Geology

The Chrystalls Beach Complex is interpreted as an accretionary me´lange within the Otago Schist on the South Island of New Zealand. Its stratigraphic position within the New Zealand Mesozoic accretionary prism is not well constrained, and the terrane affinity of the complex has remained enigmatic. Previous studies have focused on age relationships and sediment geochemistry. In this contribution we present geochemical data for metabasalts within the complex. Two distinctly different basalt compositions are found in the me´lange. Metabasalts outcropping at the northern end of the complex have an inferred mid-ocean ridge affinity, while metabasalts in the central part of the assemblage are suggested to represent ocean island basalts. It is speculated that the northern mid-ocean ridge basalts represent blocks from the crust of a subducting slab, while the ocean island basalts are part of a subducting seamount. These tectonic affinities are in agreement with me´lange formation during sub...

On the north side of the Mulock Glacier and at Cape Teall in southern Victoria Land, Antarctica, deformed greenschist facies Skelton Group metasediments are intruded by the post-kinematic A-type Mulock Granite. Geochemical data indicate that this intrusive complex is similar to A-type granitoids previously described both to the north (Glee Intrusives and Penny Hill Granite), where they form part of the Koettlitz Glacier Alkaline Province, and to the south (Foggydog Granite Suite). A U-Pb zircon date of 546 ± 3 Ma on the Mulock Granite places a minimum constraint on the age, and timing of deformation of the Skelton Group rocks in this area, and indicates that the Mulock Granite was emplaced during the initial stages of the Ross Orogeny. This age also confirms that crystallisation of this granite body was synchronous with that of A-type granitoids from the Royal Society Range to Skelton Glacier area immediately to the north. During the late Neoproterozoic, extension or transtension along this part of the paleo-Pacific margin of Gondwana allowed crustal-scale thinning to occur. This, coupled with the addition of an external heat supply through mafic underplating and/or asthenospheric upwelling, caused lower crustal anatexis and the production of small volumes of A-type granitoid melt. Although the exact nature of this anatectic process remains unclear, it seems probable that melting did not occur under strictly anhydrous conditions, and an external water supply played a crucial role in melt generation.

The Fontaine Pluton is a previously undescribed mafic intrusion outcropping at Fontaine Bluff on the south side of the Carlyon Glacier in southern Victoria Land, Antarctica. It is the southern‐most member of a laterally extensive mafic suite emplaced at mid‐crustal depths during the initial stages of the Ross Orogeny. The pluton comprises recrystal‐lised hornblende‐biotite gabbro, which in places shows well‐defined centimetre to metre scale primary igneous layering. Recrystallised ultramafic enclaves composed of amphibole‐ ...

The Marguerite Amphibolite and associated rocks in northern Fiordland, New Zealand, contain evidence for retention of Carboniferous metamorphic assemblages through Cretaceous collision of an arc, emplacement of large volumes of mafic magma, high-P metamorphism and then extensional exhumation. The amphibolite occurs as five dismembered aluminous meta-gabbroic xenoliths up to 2 km wide that are enclosed within meta-leucotonalite of the Lake Hankinson Complex. A first metamorphic event (M1) is ...

Previous U-Pb zircon dating of the Pomona Island Granite (PIG) pluton (South Island, New Zealand) yielded either Permo-Carboniferous or Late Jurassic ages for five samples essentially indistinguishable in their field, petrographic, and geochemical characteristics. Detailed cathodoluminescence imaging and LA-ICP-MS dating of zircon in new and previously dated samples reveal that portions of the pluton contain either delicately oscillatory-zoned Late Jurassic zircon grains with rare Permo-Carboniferous cores, or Permo-Carboniferous grains with ubiquitous but thin Late Jurassic rims. Based on zircon dissolution-overgrowth textures, zircon rim and core trace element compositions, and the limited extent of sub-solidus rock recrystallisation textures, the bipartite age distribution is unlikely to reflect variable Pb-loss or metamorphic re-equilibration. Magmatic Zr-saturation temperatures were ≥851°C for samples dominated by Jurassic zircon and ≤809°C for samples with a predominance of Permo-Carboniferous zircon. Together, these data are consistent with PIG magmas having been derived from partial melting of a Permo-Carboniferous felsic igneous source at variable temperature wholly in the Late Jurassic (157 ± 3 Ma). The lowest temperature melts would have been incapable of dissolving significant amounts of pre-existing zircon and consequently generated inheritance-rich magmas, with the very thin rims on the pre-existing zircon grains the only evidence of the Late Jurassic magmatic age. As the partial melting temperature increased and nearly all pre-existing zircon grains dissolved into the magma, an inheritance-poor batch of melt was generated, which precipitated new zircon grains upon crystallisation. Concentrations of major and many trace elements in both magma batches may have been buffered by retention of residual quartz and feldspar in the source, which would explain the limited geochemical differences between inheritance-rich and inheritance-poor portions.

