Modelling the production of linear trends in granitoids using the Magma Chamber Simulator: a case study of the Jindabyne Suite from the Lachlan Fold Belt, Australia

2021 ◽  
Author(s):  
Kieran Iles ◽  
Jussi Heinonen
Keyword(s):  
Phase Equilibria ◽  
New England ◽  
Magma Chamber ◽  
Magma Mixing ◽  
Major Elements ◽  
Fractional Crystallisation ◽  
Geochemical Evolution ◽  
Geochemical Data ◽  
Linear Trends

<p>Understanding the causes of major and trace element variations of granite samples as well as their isotopic signatures is central to attempts to place these rocks in the context of broader geologic processes and continent evolution. For the granites of the Lachlan and New England Fold Belts (LFB and NEFB) of Australia there has been great debate between competing petrogenetic models. The open-system view that the isotopic variability and within-suite compositional trends can be accounted for by magma mixing and fractional crystallisation stands in contrast to the restite unmixing model, in which the geochemical features of certain granites are inherited from protoliths that underwent partial melting to produce magmas entraining varying proportions of residual material. Reconciling all aspects of the geochemical data in a mixing model is contingent on a plausible fractionation regime to produce the observed consistently linear (or near-linear) trends on Harker diagrams; however, the plausibility of existing fractional crystallisation models for LFB granites has not previously been tested with consideration of phase equilibria.</p><p>The Magma Chamber Simulator (MCS) models fractional crystallisation alone or with assimilation (AFC), constraining phase equilibria using MELTS and accounting for the thermal budget. This sophisticated modelling tool was used to conduct a case study of the I-type Jindabyne Suite of granites from the LFB, testing whether thermodynamically feasible geochemical trends matching the observed linear variations can arise through fractional crystallisation (with or without assimilation of supracrustal material). The results of 112 MCS models show (1) that for major elements liquid lines of descent (LLDs) may be sensibly linear over limited compositional ranges, (2) that the involvement of assimilation extends the range in which trends are relatively simple and near-linear, and (3) that, despite these observations, neither fractional crystallisation nor AFC are able to correctly reproduce the geochemical evolution of the I-type Jindabyne Suite granitoids as an LLD (contrary to existing models), instead persistently producing curved and kinked trends. The output of these simulations were further used to explore models in which: (a) crystal-bearing magmas evolve via fractional crystallisation or AFC (with chemical isolation assumed to be achieved through crystal zoning) and undergo varying degrees of melt-crystal segregation at different stages to produce the sample compositions; and (b) in situ crystallisation occurs via fractional crystallisation within the crystallisation zone, driving the evolution of a liquid resident magma, which the samples represent. These models are able to reproduce the Jindabyne Suite trends reasonably well. The modelling implies that fractional crystallisation, or some variant thereof, is a viable explanation for the linear trends in Jindabyne; however, tendency for grossly non-linear LLDs highlights that it should not be assumed that fractional crystallisation can generally explain linear trends in granites without careful modelling such as shown here.</p>

scholarly journals Diagnosing open-system magmatic processes using the Magma Chamber Simulator (MCS): part I—major elements and phase equilibria

2020 ◽  
Vol 175 (11) ◽  
Author(s):  
Wendy A. Bohrson ◽  
Frank J. Spera ◽  
Jussi S. Heinonen ◽  
Guy A. Brown ◽  
Melissa A. Scruggs ◽  
...  
Keyword(s):  
Phase Equilibria ◽  
Magma Chamber ◽  
Open System ◽  
Major Elements ◽  
Magmatic Processes

Mineral chemistry of the Mull-Morvern Tertiary lava succession, western Scotland

1998 ◽  
Vol 62 (3) ◽  
pp. 295-312 ◽  
Author(s):  
Andrew C. Kerr
Keyword(s):  
Trace Element ◽  
Magma Chamber ◽  
Magma Mixing ◽  
Mineral Chemistry ◽  
Fractional Crystallisation ◽  
Basic Material ◽  
Mixing Processes ◽  
Trace Element Chemistry ◽  
Wide Range ◽  
Mineral Compositions

