Timing and setting of Guanjiagou conglomerate in South Qinling and their tectonic implications

Located in the southern Qinling Mountains of central China, the Guanjiagou Formation has been a controversial issue with regard to its depositional age and tectonic implications. Being comprised of an approximately 2050m thick succession of texturally and compositionally immature, presumed marine tu...

Full description

Saved in:
Bibliographic Details
Published in:Chinese science bulletin 2004-08, Vol.49 (16), p.1722-1729
Main Author: YAN, Quanren
Format: Article
Language:English
Subjects:
40Ar／^39Ar定年
关家沟
构造意义
残余海洋盆地
沉积年代
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Located in the southern Qinling Mountains of central China, the Guanjiagou Formation has been a controversial issue with regard to its depositional age and tectonic implications. Being comprised of an approximately 2050m thick succession of texturally and compositionally immature, presumed marine turbiditic sandstones and conglomerate, the Guanjiagou Formation consists of an overall prograding- and coarsening-upward megasequence. Although bounded by faults on both its northern and southern margins, it is weakly metamorphosed and deformed. To the north is the Devonian Sanhekou Group and to the south is the Neoproterozoic Hengdan Group. The lower portion of the sequence contains granitic and volcanic clasts (Guanjiagou conglomerate). The feldspars from these clasts were dated using the ^40Ar/^39Ar method. Two cooling ages of 219.69+0.49 and 216.46±0.59 Ma, for K-feldspar from a granitic clast and plagioclase from a volcanic clast, respectively, were obtained. These ages are identical to the time of regional igneous activities (ca. 240—220 Ma) and are interpreted as the products of magmatism associated with collision in the Qinling orogenic belt in the Early Mesozoic, suggesting that the Guanjiagou Formation was deposited in the Norian of the Late Triassic, ca. 220 Ma. Therefore, ^40Ar/^39Ar and sedimen-tary analyses suggest that the Guanjiagou Formation contains sediments that may have filled in a remnant ocean basin, which might be part of the Anyemaqen-Mianliie ocean, or Tethys on the southern side of Central Orogenic Belt in China during the Late Paleozoic to Early Mesozoic.
ISSN:1001-6538
1861-9541
DOI:10.1360/03wd0160