No abstract

During the late Cenozoic the Pacific plate has been converging obliquely with the Australia plate in South Island, New Zealand. A result of this convergence has been the growth of a major mountain range (the Southern Alps) at the leading edge of the Pacific plate. The results of fission track analysis of 140 samples from 13 transects across the Alps reported here establish the late Cenozoic vertical kinematics (amount, age, and rate of rock uplift) of the Pacific crust underlying the Alps. The late Cenozoic rock uplift of the Pacific crust is asymmetrical with respect to the Alpine fault, being a maximum (19 km) immediately east of the central part of the fault, with lesser values at the eastern (3 km), northern (10 km), and southern (8 km) extremities of the Alps. The age of the start of rock uplift varies spatially across the Southern Alps, the earliest indications from fission track analysis being at 8 Ma at the southern end of the Alps, decreasing to 5 Ma at the northern end and 3 Ma along the southeastern margin. This age variation reflects the longer time over which the southern parts of the Alps have been in collision. The rate of propagation of rock uplift southeastward into the Pacific plate has been 30 mm/yr, nearly 4 times the late Cenozoic average rate of convergence normal to the plate boundary. Late Cenozoic mean rock uplift rates range from a maximum of ∼2.8 mm/yr at the Alpine fault to a minimum of ∼1.0 mm/yr in the east and have been sustained for periods of 3–8 m.y. Accompanying denudation has exhumed amphibolite grade rocks immediately east of the Alpine fault. The rock uplift has been controlled by oblique‐slip displacement on the Alpine fault. A continental crustal section at least 19 km thick has been uplifted on the Alpine fault. Comparison of the late Cenozoic mean rock uplift rates with uplift rates derived from reset zircon data (2–10 mm/yr) near the Alpine fault shows that uplift has accelerated over time, but only significantly since 1.3 ± 0.3 Ma. The amount of Mesozoic uplift ranged from minimal amounts north of Arthur's Pass, to ∼3 km near Mount Cook, to 10 km in the south at Lake Wanaka.

A relatively new field in provenance analysis is detrital fission-track thermochronology which utilizes grain ages from sediment shed off an orogen to elucidate its exhumational history. Four examples highlight the approach and usefulness of the technique. (1) Fission-track grain age (FTGA) distribution of apatite from modern sediment of the Bergell region of the Italian Alps corresponds to ages obtained from bedrock studies. Two distinct peak-age populations at 14.8 Ma and 19.8 Ma give calculated erosion rates identical to in situ bedrock. (2) Zircon FTGA distribution from the modern Indus River in Pakistan is used to estimate the mean erosion rate for the Indus River drainage basin to be about 560 m Ma −1 , but locally it is in excess of 1000 m Ma −1 . (3) FTGA distribution of detrital apatite and zircon from the Tofino basin records exhumation of the Coast Mountains in the Canadian Cordillera. Comparison of detrital zircon and apatite FT ages gives exhumation rates of c. 200 m Ma −1 during the interval between c. 34 and 54 Ma, but higher rates ( c. 1500 m Ma −1 ) at c. 56 Ma. (4) FTGA analysis of apatite grain ages from a young basin flanking Fiordland in New Zealand indicates that removal of cover strata was followed by profound exhumation at c. 30 Ma, which corresponds to plate reorganization at this time. Exhumation rates at the onset of exhumation were c. 2000–5000 m Ma −1 . These studies outline the technique of detrital FTGA applied to exhumation studies and highlight practical considerations: (1) well-dated, stratigraphically coordinated suites of samples that span the exhumation event provide the best long-term record; (2) strata from the basin perimeter are the most likely to retain unreset detrital ages; (3) the removal of ‘cover rocks’ precedes exhumation of deeply buried rocks, which retain a thermal signal of the exhumation event; (4) steady-state exhumation produces peak ages that progressively young with time and have a constant lag time; (5) same-sample comparison of zircon and apatite peak ages is best in sequences with high-uranium apatite grains (>50 ppm), and peak-ages statistics can be improved by counting numerous apatite grains (>100).

The ratite moa (Aves: Dinornithiformes) were a speciose group of massive graviportal avian herbivores that dominated the New Zealand (NZ) ecosystem until their extinction Ϸ600 years ago. The phylogeny and evolutionary history of this morphologically diverse order has remained controversial since their initial description in 1839. We synthesize mitochondrial phylogenetic information from 263 subfossil moa specimens from across NZ with morphological, ecological, and new geological data to create the first comprehensive phylogeny, taxonomy, and evolutionary timeframe for all of the species of an extinct order. We also present an important new geological/paleogeographical model of late Cenozoic NZ, which suggests that terrestrial biota on the North and South Island landmasses were isolated for most of the past 20 -30 Ma. The data reveal that the patterns of genetic diversity within and between different moa clades reflect a complex history following a major marine transgression in the Oligocene, affected by marine barriers, tectonic activity, and glacial cycles. Surprisingly, the remarkable morphological radiation of moa appears to have occurred much more recently than previous early Miocene (ca. 15 Ma) estimates, and was coincident with the accelerated uplift of the Southern Alps just ca. 5-8.5 Ma. Together with recent fossil evidence, these data suggest that the recent evolutionary history of nearly all of the iconic NZ terrestrial biota occurred principally on just the South Island.ancient DNA ͉ Oligocene Drowning ͉ Dinornithiformes ͉ phylogeny ͉ taxonomy

The Xianshuihe‐Xiaojiang fault system extending from eastern Tibet to central Yunnan, China, is a major left‐shear structural boundary, accommodating the clockwise rotation of crustal rocks between the Eastern Himalayan syntaxis and the South China Block. Zircon and apatite fission track (FT) data are reported for 111 samples of basement collected from both sides of the northern part of this fault and spanning 300 km across the eastern margin of the Tibetan Plateau, where its mean elevation drops from 3500 to 1500 m above sea level. The zircon FT ages define two fossil partial annealing zones at different elevations, one fossilised at circa 130 Ma, and the other at circa 21 Ma as a result of cooling probably via regional denudation. The apatite FT ages are mostly less than 25 Ma, but a few granitoids higher up on the plateau retain late Cretaceous apparent ages. Within the apatite FT data with Neogene ages, there may be several partial annealing zones, with mixture modeling identifying age components suggestive of discrete cooling phases at circa 22, 7 and 2 Ma. The first‐order pattern of the minimum amount of Neogene denudation for a section across the plateau margin immediately northeast of Xianshuihe Fault suggests that a relatively uniform 4–6 km has been eroded from the inner part of the plateau margin, increasing to 7–10 km at Kangding, where the oldest rocks (Precambrian) are exposed, and then decreasing markedly into Sichuan Basin. These new FT data combined with published FT data suggest that the present extent of the Tibetan Plateau was defined during the early Miocene.