User:Sarcastaball/sandbox

Plate Tectonics:

• Page is frequently edited
• Debates on Talk page include creationist viewpoints and alternate methods of explanation. Pseudoscience believers attempt to interject and include their points of view on the article.
• Article was formally a "Featured Article", but was demoted 10 years ago
• Rated C for quality and listed as a "Level-3 Vital Article"
• Some citations may need work. For example, in the first paragraph, it states that Seafloor Spreading was validated in the 1950-60s and from what I found, the article did not mention or cite such information.
• Key Principles section is well organized and cited. Some similar wording used from various articles, but no plagiarism found after a few checks. No new information learned here.
• Plate Boundaries section gives good general overview and provides examples. Well sourced and linked articles provide in depth detail. No new information learned here.
• Mantle Dynamics Notes: Mantle has varying lateral density distributions (Material, mineral, and thermal) 2. Friction and gravity are the 2 biggest influences of plate motion 3. Ridge Push could have been added as a driving force. 4. Plume Tectonics is another popular explanation of the mantle driving forces, having large plumes coming from deeper parts of the mantle driving most of the convection.
• Gravity Notes: 1.Ridge Push is mentioned here 2. Flexural Bulging is a new concept to me, but no citation given. 3. Mantle domes causing gravitational sliding is also a new concept.
• Earth Rotation: 1. Not sure if anything past Tidal Drag should be included as they are only considered in other models that don't include Plate Tectonics, which is the direct subject of the article. Information doesn't seem well cited either.
• Development of Theory and organized well in both the chronological sense and subjects. Exact timelines and small details are the only new information to me. This is probably one of the most well-cited areas of the article. Un-biased views are used and many debates are discussed. No plagiarism found on the few citations I checked.
• I am also curious to find more information on how we know plate motions began 3-3.5 billion years ago when the Earth formed ~4.5 billion years ago. Somebody has already noted this.
• Celestial Bodies section is a good addition to the page. I feel this will become more prevalent and utilized later in space exploration.

Easter Microplate

Easter Plate is located to the west of Easter Island off the west coast of South America in the middle of the Pacific Ocean, bordering the Nazca plate to the east and the Pacific plate to the west. It was discovered from looking at earthquake distributions that were offset from the previously perceived Nazca-Pacific Divergent boundary. This young plate is 5.25 million years old and is considered a microplate because it is small with an area of approximately 160,000 km². Seafloor spreading along the Easter microplate's borders have some of the highest global rates, ranging from 50 to 140 mm/yr.

Structure and Tectonics (Present)

From the 1970s to 1990s, multiple efforts were made to collect data on the area, including several magnetic and gravitational anomaly surveys.

These surveys show that Easter plate is uniquely shallow, bordered by spreading centers and transform boundaries, with a triple junction located at the southern and northern tip.

Along the eastern border, there are several spreading centers south of 27°S and 3 northward propagating rifts to the north of 27°S. The axis further north is a graben reaching a depth of approximately 6000 m. Northward propagation of the eastern rifts is continuous at a speed of 150 mm/yr. The spreading ridge between 26°S and 27°S has a spreading rate of 120 mm/yr, but is asymmetrical on Nazca plate side. Bathymetry data shows the depth is 2100 m near 26°30'S and progressively gets deeper to the north, reaching depths of 3300 m in an axial valley. There is approximately a 25 km gap at the northern end of the east rift with no rift connecting the northern boundary to the eastern boundary.

Easter microplate (from GeoMapApp) with rough plate boundaries according to author

The northern border has wide ridges, greater than 1 km tall, linked side-by-side with the steeper slopes to the south. The southern trough area sits deeper than the areas to the north. The very eastern end of the northern border has pure strike-slip motion, while the the western end is marked by the Northern Pacific-Nazca-Easter triple junction. This triple junction is a stable rift-fracture-fracture zone with anomalous earthquakes occurring to the northeast portion, indicating a possible second spreading axis. The rest of the northern boundary to the east and west of the triple junction are colinear transform boundaries. A trough, approximately 3700 m deep, borders the north along this transform boundary to the east connecting to a 5300 m deep hole, called the "Pito Deep" because of its close proximity to the Pito Seamount, at the northeastern limit.

The western border is divided into two parts. The west section has 2 spreading segments running north to south with spreading rates that approximately range from 120-140 mm/yr. These segments are connected by sinistrally slipping transform faults around 14°15'S . A relay basin runs north to south along the southernmost segment as a result of past counter-clockwise rotation. The southwest consists of one slower spreading center (50-90 mm/yr) that runs northwest to southeast until joining the southern transform boundary.

Like the western end of the northerner border, the southern end also has an inferred rift-rift-fracture triple junction, but no data has been gathered yet to verify its existence. A single transform fault runs west to east and is home to the most rugged and shallow terrain with high seismic activity.

Evolution

In 1995, routine magnetic, gravity, and echosounder data, supplemented with data from GLORIA (a long-range side scan sonar), German Sea Beam, SeaMARC II, and data from the World Data Center in Boulder, CO were all utilized to construct a two-stage model for the evolution of the Easter microplate.

