The Origin and Age of the Pacific Islands - Report Example

Running Head: GLОBАL ТЕСТОNIСS Student’s Name: Course Code: Lecture’s Name: Date of presentation: Table of Contents 1. Palaeomagnetic Data Hawaiian Islands 6 2. Gravity and other geophysical data in Hawaii 9 3. Marine magnetic anomaly data 13 4. Seismology studies in Hawaii 14 5. Basins studies in Hawaii 22 6. References 27 List of Figures ‎1‑1: Map and position of Hawaiian Islands 4 ‎1‑2: Map of the Pacific Ocean indicating the location of the Major Geological Features and the Islands 6 ‎4‑3: Seismicity status in the Big Hawaiian Island for the year 2000 15 ‎4‑4: The Ewa Coastal Plain, Oahu, Hawaii and the Surrounding area 18 ‎4‑5: Well Logging Information Data 18 ‎4‑6: Section Structure of Ewa Plain, Hawaii 19 ‎4‑7: Composite Picture of Seismic Refraction Results around major islands of Hawaii 21 ‎4‑8: Global Magnetic anomaly grid in the 3D display software. The image is shown from northward Hawaii 22 ‎5‑9: Block diagram of the shield stage 23 ‎5‑10: Thin lava flows from the shield stage of the Koolau Volcano 23 ‎5‑11: Diagram showing groundwater occurrence in shield-stage lavas 24 ‎5‑12: Block diagram showing the post shield stage. 25 ‎5‑13: Example of Cinder cones of the postshield stage of Mauna Kea, Big Island 25 ‎5‑14: Block diagram of the rejuvenation stage 26 ‎5‑15: Rejuvenated Cone at Koko Crater 26 The origin and age of the Pacific islands: a geological overview ‎1‑1: Map and position of Hawaiian Islands The Pacific Ocean developed from the Panthalassic Ocean that was created as a result of the lifting apart of Rodinia around ca 750Ma (Aitchison J.C, Clarke, & Cluzel, 1995). The initial ocean floor attributed to the present Pacific Plate was formed in 160Ma, rising from the west and spreading to the central Pacific, finally developing to form the largest oceanic plate on earth. Other tectonic plates such as Juan de Fuca, Cocos and Nazca were initially a single plate, formed eastward of the original spreading centre (Broyles, 1978). The Pacific islands have developed as; linear strings of volcanic islands on top of each plates via mantle plume or through propagation of atolls, fracture origins, fragments of continental crust, uplifted coral reefs, abducted sections of the bordering lithospheric plates and islands emanating from subduction along convergent plate boundaries (Christie D.M, 1992). Some of these islands include Hawaii, Japan, New Zealand, Samoa, society, Fiji and Galapagos. Understanding the geological development of Hawaii requires the comprehension of the geological history of the Pacific Ocean and the thousands of islands in it. Origin of the Pacific Ocean The origin dates back to 7650Ma during the period of the rifting of the Proterozoic continent, Rodinia. The continent separated into two leading to the creation of the Panthalassic Ocean, a predecessor of the Pacific Ocean. After a number of break-away, the earth began to attain its present form by 50Ma, the Pacific plate spread to ultimately occupy about two thirds of the present day Pacific Ocean (Bonneville A, 2006). The creation of the volcanic island seamounts and chains The formation of the Hawaiian chain islands can be described by the lithosphere shifting over a stationary hot pustule in the mantle. Each of the Hawaiian Islands could have been formed in after basaltic magma lifted through the lithosphere through the surface creating active mass shield volcanoes. As the plate shifted, the alignments of the extinct volcanic islands record the timing and direction of the apparent movement with regard to the reference frames of the stationary hot spots. McDougall, (1979) proposed that the stationary hot spots were perpetually supplied by a plume emanating from the deep mantle. He also suggested that these pacific volcanic islands were created along a propagating or pre e- existing fracture within the lithospheric plate as a result of internal stresses transmitted from the margins of the plate. (Tarduno, 1997), suggested three mechanisms were responsible for the formation of the hot spots i.e. (i) the transition area between the lower and upper mantle, (ii) deep lower outer/ mantle core, (iii) from beneath the lithosphere but within the upper mantle (Bonatti E, 1977). ‎1‑2: Map of the Pacific Ocean indicating the location of the Major Geological Features and the Islands With the movement of the volcanic islands from the points of formation, the oceanic crust becomes progressively denser and colder, settling from its formation level. Consequently, each volcanic island slowly sinks as it progresses further from its starting point. In tropical ware the growth of the coral growth leads to the formation of fringing reefs (Christie D.M, 1992). 