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The Central Pontides of N Turkey represents a mobile orogenic belt of the southern Eurasian margin that experienced several phases of exhumation associated with the consumption of different branches of the Neo-Tethys Ocean and the amalgamation of continental domains. Our new low-temperature thermochronology data help to constrain the timing of these episodes, providing new insights into associated geodynamic processes. In particular, our data suggest that exhumation occurred at (1) similar to 110 to 90Ma, most likely during tectonic accretion and exhumation of metamorphic rocks from the subduction zone; (2) from similar to 60 to 40Ma, during the collision of the Kirehir and Anatolide-Tauride microcontinental domains with the Eurasian margin; (3) from similar to 0 to 25Ma, either during the early stages of the Arabia-Eurasia collision (soft collision) when the Arabian passive margin reached the trench, implying 70 to 530km of subduction of the Arabian passive margin, or during a phase of trench advance predating hard collision at similar to 20Ma; and (4) similar to 11Ma to the present, during transpression associated with the westward motion of Anatolia. Our findings document the punctuated nature of fault-related exhumation, with episodes of fast cooling followed by periods of slow cooling or subsidence, the role of inverted normal faults in controlling the Paleogene exhumation pattern, and of the North Anatolian Fault in dictating the most recent pattern of exhumation.
The Misho complex in Northwest Iran is a prominent topographic massif bounded by well known active faults. Our new structural analysis of this area indicates that faulting has important role in the exhumation of this complex. The conjugate orientation of the North and South Misho Faults caused uplift in the Misho and exhumation of the Precambrian crystalline basement. Our structural and stratigraphic data shows that rapid uplift could have been initiation since the 21-22 Ma and exhumation rate was about 0.16 to 0.24 km/Ma. To refine this age, we performed U/Pb analysis of detrital zircon from the Upper Red Formation using LA-ICP-MS. We conducted AFT analysis on 6 basement samples from the hanging wall and 1 sample from the Upper Red Formation in the footwall NMF. Uplift in the hanging wall of NMF led to resting of sample 916 marl. This geochronologic and thermochronologic data shows that exhumation in the MC is diachronously along strike and affected by faults. The phase of exhumation is documented in the study area and entire Iranian plateau is related to the final closure of the Neo-Tethys and northward motion of the Arabian Plate.
The northward indentation of the Pamir salient into the Tarim basin at the western syntaxis of the India-Asia collision zone is the focus of controversial models linking lithospheric to surface and atmospheric processes. Here we report on tectonic events recorded in the most complete and best-dated sedimentary sequences from the western Tarim basin flanking the eastern Pamir (the Aertashi section), based on sedimentologic, provenance, and magnetostratigraphic analyses. Increased tectonic subsidence and a shift from marine to continental fluvio-deltaic deposition at 41Ma indicate that far-field deformation from the south started to affect the Tarim region. A sediment accumulation hiatus from 24.3 to 21.6Ma followed by deposition of proximal conglomerates is linked to fault propagation into the Tarim basin. From 21.6 to 15.0Ma, increasing accumulation rates of fining upward clastics is interpreted as the expression of a major dextral transtensional system linking the Kunlun to the Tian Shan ahead of the northward Pamir indentation. At 15.0Ma, the appearance of North Pamir-sourced conglomerates followed at 11Ma by Central Pamir-sourced volcanics coincides with a shift to E-W compression, clockwise vertical-axis rotations and the onset of growth strata associated with the activation of the local east vergent Qimugen thrust wedge. Together, this enables us to interpret that Pamir indentation into Tarim had started by 24.3Ma, reached the study location by 15.0Ma and had passed it by 11Ma, providing kinematic constraints on proposed tectonic models involving intracontinental subduction and delamination.
The Pamirs represent the indented westward continuation of the northern margin of the Tibetan Plateau, dividing the Tarim and Tajik basins. Their evolution may be a key factor influencing aridification of the Asian interior, yet the tectonics of the Pamir Salient are poorly understood. We present a provenance study of the Aertashi section, a Paleogene to late Neogene clastic succession deposited in the Tarim basin to the north of the NW margin of Tibet (the West Kunlun) and to the east of the Pamirs. Our detrital zircon U-Pb ages coupled with zircon fission track, bulk rock Sm-Nd, and petrography data document changes in contributing source terranes during the Oligocene to Miocene, which can be correlated to regional tectonics. We propose a model for the evolution of the Pamir and West Kunlun (WKL), in which the WKL formed topography since at least similar to 200 Ma. By similar to 25 Ma, movement along the Pamir-bounding faults such as the Kashgar-Yecheng Transfer System had commenced, marking the onset of Pamir indentation into the Tarim-Tajik basin. This is coincident with basinward expansion of the northern WKL margin, which changed the palaeodrainage pattern within the Kunlun, progressively cutting off the more southerly WKL sources from the Tarim basin. An abrupt change in the provenance and facies of sediments at Aertashi has a maximum age of 14 Ma; this change records when the Pamir indenter had propagated sufficiently far north that the North Pamir was now located proximal to the Aertashi region.
