Evolution of Volcanoes and Magmas in the Northern Luzon Arc
Date Issued
2012
Date
2012
Author(s)
Lai, Yu-Ming
Abstract
The Northern Luzon Arc includes the destroyed volcanoes in the Coastal Range (CR) of eastern Taiwan and volcanic islands between Taiwan and Luzon Island. According to the volcanic facies associations, the Sr-Nd isotopic geochemistry, and the geography of the region, four volcanoes were identified in the CR, namely Yuemei, Chimei, Chengkuangao and Tuluanshan. Moreover, the near-vent facies association showed different degrees of erosion in the volcanic edifices for Chimei, Chengkuangao and Tuluanshan. This implies that Yuemei’s main volcanic body may have been destroyed and submerged into the trench with the northward subduction of the Philippine Sea Plate. A hypothesis can be given for the evolution of volcanism and geomorphology during the arc’s growth and the arc-continental collision in the northern Luzon Arc. These volcanoes were built up from the seafloor to emerge as islands during the arc’s volcanism, and then they ceased. They were then uplifted and accreted after the collision. The oldest volcano, Yuemei, may have already been subducted into the trench.
Complex rocks, consisting of different lithologic breccias and sediments in the Tungho area, were formed by magmas and magma-sediment mingling. Based on field occurrences, petrography, and mineral and rock compositions, three components: mafic magma, felsic magma, and sediments can be identified. A mafic magma generated from depth and stayed to form a stratified magma chamber. After that, some mafic magma from the deep pushed the upper felsic magma rising and intruding, and partially mingled with magmas in the chamber. Then, both magmas exploded, the mafic lava cooled slowly and flowed along the slope of the seamount, at the same time, felsic magma intruded into wet tuffaceous sediments to explode and form peperites. Finally, a viscous mafic lava flow made contact with exploding felsic magma thereby allowing these two magmas to mingle in a limited zone again.
Ignimbrites are generally crop out on the top of volcanic sequences in the CR. White volcanic breccias or bombs and peperites could be found in this sequence. Peperites showed blocky and fluidal textures due to basaltic to dacitic juvenile volcaniclasts mingled with mud, sand or suffaceous sediments. Ignimbrites with white volcaniclasts and peperites were the distinctive lithofacies indicated to the erupted environment were reached to the sea level. Volcanic facies associations from deep marine, submarine to subaerial could be reconstructed. This rule may be applied to all of the volcanic islands in the Northern Luzon Arc.
Volcanic rocks in the CR show the increasing of K2O content and the LREE-enrichment and decreasing of εNd value from the older to younger volcanics. They formed from the same source and with different degrees of fractional crystallizations and crustal contaminations. Yuemei and Tuluanshan volcanoes showed no or less effect by these influence while Chimei and Chengkuangao volcanoes showed much fractional crystallizations and changed their source characteristics after 6.6 Ma and 7.4 Ma years ago, respectively. Magmatic processes in the CR were similar to the western volcanic arc chain based on their variations of geochemistry with ages. Magma evolution in the Northern Luzon Arc included two stages: the first one was started by the subduction of the South China Sea Plate beneath the Philippine Sea Plate and formed the western volcanic arc chain. Magmas were formed from two components mixing between depleted mantle and increasing accepted terrigeous sediments before 6 to 5 Ma years ago. After that, the subducted angles changed as a result of the ridge subduction. The old pelagic sediments which were stored due to the previous subduction might be entered to the magma source and caused the divergent from the mixing curve. The second stage was the eastern volcanic arc chain erupted after 3 Ma years ago. Magma components were mixing by depleted mantle and the old pelagic sediments. Furthermore, according to other studies, crustal contaminations were also happened in some particular areas.
Subjects
The Northern Luzon Arc
Coastal Range of eastern Taiwan
volcanic evolution
magmatic evolution
peperite
SDGs
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-101-D94224002-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):da67eb7eebccfcef2a16e995f4c36cdd