Wilfried Winkler

Along-strike variations in the thermal and tectonic response of the continental Ecuadorian Andes to the collision with heterogeneous oceanic crust

Oblique to strike geological segmentation in the Andean chain has been previously recognised at various scales and is commonly attributed to changes in the convergence vectors of the oceanic and continental plates, as well as the upperplate expressions of differing along-strike subducted slab age, strength and composition. We present new white mica and biotite 40 Ar/ 39 Ar and zircon and apatite fission-track data from several traverses across the Cordillera Real of Ecuador in the northern Andes that reveal distinct along-strike differences in the timing of accelerated crustal cooling during the Cenozoic. The data record elevated cooling rates from temperatures of V380‡C during V65^55 and V43^ 30 Ma from all sampled regions of the Cordillera Real and at V15 Ma and since V9 Ma in the northern Cordillera Real. Each cooling period was probably driven by exhumation in response to the accretion and subduction of heterogeneous oceanic crust. Elevated cooling rates of up to V30^20‡C/Myr were initiated during the Palaeocene and Eocene^early Oligocene along the entire contemporaneous margin of Ecuador and were driven by the accretion of the oceanic Pallatanga Terrane and Pin ‹ on^Macuchi Block, respectively, onto northwestern South America. Both of these geological provinces originated at the southern parts of the leading and trailing boundaries of the Caribbean Plateau and accreted onto the margin during the approximately northeastward migration of the Plateau into its current position. Within Ecuador the development of higher topography and elevated cooling rates of up to 50‡C/Myr at V15 Ma and since V9 Ma are restricted to the region north of 1‡30PS and is situated above the postulated subducted flatslab section of the aseismic Carnegie Ridge. Plate convergence rate calculations suggest the Carnegie Ridge collided with the Ecuador Trench at V15 Ma, which caused the pre-existing coastal provinces to displace to the northeast, subsequently driving extension and marine ingressions in southern Ecuador and compression and uplift in northern Ecuador. fl 2001 Elsevier Science B.V. All rights reserved.

Neogene stratigraphy and Andean geodynamics of southern Ecuador

Abstract The present paper reviews Tertiary volcanic and sedimentary formations in the Inter-Andean region of southern Ecuador (between 2°S and 4°20′S) in order to develop a geodynamic model of the region. The formations occur in the southern shallow prolongation of the Inter-Andean Valley between the Cordillera Real to the east, and the Cordillera Occidental and Amotape–Tahuin Provinces to the west. One hundred fifty zircon fission-track analyses has established a detailed chronostratigraphy for the sedimentary and volcanic formations and several small intrusions. The Paleogene to early Miocene formations are dominated by intermediate and acidic volcanic and pyroclastic rocks. In addition, relics of Eocene continental sedimentary series have been identified. The Neogene sedimentary series lie unconformably on deformed and eroded metamorphic, sedimentary and volcanic formations. They were deposited in two stages, which are separated by a major unconformity dated at ≈10–9 Ma. (1) During the middle and early late Miocene (≈15–10 Ma) marginal marine deltaic, lagoonal, lacustrine and fluvial environments prevailed, which we group under the heading “Pacific Coastal sequences”. They presumably covered a greater surface area in southern Ecuador than their present occurrence in small topographic depressions. We suggest that they were deposited in the shallow marine Cuenca and Loja Embayments. Deposition in a marginal marine environment is also supported by the occurrence of brackish water ostracods and other fauna. (2) Above the regional (angular) unconformity, the coastal facies are overlain by late Miocene (≈9–5 Ma) continental alluvial fan and fluvial facies which are in turn covered by mainly airborne volcanic material. They represent the “Intermontane sequences” of the basins of Cuenca, Giron–Santa Isabel, Nabon, Loja and Malacatos–Vilcabamba. Sedimentologic and stratigraphic results are used to discuss the tectonic setting of Neogene sedimentation in the forearc and arc domain of the Ecuadorian subduction system. During the Pacific Coastal stage, northward displacement of the coastal forearc block along the Calacali–Pallatanga fault zone has driven crustal collapse in the Inter-Andean region. As a result, extensional subsidence drove the eastward ingression of shallow seas into the Cuenca and Loja Embayments from the Manabi and Progreso Basins to the west. Tectonic inversion in the forearc area during the early late Miocene (at ≈9.5 Ma) reflects the initiation of W–E oriented compression and uplift in the Inter-Andean region and the establishment of smaller Intermontane stage basins, which host the continental sequences. Coeval topographic rise of the Cordillera Occidental is indicated by the onset of clastic input from the west. The small Intermontane Basin of Nabon (≈8.5–7.9 Ma) formed during the period of maximum compression. The present data prove that the Neogene Andean forearc and arc area in southern Ecuador was a site of important but variable tectonic activity, which was presumably driven by the collision and coupling of the Carnegie Ridge with the Ecuadorian margin since ≈15–9 Ma.

