AHe ages are like those of Lease and Ehlers (2013) collected at the same elevation (e.g., MD211 sampled at ~1733 m.a.s.l. and 11PR04 sampled at ~1759 m.a.s.l., Figure 5, Table 2). Above ~1900 m.a.s.l. a marked shift toward younger AHe and AFT ages is observed. The lowest samples and those which are in the footwall of the Ollachea fault (MD 211 and MD164, Figures 2 and 4) have older AHe and AFT ages than the samples located in the hanging wall of the fault (MD 194 and MD169). The thermochronological ages might indicate a large Plio-Pleistocene uplift of the Ollachea hanging wall (Figures 4 and 5). Additionally, the thermal histories derived from the inverse modeling of thermochronometer ages using the HeFTY software (Figure 6) further indicate rapid Plio-Pleistocene cooling between 1 and 3 Ma while before the samples may have stayed in the Partial Annealing/Retention Zone during an extended period (probably at least 4-5 Ma,).

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### 3.1.3. Sub-Andean Zone

The Punquiri syncline may show a late Miocene-Pleistocene growth strata. These growth strata are highlighted by dip data projected onto seismic line Mob-97-109 (Figure 7). The growth strata from the Punquiri syncline can thus be correlated with those that are located above the late Miocene marker T2 registered in the Pongo de Coñeq area and are interpreted to be mostly late Miocene to Pliocene in age (Louterbach, 2014). Pliocene deformation is further attested by the presence of significantly deformed tuff and enclosing layers with steeply dipping beds (N90, 84E). This tuffaceous level, situated between seismic horizons T3 and T4 was dated to 3.45±0.15 Ma using the Ar-Ar method.
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475

476

In the SAZ, the three sandstones (MD28, MD29, and MD30) dated with the AFT method failed the χ2 test with P(χ2) being less than 1.4% (Table 1; Figure 6b). The best-fit peaks in each fission track grain age distribution were determined based on a binomial model described by Galbraith (1988) and Galbraith and Green (1990) using the BINOMFIT program (Brandon, 1992, 1996, 2002; Figure S2). The youngest peak ages for samples MD28, MD29, and MD30 are 5.5 ± 1.5 Ma, 4.5 ± 1 Ma, and 2.6 ± 1.1 Ma, respectively (Table 1). The youngest peak age is the dominant component for samples MD28 and MD29 containing 60% and 64% of the distribution, respectively. The youngest peak age of sample MD30, although not dominant, represents a significant part of the grain ages (~30%). The HeFTy of these samples suggests that the AFT ages are reset AFT ages (Figure 8).

## 4. Late Miocene-Pleistocene depositional evolution in the Madre de Dios Basin

In summary, the approximately 3300m thick late Miocene-Pleistocene deposits can be divided into lower and upper intervals. The lower ~2000 m are interpreted as sand-dominated deposits. The upper ~1300 m are characterized by an abrupt change to conglomerate-dominated deposits. The two sections are separated by erosive unconformities or by a stratigraphic gap. The full composite stratigraphic section can be found in detail in the Supplementary Dataset (Figures S4-S7) and is summarized in Figure 9. The sedimentary facies and facies association for these deposits are found in Tables 3 and 4, respectively.

We also report two new biostratigraphic ages and one ⁴⁰Ar/³⁹Ar age on biotite from a tuffaceous level in the Punquiri syncline (MD204). Samples MD199 and MD202 were dated based on their palynological content. The presence of *Echitricolporites spinosus* (17.41-0.14 Ma, Jaramillo et al., 2011), *Proteacidites triangulates* (24.13-3.41 Ma, Jaramillo et al., 2011) and *Cyatheacidites annulatus* (7.15-0.11 Ma, after Jaramillo et al., 2011) in the MD199 and MD202 samples suggest a late Miocene to Pliocene (ranging between 7.15 and 3.41 Ma) depositional age (Table S1; Figure S8). Our new radiometric age documented for outcrop MD 157 (3.45±0.15 Ma; Table S2; Figure S9) is consistent with the radiometric age obtained by Gil Rodriguez et al. (2001) in the same area (3.23±0.3 Ma).
<table><thead><tr><th>Facies<br>Code</th><th>Lithofacies</th><th>Sedimentary structures/other characteristics</th><th>Interpretation</th></tr></thead><tbody><tr><td>Gh</td><td>Clast-supported conglomerates. Granule to boulder, subrounded to well-rounded</td><td>Trough cross-stratification, normal grading with imbrications</td><td>Transverse bar, minor channel fill</td></tr><tr><td>Gm-Gmf</td><td>"Mud-breccias". Matrix-supported to clast-supported conglomerates (Gravel to pebble)</td><td>Planar cross-stratification</td><td>Linguoid bar, transverse bar</td></tr><tr><td>Sr</td><td>Sandstones. Very fine to medium-grained, occasionally pebbly. Moderate sorting</td><td>Rippled cross-stratification (climbing ripples)</td><td>2D or 3D ripples, upper flow regime</td></tr><tr><td>Sp</td><td>Sandstones. Very fine to medium-grained, occasionally pebbly. Moderate sorting</td><td>Planar cross-bedded, possible mud clasts at the base</td><td>Linguoid, transverse bar</td></tr><tr><td>Sh</td><td>Siltstones or very fine- to coarse-grained sandstones</td><td>Horizontal lamination</td><td>Planar bed flow (lower or upper flow regime)</td></tr><tr><td>St</td><td>Very fine- to coarse-grained sandstones</td><td>Trough cross-stratification</td><td>3D dune migration</td></tr><tr><td>Stmc</td><td>Very fine- to very coarse-grained sandstones, with scattered to aligned pebbles</td><td>Trough cross-stratification, highlighted by mud clasts or occasional lithoclasts (mm to pluri-cm). Occasional wood fragments.</td><td>Seasonal regime. 3D dune migration</td></tr><tr><td>Sm</td><td>Massive sandstones (fine to coarse-grained, with possible scattered to aligned pebbles) moderate to well sorted</td><td>No structure. Occasional wood fragments</td><td>Rapid deposition, gravity flow</td></tr><tr><td>Sfu</td><td>Massive sandstones (fine to very coarse-grained), finning upward</td><td>Frequently aligned mudclasts and lithoclasts at the base. Occasional wood fragments.</td><td>Fluvial bedforms and bars, waning flood</td></tr><tr><td>Scu</td><td>Massive sandstones (fine to very coarse-grained), coarsening upward</td><td>Frequently aligned mudclasts and lithoclasts at the base. Occasional wood fragments</td><td>Crevasse splay</td></tr><tr><td>Sb</td><td>Very fine- to medium-grained sandstones (reddish-yellow)</td><td>Bioturbation (continental)</td><td></td></tr><tr><td>Fl</td><td>Siltstones, mudstones</td><td>Lamination, very small ripples. Occasional flame-structure. Occasionally calcareous</td><td>Overbank or waning flood deposits</td></tr></tbody></table>
<table><caption>**Table 3.** Summary of the Neogene lithofacies and interpreted depositional environments in the Madre de Dios retroarc foreland basin (modified from Miall, 1996)</caption><tr><td>Fm</td><td>Siltstones, mudstones</td><td>Structureless. Occasionally calcareous</td><td>Overbank or waning flood deposits</td></tr><tr><td>Fb</td><td>Mudstones to siltstones (red to purple)</td><td>Bioturbated (continental). Red to green.</td><td>Overbank or abandoned channel, incipient soil</td></tr><tr><td>Fbl</td><td>Mudstones to siltstones (blue to grey/dark grey)</td><td>Structureless or some ripples</td><td>Backswamp, oxbow-lake, anoxic environment</td></tr><tr><td>P</td><td>Mudstones to siltstones (red to purple). Carbonaceous nodular, gypsum levels</td><td>Frequent bioturbation and rootlets, carbonaceous nodules, and stratified gypsum. Possible ferruginous pisoliths</td><td>Paleosoil</td></tr><tr><td>T</td><td>Tuffaceous deposit. May be micaceous</td><td>Structureless, rippled, or with planar lamination. Some wood debrites</td><td>Volcanoclastic lacustrine deposits</td></tr></table>