[1] The Puna-Altiplano plateau in South America is a high-elevation, low internal relief landform that is characterized by internal drainage and hyperaridity. Thermochronologic and sedimentologic observations from the Sierra de Calalaste region in the southwestern Puna plateau, Argentina, place new constraints on early plateau evolution by resolving the timing of uplift of mountain ranges that bound present-day basins and the filling pattern of these basins during late Eocene-Miocene time. Paleocurrent indicators, sedimentary provenance analyses, and apatite fission track thermochronology indicate that the original paleodrainage setting was disrupted by exhumation and uplift of the Sierra de Calalaste range between 24 and 29 Ma. This event was responsible for basin reorganization and the disruption of the regional fluvial system that has ultimately led to the formation of internal drainage conditions, which, in the Salar de Antofalla, were established not later than late Miocene. Upper Eocene-Oligocene sedimentary rocks flanking the range contain features that suggest an arid environment existed prior to and during its uplift. Provenance data indicate a common similar source located to the west for both the southern Puna and the Altiplano of Bolivia during the late Eocene- Oligocene with sporadic local sources. This suggests the existence of an extensive, longitudinally oriented foreland basin along the central Andes during this time
The Pamir is the western continuation of Tibet and the site of some of the highest mountains on Earth, yet comparatively little is known about its crustal and tectonic evolution and erosional history. Both Tibet and the Pamir are characterized by similar terranes and sutures that can be correlated along strike, although the details of such correlations remain controversial. The erosional history of the Pamir with respect to Tibet is significantly different as well: Most of Tibet has been characterized by internal drainage and low erosion rates since the early Cenozoic; in contrast, the Pamir is externally drained and topographically more rugged, and it has a strongly asymmetric drainage pattern. Here, we report 700 new U-Pb and Lu-Hf isotope determinations and >300 Ar-40/Ar-39 ages from detrital minerals derived from rivers in China draining the northeastern Pamir and >1000 apatite fission-track (AFT) ages from 12 rivers in Tajikistan and China draining the northeastern, central, and southern Pamir. U-Pb ages from rivers draining the northeastern Pamir are Mesozoic to Proterozoic and show affinity with the Songpan-Ganzi terrane of northern Tibet, whereas rivers draining the central and southern Pamir are mainly Mesozoic and show some affinity with the Qiangtang terrane of central Tibet. The epsilon(Hf) values are juvenile, between 15 and -5, for the northeastern Pamir and juvenile to moderately evolved, between 10 and -40, for the central and southern Pamir. Detrital mica Ar-40/Ar-39 ages for the northeastern Pamir (eastern drainages) are generally older than ages from the central and southern Pamir (western drainages), indicating younger or lower-magnitude exhumation of the northeastern Pamir compared to the central and southern Pamir. AFT data show strong Miocene-Pliocene signals at the orogen scale, indicating rapid erosion at the regional scale. Despite localized exhumation of the Mustagh-Ata and Kongur-Shan domes, average erosion rates for the northeastern Pamir are up to one order of magnitude lower than erosion rates recorded by the central and southern Pamir. Deeper exhumation of the central and southern Pamir is associated with tectonic exhumation of central Pamir domes. Deeper exhumation coincides with western and asymmetric drainages and with higher precipitation today, suggesting an orographic effect on exhumation. A younging-southward trend of cooling ages may reflect tectonic processes. Overall, cooling ages derived from the Pamir are younger than ages recorded in Tibet, indicating younger and higher magnitudes of erosion in the Pamir.