Neogene tectonic evolution and exhumation of the southern Ecuadorian Andes: a combined stratigraphy and fission-track approach

Abstract Coastal marine and continental sedimentary facies of Middle to Late Miocene age are exposed in the Andes of southern Ecuador (Cuenca, Giron–Santa Isabel, Loja, Malacatos–Vilcabamba and Catamayo–Gonzanama Basins). The chronostratigraphy of the basin series was established by zircon fission-track dating on a total of 120 tephra layers. Subsequently, the timing of tectonic events was estimated through the well-dated stratigraphic sequences and intervening unconformities. Sedimentation from ≈15 to 9 Ma (termed Pacific Coastal Stage) was dominantly of coastal marine type, extending over an area far greater than the present basin perimeters. It ended when a period of east–west-oriented compression at ≈9.5–8 Ma exhumed the region, and sedimentation was then restricted to smaller basins (termed Intermontane Stage). These Late Miocene continental sediments were for the first time sourced from the west in the rising Western Cordillera. Apatite fission-track analysis was applied to some of the tephras in the Cuenca Basin and also to the older (Eocene, 42–35 Ma) Quingeo Basin series in order to quantify the basin histories with respect to timing and amount of burial and later exhumation. In the Quingeo Basin burial of the oldest sediments reached temperatures of ∼100°C at 18 Ma, when they started to cool down during a period of exhumation. This process preceded the Pacific Coastal Stage development of the other basins. In the Cuenca Basin, the oldest sediments were buried to temperatures of ca. 120°C by 9 Ma, when a period of inversion began and a phase of erosion was dominant. This timing correlates well with that estimated from structural evidence. At ca. 6 Ma the cooling rate slowed down and maybe even reverted to a small increase in temperature until 3 Ma, when the final stages of exhumation took place. Assuming a geothermal gradient of 35°C/km, total uplift for this part for Ecuador is about 6100 m over the last 9 million years. Assuming a steady state continuous movement, this means a mean rock uplift rate of ∼0.7 mm/yr and a surface uplift of 0.3 mm/yr to the Present.

Low‐temperature thermochronology of the northern Cordillera Real, Ecuador: Tectonic insights from zircon and apatite fission track analysis

The post Early Cretaceous tectonic development of the northern Andean segment (north of 5°S) is loosely constrained by a series of partially and fully reset K/Ar ages. New apatite and zircon fission track data from three traverses across the Cordillera Real of Ecuador reveal distinct periods of accelerated crustal cooling during the Cenozoic. Fission track ages range from 65 to 14 Ma (zircon) and 44 to 8 Ma (apatite), with apatite mean track lengths ranging from 14.6 to 12.1 μm. These results record rapid cooling rates during ∼ 43 – 30 Ma, 23–15 Ma, and 10–0 Ma occurring at temperatures below ∼ 275°C. The events reflect up to ∼ 9 km of crustal exhumation in various regions of the Cordillera in response to relative changes in the kinematics of the Farallon, Nazca, and South American plates. The exhumation history of the Cordillera Real was not continuous but rather evolved during separate phases. These phases persisted for ∼ 10 Myr and are partly coincident with tectonic phases of the central Andes, although extend for longer time periods, possibly as a result of isostatically driven crustal exhumation. Large spatial variations in the zircon and apatite fission track data within the Cordillera Real indicate that local fault-bounded massifs have experienced different thermal histories since ∼ 43 Ma. Major variations are not restricted to the regional scale and exist within individual terranes. Faulted slivers within terranes demonstrate highly variable exhumation histories, suggesting that deformation was not dominated by terrane-bounding faults. Additionally, N-S variations in exhumation depths suggest that ∼ NE-SW trending faults have been active since ∼ 10–9Ma.