The Marguerite Amphibolite and associated rocks in northern Fiordland, New Zealand, contain evidence for retention of Carboniferous metamorphic assemblages through Cretaceous collision of an arc, emplacement of large volumes of mafic magma, high-P metamorphism and then extensional exhumation. The amphibolite occurs as five dismembered aluminous meta-gabbroic xenoliths up to 2 km wide that are enclosed within meta-leucotonalite of the Lake Hankinson Complex. A first metamorphic event (M1) is manifest in the amphibolite as a pervasively lineated pargasite-anorthite-kyanite or corundum ± rutile assemblage, and as diffusion-zoned garnet in pelitic schist xenoliths within the amphibolite. Thin zones of metasomatically Al-enriched leucotonalite directly at the margins of each amphibolite xenolith indicate element redistribution during M1 and equilibration at 6.6 ± 0.8 kbar and 618 ± 25°C. A second phase of recrystallization (M2) formed patchy and static margarite ± kyanitestaurolite-chlorite-plagioclase-epidote assemblages in the amphibolite, pseudomorphs of coronas in gabbronorite, and thin high-grossular garnet rims in the pelitic schists. Conditions of M2, 8.8 ± 0.6 kbar and 643 ± 27°C, are recorded from the rims of garnet in the pelitic schists. Cathodoluminescence imaging and simultaneous acquisition of U-Th-Pb isotopes and trace elements by depth-profiling zircon grains from one pelitic schist reveals four stages of growth, two of which are metamorphic. The first metamorphic stage, dated as 340.2 ± 2.2 Ma, is correlated with M1 on the basis that the unusual zircon trace element compositions indicate growth from a metasomatic fluid derived from the surrounding amphibolite during penetrative deformation. A second phase of zircon overgrowth coupled with crosscutting relationships date M2 to between 119 and 117 Ma. The Early Carboniferous event has not previously been recognized in northern Fiordland, whereas the latter event, which has been identified in Early Cretaceous batholiths, their xenoliths, and rocks directly at batholith margins, is here shown to have also affected the country rock. However, the effects of M2 are fragmentary due to limited element mobility, lack of deformation, distance from a heat source and short residence time in the lower crust during peak P and T. It is possible that many parts of the Fiordland continental arc achieved high-P conditions in the Early Cretaceous but retain earlier metamorphic or igneous assemblages.

Scheelite (CaWO4) is a widespread accessory mineral associated with hydrothermal veins in the Archcan gold deposits of the Kalgoorlie-Norseman region of Western Australia. Rare earth element (REE) and other trace element abundances in scheelite have been determined in situ by excimer laser ablation-inductively coupled plasma-mass spectrometry (ELA-ICP-MS) in order to constrain the composition and sources of the mineralizing fluids. The scheelites can be grouped according to the two distinct types of chondrite-normalized REE (REEN) patterns which they exhibit: hump-shaped (type I) and flat (type II). Type I scheelites have higher total and Na concentrations than type II samples and can be further subdivided into type Ia which has maximum REEN concentrations between Sm and Gd, and type Ib which has maximum REEN concentrations displaced toward Dy. Type I scheelites are dominant at Coolgardie, Kalgoorlie, and Kambalda, whereas type II samples are most abundant at Norseman. A few scheelite grains exhibit both type ! and type II characteristics.

