Program Studi Ilmu Kelautan FMIPA UNSRI GEOLOGI LAUT IV LEMPENG TEKTONIK Program Studi Ilmu Kelautan FMIPA UNSRI

Teori Lempeng Tektonik??  Teori yg Menjelaskan mengenai sifat bumi yang dinamis (mobil) Kerak bumi terdiri dari lempeng2 Lempeng-lempeng yg ada saling bergerak dan berinteraksi satu dg yg lainnya Umumnya gempa bumi dan erupsi gunung api terjadi akibat tumbukan lempeng 7 Lempeng utama Plates are made of rigid lithosphere Lempeng Pasifik (Pasific plate) Lempeng Euroasia (Eurasian plate) Lempeng India-Australia (Indian-Australian plate) Lempeng Afrika (Africa plate) Lempeng Amerika Utara (North American plate) Lempeng Amerika Selatan (South American plate) Lempeng Antartika (Antartic plate)

Lempeng tektonik on Modern Earth

Batas-batas Lempeng?? Divergen Transform Konvergen

Batas-batas Lempeng?? 1. Batas Konvergen Batas antar lempeng yg saling bertumbukan Terbagi 2: Batas subduksi (Subduction zone) : bts lempeng yg berupa tumbukan lempeng, dimana salah satu lempeng menyusup ke dalam perut bumi, dan lempeng lainnya terangkat ke permukaan. Contoh: Kepulauan Indonesia sbgai bagian dari lempeng benua asia tenggara dg lempeng samudera Hindia-Australia di sebelah selatan Sumatera, Jawa, hingga NTT.  Kepulauan Philipina sbgai hasil subduksi antara lempeng samudera Philipina dg lempeng samudera Pasifik

Convergent Boundaries There are three styles of convergent plate boundaries Continent-continent collision Continent-oceanic crust collision Ocean-ocean collision Convergent boundaries are where the plates move towards each other. There are three types of convergent boundary, each defined by what type of crust (continental or oceanic) is coming together. Therefore we can have: continent-continent collision, continent-oceanic crust collision or ocean-ocean collision….

Continent-Continent Collision Forms mountains, e.g. European Alps, Himalayas When continental crust pushes against continental crust both sides of the convergent boundary have the same properties (think back to the description of continental crust: thick and buoyant). Neither side of the boundary wants to sink beneath the other side, and as a result the two plates push against each other and the crust buckles and cracks, pushing up (and down into the mantle) high mountain ranges. For example, the European Alps and Himalayas formed this way.

Batas Konvergen– Oceanic & Continental

Continent-Oceanic Crust Collision Called SUBDUCTION At a convergent boundary where continental crust pushes against oceanic crust, the oceanic crust which is thinner and more dense than the continental crust, sinks below the continental crust. This is called a Subduction Zone. The oceanic crust descends into the mantle at a rate of centimetres per year. This oceanic crust is called the “Subducting Slab” (see diagram). When the subducting slab reaches a depth of around 100 kilometres, it dehydrates and releases water into the overlying mantle wedge (Presenter: explain all of this using the diagram). The addition of water into the mantle wedge changes the melting point of the molten material there forming new melt which rises up into the overlying continental crust forming volcanoes. Subduction is a way of recycling the oceanic crust. Eventually the subducting slab sinks down into the mantle to be recycled. It is for this reason that the oceanic crust is much younger than the continental crust which is not recycled.

Subduction Oceanic lithosphere subducts underneath the continental lithosphere Oceanic lithosphere heats and dehydrates as it subsides The melt rises forming volcanism E.g. The Andes The Andes mountain range along the western edge of the South American continent is an example of a mountain belt formed by subduction. The continental crust of the South American plate has buckled under the compressional strain of converging with the Nasca and Antarctic plates. Additionally there are many volcanoes, the result of melting of the subducting slab and the production of new material that has risen through the crust to the surface.

