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Inferring the Paleo‐Location of Proto‐Arc Magmas During Subduction Infancy in the Izu‐Bonin‐Mariana
Subduction zones are one of the principal drivers of the modern‐day plate tectonics, but the processes that develop as incipient subduction zones mature are yet to be understood. Finding modern analogs for different stages of subduction infancy remains an outstanding challenge to answer questions on how and when an oceanic subduction zone reaches a quasi‐steady state to become long‐lived. Here, we compare the southern Mariana intra‐oceanic arc, in which near‐trench spreading and infant arc magmatism developed ∼3–4 Myr ago, with the Izu‐Bonin‐Mariana (IBM) proto‐arc magmas that formed during subduction infancy ∼52 Myr ago. Building upon this comparison, we propose that the Southern Mariana may be considered as a modern analog to subduction infancy. The similarities between the Southern Mariana arc magmas and the IBM Eocene proto‐arc magmas suggest that the IBM proto‐arc crust might have formed within 80–90 km from the paleo‐trench (slab at < 90 km paleo‐depth), while the Eocene infant arc was likely located at ∼100 km from the paleo‐trench (∼100–125 km slab paleo‐depth). We use our constraints further to propose a new conceptual model of subduction evolution for IBM. In this model, development of the subduction channel during arc infancy facilitated downward slab penetration and intensified corner flow in the sub‐arc asthenosphere of the mantle wedge. As such, cooling and serpentinization of the fore‐arc mantle might be considered as the principal drivers of subduction maturation and stabilization over the IBM lifetime. Key Points We use the Southern Mariana to place constraints onto the petrogenesis of the Izu‐Bonin‐Mariana (IBM) proto‐arc crust The IBM proto‐arc magmas developed within 90 km from the paleo‐trench and overlaid a paleo‐slab within 90 km depth The subduction channel likely played an important role in the evolution and stabilization of the IBM convergent margin
Journal Article
Afetna Point, Saipan : archaeological investigations of a Latte Period village and historic context in the Commonwealth of the Northern Mariana Islands
When Ferdinand Magellan first anchored off the island of Guam in 1521, the inhabitants of the small Chamorro village at Afetna Point on the southwest coast of Saipan were likely unaware. Archaeological investigations of the traditional village yielded Latte Period burials, ceramics, stone and shell tools, microfossils from food remains, and charcoal from cooking features dating between A.D. 1450 and 1700. No direct evidence of Spanish Contact before forced abandonment of the island circa 1730 was encountered, after which time Saipan remained virtually unpopulated until the arrival of Carolinian and Chamorro settlers from Guam nearly a century later. Spanish settlement in 1668, the German occupation from 1898-1914, and the Japanese sugarcane period from 1914-1944 left few traces at the site until WWII and subsequent American administration. Afetna Point and Saipan have therefore been a contested landscape for centuries, but the island's prehistory has deep roots that tie the Mariana Islands and its modern culture to ancestral SE Asia.
Book
Saipanese English : local and global sociolinguistic trends
In this volume, the emergence of English in Saipan is being examined in the complex context of its colonial past. The focus lies on the influence of the American era on the linguistic outcomes in Saipan. Sociolinguistic interviews with indigenous Chamorros and Saipan Carolinians were analyzed using qualitative and quantitative methods.
eBook
The highest and the lowest
\"Learn all about the highest and lowest places on Earth and find out what it takes for life to survive in these extreme locations.\"-- Provided by publisher.
Book
Yellow Beach 2 after 75 Years
On June 15, 1944, Afetna Point was called 'Yellow Beach 2' by the U.S. Marines and Army infantry braving Japanese resistance to establish a beachhead before capturing As Lito airfield in the following days. After 75 years, this book presents archaeological evidence, archival records, and respected elders' accounts from WWII.