Coupled O and Hf isotopic compositions of zircons from Early Cretaceous (113-124 Ma) granitoids of the Separation Point Suite (SPS), New Zealand, obtained by cathodoluminescence imaging-guided micro-beam methods (SIMS, LA-ICPMS), are used as a record of evolving magma compositions in a prominent Mesozoic arc system. Eight representative SPS samples from individual plutons in the Nelson and Fiordland regions yield magmatic zircons with initial Hf isotope ratios (expressed in ε Hf ) ranging from − 4 to + 11 (Nelson) and + 5 to +12 (Fiordland), respectively. Initial Hf isotope ratios of zircons are extremely heterogeneous within individual samples, with the vast majority of values distinctly less radiogenic than depleted mantle at~120 Ma (ε Hf~+ 16). O isotope ratios are likewise variable, with δ 18 O zircon (SMOW) values of 2-8‰ (Nelson) and 0-7‰ (Fiordland). The within-rock variability in both zircon Hf and O isotope ratios is testimony to open-system processes that operated during magma evolution and zircon crystallisation. Average δ 18 O zircon for cores and rims allow constraints to be placed on the O isotopic composition of magmas from which zircon precipitated (δ 18 O magma~4 -8‰). Elevated δ 18 O magma (N 6.5‰) require involvement of 18 O-enriched supracrustal material (weathered continental crust or low-T seawater-hydrothermally altered oceanic crust), while δ 18 O magma b 5.5‰ imply contribution from a 18 Odepleted crustal component. Whole rock Sr isotope, Nb/Ta and Nd/Pb systematics are inconsistent with 18 O-depleted slab melts (δ 18 O~0-6‰) as a source component for SPS magmas. Instead, low δ 18 O values suggest incorporation of high-T meteoric-hydrothermally altered country rocks similar to those of the Largs terrane presently exposed in northern Fiordland. In diagrams of SiO 2 versus inferred δ 18 O magma the most primitive SPS samples from the Nelson and Fiordland regions plot close to the expected composition for primitive arc magmas. More evolved granitoids, however, show strongly divergent trends of O isotope composition as a function of SiO 2 , suggestive of assimilation coupled to fractional crystallisation (AFC) in contrasting crustal environments. Emplacement-level contamination by local crust is supported by age distributions of inherited zircons, which indicate a predominance of Palaeozoic and Mesozoic zircons in Nelson and Fiordland granitoids, respectively.

ELA-ICP-MS U–Pb zircon geochronology has been used to show that the porphyritic intrusions related to the formation of the Bajo de la Alumbrera porphyry Cu–Au deposit, NW Argentina, are cogenetic with stratigraphically well-constrained volcanic and volcaniclastic rocks of the Late Miocene Farallón Negro Volcanic Complex. Zircon geochronology for intrusions in this deposit and the host volcanic sequence show that multiple mineralized porphyries were emplaced in a volcanic complex that developed over 1.5 million years. Volcanism occurred in a multi-vent volcanic complex in a siliciclastic intermontane basin. The complex evolved from early mafic-intermediate effusive phases to a later silicic explosive phase associated with mafic intrusions. Zircons from the basal mafic-intermediate lavas have ages that range from 8.46±0.14 to 7.94±0.27 Ma. Regionally extensive silicic explosive volcanism occurred at ~8.0 Ma (8.05±0.13 and 7.96±0.11 Ma), which is co-temporal with intrusion of the earliest mineralized porphyries at Bajo de la Alumbrera (8.02±0.14 and 7.98±0.14 Ma). Regional uplift and erosion followed during which the magmatic-hydrothermal system was probably unroofed. Shortly thereafter, dacitic lava domes were extruded (7.95±0.17 Ma) and rhyolitic diatremes (7.79±0.13 Ma) deposited thick tuff blankets across the region. Emplacement of large intermediate composition stocks occurred at 7.37±0.22 Ma, shortly before renewed magmatism occurred at Bajo de la Alumbrera (7.10±0.07 Ma). The latest porphyry intrusive event is temporally associated with new ore-bearing magmatic-hydrothermal fluids. Other dacitic intrusions are associated with subeconomic deposits that formed synchronously with the mineralized porphyries at Bajo de la Alumbrera. However, their emplacement continued (from 7.10± 0.06 to 6.93±0.07 Ma) after the final intrusion at Bajo de al Alumbrera. Regional volcanism had ceased by 6.8 Ma (6.92±0.07 Ma). The brief history of the volcanic complex hosting the Bajo de la Alumbrera Cu–Au deposit differs from that of other Andean provinces hosting porphyry deposits. For example, at the El Salvador porphyry copper district in Chile, magmatism related to Cu mineralization was episodic in regional igneous activity that occurred over tens of millions of years. Bajo de la Alumbrera resulted from the superposition of multiple porphyry-related hydrothermal systems, temporally separated by a million years. It appears that the metal budget in porphyry ore deposits is not simply a function of their longevity and/or the superposition of multiple porphyry systems. Nor is it a function of the duration of the associated cycle of magmatism. Instead, the timing of processes operating in the parental magma body is the controlling factor in the formation of a fertile porphyry-related ore system.