AbstractThe 1800 m thick preserved remnant of the Tertiary lava succession of Mull and Morvern consists of three basic mantle-derived magma types, with compositions varying from tholeiitic to mildly alkalic, and from picritic basalts to trachytes. This results in a similarly wide range in mineral compositions. Contrary to the suggestions of previous workers the mineral chemistry of the lava succession (in conjunction with published major and trace element chemistry) is strongly supportive of a fractional crystallisation origin for the more evolved lavas.Resorped and regrown (with more basic material) plagioclase phenocrysts found in the more-evolved are indicative of magma mixing processes involving replenishment of an evolving magma chamber with more-basic magma. Lavas containing 15–20 vol.% plagioclase phenocrysts probably represent eruptions from the top of a magma chamber where flotation cumulates of plagioclase had developed. Fragmental phenocrysts found in some highly plagioclase phyric lavas (from near the top of the preserved lava succession) suggest that the eruption of lavas may have been explosive.

scholarly journals The dynamics of the Campi Flegrei caldera magma chamber.

2021 ◽  
Author(s):  
Chiara Montagna ◽  
Paolo Papale ◽  
Antonella Longo
Keyword(s):  
Mathematical Modelling ◽  
Magma Chamber ◽  
Magma Mixing ◽  
Campi Flegrei ◽  
Magmatic System ◽  
Remarkable Case ◽  
Volcanic System ◽  
First Order ◽  
Magma Convection

The Campi Flegrei volcanic system is certainly a remarkable case study for what concerns magma chamber dynamics. In fact, its magmatic and volcanic history appears to have been largely driven by chamber processes like fractional crystallization, magma mixing, and volatile degassing. These processes have been intensely investigated with a variety of approaches that are described in many chapters of this book, and more specifically, in Chapters 2 to 5. Here we employ physico-mathematical modelling and numerical simulations in order to study the dynamics of magma convection and mixing in a vertically extended, geometrically complex, compositionally heterogeneous magmatic system representing a schematic simplification of an overall picture emerging from previous studies at Campi Flegrei. Although clearly a simplification, a number of first order characteristics of possible real magmatic systems at Campi Flegrei are accounted for, including the more chemically evolved, partially degassed nature of magmas emplaced at shallow depths, and the likely occurrence of multiple reservoirs with different depth, size and shape which can be connected at certain stages during system evolution, allowing deeper, CO2-rich magmas to rise and rejuvenate the shallow magmas.

scholarly journals Rapid assembly of high-Mg andesites and dacites by magma mixing at a continental arc stratovolcano

Geology ◽  
2020 ◽  
Vol 48 (10) ◽  
pp. 1033-1037 ◽  
Author(s):  
Chris E. Conway ◽  
Katy J. Chamberlain ◽  
Yumiko Harigane ◽  
Daniel J. Morgan ◽  
Colin J.N. Wilson
Keyword(s):  
Time Scales ◽  
Crystal Orientation ◽  
Magma Mixing ◽  
Diffusion Time ◽  
Geochemical Data ◽  
Orientation Data ◽  
Continental Arc ◽  
Reverse Zoning ◽  
Ruapehu Volcano

Abstract Studies of pre-eruptive processes at active volcanoes require precise petrochronological constraints if they are to contribute to hazard assessment during future eruption events. We present petrological and geochemical data and orthopyroxene diffusion time scales for samples from Late Pleistocene high-Mg andesite-dacite lavas (Mg# 53–69) at Ruapehu volcano, New Zealand, as a case study of rapid magma genesis and eruption at a continental arc stratovolcano. Assembly of Ruapehu high-Mg magmas involved the mixing of primitive magmas plus entrained mantle-equilibrated olivines with mid-crustal felsic mush bodies, yielding hybridized magmas with ubiquitous pyroxene reverse-zoning patterns. Orthopyroxene Fe-Mg interdiffusion time scales linked to quantitative crystal orientation data show that most lavas erupted <10 days after resumption of crystal growth following magma mixing events. The eruption of lavas within days of mixing events implies that pre-eruptive warnings may be correspondingly short.

Asian American Dropouts: A Case Study of Vietnamese and Chinese High School Students in a New England Urban School District

2009 ◽  
Vol 7 (1) ◽  
pp. 83-104 ◽  
Author(s):  
Phitsamay Uy
Keyword(s):  
High School ◽  
High School Students ◽  
New England ◽  
Asian American ◽  
Dropout Rates ◽  
School Students ◽  
Study Support ◽  
Asian American Student ◽  
K 12

In the world of K–12 education, the growing numbers of dropouts are a major concern. This article examines the dropout rates of Chinese and Vietnamese high school students. Using logistic regression analysis, this article examines the influence of ethnicity, gender, and socioeconomic status (SES) on dropout rates. The distinct contribution of this analysis lies within the intraethnic comparisons within the Asian American student population and its use of longitudinal data. The results of the study support existing research that gender and SES are related to dropout rates. Moreover, an interesting interaction between ethnicity and SES exists.

