A global review and digital database of large-scale extinct spreading centers

Abstract

Extinct mid-ocean ridges record past plate boundary reorganizations, and identifying their locations is crucial to developing a better understanding of the drivers of plate tectonics and oceanic crustal accretion. Frequently, extinct ridges cannot be easily identified within existing geophysical data sets, and there are many controversial examples that are poorly constrained. We analyze the axial morphology and gravity signal of 29 well-constrained, global, large-scale extinct ridges that are digitized from global data sets, to describe their key characteristics. Additionally, the characteristics of a representative collection of active spreading centers are analyzed to review the present-day variation in the bathymetry and gravity signal of ridges in different tectonic settings such as backarc basin ridges, microplate ridges, and large-scale plate boundaries with varied spreading rates. Uncertain extinct ridge-like structures are evaluated in comparison with the signals of well-defined extinct ridges, and we assess whether their morphology and gravity signals are within the range seen at extinct (or active) ridges. There is significant variability in extinct ridge morphology; yet we find that the majority of well-defined extinct ridges have a trough form and a negative free-air gravity anomaly. We compile available data on the spreading characteristics of extinct ridges prior to cessation, such as their spreading rates and duration of spreading, and find significant differences between ridge subtypes and between oceans. Largescale extinct mid-ocean ridges persist much longer than extinct microplate spreading ridges and extinct backarc basin spreading ridges before cessation. Extinct fragmented plate and microplate spreading centers have the highest pre-extinction spreading rates, and they have greater median relief at their axial segments, suggesting that different crustal accretion styles could lead to different morphology after spreading cessation. Backarc basin ridges have more pronounced relief when they have been active for longer before cessation, which supports theories of reduced magmatic supply as the basin width increases. Extinct ridges in the Atlantic Ocean have the lowest spreading rates prior to cessation and tend to persist for twice as long as those in the Pacific before extinction. There are a larger number of extinct ridges preserved within marginal basins than expected for their combined area; these ridges may relate to the complexity of the plate boundaries in these regions. Our review of a large number of controversial extinct ridge locations offers some insight into which proposed locations are more likely to have been former spreading centers, and our analysis further leads to the discovery of several previously unidentified structures in the south of the West Philippine Basin that likely represent extinct ridges and a possible extinct ridge in the western South Atlantic. We make available our global compilation of data and analyses of individual ridges in a global extinct ridge data set a...

Moho depth and equivalent elastic thickness of the lithosphere over the Vema Channel: A new evidence of an aborted ridge

“…Extinct mid-ocean ridges record past plate boundary reorganization, and identifying their location is crucial to develop a better understanding on the main drivers of plate tectonics and also about oceanic crustal accretion. The flexural rigidity over the Vema Channel indicates a weak crust, supporting the theory that there may have been a ridge in the past, probably extinct after 11 Ma of being active (MacLeod et al, 2017). The presence of seamounts directly to the East of the center may reflect significant volcanic activity around the time of the reorganization.…”

“…Higher elastic thickness values characterize a rigid structure and lower thickness values indicate a weak lithosphere (Wienecke, 2006;Kearey et al, 2013). A low rigidity, due to low elastic thickness values, represents an important support for a possible aborted rigde through VAR, as suggest by P erez-Díaz and Eagles (2014), Constantino et al (2017), andMacLeod et al (2017). The basement interpretation (Fig.…”

“…They found a strong asymmetry of accreted oceanic crust in the spreading corridor occupied by the trough suggesting that a ridge jump may have occurred. MacLeod et al (2017) compiled largescale extinct spreading centers spreads around the world and included the Vema Channel as a possible aborted ridge, although, they suggest that this information should be target for future surveys were additional data must be used to reinforce this hypothesis. Constantino et al (2017), from a combined analysis of geophysical data, estimated the basement depth for the Rio Grande Rise and interpreted a possible extinct spreading center, which we will call in this paper as the Vema Aborted Ridge (VAR) ( Fig.…”

“…Bringing new evidences to support the Vema Channel as an oceanic extinct spreading center (Bassetto et al, 2000;P erez-Díaz and Eagles, 2014;Constantino et al, 2017;MacLeod et al, 2017), would lead us for a new understanding on the tectonic evolution of the South Atlantic, as well as improving models such as age and spreading taxes of the oceanic crust. A key issue in the understanding of the structure of the extinct ridge is the determination of the spatial variations of the flexural rigidity or equivalent elastic thickness, as it brings implications for how we describe the tectonic processes of a specific area (P erez-Gussiny e et al, 2004; Kalnins and Watts, 2009).…”

Pulsated Global Hydrogen and Methane Flux at Mid‐Ocean Ridges Driven by Pangea Breakup

“…Relict strike‐slip plate boundaries, evidenced by fracture zones, are defined by valleys 1 to 6 km deep and 15 to 40 km wide (Dick, 1989), and changes in the azimuth and velocity of plate motion over time can cause broad heterogeneities that are impossible to capture through dredged material (Fox et al, 1976). For this analysis we use a fixed width of 1 km for each OTF segment; however, more meaningful incorporation of OTFs and fracture zones (MacLeod et al, 2017; Matthews et al, 2011) into the hydrogen budget should be an important and interesting developmental avenue.…”