The late Cretaceous A-type Karaçayır pluton in Central Anatolia, Turkey, intrudes and entrains xenoliths of Palaeozoic limestone. Carbonatitic magmatic rocks within the syenite have been previously interpreted (Schuiling in Nature, 192:1280, 1961) to result from metasomatic alteration and syntectic melting of marble. Carbonatites and associated calcite-syenites exhibit mineralogical characteristics (Ab-rich plagioclase, Ba-rich K-feldspar, low-Mg# biotite) that are petrogenetically more evolved than the host syenitic suite. Geochemically, carbonate-rich magmatic rocks are greatly enriched in Sr, Ba, Th, and REE and have higher LREE/HREE ratios than either syenites or marbles. In terms of O-C-Sr-Pb isotope ratios, the carbonatite/calcite-syenite suite form a consistent and geochemically coherent group that is distinct from the marble country rock and xenolith population, but similar to some of the syenitic, and particularly the nepheline syenite components of the Karaçayır pluton. Other silicate magmatic rocks are geochemically, isotopically, and geochronologically different, suggesting the pluton is composite. Overall, the mineralogical and geochemical characteristics of the carbonatites are incompatible with binary mixing of syenite and marble but are consistent with derivation of carbonatite from petrogenetically evolved foid syenite. Carbonate-silicate rock types have modal variations compatible with an origin by fractional crystallisation, rather than by liquid immiscibility.

A massive pulse of granitic magma was rapidly emplaced into the once contiguous West Antarctic and New Zealand segments of the palaeo-Pacific margin of the Gondwana supercontinent at~371 Ma. In New Zealand, these Late Devonian S-type granitoids cover an areal extent of N 3400 km 2 , but the tectonic setting for crustal partial melting has remained unclear because most of the exposure represents either emplacement-level, or rocks that have been reworked during Cretaceous orogenesis. New petrologic data indicate that aluminous paragneisses and orthogneisses in the Bonar Range represent a rare portion of Devonian middle crust that preserves evidence for the initiation of crustal melting. The investigated rocks outline the tail of a clockwise P-T path that involved partial melting at peak conditions (~670°C, 5.1 kb), deformation during the immediately following near-isothermal decompression, and then partial re-equilibration under static conditions. Syn-to post-kinematic growth of zoned monazite establishes the timing of recrystallisation to a~16 Ma period that began at 373.4 ± 4.1 Ma. This age overlaps with the initiation of regional Karamea S-type granitic magmatism. Although estimated metamorphic conditions were insufficient for large amounts of melt to have been produced from Bonar Range pelites (calculated melt volumes are b 10%), they do provide evidence consistent with widespread heating and partial melting in the deeper crust. This heating episode was contemporaneous with partial melting in Fiordland (New Zealand) and West Antarctica, although Mesozoic thermal and deformational events complicate the Palaeozoic record in both those areas. Nevertheless, the apparent 1000 s km of along-strike crustal partial melting indicates that a continental-scale tectonic plate margin re-organisation took place at this time. The cause in the New Zealand segment was most likely, but not unequivocally, an extensional tectonic regime with an elevated geothermal gradient caused by conductive heating from a shallowed lithospheric mantle.

