Orogenic gold and geologic time: a global synthesis

Terra Australis Orogen: Rodinia breakup and development of the Pacific and Iapetus margins of Gondwana during the Neoproterozoic and Paleozoic

The concept of 'Gondwana', an ancient Southern Hemisphere supercontinent, is firmly established in geological and biogeographical models of Earth history. The term Gondwana (Gondwanaland of some authors) derives from the recognition by workers at the Indian Geological Survey in the mid- to late 19th century of a distinctive sedimentary sequence preserved in east central India. This succession, now known to range in age from Permian to Cretaceous, is lithologically and palaeontologically similar to coeval non-marine sedimentary successions developed in most of the Southern Hemisphere continents suggesting former continuity of these landmasses. Palaeomagnetic data and tectonic reconstructions suggest that the main assembly of Gondwana took place around the beginning of the Palaeozoic in near-equatorial latitudes and that the supercontinent as a whole shifted into high southern latitudes, allowing widespread glaciation by the end of the Carboniferous. From Carboniferous to Cretaceous times the southern continents had broadly similar floras but some species-level provincialism is apparent at all times. The break-up of Gondwana initiated during the Jurassic (at about 180 million years ago) and this process is continuing. The earliest rifting (crustal attenuation) within the supercontinent initiated in the west (between South America and Africa) and in general terms the rifting pattern propagated eastward with major phases of continental fragmentation in the Early Cretaceous and Late Cretaceous to Paleogene. Gondwanan floras show radical turnovers near the end of the Carboniferous, end of the Permian and the end of the Triassic that appear to be unrelated to isolation or fragmentation of the supercontinent. Throughout the late Palaeozoic and Mesozoic the high-latitude southern floras maintained a distinctly different composition to the palaeoequatorial and boreal regions even though they remained in physical connection with Laurasia for much of this time. Gondwanan floras of the Jurassic and Early Cretaceous (times immediately preceding and during break-up) were dominated by araucarian and podocarp conifers and a range of enigmatic seed-fern groups. Angiosperms became established in the region as early as the Aptian (before the final break-up events) and steadily diversified during the Cretaceous, apparently at the expense of many seed-fern groups. Hypotheses invoking vicariance or long distance dispersal to account for the biogeographic patterns evident in the floras of Southern Hemisphere continents all rely on a firm understanding of the timing and sequence of Gondwanan continental breakup. This paper aims to summarise the current understanding of the geochronological framework of Gondwanan breakup against which these biogeographic models may be tested. Most phytogeographic studies deal with the extant, angiosperm-dominated floras of these landmasses. This paper also presents an overview of pre-Cenozoic, gymnosperm-dominated, floristic provincialism in Gondwana. It documents the broad succession of pre-angiosperm floras, highlights the distinctive elements of the Early Cretaceous Gondwanan floras immediately preceding the appearance of angiosperms and suggests that latitudinal controls strongly influenced the composition of Gondwanan floras through time even in the absence of marine barriers between Gondwana and the northern continents. Go na br nd prn ti l S.ou

The breakup history of Gondwana and its impact on pre-Cenozoic floristic provincialism

New Zealand's Geological Foundations

Reconstructions of the New Zealand subcontinent from 40 Ma to the Present are presented. Assumptions that have constrained the model include: semi‐straight initial alignment of basement terranes and markers; Australian plate fixed; onset of Emerald Basin spreading at c. 45 Ma; and Pacific plate subduction north of New Zealand from c. 30 Ma. Five independent, rigid, crustal blocks are employed, including: Northland‐Taranaki‐western South Island (combined), East Coast (North Island), east Nelson (Marlborough Sounds), eastern South Island, and Fiordland. At 40 Ma the Pacific/Australian rotation pole was located close to or within the Wanganui region. A proto‐plate boundary zone was propagating through western New Zealand, as an incipient link between Emerald Basin spreading in the south and subduction in the northwest. Lateral offset on the Alpine Fault was initiated by c. 23–22 Ma, mainly as an effect of changing subduction kinematics and increasing relative motion of the Australian and Pacific pla...

https://www.tandfonline.com/doi/pdf/10.1080/00288306.2000.9514913

Tectonic reconstructions of New Zealand: 40 Ma to the Present

Broad chemical characteristics of sedimentary rocks from the Buller and Takaka Terranes have been examined, and provenance and tectonic setting inferred, using whole‐rock major and trace element data from 208 samples. Buller Terrane rocks west of the Karamea Batholith (Greenland Group) have chemistry typical of turbidite sediments deposited at a weathered passive continental margin. Bulk chemical characteristics confirm earlier work, except that a small spatial chemical variation is seen, consistent with the presence of a small volcanogenic component in the south, decreasing to the north. East of the batholith, compositions of the Webb and Roaring Lion Formations overlap with those of the western Buller rocks, supporting equivalence (at least in part) with the Greenland Group. Passive margin chemical characteristics are maintained throughout the succeeding Ordovician formations. Within the Takaka Terrane there are sharp contrasts in chemistry between the Cambrian and post‐Cambrian (Ordovician—Sil...

A. J. Tulloch

Papers

Reconnaissance sandstone geochemistry, provenance, and tectonic setting of the lower Paleozoic terranes of the West Coast and Nelson, New Zealand

Early Palaeozoic terranes in New Zealand and their relationship to the Lachlan Fold Belt