<table><caption>**Table 4.** Facies association for the Neogene deposits in the Madre de Dios retroarc foreland basin</caption><thead><tr><th></th><th>Interpretation</th><th>Facies</th></tr></thead><tbody><tr><td>FCcg</td><td>Braided (?) river. Mainly gravelly to conglomeratic fluvial channel filling</td><td>Gh, Gp, Gt, Stmc, St, Sm, Sh, Sfu</td></tr><tr><td>FCs</td><td>Meandering fluvial channel filling with conglomeratic levels at the base</td><td>Sfu, Sm, Sr, Sh, Sp, St, Stmc, Fl, Gt, Gh, Gp, Gm-Gmf, (Fb)</td></tr><tr><td>O</td><td>Overbank: abandoned channel, waning flow deposit and paleosol, continental swamp or oxbow lake (Osw). Possible coarsening upward sandy crevasse splays (Ocp)</td><td>Fm, Fl, Fb, P, Sfu, Sm, Scu, Sr, T</td></tr></tbody></table>
477 4.1. Lower section: sandstone-dominated interval

478 4.1.1. *Fluvial channel sandy deposits (FCs)*

479 **Description:** Facies association FCs is mainly made up of arkosic fine- to coarse-
480 grained sandstones fining upsection into fine-grained to silty deposits (Figure 9). Sandy
481 to gravelly conglomeratic facies may be occasionally present at the base of the fining-
482 upward units. The base of facies association FCs is characterized by a slight deeply
483 erosive and channelized surface. A 10 to 30-cm-thick mud breccia (Gm, Table 1) can
484 also occur at the base of the facies association. Clasts (<2 cm) are angular to
485 subrounded and consist of reworked mud clasts and extraformational ferruginous
486 clasts (Gmf, e.g., in Section 1, at 1175 m, Figure S4). These Gm deposits can be either
487 clast- or matrix-supported. The basal parts of the channel infillings can also be
488 constituted by Gt, Gh, or Gp facies (Table3). Gt facies corresponds to conglomeratic
489 deposits, 30 cm- to more than 3 m-thick, with trough crossbedding. Gh and Gp facies
490 correspond to horizontally and planar bedded conglomerates, respectively, with normal
491 to inverse grading and occasional pebble imbrications. The channel fillings typically
492 evolve upsection into fine- to medium-grained sandstones. These sandstones are 10
493 cm to pluri-metric thick and can be massive (Sm), with trough cross-stratification (St),
494 with planar (Sp), or horizontal bedding (Sh). Frequent mud clasts commonly highlight
495 the sedimentary structures, particularly the trough cross-bedding structures situated at
496 the base of the sandy channel-shaped bodies (Stmc). The top of Facies association
497 FCs is characterized by 10 cm-100 cm thick finer deposits such as fine-grained rippled
498 sandstones (Sr) or laminated siltstones to mudstone (Fl). Facies Sfu corresponds to
499 50-300 cm-thick fining-upward sandstones. Overall, facies association FCs
500 corresponds to a single thick channelized sedimentary unit ranging in thickness
501 between 50cm and 5m, or a series of 1m to 30m sandy stacked channel filling units
502 (vertically stacked CH components). There are no lateral accretion characteristics.

