The Godzilla Megamullion, the largest oceanic core complex on the earth: a historical review

Abstract

The Godzilla Megamullion is the largest known oceanic core complex (OCC) on the Earth, located in the Parece Vela Basin in the Philippine Sea. In this article, the history of Godzilla Megamullion study is reviewed for the first time, dividing it into three major phases: (i) the early studies done before Japan's extended continental shelf survey program; (ii) the studies during Japan's extended continental shelf survey program that discovered the OCC; and (iii) the studies by the post-discovery cruises. The early studies included an interpretation of US nautical chart of the southwestern Pacific and the site surveys for Deep Sea Drilling Project cruises (DSDP Legs 6, 31 and 59). The early studies recognized the presence of the Parece Vela Rift, the extinct spreading axis of the Parece Vela Basin, and established the currently accepted model that the Philippine Sea evolved with eastward progression of backarc spreading and arc migration. The modern understanding of the Parece Vela Basin comes from Japan's extended continental shelf survey program. The program revealed the ultramafic petrology as well as a two-stage evolution model of the basin. Following these results, the discovery of the Godzilla Megamullion was made in 2001. The studies by the post-discovery cruises further revealed important characteristics of the OCC, such as the presence of abundant plagioclase-bearing peridotite and the systematic temporal changes in both deformation microstructures and composition of plagioclase and amphibole in gabbroic mylonites and ultramylonites. Zircon U-Pb ages of gabboric and leucocratic rocks indicate that the terminal phase of Parece Vela Basin spreading was with a significant decline in spreading rate and asymmetry accompanying formation of the Godzilla Megamullion. The estimated denudation rate of the OCC was approximately 2.5 cm/yr; significantly slower than the previous estimate based on poorly constrained magnetic data.

The effect of a hydrous phase on P‐wave velocity anisotropy within a detachment shear zone in the slow‐spreading oceanic crust: A case study from the Godzilla Megamullion, Philippine Sea

“…). A total of 67 samples were obtained from this dredge site during cruise KH07‐02 (Leg 4) aboard the R/V Hakuho‐maru (Ohara ). Fifty‐seven gabbroic rocks of the 67 samples consist mainly of Fe–Ti oxide gabbro with minor gabbro, and are generally hydrated, deformed, and Mn‐coated.…”

“…; Ohara et al . , ; Ohara ). Based on zircon U–Pb dating of Godzilla gabbroic and leucocratic rocks, Tani et al .…”

“…Diverse gabbroic rocks have been collected from the Godzilla Megamullion, which is the largest known oceanic core complex (OCC) on the Earth, located on the southwestern flank of the inactive S1 spreading segment of the Parece Vela Rift ( Fig. 1; Ohara et al 2001Ohara et al , 2003Ohara 2015). Based on zircon U-Pb dating of Godzilla gabbroic and leucocratic rocks, Tani et al (2011) suggested that the Godzilla Megamullion exhumed in a slowspreading environment with a denudation rate (halfspreading rate) of around 2.5 cm/y.…”

Geochemical/Petrological Interactions between Subducting Lithosphere and Petit-spot Magmas

“…トランスフォーム断層帯に露出する"abyssal peridotite" (Dick, 1989;Warren, 2016)や，マ グマ供給率が低い低速拡大軸で発生する"oceanic core complex"または"megamullion" (Dick et al, 2008;Ohara, 2015 (Hirano et al, 2006) 。溶岩の組成は，プレート 直下のアセノスフェアの情報を多く残している可 能性が高い。さらに，噴出した溶岩は，海洋地殻 からマントルにかけてそれぞれ捕獲岩または捕獲 結晶を含有している (Hirano et al, 2004(Hirano et al, , 2006Harigane et al, 2011;Yamamoto et al, , 2014 1． トンガ海溝海側斜面 (Hirano et al, 2008) 2． チリ海溝海側斜面 (Hirano et al, 2013) 3． 北 米 Basin and Range(Valentine and 4． グ リ ー ン ラ ン ド 南 方 海 域 (Uenzelmann-Neben et al, 2012) 5． コスタリカ付加体 (Buchs et al, 2013) 6． ジャワ海溝海側斜面・クリスマス島(Taneja et al, 2015) 7． フレンチポリネシア周辺海域 (Hirano et al, 2016) (Clouard and Bonneville, 2001) (Wang et al, 2006;Yoshino et al, 2006;Mierdel et al, 2007;Gaillard et al, 2008;Kawakatsu et al, 2009;Rychert and Shearer, 2009;Conrad et al, 2011;Sakamaki et al, 2013;Sifré et al, 2014;Beghein et al, (Hirano et al, 2001(Hirano et al, , 2004(Hirano et al, , 2006 Hirano et al (2006) 中の Fig. S2 を参照されたい． Fig.…”

Virtual special issue: Understanding of the largest oceanic core complex on the Earth, Godzilla Megamullion

“…This virtual special issue is derived from the successful workshop, summarizing the current understanding of the OCC. Ohara () reviewed the history of the Godzilla Megamullion studies, providing a sound background information for studying the OCC to the ocean lithosphere communities. Sanfilippo et al () reported the trace element compositions of the clinopyroxene and plagioclase of the Godzilla troctolites, discussing the importance of melt‐mantle interaction of the composition of the lower oceanic crust, and its importance for the evolution of Mid‐Ocean Ridge Basalt.…”