Km Of Uplift Research Articles

Kinematic history of a foreland uplift from Paleocene synorogenic conglomerate, Beartooth Range, Wyoming and Montana

An integrated structural, sedimentological, and provenance study of the upper Paleocene Beartooth Conglomerate along the eastern flank of the Beartooth Range in Montana and Wyoming yields new information about Laramide tectonics in the northern Rocky Mountain foreland and has implications for models of fault-propagation folding and the development of synorogenic basins in thrust-faulted terranes. During the Laramide orogeny, the Beartooth Conglomerate was deposited by alluvial fans and a coarse braided fluvial system along the eastern flank of the range in response to displacement on the Beartooth fault, a 30°-35° west-dipping thrust fault that places Precambrian rocks on Paleozoic and Mesozoic cover rocks. Displacement along the Beartooth fault produced a large fault-propagation fold (Berg's fold-thrust) that eventually was transected by the fault along the entire eastern flank of the range. Lithologic provenance modeling indicates that the Beartooth Conglomerate was produced by unroofing of the Upper Cretaceous through Precambrian section of the eastern Beartooth Range. The model results indicate that source-area relief during deposition of the lower part of the Beartooth Conglomerate was relatively low (∼600 m) while the soft, mudstone-dominated Upper Cretaceous part of the source section was being eroded from the crest of the uplift. Coarse, alluvial-fan accumulation commenced when resistant Paleozoic carbonate and quartz-arenitic rocks were exposed and source-area relief increased to ∼1,400 m. Relief steadily diminished thenceforth to ∼600-800 m, as the upper part of the source section was eroded from the Beartooth Range, leaving only a resistant carapace of Paleozoic carbonate rocks and Precambrian crystalline rocks. Source-area relief was controlled both by bedrock composition of the source terrane and by individual episodes of uplift. Like many thrust-derived conglomerates, the Beartooth Conglomerate contains intraformational, syndepositional folds, faults, and angular unconformities that can be used with provenance modeling to define the kinematics of uplift during conglomerate deposition. By utilizing the results of our provenance modeling and the orientations of the basal and intraformational angular unconformities, we have been able to retrodeform stepwise an area-balanced cross section through the eastern Beartooth uplift. Retrodeformation of the cross section indicates that 3.8 km of uplift occurred before deposition of the oldest part of the proximal Beartooth Conglomerate. Further uplift of ∼1.7 km and total horizontal shortening of ∼3.7 km accompanied ∼1.3 km of displacement on the Beartooth fault. Cross sections indicate that additional uplift of ∼1 km and horizontal shortening of ∼2 km accompanied displacement on the Line Creek fault. Our data indicate that during the early stages of uplift by fault-propagation folding, sediment derived from the uplift bypassed the proximal realm and was deposited in distal settings. Bypassing occurred because the eventual footwall of the Beartooth fault was uplifted during fault-propagation folding. Viewed from this perspective, the early fine-grained fills of many Laramide basins may owe their existence to a combination of fine-grained source material and sediment bypassing during the early stages of Laramide uplifts.

Constraints on the Central Indian Basin thermal structure from heat flow, seismicity and bathymetry

The lithosphere beneath the Central Indian Basin is characterized by high heat flow, widespread deformation of sediment and acoustic basement, and unusually high seismicity. The high heat flow suggests that temperatures in the lithosphere may be higher than expected for its age. We explore the constraints on the temperature distribution with depth by combining heat flow, bathymetry, and seismicity data. The high heat flow (~30 mW m −2 greater than expected) constraints the near-surface temperature distribution. The bathymetric depths (on average those expected for these lithospheric ages after corrections for sediment loads) constrain the integral of the temperature with depth. Since the depths of oceanic intraplate earthquakes appear to be limited by an isotherm (~ 750°C), the maximum earthquake depth (40 km) constrains the minimum depth of deformation and the maximum temperature there. The present thermal structure is investigated by examining different models matching these three observational constraints. First, the possibility is examined that the high heat flow results from anomalous lithosphere with a basal temperature or thickness different from typical oceanic lithosphere. In this case the temperature constraints from the earthquake depths restrict the additional heat flux to less than 20 mW m −2. However, since the heat flux anomaly requires plate thicknesses substantially thinner than usually assumed, it appears that at most 10 mW m −2 can be added by this mechanism. Second, the possibility is examined that the extra flux results from reheating the bottom portion of the lithosphere to asthenospheric temperatures. Substantial reheating 30–40 km below the surface is required to match the high heat flow. Such reheating should produce $ ̃ 1 km of uplift, whereas the average basement depth is no shallower than expected for its age. Thus, significant deep lithospheric reheating cannot be widespread over the deformed region. Third, the effects of a temperature perturbation within the lithospheric column and the resulting change in surface heat flux with time are examined. A temperature perturbation at shallow depths could produce the present heat flow anomaly, but no evidence for shallow intrusion or other mechanism for such an effect exists. It is concluded that, despite the heat flow anomaly, the lack of an average bathymetric anomaly and the observation of seismicity to a depth of 40 km indicate that lithospheric temperatures in the Central Indian Basin are not significantly different from those expected for its age.