Stage 1: 5.25 to 2.25 million years ago

Approximately 5.25 million years ago, the boundary between the Pacific and Nazca plates was not connected and did not completely separate the two plates. The Easter microplate began to grow to the north-south throughout this period. The eastern rift, having not yet connected to the western rift, began to propagate northward by pseudofaults that appear to the west and east of the rift and continued until approximately 2.25 million years ago when the tip reached 23°S. While this was occurring, the west rift was propagating southward, north of the east rift, breaking into segments connected by transform faults that trend towards the southwest. The entire microplate continued a counter-clockwise rotation rate of 15° every million years throughout the entire history of the Easter microplate.

Stage 2: 2.25 million years ago to present

The Easter microplate grew at a slower rate in the east-west dimension during this period, as it stopped growing north-south due to the cessation of east rift propagation. The east rift did continue angular spreading while keeping the same growth rate, but did not propagate any further northward. The west rift continued adjusting with more segmenting until the southwest rift began to open and propagate to the east. The southwest rift continued propagation until the present day southern triple junction was created.

Future Predictions

Though other evolution models have argued that the microplate was created approximately 4.5 million years ago, there is currently only one hypothesis for future evolution of the Easter microplate. It is believed that due to the slowing spreading rates at the southwest rift and the northern end of the east rift, the southwest and west rift will cease spreading activity and completely transfer the microplate from the Nazca to the Pacific plate. This has been the case for other areas where extensive rift propagation studies have been conducted.

Dynamics

Driving Forces

Divergence of the Nazca and Pacific plates generate a pulling force acting on the Easter microplate, causing its rotation. Two types of driving forces are believed to act on the Nazca-Pacific plate divergence: shear and tension. Shear driving forces occur along the north and south boundaries, which explain failures due to compression in the northern end of the plate. Tension driving forces occur at the east and west rifts. Because of the fast spreading rates along these boundaries, the Easter microplate has a thin lithosphere. The normal tensional forces applied across the east and west rifts is enough to drive the microplate's rotation. Due to the slowing trend of these spread rates along these rifts to the north, it is believed the lithosphere gets thicker near the north and the shear forces are believed to contribute to the overall driving force.

Resisting Forces

Mantle basal drag accounts for 20% of the forces applied to the Easter microplate. Mantle basal drag force is calculated using the equation: ${\vec {F}}_{D}=D{\vec {V}}$ , where ${\vec {F}}_{D}$ is the mantle drag force per unit area, $D$ is the proportionality constant, and ${\vec {V}}$ is absolute velocity of microplate using a fixed hotspot as the reference frame. The value for ${\vec {F}}_{D}$ represents a quantification of the total resisting force that the ductile asthenosphere applies to the brittle lithosphere floating on top.

The other 80% of the resisting forces come from the rotation of the Easter microplate. As the microplate is rotating, normal resistances are applied to the microplate at the north and south ends where there are no rifts to help microplate adjustment. Both tension and compression contribute to the resistance, but compressional forces along the ends of the rifts have more of an impact. These compressional forces are what create the elevated regions that surround the "Pito Deep".

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Instructor comments 5/8/18

You have a good rough draft and I think you have distilled the key points from your source but there are two things you need to do to turn it into a draft that is ready for peer review and copy editing

1. Turn the notes into prose and format the sections so it starts to look like a Wikipedia article

2. You need to add citations to each statement so the reader knows where the statement comes from (at present you are just listing all your sources but not linking them to the text. Adding citations is easy to do in the visual editor with the cite tool.

To improve your draft.

I think your lead should start by stating where the plate is located (not a latitude/longitude) but general area and what plates it is sandwiched between - the current lead does this. I also think your lead is too long, and while all good material you might want to think what should be saved for the following sections.

I suggested several additional sources previously (on your talk page) and I do not think you have incorporated those yet. It would strengthen your article to have more than one source per section and Richard Hey has been pretty influential in understanding this area so not citing him is odd

A couple of factual corrections.

1. I do not think you can say that the Easter MP is the 7th smallest plate in the world. It is the 7th smallest in the list you cite but that list is not comprehensive because it becomes subjective when one decides what constitutes a small plate and what does not. So perhaps you want to say small plate and cite this source or just cite it for the area.

2. I do not know where you got 9 cm/yr from (no citation) but the fastest spreading center in the world is 15 cm/yr full rate ( http://www.soest.hawaii.edu/HIGP/Faculty/hey/fastest.html) and I think that is pretty close to your location but you would need to check.

William Wilcock (talk) 04:13, 9 May 2018 (UTC)

Easter Plate Sources:

• - Easter plate has rapid changes in rate and direction of motion
• - Easter plate is bounded on the north by transform faults and on the south by spreading centers
• - The microplate's East Rift first started to propagate northward at around 5.25 Ma
• - Easter plate is 130,000 sq. km
• - Unavailable online. Contains bathymetry and geophysical studes such as magnetic anomalies