503 **Interpretation:** The channel-shape geometries and fining-upward sequences show that
504 facies association FCs is mostly generated by sandy stream floods at the end of
505 significant flow episodes in the channels. The repeated vertical stacking patterns of the
506 fining-upward units suggest that flow velocity fluctuates regularly. The presence of
507 facies Sp, St, and Sh (Figure 10), as well as the lack of lateral accretion features, imply
508 that sand bodies are the result of limited, high-energy stream floods and record
509 deposition linked with subaqueous dunes and upper-stage flat beds (Miall, 1996).
510 Facies Sm corresponds to massive sandstones deposited during sediment gravity flow
511 or rapid deposition. Facies Sfu, Sr, and Fl, situated at the top of the channel filling
512 sequences, are associated with a loss of stream flood energy during the channel
513 abandonment phase. The poorly developed, disorganized, and matrix-supported
514 conglomeratic bedforms (Gm-Gmf) described at the base of the sequences suggest
515 high sedimentation fallout rates and/or shallow flow depth (e.g., in Jo et al., 1997; Uba
516 et al., 2005). We interpret facies Gt, Gh, and Gp as being deposited by occasional high
517 energy stream floods equivalent to those produced by gravel-laden streams in poorly
518 to well-confined channels (e.g., in Ridgway and DeCelles, 1993; Uba et al., 2005).
519 Because facies association FCs is associated with continental fine-grained overbank
520 deposits (O) the sandy facies of FCs have been interpreted as fluvial channel-filling
521 deposits. Depending on the geometry of the sandy units and their vertical stacking
522 pattern, deposits can be associated with a single-story fluvial channel (single fining-up
523 sandy unit) or multi-stories channel complex (sandy units displaying an important
524 vertical stacking).

525

526 4.1.2. Overbank deposits (O)

527 **Description:** Facies association O is common in the studied sedimentary sections
528 (Supplementary Figures S4-S7) and frequently overlying the FCs and FCg associations.
529 It consists of massive mudstone or siltstone (facies Fm, Table 3), laminated mud or silt
530 deposits (facies Fl, Table 3), bioturbated reddish or varicolored mudstone to siltstone
531 (facies Fb, Table 3) or blue to dark structureless or rippled mudstone to siltstone
532 (Facies Fbl, Table 3) occasionally interbedded with silty or sandy bodies. Facies Fb
533 can also present occasional desiccation traces. In muddy Root traces, carbonates
534 nodules, and bioturbations can often be observed in muddy to silty layers these fine-
535 grained overbank deposits range from 20 cm- to 20 m in thickness. Coarser-grained
536 sandy deposits with thicknesses ranging from 20 to 200 cm of massive or fining-
537 upwards fine-grained to medium-grained sandstones (Sm or Sfu), rippling sandstones
538 (Sr), or coarsening-upwards sandstone (Scu) can be intercalated within the fine-
539 grained overbank deposits. Additionally, within the overbank fine-grained sequences
540 of the Inambari transect, two tuffaceous layers have been described (outcrop MD 2019-
541 08 at 1615 m in Figure S2 and outcrop MD 2019-09 at 2465 m in Figure S5). These
542 tuffaceous layers range in thickness from 30 to 100 cm and may exhibit ripples or flat
543
544

horizontal sedimentary features (T, Figure 11-C). These facies are rich in wood pieces and leaf remnants.

545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569

*Interpretation:* Palynomorphs determined in MD 199 and MD 202 suggest a continental paleoenvironment for this facies association (Table S1). Furthermore, the facies of facies association O are usually strongly associated with facies associations FCs and FCcg, both of which are interpreted as continental. We interpreted that facies association O represents deposition in a floodplain environment (Fm, Fb, Fbl, P) occasionally disturbed by waning flow deposits (Sr, Sm, Fl) and crevasse sand bodies (Scu). Facies Fm represents deposition from low-energy flows or from standing water pools after channel abandonment (Miall, 1996). The absence of desiccation cracks, the existence of sporadic root traces, and the general reddish-to-purple color of Facies Fb imply oxidizing circumstances (e.g., Turner, 1980; Miall, 1996; Retallack, 1997) with common subaerial exposure (e.g., Esteban and Klappa, 1983). The dark color of facies Fbl and its proximity to a fluvial system are consistent with deposition in an anoxic environment such as an oxbow lake or continental swamp (Miall, 1996). The thin carbonate layers, occasional carbonate nodules, and numerous root traces and continental bioturbation of facies P show pedogenic alteration following deposition (e.g., Wright and Tucker, 1991; Retallack, 1997) and are linked with a well-developed paleosol horizon. Thin layers of fine-grained silty to sandy deposits organized by thin lamination and occasional ripples (Fl and Sr) might be suggestive of low-energy streams (waning floods) linked with deposition in remote floodplains (e.g., Uba et al., 2006). The sporadic coarsening-upward and massive sandstones of facies Sm and Scu can be attributed to crevasse splay deposits and crevasse-channel fills that occur in a proximate floodplain environment. It should be noted that these sandy units can be found in some sedimentary successions regarded as overbank deposits and may represent evidence of active channel avulsion processes at the time (e.g., DeCelles and Horton, 2003).

570
571
572
573
574 4.2. Upper Interval: conglomerate-dominated deposits

575 4.2.1. *Fluvial channel conglomerate deposits (FCcg)*

576 **Description:** Facies association FCcg occurred mostly in the Plio-Pleistocene deposits
577 although it can be present in the Miocene sedimentary rocks (Figure S6). It is
578 associated with facies associations O (overbank) and FCs (Fluvial channel sandy
deposits). Its thickness ranges between 2 and 15 m. Facies association FCcg always
579 starts with an erosive surface overlaid by the conglomerate deposits with trough cross-
580 bedding (Gt, see Table 1 for detailed facies descriptions) and planar or horizontal
581 bedding (Gp and Gh, respectively). The matrix of the clast-supported conglomerate
582 facies consists of medium to very coarse-grained arkosic sandstone. Conglomerate
583 bodies are 1m to 3 m thick. They can evolve upwards into finer-grained deposits,
584 displaying an overall fining-up trend, or be eroded by another conglomerate body
585 forming then an important stacking pattern (see Figures S5 and S6, from 2309 to
586 2407m). Clasts are dominated by metamorphic and granitic, can be up to > 40 cm in
587 diameter, are sub-rounded to well-rounded, and are moderately sorted. The clast-size
588 distribution is polymodal and shows inverse to normal grading. Imbricated clasts are
589 present. Finer-grained deposits of facies association FCcg can be massive or fine
590 upward from very coarse to fine-grained sandstones (Sm, Figure 11-D and Sfu,
591 respectively), sandstones with trough cross-bedding (St, Figure 11-E) occasionally
592 highlighted by mud clasts (Stmc), and sandstones with planar bedding (Sp). Outcrop
593 MD 206 shows this fining-up trend from conglomerates to sandstone facies (Figure S6,
594 from 2805 to 2825 m).
595