Fission track analysis reveals character of collisional tectonics in New Zealand

During the late Cenozoic, the Pacific plate has been obliquely converging with the Australia plate in South Island, New Zealand. This has resulted in westward obduction of continental crust of the Pacific plate, and consequently, a major mountain range, the Southern Alps, has formed east of the Alpine fault and within the leading edge of the Pacific plate. We have applied the apatite and zircon fission track dating technique to a suite of outcrop samples from three transects across the Southern Alps, starting at the Alpine fault, to better understand the uplift age and structure of the continental collision. The results show the following: (1) Uplift was underway at 7 Ma in the south at Haast Pass and by 5 Ma in the north at Arthur's Pass. (2) Profiles of the total amount of late Cenozoic uplift show an exponential increase toward the Alpine fault. Adjacent to the Alpine fault there has been 14.5 to 21.5 km of uplift in the vicinity of Haast Pass, 14.5 to 21 km near Mt Cook, and 12.5 to 15.5 km in the Arthur's Pass transect. Adjacent to the Alpine fault in the Mount Cook region the average uplift rate from ∼5.5 Ma to ∼1 Ma was 2.3 to 2.5 mm/yr; between ∼1 Ma and the present it has averaged 6.2 mm/yr. The strongly asymmetric uplift pattern is responsible for the exposure of a 13–25 km wide belt of greenschist to midamphibolite facies rocks immediately east of the Alpine fault known as the Alpine schists. (3) Late Cenozoic uplift of Torlesse greywackes and Alpine schists was preceeded during the Jurassic‐early Cretaceous by 5–8 km of uplift. The Otago schist belt to the south was uplifted much more during this interval, and in addition, western parts of the Otago schists were uplifted 5–6 km during the late Cretaceous. (4) The fission track data do not support the notion of significant late Cenozoic shear heating about the Alpine fault, as previously suggested from spatial variations in K‐Ar ages of the Otago and Alpine schists.

Fission-track geochronology, tectonics and structure of the transantarctic mountains in Northern Victoria land, antarctica

A regional fission-track dating study in northern Victoria Land (NVL) provides information on the amount, timing and variable rates of uplift of the Transantarctic Mountains (TAM) at their northernmost extent. Apatite ages increase systematically with elevation and together with confined track length distributions, define a two-stage uplift history, although a variety of thermal histories, resolvable by use of confined track length distributions, exist for different parts of NVL. A pronounced “break in slope” in the apatite age-elevation profile for results from most of NVL occurs at ∼ 50 Ma, approximating the start of uplift of the mountains. This marks the base of an uplifted apatite annealing zone. Prior to uplift, samples above this break lay within the apatite annealing zone whereas those samples below it had an apatite fission-track age of zero. For most of NVL, ∼ 5 km of uplift have been calculated. In the southeastern coastal region, however, uplift of the order of 10 km has been estimated, exposing apatite ages of only 25–35 Ma. Sphene and zircon ages from this area also appear reduced relative to the regional pattern, suggesting that the partial annealing zones for these minerals have been revealed. Confined track length distributions from the lower part of the apatite age profile indicate an initially rapid period of uplift (∼ 200–400 m Ma −1) from ∼ 50 Ma. In the Lichen Hills-Outback Nunataks area, in the west of NVL, apatites have not been completely overprinted by the Jurassic thermal event associated with emplacement of the Ferrar Dolerite, and uplift here is of the order of only 4 km. Block faulting associated with uplift of the TAM is considered to be the same event as Rennick Faulting leading to the formation of the Rennick Graben.

Shatter cones at the Lawn Hill circular structure, northwestern Queensland: presumed astrobleme

The Lawn Hill circular structure is a ring of low hills 18 km in external diameter composed of brecciated Cambrian limestone and chert. The circular structure surrounds a plain about 8 km across of fractured Proterozoic siltstone, sandstone and, at the centre of the ring, flow‐folded igneous rock containing abundant devitrified glass. The Proterozoic rocks crop out also outside the ring, and their macroscopic geometry indicates about 2 km of uplift inside the ring. The centre of the structure is located 7 km from the intersection of two major faults. An aeromagnetic dipole anomaly indicates a magnetic body beneath the northeastern part of the ring. Well formed radially striated shatter cones of Proterozoic siltstone and sandstone are present inside the ring, mostly as colluvial float, although five in situ outward‐pointing cones are also known. Intersecting sets of closely spaced planar lamellae are present in qu.artz grains in the cones, but anomalous birefringence, vitreous phases, reduced refractive in...

