Petrology, geochemistry and geodynamics of basic granulite from the Altay area, North Xinjiang, China

Our plain-English summary of Petrology, geochemistry and geodynamics of basic granulite from the Altay area, North Xinjiang, China, by Z.L. Li, H.L. Chen, S.F. Yang, et al (Journal of Zhejiang University. Science, 2004).

The study

• Authors: Z.L. Li, H.L. Chen, S.F. Yang, C.W. Dong, W.J. Xiao
• Journal: Journal of Zhejiang University. Science
• Published: 2004;5(8):979-84
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The basic granulite of the Altay orogenic belt occurs as tectonic lens in the Devonian medium- to lower-grade metamorphic beds through fault contact. The Altay granulite (AG) is an amphibole plagioclase two-pyroxene granulite and is mainly composed of two pyroxenes, plagioclase, amphibole and biotite. Its melano-minerals are rich in Mg/(Mg+Fe2+), and its amphibole and biotite are rich in TiO2. The AG is rich in Mg/(Mg+Fe2+), Al2O3 and depletion of U, Th and Rb contents. The AG has moderate SigmaREE and LREE-enriched with weak positive Eu anomaly. The AG shows island-arc pattern with negative Nb, P and Ti anomalies, reflecting that formation of the AG may be associated with subduction. Geochemical and mineral composition data reflect that the protolith of the AG is calc-alkaline basalt and formed by granulite facies metamorphism having peak P-T conditions of 750 degrees C-780 degrees C and 0.6-0.7 Gpa. The AG formation underwent two stages was suggested. In the early stage of oceanic crustal subduction, calc-alkaline basalt with island-arc environment underwent granulite facies metamorphism to form the AG in deep crust, and in the late stage, the AG was thrust into the upper crust.

In plain English

This article is a geology study, not a medical or asbestos study. It does not mention asbestos, fibers, workers, exposure or health. The authors examined a newly found body of granulite, a metamorphic rock formed deep in the Earth's crust, at Wuqiagou in the Altay mountain belt of North Xinjiang, China. They focused on its coarse-grained part and reported chemical analyses of two samples. The rock was made mainly of two pyroxenes, plagioclase, amphibole and biotite. The amphibole was identified as magnesium-hornblende, a rock-forming mineral, and the article does not describe it as asbestos or as fibrous. Chemical plots placed the samples in the field of calc-alkaline basalt and showed a volcanic-arc pattern. The authors estimated peak metamorphic conditions of about 750 to 780 degrees Celsius and about 0.6 to 0.7 GPa, followed by a later, lower-pressure amphibolite-facies stage. The authors concluded that the original rock was island-arc basalt. In their account, it was metamorphosed deep in the crust during subduction of oceanic crust and later thrust up into the upper crust.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Field, petrological and geochemical study of rock samples (geology; no human or animal subjects)
• Who was studied: A granulite rock body (the coarse-grained main phase) at Wuqiagou, east of Fuyun, in the Altay orogenic belt, North Xinjiang, China; whole-rock analyses of two samples (ALT0310 and ALT0311)
• Main results:
  • The rock's minerals were hypersthene, augite, plagioclase, amphibole and biotite
  • The amphiboles were magnesium-hornblendes with TiO2 of 1.81% to 2.36%
  • The granulite samples plotted in the calc-alkaline basalt field
  • The rock showed affinity with a volcanic-arc tectonic setting
  • Estimated peak metamorphic temperature was about 750 to 780 degrees Celsius (unit lost in the OCR; given as degrees C in the article's abstract on PubMed)
  • Estimated peak pressure was about 0.6 to 0.7 GPa
  • A later amphibolite-facies stage was estimated at 700 to 720 degrees (unit lost in the OCR) and 0.23 to 0.37 GPa
• The authors' conclusion: The authors concluded that the rock's protolith was calc-alkaline basalt formed in an island-arc setting. They suggested that it formed in two stages: granulite-facies metamorphism in the deep crust during subduction of oceanic crust, then thrusting into the upper crust.

Topics

Medical terms in this study, explained in our Lexicon: Amphibole Group, Pyroxene, Protolith, Metamorphism.

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