Relaxation of Tibetan Lower Crust and Afterslip Driven by the 2001 Mw7.8 Kokoxili, China, Earthquake Constrained by a Decade of Geodetic Measurements

2021 ◽  
Vol 126 (4) ◽  
Author(s):  
Dezheng Zhao ◽  
Chunyan Qu ◽  
Roland Bürgmann ◽  
Wenyu Gong ◽  
Xinjian Shan
Keyword(s):  
Lower Crust ◽  
Geodetic Measurements ◽  
China Earthquake

NEW METHODS OF ACCOUNTING FOR VERTICAL REFRACTION WITH TRIGONOMETRIC LIVELING IN THE CONDITIONS OF THE REPUBLIC OF UZBEKISTAN

2018 ◽  
pp. 55-57
Author(s):  
A.S. Suyunov ◽  
U.A. Berdiculov ◽  
Sh.A. Suyunov
Keyword(s):  
Refraction Coefficient ◽  
Geodetic Measurement ◽  
Ordinary Method ◽  
New Methods ◽  
Geodetic Measurements ◽  
The Republic ◽  
Vertical Gradients

In the conditions of Uzbekistan, a simple and ordinary method of refraction is used to determine the relative elevations without vertical refraction coefficient or angle. Described that these methods require a two-sided simultaneous or non-simultaneous geodetic measurements. Working formulas for vertical refraction are presented by calculating vertical gradients in geodetic measurement points.

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

2018 ◽  
Author(s):  
Griffin A. Moyer ◽  
◽  
Jesse Lee ◽  
Christopher Eddy ◽  
Elena A. Miranda ◽  
...  
Keyword(s):  
New Zealand ◽  
Lower Crust ◽  
3D Kinematics ◽  
Magmatic Arc

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

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

In-situ reaction-replacement origin of hornblendites in the Early Cretaceous Laiyuan complex, North China Craton, and implications for its tectono-magmatic evolution

2021 ◽  
Author(s):  
Jia Chang ◽  
Andreas Audétat ◽  
Jian-Wei Li
Keyword(s):  
Partial Melting ◽  
North China Craton ◽  
Lithospheric Mantle ◽  
Lower Crust ◽  
North China ◽  
Ultramafic Rocks ◽  
Magmatic Evolution ◽  
Mafic Magmas ◽  
Felsic Rocks

Abstract Two suites of amphibole-rich mafic‒ultramafic rocks associated with the voluminous intermediate to felsic rocks in the Early Cretaceous Laiyuan intrusive-volcanic complex (North China Craton) are studied here by detailed petrography, mineral- and melt inclusion chemistry, and thermobarometry to demonstrate an in-situ reaction-replacement origin of the hornblendites. Moreover, a large set of compiled and newly obtained geochronological and whole-rock elemental and Sr-Nd isotopic data are used to constrain the tectono-magmatic evolution of the Laiyuan complex. Early mafic‒ultramafic rocks occur mainly as amphibole-rich mafic‒ultramafic intrusions situated at the edge of the Laiyuan complex. These intrusions comprise complex lithologies of olivine-, pyroxene- and phlogopite-bearing hornblendites and various types of gabbroic rocks, which largely formed by in-situ crystallization of hydrous mafic magmas that experienced gravitational settling of early-crystallized olivine and clinopyroxene at low pressures of 0.10‒0.20 GPa (∼4‒8 km crustal depth); the hornblendites formed in cumulate zones by cooling-driven crystallization of 55‒75 vol% hornblende, 10‒20 vol% orthopyroxene and 3‒10 vol% phlogopite at the expense of olivine and clinopyroxene. A later suite of mafic rocks occurs as mafic lamprophyre dikes throughout the Laiyuan complex. These dikes occasionally contain some pure hornblendite xenoliths, which formed by reaction-replacement of clinopyroxene at high pressures of up to 0.97‒1.25 GPa (∼37‒47 km crustal depth). Mass balance calculations suggest that the olivine-, pyroxene- and phlogopite-bearing hornblendites in the early mafic‒ultramafic intrusions formed almost without melt extraction, whereas the pure hornblendites brought up by lamprophyre dikes required extraction of ≥ 20‒30 wt% residual andesitic to dacitic melts. The latter suggests that fractionation of amphibole in the middle to lower crust through the formation of reaction-replacement hornblendites is a viable way to produce adakite-like magmas. New age constraints suggest that the early mafic-ultramafic intrusions formed during ∼132‒138 Ma, which overlaps with the timespan of ∼126‒145 Ma recorded by the much more voluminous intermediate to felsic rocks of the Laiyuan complex. By contrast, the late mafic and intermediate lamprophyre dikes were emplaced during ∼110‒125 Ma. Therefore, the voluminous early magmatism in the Laiyuan complex was likely triggered by the retreat of the flat-subducting Paleo-Pacific slab, whereas the minor later, mafic to intermediate magmas may have formed in response to further slab sinking-induced mantle thermal perturbations. Whole-rock geochemical data suggest that the early mafic magmas formed by partial melting of subduction-related metasomatized lithospheric mantle, and that the early intermediate to felsic magmas with adakite-like signatures formed from mafic magmas through strong amphibole fractionation without plagioclase in the lower crust. The late mafic magmas seem to be derived from a slightly different metasomatized lithospheric mantle by lower degrees of partial melting.

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