Uplift history and structure of the Transantarctic Mountains: new evidence from fission track dating of basement apatites in the Dry Valleys area, southern Victoria Land

Fission track analysis of apatites from basement rocks of the Wright Valley in southern Victoria Land provides information about the timing, the amount and hence the rate of uplift of the Transantarctic Mountains in this area. Apatite ages increase systematically with elevation, and a pronounced break in the age versus elevation profile has been recognised at about 800 m on Mt. Doorly near the mouth of Wright Valley. The apatite age of about 50 Ma at this point approximates the time at which uplift of the mountain range began. Samples lying above the break in slope lay within the apatite fission track annealing zone prior to uplift, during a Cretaceous to Early Cenozoic period of relative thermal and tectonic stability. At the lower elevations samples had a zero apatite fission track age before the onset of rapid uplift and have track length distributions indicating rapid cooling. Some 4.8–5.3 km of uplift are estimated to have occurred at an average rate of about 100 ± 5m/Ma since uplift began. From the total stratigraphic thickness known above the uplifted apatite annealing zone it can be estimated that the Late Cretaceous/Early Cenozoic thermal gradient in the area was about 25–30°C/km. The occurrence and pattern of differential uplift across the Transantarctic Mountains can be estimated from the vertical offsets of different apatite fission track age profiles sampled across the range. These show the structure of the mountain range to be that of a large tilt block, dipping gently to the west under the polar ice-cap and bounded by a major fault zone on its eastern side. Offset dolerite sills at Mt. Doorly show the mountain front to be step-faulted by 1000 m or more down to the McMurdo Sound coast from an axis of maximum uplift just inland from Mt. Doorly.

On the Cenozoic uplift and tectonic stability of the Colorado Plateau

The Colorado Plateau is a major tectonic and physiographic province in the southwestern United States which has been relatively stable during the Phanerozoic, but has been epeirogenically uplifted about 2 km in the Cenozoic. Minor deformation occurred within the Plateau during Late Cretaceous-early Tertiary compressional orogeny, and three phases of Cenozoicigneous activity are represented on the Plateau. Constrains on timing of plateau uplift are poor, but there appears to have been at least two phases of uplift, the most recent being during the last 5 Ma. Numerous mechanisms for plateau uplift can be divided into three groups: 1. Thermal expansion, 2. crustal thickening, and 3. phase changes, and simple models indicate that each of these models seems physically capable of producing the required uplift. When the geologic and geophysical data for the Plateau are considered, however, it seems likely that more than one mechanism is required to explain the 2 km of uplift. Thermal expansion associated with lithospheric thinning and magmatic crustal thickening seem the most reasonable mechanisms to have caused Cenozoicuplift of the Plateau. Early Cenozoicstability of the Plateau was possibly related to the relatively cool geotherm and thus high strength in the Plateau lithosphere relative to the adjacent Basin and Range and Southern Rocky Mountain-Rio Grande rift provinces. Local topography could also have been a factor in maintaining the mechanical integrity of the Plateau. As the Plateau lithosphere has been heated and uplift has occurred, the stability of the Plateau appears to have decreased, and it may now be breaking up, especially in its margins.

Uplift history of the Transantarctic Mountains in the Dry Valleys area, southern Victoria Land, Antarctica, from apatite fission track ages

Abstract Apatite fission track ages of basement sampIes from Wright and Victoria Valleys increase systematically with sam pIe elevation.These ages reflect the times at wh ich different sampIes cooled below a temperature of about 100°C and began to retain stable fission tracks.The rate at which the apatite ages change with elevation is largely controlled by the uplift rate. The observed ages range from 154 ± 7 to 66 ± 4 m.y. and indicate a steady, slow uplift over this period at about 15 m/m.y., assuming a constant thermal gradient with time. Taken in conjunction with the present thermal gradient in this area, the youngest ages indicate a greatly increased rate ofuplift during the Cenozoic, and give a reliable older limit to the onset of the Victoria Orogeny.The results indicate that nearly 4 km of uplift has occurred during the Cenozoic, with a minimum average uplift rate of about 55 m/m.y., again assuming the thermal gradient has remained constant over that time.

Frictional metamorphism, argon depletion, and tectonic stress on the Alpine Fault, New Zealand

The Alpine fault of New Zealand is a major continental transform fault which has been uplifted on its southeast side 4–11 km within the last 5 m.y. This uplift has exposed the Alpine schists, which have been metamorphosed from the adjacent Torlesse graywackes. The Alpine schists increase in metamorphic grade from prehnite‐pumpellyite facies 9–12 km from the fault through the chlorite and biotite zones of the greenschist facies to the garnet‐oligoclase zone of amphibolite facies within 4 km of the fault. These metamorphic zone boundaries are subparallel to the fault for 350 km along the strike. The K‐Ar and Rb‐Sr ages of the schists increase with distance from the fault: from 4 m.y. within 3 km of the fault to approximately 120 m.y. 20 km from the fault. Field relations show that the source of heat that produced the argon depletion aureole was the fault itself. Adopting a friction model for the fault and applying the known geological history of motion of the Alpine fault, we show that the metamorphism resulted from frictional heating during the 360‐km right lateral slip on the Alpine fault during the Mesozoic (Rangitata) period of fault motion (140–80 m.y. ago). Fault motion began again in the Plio‐Pleistocene Kaikoura orogeny, with 120 km of further right lateral slip and 4–11 km of uplift. Frictional heating during this episode produced the argon depletion. Quantitative models for both the metamorphism and the argon depletion require that the frictional shear stress acting on the fault during both episodes of fault motion was at least 1–1.5 kbars. If, alternatively, it is assumed that all fault motion took place in the last 30 m.y., this does not change our conclusion with respect to the stress required for the argon depletion.