596 **Interpretation:** Occasional cross-stratification and rare clast imbrications of the clast-
597 supported pebble-to-boulder conglomerates facies associated with basal erosive
598 surfaces suggest deposition from high-energy floods such as those produced by
599 gravel-laden streams in poorly to well-confined channels (e.g., in Ridgway and
600 DeCelles, 1993; Uba et al., 2005). The organized clast-supported conglomerate facies
601 (Gt, Gh, and Gp) with weak imbrications may be the result of incised-channel gravel
602 bedload sedimentation under low- to waning-energy flows (Jo et al., 1997; Uba et al.,
603 2005). This interpretation is supported by the presence of frequent erosive surfaces
604 associated with overall stacking patterns. Consequently, Gt, Gh, and Gp facies may
605 correspond to transverse or lingoid bars (Miall, 1996). Trough cross-bedded sand (St)
606 and conglomerate bodies (Gt) mainly represent channel deposits (Miall, 1996). Sandy
facies such as Sfu, Sm, Sp, or Sh deposits are less frequent and mainly situated at the top of the fining-up sequences. They are interpreted to have been deposited following a loss of energy from the stream floods. Because facies association FCcg is strongly associated with the Overbank facies association (O), where only continental palynomorphs have been found (Table S1), it is interpreted to be deposited by high-energy braided fluvial rivers deposits laterally changing into a fine-grained fluvial floodplain environment.

## 4.3. Provenance

### 4.3.1. Sr-Nd Isotopes

The $^{87}$Sr/$^{86}$Sr isotopic composition of five fine-grained Neogene samples analyzed ranges from 0.72475 to 0.73358, and the $\mathcal{E}$Nd is between -11.7 and -12.6 (Table 5). The Sr-Nd isotopic fingerprint of suspended particulate matter (SPM; Allègre et al., 1996; Viers et al., 2008; Santos et al., 2015; Rousseau et al; 2019) and bulk mudstone (Roddaz et al., 2005b; Hoorn et al., 2017; van Soelen et al., 2017; Hurtado et al., 2018; Chavez et al., 2022; Moizinho et al., 2022) has been extensively used as provenance tracer to distinguish between Andean and cratonic sources in different Amazonian rivers. In Figure 12 we plotted the $^{87}$Sr/$^{86}$Sr and $\mathcal{E}$Nd(0) composition of relevant Andean sources and the SPM from the main tributaries in the Amazon drainage basin. Our data highlights that all analyzed Neogene mudstone samples from the Madre de Dios Basin fall into the Sub Andean Zone isotopic fingerprint. This is the same field of the present-day SPM transported by the Madeira River, and of other sedimentary rocks from the south Amazonian foreland basin (SAFB; Roddaz et al., 2005b).

<table><thead><tr><th>Sample</th><th>Age</th><th>Sr<br>(ppm)</th><th>Nd<br>(ppm)</th><th><sup>87</sup>Sr/<sup>86</sup>Sr</th><th>±2σ</th><th><sup>143</sup>Nd/<sup>144</sup>Nd</th><th>±2σ</th><th>εNd(0)</th></tr></thead><tbody><tr><td>MD197</td><td>Early Miocene</td><td>113,2</td><td>51,37</td><td>0,724753</td><td>9</td><td>0,512038</td><td>6</td><td>-11,7</td></tr><tr><td>MD199</td><td>Late Miocene-<br>Pliocene</td><td>102,4</td><td>44,17</td><td>0,733581</td><td>7</td><td>0,511991</td><td>5</td><td>-12,6</td></tr><tr><td>MD 200B</td><td>Late Miocene-<br>Pliocene</td><td>117,9</td><td>41,65</td><td>0,728020</td><td>11</td><td>0,511997</td><td>5</td><td>-12,5</td></tr><tr><td>MD 202D</td><td>Late Miocene-<br>Pliocene</td><td>86,33</td><td>38,49</td><td>0,728579</td><td>8</td><td>0,512011</td><td>6</td><td>-12,2</td></tr></tbody></table>
MD 204B Pliocene 106 40,16 0,729826 12 0,512023 7 -12

Table 5. Sr-Nd isotopic compositions of the analyzed Neogene sedimentary rocks from the Madre de Dios foreland basin.

### 4.3.2. Detrital zircon U-Pb ages and morphology

Of the ten samples examined, three originate from the lower sand-dominated interval, while the remaining seven hail from the upper conglomerate-dominated interval (refer to Figure 9). Results of the U-Pb isotope analyses are detailed in Table S3 and showcased in Figure 13. Predominantly, the principal zircon age groups fall between 900-1300 Ma (Grenville/Sunsás) and 500-700 Ma (Brasiliano/Pampean), together making up an average of 53% of all grains studied. Another discernible group, spanning 250-130 Ma (Triassic-Jurassic), appears in every sample and constitutes an average of 15.2% of the grains. Additionally, less dominant populations from both the Precambrian and Phanerozoic eras are evident, particularly within the 1300-1540 Ma (Rondonia-San Ignácio), 500-400 Ma (Famatinian), and 400-250 Ma (Paleozoic) clusters. While these age groups are consistently present across the section, a minor fluctuation in the proportion of Triassic ages can be noticed from sample MD2019-5A to MD2019-16B. It seems that during periods of increased Triassic on the detrital zircon population, there was a corresponding decrease from other age groups.