Differential exhumation in the Puna Plateau and Eastern Cordillera of NW Argentina is controlled by inherited paleostructures and resulting paleotopography related to the Cretaceous Salta Rift paleomargins. The Ceno zoic deformation front related to the development of the Andean retro-arc orogenic system is generally associated with >4 km of exhumation, which is recorded by Cenozoic apatite fi ssion-track (AFT) and (U-Th-[Sm])/He ages (He ages) in the Eastern Cordillera of NW Argentina. New AFT ages from the top of the Nevado de Cachi document Oligocene (ca. 28 Ma) cooling, which, combined with existing data, indicates exhumation of this range between ca. 28 Ma and ca. 14 Ma. However, some of the highest ranges in the Eastern Cordillera preserve Cretaceous ages indicative of limited Cenozoic exhumation. Samples collected from an similar to 3-km-elevation transect along the northern part of the Sierra de Quilmes paleorift fl ank (Laguna Brava) show AFT ages between ca. 80 and ca. 50 Ma and He ages between ca. 45 and ca. 10 Ma. Another set of samples from an similar to 1-km-elevation transect farther to the southwest (La Quebrada) shows Cretaceous AFT ages between ca. 116 Ma and ca. 76 Ma, and mainly Cretaceous He ages, in agreement with AFT data. Analysis of existing AFT and He ages from the area once occupied by the Salta Rift reveals a pattern characterized by Cretaceous ages along paleorift highs and Cenozoic ages within paleorift hanging-wall basins and later foreland basin depocenters. This pattern is interrupted by the Sierras Pampeanas at similar to 28 degrees S, which record mid-Cenozoic ages. Our data are consistent with a complex inherited pattern of pre-Andean paleostructures, likely associated with paleotopography, which was beveled by the Cenozoic regional foreland basin and reactivated during the late Neogene (ca. <10 Ma), strongly controlling the magnitude of Cenozoic uplift and exhumation and thus cooling age distribution. This, combined with variable lithologic erodibility, resulted in an irregular distribution of themochronological ages.
Intramontane sedimentary basins along the margin of continental plateaus often preserve strata that contain fundamental information regarding the pattern of orogenic growth. The sedimentary record of the elastic Miocene-Pliocene sequence deposited in the Fiambala Basin, at the southern margin of the Puna Plateau (NW Argentina), documents the late Miocene paleodrainage evolution from headwaters to the west, towards headwaters in the ranges that constitute the border of the Puna Plateau to the north. Apatite Fission track (AFT) thermochronology of sedimentary and basement rocks show that the southern Puna Plateau was the source for the youngest, middle Miocene, detrital population detected in late Miocene rocks; and that the margin of the Puna Plateau expressed a high relief, possibly similar to or higher than at present, by late Miocene time. Cooling ages obtained from basement rocks at the southern Puna margin suggest that exhumation started in the Oligocene and continued until the middle Miocene. We interpret the basin reorganization and the creation of a high relief plateau margin to be the direct response of the source-basin system to a wholesale surface uplift event that may have occurred during the late Cenozoic in the Puna-Altiplano region. At this time coeval paleodrainage reorganization is observed not only in the Fiambala Basin, but also in different basins along the southern and eastern Puna margin, suggesting a genetic link between the last stage of plateau formation and basin response. However, this event did not cause sufficient exhumation of basin bounding ranges to be recorded by AFT thermochronology. Our new data thus document a decoupling between late Cenozoic surface uplift and exhumation in the southern Puna Plateau. High relief achieved at the Puna margin by late Miocene time is linked to Oligocene-Miocene exhumation; no significant erosion (< 3 km) has occurred since in this and highland.
In response to collision and convergence between India and Asia during the Cenozoic, convergence took place between the Pamir and South Tian Shan. Here we present new detrital zircon U-Pb ages coupled with conglomerate clast counting and sedimentary data from the late Cenozoic Wuheshalu section in the convergence zone, to shed light on the convergence process of the Pamir and South Tian Shan. Large Triassic zircon U-Pb age populations in all seven samples suggest that Triassic igneous rocks from the North Pamir were the major source area for the late Cenozoic Wuheshalu section. In the Miocene, large populations of the North Pamir component supports rapid exhumation in the North Pamir and suggest that topography already existed there since the early Miocene. Exhumation of the South Tian Shan was relatively less important in the Miocene and its detritus could only reach a limited area in the foreland area. Gradually increasing sediment loading and convergence of the Pamir and South Tian Shan caused rapid subsidence in the convergence area. Since ca. 6-5.3 Ma, the combination of a major North Pamir component and a minor South Tian Shan component at the Wuheshalu section is consistent with active deformation of the South Tian Shan and the North Pamir. During deposition of the upper Atushi Formation, a larger proportion of North Pamir-derived sediments was deposited in the Wuheshalu section, maybe because faulting and northward propagation of the North Pamir caused northward displacement of the depocenter to north of the Wuheshalu section.