T181 Cratonic Assembly in the Precambrian: Forming the Core of Modern and Ancient Landmasses (Posters)

Monday, 23 October 2017
9:00 AM - 6:30 PM
Halls 4EF

GROWTH OF THE NORTH CHINA CRATON BY ARCHEAN THROUGH PALEOPROTEROZOIC ACCRETIONARY OROGENESIS

Paper number: T181-2
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

We propose an actualistic tectonic division of the North China Craton using a multi-disciplinary approach to define sutures, their ages, the nature of rocks between them, to determine their mode of formation and means of accretion or exhumation, and to compare with appropriate modern analogues. The eastern unit of the craton consists of several small blocks assembled between 2.7-2.6 Ga that resemble fragments of an accreted archipelago similar to those in the extant SW Pacific. A thick Atlantic-type margin developed on the western side of the newly assembled Eastern Block by 2.6-2.5 Ga, then a >1,300 km- long arc and accretionary prism collided with this margin at 2.5 Ga, obducting ophiolites and ophiolitic mélanges, and depositing a thick clastic wedge in a foreland basin over the Eastern Block. Arc-polarity reversal followed, leading to short-lived injection of mantle wedge-derived melts to the base of the crust generating mafic dikes and arc-type granitoid plutons with associated metamorphism. By 2.43 Ga, the remaining open ocean west of the accreted arc closed with the collision of an oceanic plateau preserved as the Western Block with the collision-modified margin of the Eastern Block, causing further deformation that gave rise to the Central Orogenic Belt. Rifting at 2.4-2.35 Ga of the newly amalgamated continent led to a rift preserved along its center, and new oceans within the other two rift arms, which removed a still-unknown continental fragment from its northern margin. By 2.3 Ga an arc collided with a new Atlantic-type margin developed over the rift sequence along the northern margin of the craton, converting it to an Andean margin. Andean margin tectonics affected much of the craton from 2.3 to 1.9 Ga, giving rise to a broad E-W swath of continental margin magmas, and retro-arc basins. The across-strike extent of these tectonic components is similar to that across the present-day Andes. From 1.88 to 1.79 Ga a granulite facies metamorphic event was superimposed across the entire continental block with high-pressure granulites and eclogites in the north, and medium-pressure granulites across the whole craton. The scale of this event is similar to that in Central Asia that resulted from the Cenozoic India-Asia collision, which has an across-strike width of 1,000 km, and a duration of ~90 Ma.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-302837

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