1. Palaeomagnetic Data Hawaiian Islands The Hawaiian Islands are principally volcanic, wholly shield volcanoes created over the Hawaiian hot spot when the Pacific plate shifted progressively towards the WNW as shown in the figure below The oldest part of the Hawaiian Islands is the Kure Atoll which occurs in the western end of the chain, was formed in ca 25Ma (Bird P, 2003). The islands become gradually larger and younger as you move towards ESE, where the newest and still active volcanically is the island of Hawaii 910458km2) (McDougall, 1979). The entire land mass of the state of Hawaii is 16705 km2. The island is also home to a number of high peaks in the Mauna Kea archipelago (5204m above sea level) and Mauna Loa 4069M0, about two- thirds of the island is above 610m. In terms of age, the youngest and second largest in size is Maui (1888 km2) dating between 1.32- 0.75Ma, followed by Molokai dating between 1.75 to 1.9Ma. Oahu has an approximate size of 1433 km2 and dates between 2.6 and 3.7Ma. The total coastline of the Hawaiian Islands is approximately 1207km (Neal, 2013). The large island of Hawaii is the closest existing island to the hot spot of Hawaii, thought to be the in the vicinity of the Loihi Seamount at 19˚N, 155˚W. The resultant chain then extends towards northwest through the Hawaiian Islands to Midway (32˚N 173˚ E) where there is a remarkable directional change to the north creating then Emperor Seamount Chain (Neal, 2013). With a more distance from source, the 1209 volcanoes within the chain ultimately subside with heir associated oceanic plate to a depth of about 2km (Bonneville A, 2006). Meiji occurs in the northern terminus, once likened to Hawaii that is next to be subducted to the Aleutian Trench, a distance of about 6000km from Hawaii. The age of the bend in arrangement of the volcanic chain has been dated to about 47Ma (Tarduno J.A, 2003). Earlier along this was interpreted as a shift in the movement of the pacific plate over the Hot spot of Hawaii, however new palaeomagnetic research study information have suggested that in the period between 76Ma and 47Ma when the Emperor Seamount Chain was being formed, the Hawaii hot spot also shifted southwards as a rate of about 30mm per year over the WNW consequently shifting the Pacific Plate. Since that period, the Hawaiian Hotspot seems to have remained fixed to the Earth’s spin axis (Bird P, 2003). Notwithstanding the study information, the ages of the Hawaiian Islands reveal a very standard time- progressive path. On the other hand, the islands chain may have been formed by a propagating fracture attributed by the direction of the regional stresses, caused by the earlier erupted volcanoes, and or the fabric of the sea floor (Bonatti E, 1977). 2. Gravity and other geophysical data in Hawaii Introduction The Hawaiian Institute of Geophysics established 750 gravity stations over the Hawaiian chain in between 1963 and 1964. Majority of these centers were established in main Hawaiian Islands of Lanai, Kahoolawe, Maui, and Oahu. According to (Rose and Belshe, P.374), shipboard gravity surveys have been used to produce large volumes of gravity data have been generated from surrounding ocean areas of the major islands in Hawaii (Duerksen, 1943). The data was used to prepare a composite anomaly map of a section of Hawaiian Ridge between Maui and Oahu as shown in the figure below. The produced gravity data, coupled with the increase in other forms of geophysical and geological knowledge regarding the Hawaiian Islands, now enables the possibility of a significant interpretation of the gravity data in terms of the general structure of the Hawaiian Swell (Furumoto A. S., 1967). This paper presents a view of the structure of the Hawaiian Swell, which satisfies both the observed field gravity data and other available geophysical and geological information. Summary on Density Information of Hawaiian Islands It is important to note that