Fission track analyses indicate that the Red Sea initially opened simultaneously along its entire length. Two distinct pulses of uplift and erosion characterized the early stages of rifting in the Red Sea throughout Egypt and in southwestern Saudi Arabia. The first pulse began at ∼34 million years ago (Ma). The second pulse began in the early Miocene (21 to 25 Ma) and marked the start of the main phase of extension. These data support a rigid plate model for continental extension. These results also indicate that the initiation of rift flank uplift, and therefore rifting, and volcanism occurred nearly simultaneously. This conflicts with classical models of active and passive extension that predict sequential development of these features.

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The Brooks Range is the northernmost orogenic belt in Alaska. From south to north it consists of a thin belt of oceanic basalt and chert, followed by two belts of high‐pressure/low‐temperature metamorphic rocks (the schist and central belts), a basement‐cored anticlinorium (the Doonerak Window), a fold and thrust belt, and a foreland basin (the Colville Basin). We have used apatite and zircon fission‐track (FT) and 40Ar/39Ar white mica analyses of a N‐S transect of the central Brooks Range to study the cooling history. These data are used with a balanced cross section to constrain the timing of deformational events in northern Alaska. The oldest cooling ages from this study were clusters of ∼185 Ma and ∼135 Ma zircon FT ages from the fold and thrust belt. Based on the similarity of the 185 Ma ages with the age of crystallization of the western Brooks Range ophiolites [Wirth et al., 1993], we suggest that the Brooks Range orogeny in northern Alaska had begun prior to this time. Cooling rates in the fold and thrust belt were very slow from 185 to 135 Ma, suggesting little or no deformation was occurring. Apatite and zircon FT analyses from the fold and thrust belt indicate that a substantial amount of cooling (caused by uplift and erosion) occurred from 135 to 95 Ma. We suggest that an increase in the rate of cooling at ∼135 Ma was caused by contractional deformation associated with renewed subduction with the opening of the Canada Basin. The 40Ar/39Ar white mica cooling ages of 130 to 120 Ma from the schist belt rocks of the southern Brooks Range indicate that peak metamorphism must have occurred prior to 130 Ma. An 40Ar/39Ar muscovite age of 113 Ma from the southernmost Brooks Range is interpreted to be the age of movement on normal faults juxtaposing lower‐grade phyllite belt rocks against schist belt rocks. At the same time, rapid deposition of Brooks Range‐derived sedimentary sequences began to the north, in the Colville foreland basin, and to the south, in the Yukon‐Koyukuk basin. Unstrained high‐level granitic plutons, which intruded the Yukon‐Koyukuk basin and Ruby terrane from 107 to 95 Ma, indicate the end of collision with the Yukon‐Koyukuk arc. By 95 Ma, cooling rates in the Brooks Range had slowed and little or no deformation was occurring. At 60 Ma, a major episode of rapid cooling occurred throughout northern Alaska, when the active plate margin in Alaska was more than 500 km to the south. In the Colville Basin, cooling was caused by thrust faulting and folding, and hence erosion, within the Albian‐age and younger sedimentary rocks. Within the interior of the Brooks Range, a large‐scale basement‐involved anticlinorium (the Doonerak Window) became active at this time. At 25 Ma, another episode of rapid cooling occurred within the Doonerak Window region. Both of these events may be related to shallow subduction of the Kula plate from the southern Alaskan plate margin.

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Results of apatite fission track analyses on 29 Ordovician through Permian sandstones from the Appalachian Basin in Pennsylvania are presented. Ages range from 111±17 to 184±10 Ma. Mean track lengths of 10.71±0.29 to 13.10±0.17 μm with unimodal, negatively skewed length distributions are indicative of slow cooling. The data separate into two groups on an age versus mean length plot. The younger group (111–144 Ma) is found in the structural depressions of the Anthracite Basin and the Broad Top Basin and adjacent Appalachian Plateau. The older group (144–184 Ma) is found in the structurally higher southwestern Appalachian Plateau and Juniata Culmination and adjacent central plateau. Fission track data suggest that the basin cooled slowly after the Alleghanian Orogeny, with culminations cooling earlier than depressions. Cooling histories modeled from apatite fission track data, with maximum temperatures constrained by vitrinite reflectance, indicate cooling beginning soon after the Alleghanian Orogeny except in the Juniata Culmination, which apparently experienced synorogenic cooling and unroofing during formation of the underlying duplex. Model cooling histories and available geologic information indicate that the foreland basin did not experience Mesozoic reheating. Unroofing histories were modeled from fission track cooling histories using heat flow estimates and burial depths derived from vitrinite reflectance profiles. The models suggest that the unroofing history of the Appalachian Basin in Pennsylvania can be divided into three episodes. An initial episode of relatively rapid cooling and unroofing (Late Permian‐Early Jurassic) is attributed to flexural rebound of the foreland in response to erosional removal of Alleghanian topographic load. Initial unroofing rates are higher in eastern Pennsylvania than in the west, consistent with a flexural model. An episode of little to no unroofing (Middle Jurassic‐late Oligocene) began contemporaneously with the inception of drift at the Atlantic continental margin. At this time, unloading of the orogen was replaced by subsidence and sedimentation on the new margin. Without flexural rebound the driving force for unroofing of the basin was removed and unroofing slowed greatly. An episode of rapid unroofing over the full width of the basin occurred from the Miocene to the present. Although the driving mechanism for unroofing at this time has not been identified, it is consistent with increased sedimentation rates in the middle Atlantic offshore basins for the same period.