Andesites as Magmatic Liquids or Liquid-crystal Mixtures; Insights from Egmont and Ruapehu Volcanoes, New Zealand Research Article

AbstractLate Quaternary andesitic magmas in New Zealand contain complexly zoned antecrysts and glomerocrysts that are not in equilibrium with either the host whole rock compositions or siliceous groundmass glass and glass inclusions. Glass inclusions represent partial melts of mafic to gabbroic cumulates in the lower crust that mix with restite crystals, or cumulates from earlier magma batches. Assimilation of partial melts of mid-crustal rocks, represented by glass in crustal xenoliths, contributes a crustal component to the andesites. Magmas at Egmont are stored at about the brittle/ductile transition at about 10 km depth and variability in the composition of erupted material is a function of the composition of the recharging magma, and which parts of the storage system are tapped during the eruption. At Taranaki recharge occurs on a c. 1400 year cycle while interactions within the storage give rise to shorter period events. A similar process on a less well constrained timescale operates at Ruapehu. Andesites are therefore complex mixtures of fractionated mantle basalts, siliceous partial melts of both the lower crust and underplated cumulates, restite and cumulate crystals. Further modification occurs by interaction with partial melts of lower to middle crustal basement as geotherms increase with time.

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STRAIN ACCOMMODATION AND 3D KINEMATICS OF TRANSPRESSIONAL FLOW WITHIN THE LOWER CRUST OF A CRETACEOUS MAGMATIC ARC IN FIORDLAND NEW ZEALAND

10.1130/abs/2018am-322805 ◽

2018 ◽

Author(s):

Griffin A. Moyer ◽

◽

Jesse Lee ◽

Christopher Eddy ◽

Elena A. Miranda ◽

...

Keyword(s):

New Zealand ◽

Lower Crust ◽

3D Kinematics ◽

Magmatic Arc

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GARNET SM-ND AGE CONSTRAINTS ON GRANULITE METAMORPHISM IN THE LOWER CRUST OF THE FIORDLAND MAGMATIC ARC, NEW ZEALAND

10.1130/abs/2018se-312334 ◽

2018 ◽

Author(s):

Ryan L. Rogers ◽

◽

James W. Yelverton ◽

Harold H. Stowell ◽

Elizabeth M. Bollen ◽

...

Keyword(s):

New Zealand ◽

Lower Crust ◽

Magmatic Arc ◽

Granulite Metamorphism ◽

Age Constraints

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Late Quaternary paleolimnology of Onepoto maar, Auckland, New Zealand: Implications for the drivers of regional paleoclimate

Quaternary International ◽

10.1016/j.quaint.2011.02.028 ◽

2012 ◽

Vol 253 ◽

pp. 18-31 ◽

Cited By ~ 18

Author(s):

Paul Augustinus ◽

Ursula Cochran ◽

Giri Kattel ◽

Donna D’Costa ◽

Phil Shane

Keyword(s):

New Zealand ◽

Late Quaternary

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A late Quaternary stratigraphic framework for the northeastern Ruapehu and eastern Tongariro ring plains, New Zealand

New Zealand Journal of Geology and Geophysics ◽

10.1080/00288306.1997.9514752 ◽

1997 ◽

Vol 40 (2) ◽

pp. 185-197 ◽

Cited By ~ 38

Author(s):

Shane J. Cronin ◽

Vincent E. Neall

Keyword(s):

New Zealand ◽

Late Quaternary ◽

Stratigraphic Framework

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Geodetic strain and the deformational history of the North Island of New Zealand during the late Cainozoic

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1987.0009 ◽

1987 ◽

Vol 321 (1557) ◽

pp. 163-181 ◽

Cited By ~ 207

Keyword(s):

New Zealand ◽

Subduction Zone ◽

East Coast ◽

Late Quaternary ◽

Plate Boundary ◽

Boundary Zone ◽

Metamorphic Belt ◽

Volcanic Region ◽

The North ◽

Plate Boundary Zone

The subduction zone under the east coast of the North Island of New Zealand comprises, from east to west, a frontal wedge, a fore-arc basin, uplifted basement forming the arc and the Central Volcanic Region. Reconstructions of the plate boundary zone for the Cainozoic from seafloor spreading data require the fore-arc basin to have rotated through 60° in the last 20 Ma which is confirmed by palaeomagnetic declination studies. Estimates of shear strain from geodetic data show that the fore-arc basin is rotating today and that it is under extension in the direction normal to the trend of the plate boundary zone. The extension is apparently achieved by normal faulting. Estimates of the amount of sediments accreted to the subduction zone exceed the volume of the frontal wedge: underplating by the excess sediments is suggested to be the cause of late Quaternary uplift of the fore-arc basin. Low-temperature—high-pressure metamorphism may therefore be occurring at depth on the east coast and high-temperature—low-pressure metamorphism is probable in the Central Volcanic Region. The North Island of New Zealand is therefore a likely setting for a paired metamorphic belt in the making.

