TIES IN AGE AND PROVENANCE OF THE EASTERN HAYFORK AND NORTH FORK TERRANES AND THEIR RELATIONSHIP TO THE WESTERN MARGIN OF NORTH AMERICA

The Klamath Mountains are divided into four sections: the Eastern Paleozoic belt, the Central Metamorphic belt, the Western Paleozoic and Triassic belt, and the Western Jurassic belt. The rocks in each belt get younger towards the Pacific Ocean. Within the Western Paleozoic and Triassic belt, the Eastern Hayfork terrane is a mélange once part of a supra-subduction zone complex with the North Fork terrane. There are questions about how and when these terranes formed, and their relationship, because of their lithologic similarities.

The Eastern Hayfork terrane contains blocks of quartzite, meta-argillite, meta-chert, exotic greenstone, etc. Zircons from quartzite blocks are Archean to early Proterozoic and have age peaks similar to the Antelope Mountain Quartzite, a possible source for the slide blocks in the Eastern Hayfork. The most abundant rock is the meta-argillite matrix, but its provenance and age range remain poorly constrained due to its fine-grained texture. Some zircons have been recovered and indicate deposition of 272-201 Ma with continental origins. The Eastern Hayfork terrane mélange contains Permian to Late Triassic fossils, suggesting accretion could have persisted until Late Triassic. Ar/Ar ages indicate accretion could have begun in Permian time.

The North Fork terrane consists of a mix of volcanic and sedimentary rocks with oceanic characteristics, such as greenstone, mafic volcaniclastic rocks, bedded chert, etc. The terrane is a westward verging fold with volcanic and sedimentary layers on the limbs. The basement formed 245-310 Ma, and metasedimentary detrital zircon ages are Archean to Middle Jurassic. The North Fork terrane has been compared to the Eastern Hayfork terrane as there are mineralogic and lithologic similarities in metavolcanic and metasedimentary rocks. However, there is insufficient detrital zircon dating to conclude an age relationship between the two terranes.

Metamorphosed matrix sandstones from the Eastern Hayfork terrane and bedded meta-sandstones from the North Fork terrane have been collected for petrographic analysis and zircon U-Pb dating. The goal is to determine an age and provenance relationship between the Eastern Hayfork and North Fork terranes to understand how they are related to each other and how the western margin of North America developed over time.