a meaningful interpretation of gravity data must clearly define model which seeks to satisfy both the observed gravity field and known densities of available seismic and geological information of structural variations. Direct measurements of rock densities in Hawaiian Islands were started with the work at Washington (1917) and were concluded by Woo lard (1951). The measurement on a typical block of pahoehoe was quoted by Goranson (1928) as having a density of 2.0gcm-3. In 1963, Kinoshita et al. reported that 63 samples of a denser rock in Hawaiian Islands ranged from 1.8gcm-3 to 2.3gcm-3, averaging 2.3gcm-3. Flow measurement carried out by Hawaii Institute of Geophysics on the Island of Oahu, recorded varying dry densities of between 2.3gcm-3 and 2.9gcm-3. An amphibolites sample taken from Koolau Caldera in the island of Oahu, recorded a density of 3.0gcm-3, and a sample of weathered eclogite rock had a density of 2.8gcm-3. Woodland and Mangham 1951) asserts that majority of the rocks resulting from the solidifying rocks on the lava lake existing in Alae crater, Hawaii recorded densities of between 2.5 to 2.8 gcm-3. Results recorded from samples collected by U.S. geological survey conducted along the rift zones off the east coast of the Hawaii island, showed that the vesicles size and vesicle space reduced with water depth up to a water depth of 1000m below sea level. According to (Wooland, 1951), the recorded change in densities ranged from 2.2 gcm-3 at the resurface to 2.9 gcm-3 at about 1000m below sea level. It was also evident that at higher water depths, the densities rose to an optimum of 3.0gcm-3 (Broyles, 1978). Note: The recorded measurements were taken from small samples thus represent only individual rocks sampled. Additionally, there were negative effects to the bulk densities of the island masses by the vugular- type porosity relating to both interflow voids and lava tubes. The densities recorded were dry densities. In regard to the densities, of non- vesicular samples, the densities of sample grains for Hawaiian rocks ranged from approximate 2.9 and 3.0gcm-3, subject to the proportion of olivine present (Clague, 1987). Seismic work carried out presents a different picture along the main rift areas and the volcanic plugs. In this area the velocities of between 7.5- 8.0km/sec are recorded at depths of between 2 and 7km below sea level. The top material is in most cases overlain with a different material with a lower velocity of about 6.0km/sec. the difference between the Hawaiian volcanic rocks and other continental- type igneous rocks is that; (1) it contains large porosities (2)it has exceptionally high density, (3) it contains glass (Bonatti E, 1977). Volcanic Centers and Rift Zones According to Malahoff and Woolard, (1951), the magnetic work shows that the Hawaiian Islands were formed through the lavas that were extruded primarily along the faults facing either the north- southeastern or east- west and related to the Molokai fracture system. The volcanic lava pipes may have been created at the points of intersection at the points of intersection of the rifts of the formed fracture systems (Bonatti E, 1977). After a reasonable build- up of the extruded lava, the weight of the extrusive material made the ridge to sink leading the re-establishment of isostatic equilibrium. According to Moore (&&&), the depth of the Moho is approximately 15km on the ridge and close to 11km in the side of the normal , causing a thickening of about 4km as indicated on the figure below. According to Moore, the material released had approximate velocities of between 2.5- 4.0km/sec and the relative density of 2.6g/cc, with thickness of between 2 and 3km. According to tilt data and seismic activity, Eaton (1962) postulated that the lava that erupted in the mid 90s originated 60m below sea level. (Duerksen, 1943) postulates that then rift zones are basically superficial features created after the central feature of the eruptive center was closed y the solidified material (Geophysics H. I., 1965). 