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Thermodynamic constraints on assimilation of silicic crust by primitive magmas

10.5194/egusphere-egu21-1251 ◽

2021 ◽

Author(s):

Jussi S Heinonen ◽

Frank J Spera ◽

Wendy A Bohrson

Keyword(s):

Phase Equilibria ◽

Lower Crust ◽

Primitive Mantle ◽

Upper Crust ◽

Basaltic Composition ◽

Primitive Magma ◽

Partial Melts ◽

Thermodynamic Limits ◽

Melt Composition ◽

Lower Crustal

Some studies on basaltic and more primitive rocks suggest that their parental magmas have assimilated more than 50 wt.% (relative to the initial uncontaminated magma) of crustal silicate wallrock. But what are the thermodynamic limits for assimilation by primitive magmas? This question has been considered for over a century, first by N.L. Bowen and many others since then. Here we pursue this question quantitatively using a freely available thermodynamic tool for phase equilibria modeling of open magmatic systems &#8212; the Magma Chamber Simulator (MCS; https://mcs.geol.ucsb.edu).In the models, komatiitic, picritic, and basaltic magmas of various ages and from different tectonic settings assimilate progressive partial melts of average lower, middle, and upper crust. In order to pursue the maximum limits of assimilation constrained by phase equilibria and energetics, the mass of wallrock in the simulations was set at twice that of the initially pristine primitive magmas. In addition, the initial temperature of wallrock was set close to its solidus at a given pressure. Such conditions would approximate a rift setting with tabular chambers and high magma input causing concomitant crustal heating and steep geotherms.Our results indicate that it is difficult for any primitive magma to assimilate more than 20&#8722;30 wt.% of upper crust before evolving to intermediate/felsic compositions. However, if assimilant is lower crust, typical komatiitic magmas can assimilate more than their own weight (range of 59&#8722;102 wt.%) and retain a basaltic composition. Even picritic magmas, more relevant to modern intraplate settings, have a thermodynamic potential to assimilate 28&#8722;49 wt.% of lower crust before evolving into intermediate/felsic compositions.These findings have important implications for petrogenesis of magmas. The parental melt composition and the assimilant heavily influence both how much assimilation is energetically possible in primitive magmas and the final magma composition. The fact that primitive mantle melts have potential to partially melt and assimilate significant fractions of (lower) crust may have fundamental importance for how trans-Moho magmatic systems evolve and how crustal growth is accomplished. Examples include generation of siliceous high-magnesium basalts in the Precambrian and anorogenic anorthosite-mangerite-charnockite-granite complexes with geochemical evidence of considerable geochemical overprint from (lower) crustal sources.

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Synoptic climate change as a driver of late Quaternary glaciations in the mid-latitudes of the Southern Hemisphere

Climate of the Past ◽

10.5194/cp-2-11-2006 ◽

2006 ◽

Vol 2 (1) ◽

pp. 11-19 ◽

Cited By ~ 18

Author(s):

H. Rother ◽

J. Shulmeister

Keyword(s):

New Zealand ◽

Southern Hemisphere ◽

Large Scale ◽

Late Quaternary ◽

Synoptic Climatology ◽

Balance Model ◽

Last Glacial ◽

Regional Flow ◽

Quaternary Glaciations ◽

The Last Glacial

Abstract. The relative timing of late Quaternary glacial advances in mid-latitude (40-55° S) mountain belts of the Southern Hemisphere (SH) has become a critical focus in the debate on global climate teleconnections. On the basis of glacial data from New Zealand (NZ) and southern South America it has been argued that interhemispheric synchrony or asynchrony of Quaternary glacial events is due to Northern Hemisphere (NH) forcing of SH climate through either the ocean or atmosphere systems. Here we present a glacial snow-mass balance model that demonstrates that large scale glaciation in the temperate and hyperhumid Southern Alps of New Zealand can be generated with moderate cooling. This is because the rapid conversion of precipitation from rainfall to snowfall drives massive ice accumulation at small thermal changes (1-4°C). Our model is consistent with recent paleo-environmental reconstructions showing that glacial advances in New Zealand during the Last Glacial Maximum (LGM) and the Last Glacial Interglacial Transition (LGIT) occurred under very moderate cooling. We suggest that such moderate cooling could be generated by changes in synoptic climatology, specifically through enhanced regional flow of moist westerly air masses. Our results imply that NH climate forcing may not have been the exclusive driver of Quaternary glaciations in New Zealand and that synoptic style climate variations are a better explanation for at least some late Quaternary glacial events, in particular during the LGIT (e.g. Younger Dryas and/or Antarctic Cold Reversal).

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