Plate Movement (Without Wilson Cycle) PDF

GEOTEKTONIK STAG 3742 (PLATE MOVEMENT, THEIR GEOMETRIC RELATIONSHIP & HOTSPOTS) DR. NORASIAH SULAIMAN BSc UKM, PhD Leeds, UK PLATE KINEMATICS Referring to a description of the rates and directions of plate motion on the surface of the Earth. The motion takes place on the surface of a sphere thus...

GEOTEKTONIK STAG 3742 (PLATE MOVEMENT, THEIR GEOMETRIC RELATIONSHIP & HOTSPOTS) DR. NORASIAH SULAIMAN BSc UKM, PhD Leeds, UK PLATE KINEMATICS Referring to a description of the rates and directions of plate motion on the surface of the Earth. The motion takes place on the surface of a sphere thus must use the tools of spherical geometry, and to do this, we must make three assumptions: ◦ The Earth is, indeed, a sphere. ◦ The circumference of the Earth remains constant through time. ◦ Plates are internally rigid, meaning that all motion takes place at plate boundaries.  PLATE KINEMATICS 1. Absolute reference frame: describe plate motions with respect to a fixed point in the Earth’s interior. 2. Relative reference frame: describe the motion of one plate with respect to another.  PLATE KINEMATICS Absolute reference frame Relative reference frame Can be determined by: Can be determined by: I. Plotting plate motion relative I. Magnetic anomalies (Seafloor spreading rate; mid- to a fixed spot in the mantle Atlantic = 18 mm/yr, East-Pacific Rise = 150 mm/yr, Global average = 50 mm/yr) II. Hotspot II. Age of offset features III. Direct measurement Strain meters across faults [SKETCH] Space geodesy (e.g. satellite laser ranging techniques + the Global Positioning System).  ABSOLUTE MOTION Plate motion relative to a fixed reference point in the mantle (e.g., Hotspot) Not all volcanoes occur along plate boundaries. Some form above a mantle plume and is called hot-spot volcanoes. Mantle plumes appear to be independent of plate boundaries - used as the “fixed” reference points for calculating absolute plate velocities. hotspot = bila volcano tak occur kat plate boundaries but occer atas mantle plume HOT SPOT Isolated volcanoes on Earth Gives a reasonable approximation of absolute plate velocity. The age of the volcanoes in the chain increases progressively away from the plume (called hot-spot tracks) semakin jauh volcano dari hotspot track, semakin tua ia. The orientation of a hotspot track gives the direction of plate motion, and the rate of change in the age of volcanic rocks along the length of the track represents the velocity of the plate. HOT SPOT Eg., Hawaii Emperor chain in the Pacific. The 6000 km-long track Runs towards WNW and then bends abruptly NNW (at 42My) Consists of extinct volcanoes of increasing age to the NW (the oldest remaining volcanoes in this chain are older than 80 Ma).  Heat conducts out of liquid outer core. = Heat from the core warms base of the mantle, creating a hot layer named D' layer. = This hot, buoyant layer at the base of mantle forms mantle plume. = MANTLE PLUME The plume naik sbb its material is hotter, less dense, and has lower viscosity than the surrounding mantle. = Mantle plumes stay in fixed position, correlating with their origin near the core boundary. Initiate at the base of the mantle within the = Unlike mantle plumes, mid-ocean ridges have sources in the shallow mantle. D” layer (at a depth of about 2900 km). Form because heat conducting out of the liquid outer core warms the base of the mantle, creating aparticularly hot, positively buoyant layer. The plume ascends because its material is hotter (lower density and viscosity) than the surrounding mantle. The fixed position of mantle plumes correlates with their origin near the core boundary. Mid-ocean ridges have shallow mantle sources mantle plume ada saluran cylindrical dan bulbous head (yg bergerak keatas through mantle) mmbntuk broad-mushroom-like head bila reach bottom of litospehere the head mmbuatkn kenaikan permukaan dan bulging of litosphere ini juga dikaitkan dgn pemecahan continents mnybbkn extrusion of big volumes of basalt magma yg terbentuk penetrate litospheric mantle and crust mnybbkn huge amount