Zircon grains generated during the Grenville/Sunsás and Brasiliano/Pampean orogenies can be found elsewhere in the Coastal Cordillera, Altiplano, Eastern Cordillera, or Amazonian Craton, and thus are not useful to discriminate between Andean and cratonic sources (Chavez et al., 2022). The presence of zircon grains younger than 500 Ma in all analyzed samples typifies an Andean provenance (Chavez et al., 2022 and references therein). Famatinian (500-400 Ma) rocks occur in isolated Ordovician intrusions of the Marañon and Arequipa massifs (Ramos, 2009; Loewy et al., 2004). Perez and Horton (2015) also reported Famatinian detrital zircon populations in the Oligocene-Miocene sedimentary rocks from the Ayaviri Basin, a hinterland basin in the northern Altiplano Plateau, approximately 200 km southwest of the studied area. Permo-Triassic (290-216 Ma) magmatism was active along the entire length of the Peruvian Eastern Cordillera (Kontak et al., 1985; Clark et al., 1990; Soler
and Bonhomme, 1990; Sempere et al., 2002; Miskovic et al., 2009; Boekhout et al., 2018). Several Permo-Triassic plutons have been mapped in the southwest portion of the studied area (Figure 3). Middle to Late Triassic (245-220 Ma) ages are recorded by the volcano-sedimentary rocks of the Mitu Formation (Spikings et al. 2016) and batholiths (Sempere et al., 2002) in the Cordillera de Carabaya region. Jurassic (201-145 Ma) rocks in the Central Andes are associated with the Jurassic magmatic arc and attributed to extensional processes across the western Gondwana margin (Oliveros et al., 2012; Boekhout et al., 2013). Finally, zircon grains younger than 130 Ma, are characterized as the Andean arc (Chocolate and Toquepala arcs) and typify a Coastal Cordillera provenance (Chavez et al., 2022).

We compared our dataset with Paleozoic metasedimentary rocks from the Eastern Cordillera (Reimann et al., 2010; Bahlburg et al., 2011), the Middle to Late Triassic Mitu Group (Perez and Horton, 2015; Spikings et al., 2016), the Cretaceous Huancané Formation (Spikings et al., 2016) and the Paleocene sedimentary rocks from the Madre de Dios Formation (Louterbach et al., 2018b). In the MDS map (Figure 14A) the upper Miocene-Pliocene samples plot scattered, and no cluster can be discriminated, even between samples of similar depositional ages. However, our samples plot right in between the compiled detrital zircon ages dataset. This configuration might indicate a continuous input of recycled sediments in the Madre de Dios Basin and that although the proportion of the contribution of each source might oscillate over the Late Miocene-Pliocene, the sources were kept the same. On the other hand, even though connected by a solid line with one of the Neogene samples (MD2019-14A), the overall high dissimilarity with the Mitu Group might suggest that the reworking of this unit was either discrete or unlikely.

Zircon morphological analyses were performed on unbroken grains with concordant ages. The results are summarized in Table S3 and illustrated in Figures 15 and 16. Overall, the zircon grains exhibited a diverse range of lengths, spanning from 73 µm to 228 µm, and most were categorized as rounded and elongated. There seems to be a noticeable trend of a rise in the percentage of euhedral grains between samples MD2019-09B and MD2019-14A, which might indicate an increase on first cycle sediments (Augustsson et al. 2018). Furthermore, we explored the correlation between zircon grain shape, U-Pb ages, and potential zircon-producing events (Figure 16a). In our dataset, the prevalent zircon populations - Grenville, Brasiliano, and Triassic - are
consistently present in both oval and elongated shapes forms across samples.
Notably, zircons with elongation exceeding 3 are more prevalent in the Triassic
populations than in the Brasiliano and Grenville (Figure 16b).

698

699 **5.Discussion**

700 **5.1. Neogene deformation of the Sub-Andean Zone**

701 The Oligocene-middle Miocene period of thrust deformation has been recorded
702 in the EC and Altiplano zones adjacent to the study area (Perez and Horton, 2014;
703 Horton 2018). Growth strata recorded along the footwall of the Ayaviri thrust fault
704 indicate that thrust deformation along the southwest-directed, northeastern basin
705 margin of the Ayaviri thrust fault, was active at around 28-26 Ma at the EC/Altiplano
706 boundary (Perez and Horton, 2014). Additionally, an abrupt middle Miocene shift to
707 coarse alluvial fan deposition sourced from the Western Cordillera is interpreted to
708 have been driven by out-of-sequence deformation along the northeast-directed,
709 southwestern basin margin of the Pasani thrust at 18–16 Ma (Perez and Horton, 2014).
710 This northern Altiplano out-of-sequence deformation was coincident with the
711 structurally driven exhumation of the EC at 15-16 Ma as recorded by the He dates of
712 zircon grains from the Coasa pluton and Rio San Gabán transect located in the EC
713 (Perez et al., 2016). Paleo elevation models based on hydrogen isotopic compositions
714 of hydrated volcanic glasses and modern stream waters suggest that the EC was
715 slowly elevated 1.5–2 km between 25 and 10 Ma, which rate is interpreted to be
716 consistent with crustal shortening as the dominant driver of surface uplift (Sundell et
717 al., 2019). In our study area, there is no thermochronological or sedimentary record of
718 deformation before the late Miocene.

719

720 **5.2. Late Miocene-Pliocene**

721 Overall, our dataset suggests that the southern Peruvian EC and SAZ have
722 been deforming, uplifting, and propagating forward since the late Miocene as
723 evidenced by late Miocene to Pliocene AFT and AHe ages related to out-of-sequence
724 thrusting in the EC; and by the presence of growth strata geometry in the SAZ (Punquiri
725 syncline) in response to the duplex formation and development of piggyback synclines
(Figure. 15). Similar piggyback basins associated with duplexes in the hinterland have been documented in the Bolivian and Peruvian SAZ (Baby et al., 1995; Espurt et al., 2011; Mora et al., 2014; Parra et al., 2010). Analog modeling of the Bolivian SAZ suggests that the dominance of sedimentation over erosion in the foreland basin favors the forward propagation of the frontal thrust and development of piggy-back basins (active depositional basins between thrust structures; Leturmy et al., 2000). Mora et al (2014) proposed that a period of late Miocene topographic growth and an associated increase in accommodation and sedimentation rates favor the development of duplexes in the Inambari area of the southern Peruvian SAZ. Our data agree with these findings, especially regarding the Plio-Pleistocene units, in which syntectonic growth strata are associated with the development of duplexes, piggy-back synclines, and the forward propagation of the SAZ and input of recycled sedimentary rocks of the SAZ to the late Miocene-Pleistocene piggy-back syncline sediments.