eBook
Abyssal Circulation From the Yap‐Mariana Junction to the Northern Philippine Basin
The lower deep branch of the Pacific Meridional Overturning Circulation (L‐PMOC) is a crucial element of the ocean's climate and biogeochemical systems through carrying the Lower Circumpolar Water (LCPW). For the first time, the pathway and volume transport of L‐PMOC from the Yap‐Mariana Junction (YMJ) to the Northern Philippine Basin (NPB) are revealed by a six‐mooring array measurement over 2019–2021. The L‐PMOC seasonally intrudes into the western Pacific at the YMJ. Then, it is directed into the West Mariana Basin (WMB) through YMJ‐Northern Channel with 1.41 ± 1.43/0.26 (mean ± standard deviation/total rms error) Sv, and further into the NPB through Kyushu‐Palau Ridge (KPR) Channel with 0.75 ± 0.53/0.18 Sv. Their difference 0.65 ± 1.35/0.28 Sv is the net lateral flux of LCPW into the WMB over the 2.5 yr. Analyses of a data‐assimilative ocean model solution suggest that the L‐PMOC transports through the deep channels are consistent with deep pressure gradients forced mainly by upper ocean processes. Plain Language Summary The North Pacific bottom water cannot be locally formed due to the shallow connection to the Arctic. It originates from the Antarctic and is transported northward by the lower deep branch of the Pacific Meridional Overturning Circulation (L‐PMOC). We deployed a six‐mooring array over 2019–2021 to measure the L‐PMOC from the Yap‐Mariana Junction (YMJ) to the Northern Philippine Basin (NPB). The new data extend our previous observations about the pathway and volume transport of L‐PMOC intruding into the western Pacific at the YMJ, and for the first time depicts the abyssal flow from the West Mariana Basin (WMB) into the NPB through the Kyushu‐Palau Ridge (KPR) Channel. Because the YMJ‐Northern and KPR Channels are effectively the only two channels allowing the Lower Circumpolar Water (LCPW) in/out of the WMB, the positive difference of transport through them is the net lateral flux of LCPW into the WMB over the 2.5 yr. A high‐resolution data assimilative ocean model is analyzed to link the variations of the transports through deep channels to the deep pressure gradient. Key Points A six‐mooring array captured hitherto unknown abyssal flow from Yap‐Mariana Junction to Northern Philippine Basin (NPB) during 2019–2021 A single mooring in a deep channel at Kyushu‐Palau Ridge provides an exploratory transport estimate of Lower Circumpolar Water into NPB Model data reveal that lower deep branch of the Pacific Meridional Overturning Circulation transport variations through channels correspond to deep pressure gradients mainly forced by upper ocean
Journal Article
To understand subduction initiation, study forearc crust; to understand forearc crust, study ophiolites
Articulating a comprehensive plate-tectonic theory requires understanding how new subduction zones form (subduction initiation). Because subduction initiation is a tectonomagmatic singularity with few active examples, reconstructing subduction initiation is challenging. The lithosphere of many intra-oceanic forearcs preserves a high-fidelity magmatic and stratigraphic record of subduction initiation. We have heretofore been remarkably ignorant of this record, because the \"naked forearcs\" that expose subduction initiation crustal sections are distant from continents and lie in the deep trenches, and it is difficult and expensive to study and sample this record via dredging, diving, and drilling. Studies of the Izu-Bonin-Mariana convergent margin indicate that subduction initiation there was accompanied by seafloor spreading in what ultimately became the forearc of the new convergent margin. Izu-Bonin-Mariana subduction initiation encompassed ∼7 m.y. for the complete transition from initial seafloor spreading and eruption of voluminous mid-ocean-ridge basalts (forearc basalts) to normal arc volcanism, perhaps consistent with how long it might take for slowly subsiding lithosphere to sink ∼100 km deep and for mantle motions to evolve from upwelling beneath the infant arc to downwelling beneath the magmatic front. Many ophiolites have chemical features that indicate formation above a convergent plate margin, and most of those formed in forearcs, where they were well positioned to be tectonically emplaced on land when buoyant crust jammed the associated subduction zone. We propose a strategy to better understand forearcs and thus subduction initiation by studying ophiolites, which preserve the magmatic stratigraphy, as seen in the Izu-Bonin-Mariana forearc; we call these \"subduction initiation rule\" ophiolites. This understanding opens the door for on-land geologists to contribute fundamentally to understanding subduction initiation.
Journal Article
Population Size and Habitat Occupancy by the Endangered Mariana Crow
I present data on the Mariana Crow for an extensive but previously unavailable set of population and habitat surveys from 1992 to 1993. From these, I (1) compute a series of population estimates from that period during which Mariana Crow numbers were first entering a precipitous decline, (2) quantitatively assess the habitats occupied by individual birds and thereby provide a view of the range of habitats occupied during a time when the species was still widespread, and (3) provide the first direct wet-dry season comparisons of populations and habitat occupancy. Surveys yielded significantly different wet (943) and dry season (459) population estimates, which suggested wet season courtship activity preceding dry season nesting when birds became more secretive. Moreover, they indicated that the critical turning point in population decline was after 1995. Forest was the principal habitat type occupied during both wet and dry seasons, with savanna present less than half as often as forest, although birds occupied a range of additional habitats. The species was more versatile in habitat use than is often assumed, as rates of habitat occupancy and availability were similar. Versatility is an advantage for populations confined to small islands that periodically suffer catastrophic habitat damage due to typhoons.
Journal Article