of partial melting & pembentukan basaltic magma kt base of litosphere MANTLE PLUME saluran cylindrical Has cylindric conduit approximately 150 km diameter and bulbous head that moves upward through the mantle. Formed a broad mushroom-like head (up to 1000 km in diameter) when reaches the bottom of the rigid lithosphere. The head generates surface uplift and bulging of the lithosphere (thermal expansion of the heated area) (elevations > 1000 m can be attained). Huge amount of partial melting and magma generation (basaltic magma) near the base of the lithosphere (100–150 km). The magma penetrates through the lithospheric mantle and crust lead extrusion of enormous volumes of basalt. Associated with breaking up continents and cpercontinents cyces. Plume Model (Griffi ths and Campbell, 1990) 1. On continents, hot spot tracks are less noticeable and usually don't form clear chains of volcanoes. 2. The litospehere crust is thick, making it hard for magma to break through. 3. The path of the magma can be disrupted, and the composition of the magma can change, making it harder to detect these tracks. 4. Example : The track of the Mesozoic Great Meteor Plume HOT SPOT TRACKS ON THE CONTINENT  Less distinctive and commonly not marked by volcanic chains.  The thick continental lithosphere is difficult for the magmas to penetrate, and disruptions of magma paths and changes of magma composition make detection more difficult.  E.g., The track of the Mesozoic Great Meteor Plume FLOOD BASALTS (LIP) Flood basalts, also called large igneous provinces (LIP), are characterized by layered basaltic deposits several kilometers thick that form huge plateaus on land and below sea level. Flood basalt eruption: ◦ Massive ◦ Formed highest single mountain on Earth (e.g., Hawaii) ◦ Form huge flood basalt fields ◦ Silent but deadly - several episodes of mass extincitons. ◦ Thick lava flows (due to low viscosity of basalt) that cover huge areas (>100,000 km2). FLOOD BASALTS (LIP) ◦ Short duration but high lava volume (> 1 million km3 during an interval of only one or several million years). ◦ Create huge plateaus on land and below sea level. ◦ 11 have occured in the last 250my (5 are connected to mass extinctions) Global distribution of large igneous provinces in the oceans (submarine plateaus) and on land (flood basalts).  CAMP The Central Atlantic Magmatic Province (CAMP) ◦ Formed 201 my ago ◦ Covered 10 million km2 (nearly 2% of Earth Surface) ◦ Occur at the boundary of the two main landmass: Laurasia and Gondwana ◦ Slipt the Supercontinent Pangea SIBERIAN TRAP The Siberian Trap, Rusia ◦ The largest volcanic event in the last 500 my ◦ 250my ago ◦ Eruptions lasted 2my ◦ Covered 7million km2 ◦ Erupted 4 million km3 of lava ◦ The great Dying-PT mass extension (95% of all species wipe out) Copyright (c) 2009 Pearson Prentice Hall, Inc   Rotation on Euler pole (=rotation axis) RELATIVE  Displacement follows small circles MOTION  Transforms parallel to small circle segments The motion of any plate with The location of the Euler is given by the respect to another can be intersection between great circles. defined by imagining that the position of one of the plates is fixed. Euler pole: the intersection between the imaginary rotation axis and the surface of the Earth.  **Relative Motion Explained Simply:** - **Rotation on Euler Pole:** Plates move by rotating around an imaginary axis called the RELATIVE MOTION Euler pole. - **Small Circles Path:** The movement of a plate follows small circles on the Earth's surface. - **Parallel Transformations:** Transformations happen parallel to these small circle segments. The motion of a plate between time 1 and time 2 - **Finding the Euler Pole:** The Euler pole is found where great circles intersect on the  Earth's surface. is a rotation (ω) around the Euler axis. - **Fixed Plate Method:** To understand the motion, imagine one plate is fixed and observe how the other plate moves relative to it. - **Euler Pole Definition:** The Euler pole is the point where the imaginary rotation axis  Same angular velocity (w) between plates but