Palaeocurrents and petrography of the Gurnigel-Schlieren flysch: A basin analysis

Abstract The Late Maastrichtian to Middle Eocene Gurnigel-Schlieren Flysch is analysed from the point of view of tectonic control on deposition. Facies show an alternation of abyssal plain/oceanic slope, trench fill channellized and non-channellized sediments and finally lower slope deposits. The facies evolution points to a sporadically active subduction trench environment. A detailed picture of the sediment dispersal pattern is deduced from framework-grain analysis, feldspar and lithic fragment counts and conglomerate analysis on current oriented samples. This picture includes 10 major and 3 minor depositional systems which varied in time and space. Variation was influenced by tectonic movements in the basin and source areas, and by sea-level changes. Smoothing out of late Alpine deformation reveals a west-east trending elongated basin geometry and sediment distribution pattern. Flow directions which do not fit with the model are discussed: the Eocene subduction-related rotation of parts of the basin is suggested to have disrupted an initially coherent flow pattern. The sequence was deposited within a remnant of the South Penninic Ligurian ocean, in a trench environment bordered by a continental margin arc.

An integrated study of fill and deformation in the Andean intermontane basin of Nabón (Late Miocene), southern Ecuador

Abstract The Nabon basin is part of several Miocene intermontane basins related to Andean uplift, continental arc formation and coeval deformation during subduction of the Nazca plate under the South American continent. The basin sequence consists of fluvial, alluvial fan, lacustrine, and pyroclastic mass-flow deposits corresponding with intereruptive and syneruptive stages of basin-fill history. Combined zircon fission-track and palaeomagnetic measurements suggest that the series lies within the 4r chron (ca. 8.5–7.9 Ma). It overlies unconformably the ignimbrite basement dated at ca. 26-19 Ma. Synsedimentary tectonic deformation in the basin is manifested by a master reverse fault along the western margin, differential basement block uplift and related sedimentary bedding geometries such as cumulative sedimentary wedges. The spatial orientation of the tectonic and sedimentary features indicates that the basin underwent WNW-ESE maximal shortening during the fill stage. The short-lived sediment-fill history may be explained, either by subduction-related contractional pulses also recognized in the Peruvian and Colombian Andes or, by the particular position of the basin in the central axial part near the weak fault of a regional translational system.

Tectono-sedimentary evolution of the Upper Prealpine nappe (Switzerland and France): nappe formation by Late Cretaceous-Paleogene accretion

AbstractThe Upper Prealpine nappe of the Swiss and French Prealps consists of a composite stack of various tectonic slivers (Gets, Simme, Dranse and Sarine sub-nappes, from top to bottom). The structural superposition and stratigraphic content of the individual sub-nappes suggests a successive stacking at the South Penninic/Adriatic transition zone during the Late Cretaceous and Early Paleogene. The present paper deals with two aspects. (1) new data obtained from the Complexe de base Series of the Dranse sub-nappe which underlies the Helminthoid Sandstone Formation, and (2) the development of a geodynamic accretionary model for the Upper Prealpine nappe stacking.The Complexe de base Series reveals a succession of black shales at the base, grading upward into variegated red/green and red shales which were deposited in an abyssal plain environment starved of clastic input. It is overlain by the Helminthoid Sandstone Formation. The combined analysis of planktic and agglutinated benthic foraminifera and compa...

Provenance study on Eocene–Miocene sandstones of the Rakhine Coastal Belt, Indo-Burman Ranges of Myanmar: geodynamic implications

Abstract The Indo-Burman Ranges (IBR) represent an accretionary wedge, which is the result of subduction of the Indian plate beneath the Asian plate. In the Rakhine Coastal Belt it comprises a thick stack of Cretaceous to Neogene turbiditic sediments and localized thrust sheets of oceanic plate mafics and pelagic sediments. We investigate Eocene–Miocene sandstones, aiming to reveal the provenance of the detrital material using modal framework grain, heavy mineral and detrital zircon analysis (U–Pb laser ablation ICP-MS dating, Hf isotope geochemistry and typology). The results show a predominant derivation of the clastic material from: (i) Late Cretaceous to Oligocene igneous rocks, which are often bimodal with a low number of zircons spanning the Cretaceous–Palaeogene boundary, and (ii) recycled orogenic terrane sources comprising ophiolitic rocks. Age corrected Hf isotope ratios confirm subduction-related mixed mantle-crust sources. We also observe minor reworking of older magmatic zircons. By comparing our obtained petrographic parameters and zircon characteristics with potential Himalayan, Indian continent and Burman margin sources we conclude a Burman margin and arc origin provenance. With regard to hydrocarbon exploration in the IBR, a forearc and trench basin system model linked with the Burman arc appears more appropriate for evaluating the petroleum system. Supplementary material: sandstone modal composition, heavy mineral contents, detrital zircon U–Pb LA-ICPMS dating and hafnium results are available at http://www.geolsoc.org.uk/SUP18651.