Our provenance proxies show that the source of sediments being eroded in the southern portion of the Madre de Dios basin did not change significantly throughout the Neogene (Figure 13). Besides the always present Precambrian ages from the crystalline basement found elsewhere in the Andes and Western Amazonia, the Permian, Triassic, and Jurassic were the main detrital zircon ages populations observed. These ages represent different extensional magmatic events, and their distribution varies across strike in the Eastern Cordillera (Chavez et al., 2022). In fact, our data reveals a high similarity between the detrital zircon populations and Sr-Nd isotopic compositions of Late Miocene -Pliocene sedimentary rocks and older SAZ sedimentary successions which supports the input of recycled Paleozoic to Cretaceous sediments from the SAZ (Figures 14 and 15). This hypothesis is further supported by the rounded nature of most grains observed, signaling longer transportation processes or sediment recycling.

However, the observed increase on the proportion of Triassic-aged zircons, together with the reduced presence of Grenville and Brasiliano zircons and an increase in euhedral grains between samples from the upper interval (MD2019-09B to 16B), might indicate that, for a time, a Triassic terrain was more fertile and sourced the Madre de Dios basin with first cycle zircon grains. Permo-Triassic plutonic rocks crop out extensively on the EC (see Figure 3a), which we interpret to suggest erosion of the EC.
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These results are consistent with what is recorded in the central Peruvian SAZ, north of our study area, where the Pliocene reactivation of Paleozoic thrusts has also been observed (Gautheron et al., 2013). In that region, 23 km of shortening affecting the Camisea SAZ (12°S) has accumulated since 6 Ma (Espurt et al., 2011), demonstrating that a significant amount of deformation has affected the EC-SAZ since the Pliocene. This is also consistent with the Ecuadorian, Bolivian and Argentinian Andes where the Sub-Andean thrust wedge has continued propagating until the present and notably during the Plio-Pleistocene (Horton and DeCelles, 1997; Echavarria et al., 2003; Uba et al., 2009a; Espurt et al., 2011; Gautheron et al., 2013; Eude et al., 2015; Anderson et al., 2018; Margirier et al., 2022). Additionally, the propagation of the Sub-Andean thrust wedge could also be supported by the overall coarsening-up trend of the Madre de Dios SAZ's Neogene sedimentary infill, which we interpret as a depositional megasequence characterized by a significant rise in sedimentation rates. This is demonstrated by the presence of distal sand-dominated deposits in the Neogene (lower interval), which evolved into conglomerate-dominated deposits in the Late Miocene to Pleistocene (upper interval) periods (Figures 9 and 15).

### 5.3. Tectonic vs. Climatic controls in the erosion of the EC and SAZ

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Large scale kinematics of fold and thrust belts obey the theory of a tapered orogenic wedge (Chapple, 1978; Davis et al., 1983; Dahlen, 1984, 1990; Dahlen et al., 1984; DeCelles and Mitra, 1995). This suggests that the fronts of orogenic wedges develop taper toward their undeformed forelands and advance when the sum (θ) of their basal (β) and upper (α) slopes reach a critical value θc. When changes in (β) and (α) force the wedge out of the critical state into a "supercritical" or "subcritical" state, the wedge responds by deforming to alter its geometry until the critical condition is regained (DeCelles and Mitra, 1995; Horton, 1999). For instance, an orogenic wedge that becomes subcritical may attempt to regain a critical state through internal deformation by out-of-sequence thrusting, synchronous thrusting, or duplexing (e.g., Boyer, 1992; DeCelles and Mitra, 1995; Mitra and Sussman, 1997; Horton, 1999; Uba et al., 2009b). In turn, processes such as erosion, which reduce surface slope, may ultimately tend to induce internal deformation within the wedge (DeCelles, 1994; DeCelles and Mitra, 1995). We interpret the surface uplift of the EC, as the presence
of out of sequence thrusting and the EC provenance of Neogene sedimentary rock as indicating that the southern Peruvian Amazonian EC and SAZ orogenic wedge existed under subcritical conditions. This is consistent with previous studies suggesting that the propagation and width of the Andean orogenic wedge has been limited by focused erosion (Horton, 1999) on the EC, potentially driven by a wetter climate since the Miocene (McQuarrie et al., 2008b).

Many studies have emphasized the potential climatic controls on the Neogene erosion, exhumation, and deformation in the EC and SAZ (McQuarrie et al., 2008b; Uba et al., 2009b; Lease and Ehlers, 2013). In the studied area, Plio-Pleistocene climatic forcing has previously been inferred based on the presence of widespread Pliocene AHe erosional cooling ages in the EC and from the assumption that tectonic activity has been lacking for the past 4 My both in the EC and SAZ (Lease and Ehlers, 2013). This Pliocene erosion of the Bolivian and southern Peruvian EC has been interpreted as being controlled by a "shift in global climate from early Pliocene warmth to late Pliocene cooling driven by sea surface temperature changes". It is possible that after having reached a critical elevation in the Miocene leading to higher rainfall and erosion gradients across the EC, focused erosion led to accelerated exhumation and increasing deformation in the adjacent SAZ. Such a climatic forcing has been invoked in the EC of Colombia to explain the differences in exhumation and deformation rates between a drier western flank and a humid eastern flank (Mora et al., 2008) although this view has recently been challenged (Pérez-Consuegra et al., 2021). Our thermochronological cooling ages advocate for Plio-Pleistocene uplift and related erosion both in the EC and the SAZ, consistent with the ~ 4 Ma cooling age data presented by Lease and Ehlers (2013). In contrast with the climatic driver of exhumation proposed by these authors, coeval uplift induced the exhumation of the SAZ, the EC, and Pliocene growth strata, which all support the 4 Ma to present tectonic uplift in the EC as an important driver of exhumation; these also provide evidence against the assumption that deformation was absent in the SAZ during this time.