meets the Earth's surface. different linear velocity (v) as function of **Motion Over Time:** - **Rotation Between Times:** Between two points in time, the plate's motion is a rotation distance from Euler pole (v = r sin θ, where θ is around the Euler axis. - **Same Angular Velocity:** Plates have the same angular velocity (rate of rotation) around the angle between r and the Euler axis) - the Euler axis. - **Different Linear Velocity:** The linear velocity (speed in a straight line) varies depending meaning that the relative linear velocity between on how far the point is from the Euler pole. The formula for linear velocity is \( v = r \sin \theta \), where: - \( v \) is linear velocity two plates changes along the length of a plate - \( r \) is the distance from the Euler pole - \( \theta \) is the angle between the point and the Euler axis boundary. This means that the speed at which two plates move relative to each other changes along their boundary. Copyright (c) 2009 Pearson Prentice Hall, Inc  (R-T transform fault) PLATE INTERACTION- TWO-PLATE SYSTEM Several different geometries/configuration; I. Transform connect two segments of growing plate boundaries (R-R transform fault/ RRF), II. One growing and one subducting plate boundary (R-T transform fault/ RTF) III. Or two subducting plate boundaries (T-T transform fault/ TTF) PLATE Triple junction between a divergent boundary, a convergent boundary, INTERACTION- and a transform boundary, known as ridge-trench-transform (RTF) TRIPLE = three plate system triple junctions - (e.g., off the west JUNCTIONS coast of northern California). There are some localities where three plates are in contact, and these are termed triple junctions. Triple junctions between three ocean ridges, are known as ridge-ridge-ridge, or RRR triple junctions - (e.g., between African, Indo- Australian, and Antarctic plates in the Indian Ocean)  PLATE INTERACTION-TRIPLE JUNCTIONS Stable triple junction: can exist for a long time, even though the location of the triple junction Ustable triple junction: change rapidly to create a new arrangement of plate boundaries.  PLATE-DRIVING FORCES The movement of the Earth’s plate is partly the result of heat convection cells (magma) in the mantle due to pressure differences in the earth- a convection-cell model These convective cells carry hot molten material (magma) from deep in the earth to the surface at the divergent boundary. This material cools, loses heat and then descends back into the earth at the convergence boundary, dividing the lithosphere into large pieces. mnybbkn convectice cells carry magma magma menyejuk, litospehere from deep in the earth to descend back into earth divided into large surface at divergent boundary at convergent boundary pieces PLATE-DRIVING FORCES ◦ Slab-pull forces: negative buoyancy of slab ◦ Ridge-push forces: topographic spreading ◦ Drag forces/resistive forces) under the moving plates  RIDGE PUSH Ridge-push force is the outward directed force that pushes plates away from the axis of a mid-ocean ridge - cause seafloor spreading. It exists because oceanic lithosphere is higher along midocean ridges than it is in the abyssal plains. Gravity pushes the oceanic crust away from the higher spreading ridges, towards the trench. SLAB PULL Slab-pull force is the force that pulls lithosphere into a convergent margin. The subducting cold slab of lithosphere, being denser than the surrounding warmer asthenosphere, pulls the rest of the plate along as it descends into the asthenosphere. Phase transformations (PT) change basalt to much denser eclogite, thus,“pulls” the rest of the plate down with it.  BASAL DRAG FORCES The flow of asthenosphere due to convection does create some basal drag at the base of plates, that can assist or retard motion - are relatively small.  Asthenosphere flows in the same direction as the plate motion - basal drag may accelerate the motion.  Asthenosphere flows in a direction opposite - basal drag may retard the motion.  Asthenosphere flows at an angle to the plate motion - basal drag may change the direction of motion.