In order to establish southern and western limits to possible points of origin of terranes, we calculated the routes or trajectories by which terranes were carried aross the Pacific basin and along the margin of North America. These trajectories were then tested for internal consistency with paleomagnetic results. Beginning with specific plate tectonic models that describe the motion of adjacent oceanic plates relative to North America, we found a set of terrane trajectories that show the position of terranes as a function of time as the terranes moved with the oceanic plates or were driven by them tangentially along the continental margin. Elements used to define a trajectory are (1) the stage poles describing the motion of the oceanic plates relative to the continent, (2) the sequence of plates carrying the terrane, (3) the time of docking of the terrane, and (4) the coordinates of the point of docking. Additional constraints are that terranes are not permitted to migrate across ridges and that the oceanic plate carrying a terrane cannot be younger than the terrane. The plate model of Engebretson and others (1985) and several of its variants were used in our analysis. For docking times of 30 Ma, trajectories are short because the Pacific-Farallon spreading system is close to the margin. For docking times of 60 Ma, terrane trajectories indicate northward transport by as much as 60° of latitude. For docking times of 120 and 90 Ma, trajectories indicate easterly transport across as much as 60° of longitude. For the Wrangellia, Central Salinia, and Point Arena terranes and the Laytonville Limestone, paleolatitudes were found as a function of time for different plate models, and these results were compared with paleomagnetically determined paleolatitudes from the terranes. The two sets of paleolatitudes were generally consistent only for plate models in which, when the Farallon plate rifted at 85 Ma to form a Kula plate in the north, leaving a smaller Farallon plate in the south, the newly formed Kula plate occupied a large region adjacent to North America, so that the Central Salinia and Point Arena terranes and the Laytonville Limestone were all located north of the Kula-Farallon rift. In addition, a rapid rate of spreading between the Farallon and Pacific plates during the Cretaceous normal superchron is required to model the paleolatitude of the Laytonville Limestone but not that of the other terranes. No terrane trajectory for Wrangellia was found that placed this terrane in the southern hemisphere during Jurassic time, as has been suggested on the basis of paleomagnetic data. The Wrangellia trajectories are consistent with the model of Irving and others (1985) in which Wrangellia arrived at the continental margin at the present latitude of Baja California at ∼100 Ma, was intruded at that latitude by the Coast Plutonic Complex, and then moved tangentially along the coast driven by oblique convergence of the Farallon and Kula plates.

ABSTRACT Numerical models of meteorite delivery from impacts on the Moon have demonstrated that the impact event forming the lunar crater Tycho (~85 km diameter; ca. 109 Ma age) would have delivered considerable amounts of ejected material to Earth. The ejecta, containing lunar Ti- and V-rich chrome spinels, would have been distributed globally and admixed with seafloor sediments over a few meters of a typical marine stratigraphic interval. In order to locate such ejecta, samples weighing ~12–25 kg each, with one-meter spacing were extracted over an ~30 m interval of the deep-sea formed Calera Limestone, Albian and Aptian age (ca. 103–117 Ma), from the Pacifica Quarry, south of San Francisco. The limestone samples were leached in acids and residues searched for possible lunar Ti-rich chrome-spinel grains. In a total of 689 kg of limestone, 1154 chrome-spinel grains were found. Of these, 319 contain >0.45 wt% V 2 O 3 , of which 227 originate from equilibrated ordinary chondrites. The majority of the other 92 grains with >0.45 wt% V 2 O 3 are most likely from different types of achondritic meteorites. Among these, we found eleven particularly Ti-rich chrome-spinel grains. The elemental abundances of these grains were compared with chrome spinel from lunar, howardite-eucrite-diogenite (HED) and R-chondritic meteorites. This showed that only one of these grains could potentially be of lunar origin. The bulk of the other grains likely originate from HED meteorites based on oxygen isotopic analysis of similar grains in previous studies. Grains with TiO 2 >10 wt%, common among lunar spinels are not found, further supporting an HED source for the Ti-rich grains. In summary, Albian and Aptian strata in the Pacifica quarry do not likely record any major lunar impact event. Either the timing of the impact is located within a ca. 110–114 Ma unconformity in the middle part of the section or the impact is likely older than the interval searched.

ABSTRACT Rocks of the Coast Ranges of northern California and southwest Oregon are divided into three principal associations: the Franciscan Complex of northern California (and its lateral equivalent in Oregon), tectonic slices of the Coast Range ophiolite and the Great Valley sequence (and lateral equivalents in Oregon), and tectonic slices of the Western Klamath terrane, all of which are locally overlain by Cenozoic cover rocks. The predominant lithologies are upper Mesozoic and Cenozoic graywacke and argillite that are commonly metamorphosed to zeolite, prehnite-pumpellyite, or blueschist facies. The Franciscan Complex consists of three belts: the Eastern Franciscan belt, which consists of imbricate thrust sheets of Jurassic and Cretaceous rocks that were metamorphosed to blueschist facies in Cretaceous time; the Central Franciscan belt, which is a tectonic melange containing rocks that range in age from Early Jurassic to Tertiary(?); the Coastal Franciscan belt, which is an accretionary complex of predominantly Tertiary age. These belts are further divided into units of different lithologic association, age, and deformational history. These include: the King Range, Coastal, and Yager terranes of the Coastal Franciscan belt; blocks and slabs of sandstone, volcanic rock, radiolarian chert and limestone of the Central Franciscan belt; and the Pickett Peak and Yolla Bolly terranes of the Eastern Franciscan belt. The Franciscan Complex in northern California is dominated by north-northwest trending structures, including shear zones, faults, folds and elongate fault-bound slices. In Oregon, slices of the Coast Range ophiolite and Great Valley sequence correlatives, Western Klamath terrane, and the Gold Beach terrane are typically faulted against and surrounded by Franciscan-type rocks. The rocks of the northern Coast Ranges record a protracted history of late Mesozoic and Cenozoic convergence that was dominated by subduction throughout much of that time. However, the history was also punctuated by times of either strike-slip or highly oblique convergence, particularly in the latest Cretaceous and early Tertiary, as well as during the present tectonic regime associated with the passing of the Mendocino triple junction.