Delineating Lake Types of the Jurassic East Berlin Formation, Hartford Basin, Newark Supergroup

2016 ◽  
Author(s):  
Alexander A. Conti ◽  
◽  
Elizabeth H. Gierlowski-Kordesch
Keyword(s):  
New England ◽  
Tholeiitic Basalt ◽  
Geochemical Evolution ◽  
Lake Basin ◽  
East Berlin ◽  
Definitive Evidence ◽  
Lacustrine Facies ◽  
Lake Deposits ◽  
First Time ◽  
Biomarker Data

The Mesozoic Hartford Basin, a fault-bounded half-graben in New England, is composed of four sedimentologic units displaying lacustrine, playa, and alluvial conditions separated by three tholeiitic basalt flows. Limited outcrop, however, has restricted analyses across the basin. The Jurassic East Berlin Formation, in particular, crops out only in the southern and northern extents of the basin, exposing the upper 100-118-m of deposits. As a result, a new core analysis across a 600-m-transect of East Berlin rocks has been completed in the central region of the basin, exposing the entire 195-m thickness of the formation for the first time. Cores expose eight 3-m-thick lacustrine mudrock units, the upper six of which are correlative to lake deposits identified in the southern and northern extents of the basin. Additionally, thin chicken-wire evaporites demarcate the lowermost, previously unexposed, lacustrine unit, 7-m beneath a 15-cm-thick tufa horizon. Thin playa deposits and thick sheetflood and Vertisol packages separate these lake sequences over 5-30-m of vertical distance.To supplement these sedimentologic data, and better understand lake geochemistry of the basin during East Berlin time, new biomarker analyses have been applied to each of the eight lacustrine mudrock units for the first time. Biomarker data are useful for determining the lake-basin type, a paleolake classification system derived by Bohacs, Carroll, and others to describe predictable physical and geochemical evolution within rift basins from fluvial facies to over-filled, balance-filled, and under-filled lacustrine facies; subsequently, balance-filled lacustrine facies grade to a terminal fluvial facies during changes in accommodation space through time. While fluvial facies envelope lake deposits within the Hartford Basin, identifying the lake types within the East Berlin has been problematic because of limited exposures. These new sedimentologic and biomarker analyses, however, suggest balance-filled lacustrine conditions at the base of the East Berlin that grade into under-filled conditions upsection. These new biomarker data finally provide definitive evidence for changing lake types during East Berlin time.

Feldspar crystallization under magma-mixing conditions shown by cathodoluminescence and geochemical modelling – a case study from the Karkonosze pluton (SW Poland)

2004 ◽  
Vol 68 (4) ◽  
pp. 561-577 ◽  
Author(s):  
E. Słaby ◽  
J. Götze
Keyword(s):  
Magma Mixing ◽  
Main Tool ◽  
Precise Determination ◽  
Geochemical Modelling ◽  
Magma Evolution ◽  
Sw Poland ◽  
Crystallization Path ◽  
Geochemical Mass Balance

AbstractFeldspars from the Karkonosze pluton (SW Poland) display many features compatible with magma mixing. The mixing hypothesis has been tested using a geochemical mass balance law resulting in two possible paths of magma hybridization. Based on the results of the geochemical calculation, feldspar samples have been chosen along both mixing lines for cathodoluminescence (CL) investigation which was used as the main tool for the reconstruction of their crystallization path. Changes in the conditions of nucleation and crystallization of the feldspars as well as their movement within the magma chamber have been recognized due to different luminescence characteristics. These changes in the conditions of crystallization obtained by CL allow a precise determination of the genetic affinity of the samples to more mafic or more felsic environments.The results of the present study proved CL to be a valuable tool for the study of crystal-growth morphologies in a dynamic, turbulent environment and also as a geochemical tool for the reconstruction of various petrogenetic mechanisms (e.g. magma hybridization). Accordingly, the combination of CL with geochemical modelling provides corresponding information about magma evolution in an open system.

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