3. Marine magnetic anomaly data A Earth’s Magnetic Anomaly Grid (EMAG2) is compiled from data collected from ship, airborne and satellite magnetic measurements. This creates a significant update of [previous candidate grid data for the World Magnetic Anomaly Map. The resolution of EMAGS has been advanced from 3 arc min to 2 arc min; the altitude above the geoid has been decreased from 5km to 4km. In addition grid and track line is usually added, both over oceans and lands. The guiding principles for production of the magnetic anomaly grid to offer a homogeneous grip whose horizontal derivatives were dominated by geophysical and geological features instead of data artifacts (Christie D.M, 1992). This Marine magnetic anomaly data is mainly used in development of the plate tectonics. 4. Seismology studies in Hawaii Most of the studies available concerning the upper crust in the Central Pacific Basin have been basically of geophysical in nature; real samples are needed to correlate the published theoretical geophysical information and data with the suggested stratigraphic and lithologic interpretations. In Oahu, Hawaii, seismic studies were carried through, traction, refraction and data logging methods in 1965, in association with core sample drilling carried out in Ewa Coastal Plain, Oahu Hawaii. Vast volumes of seismic data and information offer a lot of knowledge on the present day active volcanic sites in Hawaii; as well as the volcanic processes occurring beneath the Hawaiian volcanoes (Bonatti E, 1977). This is in particular, the volcanic and tectonic earthquakes as they relate to other main fault zones and to the intrusion and eruptions of magma to the surface. The map below represents the seismic status in the Hawaiian region (Clague, 1987). ‎4‑3: Seismicity status in the Big Hawaiian Island for the year 2000 Volcanic earthquakes are related directly to the magma movement underneath; earthquakes often precede or accompany this magma movements and intrusions. In most cases, the earthquakes happen before the intruding magma, allowing us to anticipate the likely location of magma outbreak. On the side, tectonic earthquakes occur in the fault regions and zones far from the key areas of magma movements. A study of the core- mantle structure beneath the Hawaiian hotspot, reveal that an earthquake of magnitude between 5.0 and 7.0 around the region of Tonga and Fiji, produced deep seismic waves that crossed beneath the Hawaiian hotspots prior to their detection by seismic measuring instruments set out in West Coast in the US. In the recent years, a number of refraction research studies, have been carried out in the crustal surface of the Hawaiian Islands. There are three geomorphic provinces; Hawaiian Deep, Hawaiian Arch, and Hawaiian Ridge. Hawaiian Arch; This represents a wide topographic feature occurring in the North of the Hawaiian Ridge and separated but the Hawaiian Trench and Deep. ( (Furumoto A. S., 1978)) found out that the average depth is about 10.4 km, with one location recorded a low depth of 9km. the crust structure within the Hawaiian arch is described by four separate layers; Layer a, b, c, d having a velocity values of 2.15 km/sec, 4.20 km/sec, 5.56-6.41 km/sec, and 6.82-7.01 km/sec respectively (Broyles, 1978). According to the azimuth, the underlying mantle has a velocity of 7.97-8.68 km/sec. Measurements done on 22°22'N and 155°28'W, reveal the velocity of the basal crust layer is 6.97km/sec (Christie D.M, 1992). Hawaiian Deep The mantle in this category is deeper than the ordinary, 13km. The overlying layers showed similar velocity as described above in the Hawaiian arch, although layer c is significantly thinner, while layer d is relatively thicker (Wooland, 1951). The Hawaiian Ridge This refers the Moho discontinuity which had a velocity of 8.10km/sec, and which gave irregularities in the depth best explained by faulting. Another section in the Coast end of Maui, gave a depth of 15.5km to the mantle, with the crust having the below velocity of Layer, a, b, c, d as 2.68km/sec, 3.65km/sec, 4.96km/sec, 7.15km/sec respectively. ‎4‑4: The Ewa Coastal Plain, Oahu, Hawaii and the Surrounding area ‎4‑5: Well Logging Information Data The plot is evidently straightforward. Considering the subsurface structure of the well, it is evident that the sedimentary column consists of at least three layers; lower layer with a velocity of 2.8Km/sec, Intermediate layer of – 2.1km/sec, and the superficial layer of 0.87km/hr. the superficial layer is hardly detected by well- logging technique, probably due its less thickness. ‎4‑6: Section Structure of Ewa Plain, Hawaii Seismological