scholarly journals Geochemical evolution of the New England lamprophyre suite: a hotspot signature preserved in the continental crust?

2019 ◽  
Keyword(s):  
New England ◽  
Continental Crust ◽  
Geochemical Evolution

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.

scholarly journals Geochemical Evolution of Earth's Continental Crust

2018 ◽  
Author(s):  
C. Brenhin Keller
Keyword(s):  
Continental Crust ◽  
Quantitative Information ◽  
Earth’S Crust ◽  
Geochemical Evolution ◽  
Geologic Time ◽  
Open Questions ◽  
Equable Climate ◽  
Earth's Crust ◽  
Life On Earth ◽  
Underlying Processes

Earth’s unique continental crust represents the active interface between the deep earth and the surface earth system, and is crucial for the survival and diversification of life on Earth, both as a source for nutrients and a component in the silicate weathering feedback that stabilizes Earth’s equable climate on billion-year timescales. However, many open questions remain regarding the formation and secular temporal evolution of Earth’s crust – in part due to the extremely poorly-mixed nature of Earth’s continental crust such that compositional heterogeneity at any one point in geologic time typically dwarfs any systematic variation over time. New computational approaches enabled by the emergence of large, freely accessible geochemical datasets provide a way to see through this heterogeneity and extract quantitative information about underlying processes and variables that drive the evolution of Earth’s crust over geologic time.

The geochemical evolution of the continental crust

1995 ◽  
Vol 33 (2) ◽  
pp. 241 ◽  
Author(s):  
Stuart Ross Taylor ◽  
Scott M. McLennan
Keyword(s):  
Continental Crust ◽  
Geochemical Evolution

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>

The geochemical evolution of the proterozoic continental crust in northwestern Jiangxi and western Zhejiang, China

1993 ◽  
Vol 12 (4) ◽  
pp. 308-316
Author(s):  
Zhang Bangtong ◽  
Ling Hongfei ◽  
Zhang Zuhuan ◽  
Liu Jishun ◽  
Ni Qisheng ◽  
...  
Keyword(s):  
Continental Crust ◽  
Geochemical Evolution ◽  
Proterozoic Continental Crust

The deep magmatic cumulate roots of the Acadian orogen, eastern North America

Geology ◽  
2020 ◽  
Author(s):  
S. Tassara ◽  
J.J. Ague ◽  
V. Valencia
Keyword(s):  
New England ◽  
Fractional Crystallization ◽  
Geochemical Evolution ◽  
Magmatic Arc ◽  
Southern New England ◽  
Deep Crust ◽  
Fundamental Process ◽  
Appalachian Orogen ◽  
Ultramafic Cumulate ◽  
Silicic Magmatism

The dearth of cumulate magmatic roots in accretionary orogens is a cornerstone of models that postulate redistribution of mass and energy within the crust for the genesis of intermediate to silicic magmatism. Likewise, the origin of the evolved Acadian (Devonian) plutonism in the New England Appalachians (northeastern USA) has long been explained by closed-system crustal melting due to the absence of associated coeval deep mafic counterparts. Here, we report the discovery of Acadian hydrous ultramafic cumulate rocks that formed by deep-seated (~1.1 GPa) fractional crystallization processes from a mantle-derived parental melt (Connecticut, southern New England, USA). These rocks are the first of their kind identified in the Appalachian orogen, and one of only a handful of preserved deep subarc hydrous cumulates worldwide. We propose a genetic link between the studied rocks and the evolved coeval plutonism in central-southern New England, where the former represent the missing deep cumulate roots of the same magmatic arc. Our findings support the hypothesis that differentiation of mantle-derived hydrous magmas by fractional crystallization and assimilation processes in the deep crust is a fundamental process in the production of intermediate to silicic magmatism and the geochemical evolution of the continental crust.

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