## 6. Conclusions

The combination of fieldwork, structural and stratigraphic sections interpretation of depositional environments, AFT and AHe ages, interpretations of a new subsurface
dataset, and provenance data from the Eastern Cordillera and Sub Andean Zone show that significant deformation occurred in the Amazonian orogenic wedge of southern Peru during the Late Miocene-Pliocene, even though climatic changes may have enhanced erosion or modified erosional processes. The late Miocene to Pliocene deformation is recorded by AFT and AHe ages in both the EC and SAZ and by growth strata geometry in the SAZ. This period is characterized by 1) the development of piggy-back synclines and duplexes in the SAZ, as well as the overthrusting of the EC and input of recycled sedimentary rocks of the SAZ to the late Miocene-Pleistocene piggy-back syncline sediments. Additionally, the transition from distal low energy fluvial system in the Early Miocene (lower section), to a high energy proximal fluvial system in the Late Miocene to Pleistocene (upper section) indicates an increase in sedimentation rates, thus our data show that the thrust wedge has continued propagating until the present, following a period of notably active propagation during the Plio-Pleistocene.

838

839 Acknowledgments

This work received financial and institutional support from Repsol S.A., Perupetro, and the IRD (Institut pour la Recherche et le Développement). Patrick Monié is thanked for his help and interpretation of Ar dating results. We thank Jean-Claude Soula, Patrice Baby, and Stéphane Brusset for their helpful comments and discussions on previous drafts of this paper. This paper is also dedicated to the memory of Jean-Claude Soula who passed away in 2020. This work was part of the Ph.D. project of Melanie Louterbach which has been sponsored by Repsol. This study was also supported and funded by CAPES-COFECUB program Te 924/18/88881.143095/2017-01 "Paléo-Amazone: evolution Néogène de l'Amazonie Brésilienne/O PALEO AMAZONAS: evolução neogênica da Amazônia Brasileira" and by the joint Brazilian-European facility for climate and geodynamic research on the Amazon River Basin sediment (CLIM-AMAZON) project. We thank German Bayona and Mauricio Parra as well as the editor Andres Folguera for valuable reviews that improved this contribution.

854

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<figure><img src="image_3.png" /><figcaption>**Figure 1.** Topographic and bathymetric map of the central Andes showing the location of the studied area (thick black outline, Figure 2).</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>**Figure 2.** Simplified geological and structural map of the Madre de Dios foreland basin. The sedimentary sections described in this study are located along the Inambari River in the SAZ (Sections 1 and 2) and in Puerto Maldonado for the foredeep zone (Section 3). The seismic line MOB-109 utilized to interpret the Inambari transect is represented by the black, pink-dashed line.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>**Figure 3.** A) Geological map of the study area (modified after INGEMMET) with the main section. New biostratigraphic and thermochronological (AFT and AHe ages). B) Synthetic sedimentary column for the SAZ of the Madre de Dios foreland basin. Thickness and lithologies are taken from (Gil Rodriguez et al., 2001; Gil Rodriguez, 2002; Hermoza, 2004; Louterbach, 2014) and confidential reports. Simplified from Louterbach (2014).</figcaption></figure>
<figure><img src="image_6.png" /></figure>

**Figure 4.** Inambari structural cross-section interpreted in depth. See Figure 3 for location. This section has been constructed using field data and MOB-97-109 and MD-56 seismic lines. Local geochronological constraints, as well as nearby thermochronological results, have been projected onto this section (modified after Baby et al., 2018b).

<figure><img src="image_7.png" /></figure>

**Figure 5.** A) Cooling ages versus elevation. AHe, apatite (U-Th)/He; AFT, apatite Fission Track; AHe and AFT age errors are at 1σ standard for Eastern Cordillera samples.
<figure><img src="image_8.png" /><figcaption>**Figure 6.** Modeled t-T paths for the crystalline EC samples (MD 112, MD164, MD169, MD170, MD194, and MD216) using 'HeFTy' software (see section 3.1.1. Thermal Modeling for detail on data input). Green: Thermal history with an acceptable fit (criterion of 0.05). Purple: Thermal history with a good fit (criterion of 0.5). Black line: best-fit models. Note that MD112, 164,169, 170, 194, 211, and 216 records almost all the same exhumation histories with a main period of exhumation between 1 and 3 Ma</figcaption></figure>
while before the samples seem to stay in the PAZ during a long period of time (probably at least 4-5 Myr).

<figure><img src="image_9.png" /></figure>

**Figure 7.** A) Interpreted profile of seismic section MOB-97-109 (see figures 2 and 3 for location) illustrating the sedimentary infilling of the Punquiri syncline (modified from Louterbach 2014). Dated outcrops were projected onto the seismic profile. The structural style of the SAZ duplex has been simplified. Dip values of analyzed outcrops projected onto the seismic line (black thick hyphens) show a progressive decrease toward the center of the syncline indicating syntectonic sedimentation associated with the duplex growth and Punquiri syncline formation (i.e., "growth strata deposits"); Late Mio: Late Miocene; Early Plio: Early Pliocene. B) Non-interpreted seismic line MOB-97-109.
<figure><img src="image_10.png" /><figcaption>**Figure 8.** Modeled t-T paths for the SAZ samples (MD 30 (Cretaceous, SAZ), MD 29 (Cretaceous, SAZ) and MD 28 (Paleogene? SAZ) samples, using 'HeFTy' program (see section 3.1.1. Thermal Modeling for detail). Green: Thermal history with an acceptable fit (criterion of 0.05). Purple: Thermal history with a good fit (criterion of 0.5). Black line: best-fit models.</figcaption></figure>
<figure><img src="image_11.png" /></figure>

