Chrome Extension
WeChat Mini Program
Use on ChatGLM

Building a Continental Arc Section: Constraints from Paleozoic Granulite-Facies Metamorphism, Anatexis, and Magmatism in the Northern Margin of the Qilian Block, Northern Tibet Plateau

GEOLOGICAL SOCIETY OF AMERICA BULLETIN(2022)

Cited 2|Views6
Abstract
Continental arcs in active continental margins (especially deep-seated arc magmatism, anatexis, and metamorphism) can be extremely significant in evaluating continent building processes. In this contribution, a Paleozoic continental arc section is constructed based on coeval granulite-facies metamorphism, anatexis, and magmatism on the northern margin of the Qilian Block, which record two significant episodes of continental crust growth. The deeper layer of the lower crust mainly consists of medium-high pressure mafic and felsic granulites, with apparent peak pressure-temperature conditions of 11-13 kbar and 800-950 degrees C, corresponding to crustal depths of similar to 35-45 km. The high-pressure mafic granulite and local garnet-cumulate represent mafic residues via dehydration melting involving breakdown of amphibole with anatectic garnet growth. Zircon U-Pb geochronology indicates that these high-grade metamorphic rocks experienced peak granulite-facies metamorphism at ca. 450 Ma. In the upper layer of the lower crust, the most abundant rocks are preexisting garnet-bearing metasedimentary rocks, orthogneiss, and local garnet amphibolite, which experienced medium-pressure amphibolite-facies to granulite-facies metamorphism at depths of 20-30 km at ca. 450 Ma. These metasedimentary rocks and orthogneiss have also experienced partial melting involving mica and rare amphibole at 457-453 Ma. The shallow to mid-crust is primarily composed of diorite-granodiorite batholiths and volcanic cover with multiple origin, which were intruded during 500-450 Ma, recording long-term crustal growth and differentiation episode. As a whole, two episodes of continental crust growth were depicted in the continental arc section on the northern margin of the Qilian Block, including: (a) the first episode is documented in a lithological assemblage composing of coeval mafic-intermediate intrusive and volcanic rocks derived from partial melting of modified lithospheric mantle and subducted oceanic crust during southward subduction of the North Qilian Ocean at 500-480 Ma; (b) the second episode is recorded in mafic rocks derived from partial melting of modified lithospheric mantle during transition from oceanic subduction to initial collision at 460-450 Ma.
More
Translated text
求助PDF
上传PDF
Bibtex
AI Read Science
Must-Reading Tree
Example
Generate MRT to find the research sequence of this paper
Data Disclaimer
The page data are from open Internet sources, cooperative publishers and automatic analysis results through AI technology. We do not make any commitments and guarantees for the validity, accuracy, correctness, reliability, completeness and timeliness of the page data. If you have any questions, please contact us by email: report@aminer.cn
Chat Paper

要点】:本研究通过古生代甘肃北山地区的高压麻粒岩相变质作用、熔融和岩浆活动,构建了大陆弧段,记录了两次显著的大陆壳增长事件,为评估大陆建设过程提供了重要约束。

方法】:研究采用同期的岩相学、大地构造位置、锆石U-Pb定年等技术,对大陆边缘的构造带进行剖析。

实验】:实验通过对甘肃北山地区古生代地壳不同层位的高压至超高压麻粒岩相岩石进行详细的地质地球化学分析和定年,发现存在两期大陆壳增长事件:第一期为约500-480 Ma时南向北的北祁连洋俯冲过程中,由部分熔融的改造地幔和俯冲洋壳产生的同期幔源中基性侵入岩和火山岩;第二期为约460-450 Ma时从洋壳俯冲向初始碰撞转换过程中,由部分熔融的改造地幔产生的麻粒岩。