Study of the East Rift Zone of Kilauea, Puna, Hawaii A seismological study carried out in 1974 in comparison with the earthquake counts proved that the recording period was slightly higher than the normal activity but lacked large swarms that mostly occur. In this study two categories were analyzed; the Earthquakes from a section of the East rift adjacent to the Kilauea summit showed that an increased frequency material extended via the rift area to the Puna area. Earthquakes occurring within this corridor were evenly distributed up to a depth of about 7km within the rift zone. Below this 7km depth, the hypocenters were scattered vertically underneath the surface of the rift zone. Beneath the 7km, hypocenters are vertically scattered below the rift zones and slightly southwards. Lower East Rift Earthquakes Recorded by the Hawaiian Volcano Observatory Hot spots are characterized by increased temperatures, topographic swell and recent volcanic activity with isotopic signatures dissimilar from those characterized andesitic basalts or mid-ocean ridge. Hawaii is a renowned example. Hawaii also forms a perfect example of the longest- lived hotspots and when measured by the level of topographic swell created. The volcanism that is responsible for the creation of the seamounts and Hawaii islands is understood to be responsible for the shifting of the oceanic lithosphere above the mantle plume. A number of researchers studying the Hawaiian geophysical and geochemical approaches have indicated the presence of a mantle plume beneath Hawaiian Islands. A number of studies of dynamic models have suggested possible interaction between plume and lithosphere around Hawaii. A low velocity anomaly exists beneath the Hawaiian Islands and on the upper mantle. ‎4‑7: Composite Picture of Seismic Refraction Results around major islands of Hawaii ‎4‑8: Global Magnetic anomaly grid in the 3D display software. The image is shown from northward Hawaii 5. Basins studies in Hawaii Hydrogeology The main islands of Hawaaii were created through major basaltic volcanoes that were formed from the floor of the ocean a mechanism of the mid- plate hot- spot. The islands are are relatively younger in the southwest side of Hawaiian island chain. There are three stages in the life of the volcanoes of Hawaii (Oki, 1998). Shield Stage This constitutes about 90% of the shield volcano; and is characterised by a highly fluid basaltic lava which erupted at th rift and summit zones. This led to the formation of piles of numerous layers of thin flows (Nichols, 1996). ‎5‑9: Block diagram of the shield stage ‎5‑10: Thin lava flows from the shield stage of the Koolau Volcano In certain areas, for instance in the rift and summit zones; the lava- flow pile created may be obstructed by volcanic dikes. The dikes refer to vents through which magma flows out through to the surface during the active period of the volcano. These shield stage lavas create the most productive water aquifers in Hawaii. These aquifers form permeable layers that permit thousands of liters per day through horizontal hydraulic conductivities. Christie D.M, (1992) asserts that through a system called ocean- island hydrology, the shield stage lava creates freshwater lens over sea water. In Oahu for instance, the relationship between stream flow and dike- impounded water has led to erosion and faulting thus exposing widespread dike intruded regions in the island. In the recently formed islands, dikes exist beneath the rift and summit zones. Other types of rocks such as ash layers, soil and weathered rocks, thick lava layers often alter the flow of ground water (Oki, 1998). ‎5‑11: Diagram showing groundwater occurrence in shield-stage lavas Postshield Stage In this stage rocks covers the top of shield volcanoes in during and after waning and is characterized by increased viscosity of lava which leads to thicker and shorter lava flows and numerous cinder cones. Aquifers formed in this stage are reagrded to possess less hydraulic conductivity that in the earlier stage (Oki, 1998). An example is the young post shield volcanic rocks of Huallai volcano. ‎5‑12: Block diagram showing the post shield stage. ‎5‑13: Example of Cinder cones of the postshield stage of Mauna Kea, Big Island Rejuvenation Stage This results from eruptions that lead to formation of small cones and are