The petrography of sandstones and neodymium (Nd) isotope compositions of mudstones from the central Appalachians indicate changing provenances during the late Neoproterozoic through Pennsylvanian evolution of eastern North America. In contrast, sandstones from all stratigraphic units are dominated by Grenvillian (950-1250 Ma) zircons. Neoproterozoic to Cambrian rift-related sandstones are mostly feldspathic arenites and contain detrital zircons that are exclusively Grenvillian. The associated mudstones have remarkably uniform initial Nd isotope compositions ( to Ϫ5.4 at the p Ϫ4.4 Nd time of sedimentation) that also are consistent with a Grenville provenance. Cambrian passive margin sandstones are quartz arenites that contain, in addition to Grenvillian zircons, significant numbers of early Mesoproterozoic and late Paleoproterozoic (1300-1800 Ma) zircons. Intercalated mudstones have variable and low initial Nd values of Ϫ6.3 to Ϫ15.1 that, in common with the detrital zircons, indicate derivation from a mixture of Grenvillian and older crustal provinces to the west. Sandstones from the overlying foreland basin clastic wedges typically are lithic arenites. Those of Taconian age contain both sedimentary and metamorphic (polycrystalline quartz and chlorite schist) rock fragments, whereas Acadian and Alleghanian sandstones are dominated by metamorphic rock fragments (quartz-muscovite and quartz-chlorite schist, detrital mica, and polycrystalline quartz). Although detrital zircons are mainly Grenvillian, a few younger (Taconian) zircons are present in the clastic wedge sandstones, and, significantly, a Lower Pennsylvanian sandstone contains up to 10% Archean zircons of probable Superior Province heritage. Mudstones from the Taconian, Acadian, and Alleghanian clastic wedges have uniform Nd isotopic compositions (initial to Ϫ9.0) that are consistent p Ϫ7.7 Nd with recycling of the lower part of the passive margin prism with an admixture of new, freshly eroded Grenville basement. Sandstone petrography and detrital zircon geochronology indicate that Taconian-age sandstones and conglomerates were recycled from older passive margin sedimentary rocks that were uplifted in an accretionary prism in front of the approaching magmatic arc and that Acadian and Alleghanian sandstones were derived from deeper levels of this foldthrust complex. The rarity of Neoproterozoic and Paleozoic zircons in the clastic wedge sandstones is attributed to the presence of the accretionary prism as a tectonic highland between the magmatic arcs and the foreland basins.

The feasibility of in-situ 5uorination of sulfide minerals for sulfur isotope analyses has been demonstrated. Laser fluorination of powdered samples, previously analyzed by conventional bulk SOz or BrFs methods, verities that comparable precision and accuracy can be achieved with the new method. The d %&or and 6"Scnr values of powdered samples are independent of Fz gas pressure over a range of from 15 to 120 ton-. Furthermore, ij34scDT values are independent of SF6 yields from 40 to 100% for powders that do not fluorinate spontaneously at room temperature. The precision of replicate analyses of powdered pyrite, troilite, chal~pyrite, sphalerite, galena, acanthite, and greenockite is typically 0. l-0.2% Interlaboratory comparisons of previously analyzed powders agree as closely as 0.1% and disagree by as much as 0.8% over a range of S?jcnr from -30 to +34% The technique of in-situ laser fluorination was validated by comparison of analyses of side-by-side laser craters and powders from drill holes in polished sulfide mineral surfaces. For isotopically homogeneous samples, laser craters and drill hole powders agree within 0.1-0.3960 for both 6?Scnr and 13~'Sc ur, depending on the mineral analyzed.

This paper reports on aspects of the production and trade of nineteenth century Chinese opium pipe bowls based on an examination of an assemblage from a Chinese goldfields settlement in New Zealand. Using energy dispersive X-ray fluorescence (EDXRF) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) we characterised the clay sources used for pipe production. Comparing those results with a stylistic analysis of the pipe bowls we developed a model for the production of opium pipe bowls and their distribution to nineteenth century Chinese diaspora communities. This is the first study to investigate Chinese opium pipe bowls using a combination of geochemical and stylistic analysis and is a novel application of archaeological science methodologies in Overseas Chinese Archaeology. The work reveals information about a group of potters and their production structures in Southern China and their trading connections in the Trans-Pacific region that had previously been...