Cimatic evolution from Paleocene to earliest Eocene inferred from clay-minerals: A transect from northern Spain (Zumaya) to southern (Spain, Tunisia) and southeastern Tethys margins (Israel, Negev)

During the Paleogene the global climate evolved from predominantly warm conditions without major ice cover to cooler conditions with presence of the continental ice sheets from Oligocene on (e.g. Shackleton et al. 1984; Miller et al. 1987; Zachos et al. 1993, 1994). Short-lived episodes of warming and cooling punctuated this general long-term trend (e.g. Kennett & Stott 1991; Zachos et al. 1994; Corfield & Cartlidge 1992). The late Paleocene represented a cool period (Haq et al. 1977; Wolfe & Poore 1982) which is also manifested in the Tethyan Alpine domain (Winkler 1993). Isotopic and sedimentologic evidence also indicate that in the latest Paleocene and across the Paleocene– Eocene transition, a sudden warming pulse occurred (Robert & Chamley 1991; Oberhänsli 1992; Robert & Kennett 1992). The present data are mainly based on clay-mineral variations in northern (Zumaya section) and southern Spain (Caravaca section), northern (Elles section) and southern Tunisia (Seldja section) and Israel, Negev (Ben Gurion section), Fig. 1. The biostratigraphic frame is mainly based on the nannofossil zonation of Martini (1971). Clay minerals in the Zumaya section include smectite, illite, mixed illite/smectite layers, chlorite, and kaolinite. The latter (characteristic for soils in warm climates with high precipitation), is found troughout the Danian and across the broader Paleocene–Eocene transition interval. Major clay phases reveal a shift in composition from kaoliniteto smectite-dominated assemblages across the early/late Paleocene transition (NP4–NP5) and then subsequent shift to illite and chlorite dominated assemblages in the late Paleocene (NP9). The Paleocene–Eocene transition interval (NP9–NP10, P5) is marked by the strong occurrence of kaolinite (up to 45% of the clay fraction). Paleocene to early Eocene clay mineral records therefore indicate a major change from a predominantly warm and humid (perennial) climate in the early Paleocene (NP1–early NP5) to a relatively cooler and drier climate with distinct seasonality in the late Paleocene (NP5–late NP9). This trend reversed at the end of the NP9 Zone, when a global warming pulse, with enhanced precipitation, occurred. The same change in kaolinite distribution is observed at Caravaca. The palygorskite, reflecting increasing arid conditions, is present in the NP5–NP8 interval and after the P–E transition (NP10 and NP11). The clay mineral assemblage from the Elles section, located in northern Tunisia, is also characterized by abundant kaolinite in early Paleocene up to the top of the NP 4 Zone. The NP5–NP8 interval is characterized by decreasing kaolinite and increasing smectite, reflecting drier/cooler conditions. As already observed in Spain, the P–E transition is again marked by an important enrichment in kaolinite. Kaolinite disappears abruptly in the top of NP9 Zone, significantly earlier compared to Zumaya. The Seldja section located in the southern part of Tunisia, close to the Saharan platform shows a different clay mineral pattern. Kaolinite is

Detrital zircon and provenance analysis of Late Cretaceous–Miocene onshore Iranian Makran strata: Implications for the tectonic setting

A multidisciplinary provenance study, including sandstone framework, heavy mineral analysis, in situ U-Pb dating of detrital zircon, and Hf isotopic ratio analysis of dated zircons, was undertaken on Late Cretaceous−Miocene deep-marine turbiditic and deltaic sandstones of Makran accretionary wedge, SE Iran, to determine their sedimentary provenance and tectonic setting. Sandstone framework modes reveal both magmatic arc rocks as a source of Late Cretaceous−Oligocene detritus and recycling of Miocene sandstones. Heavy mineral assemblages, Cr-spinel, and blue amphibole indicate ophiolite and high-pressure−low-temperature metamorphic rocks (blueschists) as a supplementary provenance. In total, 2931 laser-ablation−inductively coupled plasma−mass spectrometry (ICP-MS) U-Pb detrital zircon ages on 21 sandstone samples yielded three major age peaks at ca. 167 Ma, 88.7 Ma, and 48.9 Ma. Also, 241 in situ Hf isotope analyses of dated zircons provide evidence for dominantly igneous source rocks. Two main detrital zircon ages are identified: (1) abundant Middle Jurassic grains with Hf isotopic compositions of continental crust, suggesting a rifting-related magmatic provenance; and (2) Late Cretaceous−Eocene grains with Hf isotopic compositions of continental crust and nondepleted mantle, suggesting a continental magmatic arc provenance. This change in provenance is attributed to the Late Cretaceous convergence between Arabia and Eurasia.