filled with depressions as a result of erosion and faulting of the original surface of the shield volcano, for instance coastal plain and caprock in southeastern Kauai (Christie D.M, 1992) ‎5‑14: Block diagram of the rejuvenation stage ‎5‑15: Rejuvenated Cone at Koko Crater 6. References Aitchison J.C, Clarke, G., & Cluzel, D. (1995). Eocene arc-continent collision in New Caledonia and implications for regional Southwest Pacific tectonic evolution. Geology , 23, 161–164. Bassiouni, M. a. (2012, May 04). Trends and shifts in streamflow in Hawai‘i, 1913-2008: Hydrological Processes. Retrieved from http://onlinelibrary.wiley.com/doi/10.1002/hyp.9298/full, Bird P. (2003). An updated digital model of plate boundaries. Geochem. Geophys. Geosyst. Bonatti E, H. C. (1977). Easter volcanic chain (Southeast Pacific): a mantle hot line. 82, 2457–2478. Bonneville A, D. L. (2006). Temporal evolution and geochemical variability of the South Pacific superplume activity. Earth Planet . Broyles, M. (1978). Crustal Structure of the Lower East Rift Zone of Kilauea, Hawaii from Seismic Refraction. Complete Structure . Christie D.M, D. R. (1992). Drowned islands downstream from the Galápagos hotspot imply extended speciation time. Nature. , 355, 246–248. Clague, D. a. (1987). The Hawaii-Emperor volcanic chain:Volcanism in Hawaii. U.S. Geological Survey Professional paper 1350 . Duerksen, J. (1943). Gravity anomalies and meridian deflections in Hawaii. American Geophysical Union . Furumoto, A. S. (1978). Nature of the Magma Conduit under the East Rift Zone of Kilauea Volcano, Hawaii. International Geodynamics Symposium, Magma . Furumoto, A. S. (1967). The internal structure of volcanoes from seismic refraction and reflection techniques. Paper presented at. International Association of Volcanology. Geophysics, H. I. (n.d.). Geophysics, H. I. (1965). Data from gravity surveys over the Hawaiian Archipelago and other Pacific islands. Geoph. Rept . Goranson, R. (1928). The density of the island of Hawaii and density distribution in the earth's crust . American journal of science . Hawaiian Volcano Observatory, U. (1995). "Evolution of Hawaiian Volcanoes". Hill, D. P. (1969). Crustal structure of the island of Hawaii from seismic refraction measurements. Bulletin of the Seismological Society . Kinoshita, W. (1961). Gravity survey of the Island of Hawaii. U.S. geological survey Prof paper . McDougall, I. (1979). Age of shield-building volcanism of Kauai and linear migration of volcanism in the Hawaiian Island chain. Earth Planet. Sci. Lett. , 46, 31–42. Neal, V. T. (2013, May 06). The age and origin of the Pacific islands: a geological overview. Retrieved from royalsocietypublishing: http://rstb.royalsocietypublishing.org/content/363/1508/3293.long Nichols, W. S. (1996). Summary of the Oahu, Hawaii, Regional Aquifer system Analysis: . U.S. Geological Survey Professional Paper , 1412-A, 61 p. . Oki, D. (1998). Geology of the central Oahu, Hawaii, ground-water flow system and numerical simulation of the effects of additional pumping:. U.S. Geological Survey Water-Resources Investigations Report 94 . Resig, J. M. (1969). Paleontological investigationsof deepborings on the Ewa Plain, Oahu,Hawaii. . HawaiiInstitute of Geophysics Re . Ryall, A. a. ( 1968.). Crustal structu re of southern Hawaii related to volcanic processesin the uppermantle. Journal of Geophysical Research . Tarduno J.A. (2003). The Emperor Seamounts: Southward motion of the Hawaiian hotspot plume in Earth's mantle. . Sci. Express. , Sci. Express. Tarduno J.A, C. R. (1997). Paleomagnetic evidence for motion of the Hawaiian hotspot during formation of the Emperor seamounts. Earth Planet. , 153, 171–180. Wooland, G. P. (1951). A gravity reconnaisance of the island of Oahu. . U.S. Geological Union . Read More

1. Palaeomagnetic Data Hawaiian Islands The Hawaiian Islands are principally volcanic, wholly shield volcanoes created over the Hawaiian hot spot when the Pacific plate shifted progressively towards the WNW as shown in the figure below The oldest part of the Hawaiian Islands is the Kure Atoll which occurs in the western end of the chain, was formed in ca 25Ma (Bird P, 2003). The islands become gradually larger and younger as you move towards ESE, where the newest and still active volcanically is the island of Hawaii 910458km2) (McDougall, 1979).