"Two fossil baleen whale (Mysticeti) dentaries from the Upper Miocene (10–12 Ma) Santa Margarita Sandstone of Central California preserve several distinct features similar to the enigmatic herpetocetine whale Herpetocetus. These features include an elongate coronoid process, a mandibular condyle with a planar articular surface, and a posteriorly extended angular process. The dentary is unknown for several Herpetocetinae (and the more inclusive clade Cetotheriidae),
including the coeval Nannocetus eremus. This occurrence would extend the known record of Herpetocetus by 6 Ma. Given the currently poor knowledge of Pacific Cetotheriidae during the Miocene, these specimens are identified
to the subfamily Herpetocetinae, despite the similarity of these specimens to Herpetocetus. As the morphology of the supposedly distinctive lectotype dentary of Herpetocetus scaldiensis (the type species of Herpetocetus) may not be unique to Herpetocetus, this study suggests that the mandibular morphology of fossil mysticetes may be more homoplastic (or conservative) than previously assumed. Mysticete taxonomy should employ autapomorphic characters beyond the morphology of the dentary alone."

"The Miocene to Pliocene Purisima Formation crops out in multiple transform fault bounded structural blocks in central California. As a result of poor exposure, strike slip fault offset, and uncertain intraformational correlations, some exposures of the Purisima Formation are not well dated. The San Gregorio section of the Purisima Formation occurs in the Pigeon Point
Block, west of the San Gregorio Fault, along the coast of southern Halfmoon Bay. Ages based on invertebrate and diatom biostratigraphy support a Late Miocene to Early Pliocene age,
while ash correlations indicate a much younger Middle to Late Pliocene (3.3-2.5 Ma) age. Abundant remains of marine vertebrates occur in the Purisima Formation. Recent fieldwork
in the San Gregorio section identified a modest assemblage of 26 taxa, including sharks (Carcharodon carcharias, Carcharodon sp., Cetorhinus maximus, cf. Hexanchus, Isurus oxyrinchus,
Pristiophorus sp., Squatina sp., and Sphyrna sp.), skates (Raja sp., cf. R. binoculata), bony fish (Paralichthys sp., Thunnus sp.), birds (Mancalla diegensis, Morus sp.), and 13 marine
mammal taxa, including several new records for the Purisima Formation. The nonmammalian vertebrates of this assemblage are described herein. The vertebrate assemblage is utilized to evaluate previous biostratigraphic and tephrochronologic age determinations for the San Gregorio section. The stratigraphic range of Carcharodon carcharias, Raja sp., cf. R. binoculata, Mancalla diegensis, and some of the marine mammals strongly indicate a Middle to Late Pliocene age for the upper and middle parts of the section, while a Late Miocene or Early Pliocene age is probable for the base of the section.
"

Background

A number of aberrant walruses (Odobenidae) have been described from the Neogene of the North Pacific, including specialized suction-feeding and generalist fish-eating taxa. At least one of these fossil walruses has been hypothesized to have been a specialized predator of other marine mammals, the middle Miocene walrus Pelagiarctos thomasi from the Sharktooth Hill Bonebed of California (16.1–14.5 Ma).
Methodology/Principal Findings

A new specimen of Pelagiarctos from the middle Miocene “Topanga” Formation of southern California (17.5–15 Ma) allows a reassessment of the morphology and feeding ecology of this extinct walrus. The mandibles of this new specimen are robust with large canines, bulbous premolars with prominent paraconid, metaconid, hypoconid cusps, crenulated lingual cingula with small talonid basins, M2 present, double-rooted P3–M1, single-rooted P1 and M2, and a P2 with a bilobate root. Because this specimen lacks a fused mandibular symphysis like Pelagiarctos thomasi, it is instead referred to Pelagiarctos sp. This specimen is more informative than the fragmentary holotype of Pelagiarctos thomasi, permitting Pelagiarctos to be included within a phylogenetic analysis for the first time. Analysis of a matrix composed of 90 cranial, dental, mandibular and postcranial characters indicates that Pelagiarctos is an early diverging walrus and sister to the late Miocene walrus Imagotaria downsi. We reevaluate the evidence for a macropredatory lifestyle for Pelagiarctos, and we find no evidence of specialization towards a macrophagous diet, suggesting that Pelagiarctos was a generalist feeder with the ability to feed on large prey.
Conclusions/Significance

This new specimen of Pelagiarctos adds to the knowledge of this problematic taxon. The phylogenetic analysis conclusively demonstrates that Pelagiarctos is an early diverging walrus. Pelagiarctos does not show morphological specializations associated with macrophagy, and was likely a generalist predator, feeding on fish, invertebrates, and the occasional warm-blooded prey item.