**Figure 9.** Simplified stratigraphic sections for the Neogene deposits in the Inambari Transect of the Madre de Dios Basin. Biostratigraphic ages are from ¹This work and ² Louterbach (2014).
<figure><img src="image_12.png" /></figure>

**Figure 10.** Two distinct vertical organizations (stacking) of alternating FCs and O facies associations. The Punquiri syncline's axis is located at the left in both images (towards the North and stratigraphic top). A) Outcrop MD 197 showing overturned strata. Isolated meter-thick and fining-upward fluvial channels (FCs) are separated by thick fine-grained overbank deposits (O). B) Outcrop MD 209 showing vertically stacked fluvial sandstones presenting a fining-upward pattern. Sandstones are mainly made up of facies Sfu, St, Stmc, Sm, and Sp. Because of the important thickness of facies association FCs (range between 10-15m), lower and upper contacts with facies association O are not visible here. Martin Roddaz for scale (1.76m).
<figure><img src="image_13.png" /><figcaption>**Figure 11.** Examples of facies found in the Neogene of the Madre de Dios foreland basin. A) Facies Fbl showing grey mudstones to siltstones. B) Facies Sm showing structureless medium-grained massive sandstones. C) Facies T showing a tuffaceous rock with plant fragments and some ripples. D) Facies Sd showing shaly fine-grained sandstone. E) Facies St showing trough cross-bedded in fine-to medium-grained sandstones.</figcaption></figure>
<figure><img src="image_14.png" /><figcaption>**Figure 12.** $^{87}$Sr/$^{86}$Sr-$\varepsilon$Nd (0) diagram for Neogene Madre de Dios foreland basin sedimentary rocks compared with several relevant source areas and modern suspended particulate material in western Amazonia. Quaternary Ecuadorian volcanic lavas are from Barragan (1998); the Mesozoic and Neogene volcanic rocks are from Kay and Rogers (1994) and Rogers; data for the Central depression, the Altiplano, the Eastern Cordillera, and the Subandean zone are taken from Pinto (2003) and Roddaz et al., (2005a). SPM from the Tapajós, Negro, Urucara, and Trompetas (Allègre et al., 1996), Madeira and Solimões rivers (Viers et al., 2008) and the Amazon, Orinoco, and Maroni rivers (Rousseau et al., 2019).</figcaption></figure>
<figure><img src="image_15.png" /><figcaption>**Figure 13.** Stratigraphic evolution of U-Pb ages on zircon grains with age distributions displayed by their Kernel Density Estimation (KDE) and Probability Density Plots (PDP; red line). C-AA: Cenozoic Andean Arc (Less than 60 Ma); K-AA: Cretaceous Andean Arc (66-120 Ma); J: Jurassic Extension & Chocolate Arc (130-216 Ma); T: Triassic rift (216-250 Ma); P: Permian magmatism (252-290 Ma); D-C: Devonian & Carboniferous magmatism (300-400 Ma); F: Famatinian (400-500 Ma); B: Brasiliano (500-700 Ma); G-S: Greenville-Sunsás (900-1300 Ma); R-SI: Rondonia-San Ignácio (1300-1540 Ma);</figcaption></figure>
RN-J: Rio Negro-Juruena (1540-1820 Ma); V-T: Ventuari-Tapajós (1820-2000 Ma); M-I: Maroni-Itacaiunas (2000-2200 Ma); CA: Central Amazon (>2200 Ma). Age ranges are from Tassinari et al. (2000), Reimann et al. (2010), and Chavez et al. (2022).

<figure><img src="image_16.png" /></figure>

**Figure 14.** A) MDS map based on the U-Pb age distributions of detrital zircons grains using the Kolmogorov-Smirnov test. The closest and second closest neighbors are linked by solid and dashed lines, respectively. Data for MD Paleocene (combination of samples MD85, 176, 177, 239, 255, and 256) can be found in Louterbach et al. (2018b); Mitu Group, Triassic magmatic rocks, and Huancané formation are from Spikings et al. (2016). Paleozoic metasedimentary rocks EC consist of the combination of the metasedimentary rocks analyzed in Reiman et al (2010) and Bahlburg et al. (2011). B) Sherd plot of the U-Pb data showing the transformation from dissimilarity to distances and disparities (Vermesch, 2013).
<figure><img src="image_17.png" /><figcaption>**Figure 15.** Roundness and elongation for detrital zircons with concordant ages. Broken grains without a clear shape in the BSE images were not included.</figcaption></figure>
<figure><img src="image_18.png" /><figcaption>**Figure 16.** Detrital zircon shape vs. concordant age. The field for oval grains (length/width=1.3/1.8) is marked by a horizontal gray bar. **A)** Plot covering all the ages observed. **B)** Close-up on detrital zircon ages younger than 500 Ma, characteristics of Andean provenance.</figcaption></figure>
<figure><img src="image_19.png" /></figure>

**Figure 17.** Sketch showing the evolution of the Southern Amazonian retro arc foreland basin system from the Early Miocene to the present day. The black line indicates the approximate location of the studied area. Early Miocene activities and related growth strata of the Pasani and Ayaviri thrust faults are reported in Perez and Horton (2014). WC: Western Cordillera; EC: Eastern Cordillera; SAZ: Sub-Andean Zone. Modified from DeCelles and Horton (2003). See text for details.
## Highlights

* Timing of Late Miocene-Pliocene uplift of the Eastern Cordillera and Sub Andean Zone constrained by AFT and AHe data.

* Transition from a low to high energy fluvial system in the Late Miocene-Pliocene

* Provenance analysis of the Madre de Dios basin indicates Eastern Cordillera denudation and recycling of SAZ sediments.
**Declaration of interests**

[x] The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

[ ] The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

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