The entire land mass of the state of Hawaii is 16705 km2. The island is also home to a number of high peaks in the Mauna Kea archipelago (5204m above sea level) and Mauna Loa 4069M0, about two- thirds of the island is above 610m. In terms of age, the youngest and second largest in size is Maui (1888 km2) dating between 1.32- 0.75Ma, followed by Molokai dating between 1.75 to 1.9Ma. Oahu has an approximate size of 1433 km2 and dates between 2.6 and 3.7Ma. The total coastline of the Hawaiian Islands is approximately 1207km (Neal, 2013).

The large island of Hawaii is the closest existing island to the hot spot of Hawaii, thought to be the in the vicinity of the Loihi Seamount at 19˚N, 155˚W. The resultant chain then extends towards northwest through the Hawaiian Islands to Midway (32˚N 173˚ E) where there is a remarkable directional change to the north creating then Emperor Seamount Chain (Neal, 2013). With a more distance from source, the 1209 volcanoes within the chain ultimately subside with heir associated oceanic plate to a depth of about 2km (Bonneville A, 2006).

Meiji occurs in the northern terminus, once likened to Hawaii that is next to be subducted to the Aleutian Trench, a distance of about 6000km from Hawaii. The age of the bend in arrangement of the volcanic chain has been dated to about 47Ma (Tarduno J.A, 2003). Earlier along this was interpreted as a shift in the movement of the pacific plate over the Hot spot of Hawaii, however new palaeomagnetic research study information have suggested that in the period between 76Ma and 47Ma when the Emperor Seamount Chain was being formed, the Hawaii hot spot also shifted southwards as a rate of about 30mm per year over the WNW consequently shifting the Pacific Plate.

Since that period, the Hawaiian Hotspot seems to have remained fixed to the Earth’s spin axis (Bird P, 2003). Notwithstanding the study information, the ages of the Hawaiian Islands reveal a very standard time- progressive path. On the other hand, the islands chain may have been formed by a propagating fracture attributed by the direction of the regional stresses, caused by the earlier erupted volcanoes, and or the fabric of the sea floor (Bonatti E, 1977). 2. Gravity and other geophysical data in Hawaii Introduction The Hawaiian Institute of Geophysics established 750 gravity stations over the Hawaiian chain in between 1963 and 1964.

Majority of these centers were established in main Hawaiian Islands of Lanai, Kahoolawe, Maui, and Oahu. According to (Rose and Belshe, P.374), shipboard gravity surveys have been used to produce large volumes of gravity data have been generated from surrounding ocean areas of the major islands in Hawaii (Duerksen, 1943). The data was used to prepare a composite anomaly map of a section of Hawaiian Ridge between Maui and Oahu as shown in the figure below. The produced gravity data, coupled with the increase in other forms of geophysical and geological knowledge regarding the Hawaiian Islands, now enables the possibility of a significant interpretation of the gravity data in terms of the general structure of the Hawaiian Swell (Furumoto A. S., 1967).

This paper presents a view of the structure of the Hawaiian Swell, which satisfies both the observed field gravity data and other available geophysical and geological information. Summary on Density Information of Hawaiian Islands It is important to note that a meaningful interpretation of gravity data must clearly define model which seeks to satisfy both the observed gravity field and known densities of available seismic and geological information of structural variations.

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