Ocean-Ocean Plate Collision When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone. The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench. The worlds deepest parts of the ocean are found along trenches. E.g. The Mariana Trench is 11 km deep! When two oceanic plates converge, because they are dense, one runs over the top of the other causing it to sink into the mantle and a subduction zone is formed. The subducting plate is bent down into the mantle to form a deep depression in the seafloor called a trench. Trenches are the deepest parts of the ocean and remain largely unexplored.

Convergent Boundary – Oceanic & Oceanic Note – plates are reversed

Batas Obduksi (Obduction zone) : bts lempeng yg merupakan tumbukan lempeng benua dengan benua yang membentuk suatu rangkaian pegunungan. Contoh: Pegunungan himalaya hasil tumbukan lempeng benua India dg benua Eurasia 2. Batas Divergen: Batas antar lempeng yang saling menjauh satu sama lainnya. Sebab pemisahan adanya gaya tarik (tensional force) yang mengakibatkan naiknya magma ke permukaan, dan membentuk material baru berupa lava.

Convergent Boundaries - Continental

Collison zones form where both sides of a convergent boundary consist of continental (buoyant) material. Modern example: Himalayas

Batas Divergen– Iceland http://pubs.usgs.gov/gip/dynamic/understanding.html

Divergent Boundary - Oceanic

Divergent Boundary - Continental

Batas Divergen: Chiefly at oceanic ridges

continent could lead to formation of oceanic lithosphere. How rifting of a continent could lead to formation of oceanic lithosphere. e.g., East Africa Rift e.g., Red Sea e.g., Atlantic Ocean

Contoh: Adanya punggung tengah samudera (Mid Oceanic Ridges) yg berada di dasar samudera atlantik. Adanya rifting yg terjadi antara benua Afrika dengan Jaxirah Arab yang membentuk Laut merah 3. Batas Transform: Batas antar lempeng yg saling berpapasan dan saling bergeser satu dg lainnya menghasilkan suatu sesar mendatar jenis strike slip fault. Patahan San Andreas di Amerika Serikat yg merupakan pergerseran lempeng samudera Pasifik dg lempeng benua Amerika Utara.

Batas Transform Where plates slide past each other The third type of boundary are transform boundaries, along which plates slide past each other. The San Andreas fault, adjacent to which the US city of San Francisco is built is an example of a transform boundary between the Pacific plate and the North American plate. Above: View of the San Andreas transform fault

Jenis batas lempeng http://pubs.usgs.gov/gip/dynamic/understanding.html

Divergent Boundary – Arabian and African Plates Arabian Plate Red Sea African Plate

Batas divergen also can rip apart (“rift”) continents

Tatanan Tektonik Muncul akibat interaksi antar lempeng yg terjadi pd bts2 lempeng konvergen, divergen, dan transform. Tatanan tektonik yg terjadi pd batas lempeng konvergen: lempeng samudera dan lempeng samudera saling bertemu menghasilkan suatu rangkaian busur gunungapi (volcanic arc) yg arahnya sejajar dg arah palung (trench). Cekungan Busur Belakang (Back Arc Basin). Contoh: Adanya rangkaian gunungapi di kepulauan philipina yg merupakan hasil tumbukan lempeng philipina dg lempeng samudera Pasifik.

Tatanan tektonik yg terjadi pd batas lempeng konvergen: lempeng samudera dan lempeng benua saling bertumbukan tatanan tektoniknya dicirikan palung, Cekungan Busur Muka (Forearc Basin), Busur Kepulauan Gunungapi (Volcanic Island Arc), Cekungan Busur Belakang (Back Arc Basin). Contoh: Kepulauan Indonesia, khususnya jalur pulau2  Sumatera, Jawa, Bali, NTB, NTT dan berakhir di kepulauan Banda.

Tatanan tektonik pd bts lempeng divergen lempeng benua mengalami pemekaran (continental drifting) dg terbentuknya laut baru . Contoh: Di Pematang Tengah samudera (pemisahan Benua Amerika dan Afrika), Laut Merah (Benua Afrika dam SemenanjungSinai/Jazirah Arab, serta rifting yang terjadi diAfrika Timur Bagian Utara

Subduction zones form at convergent boundaries if at least one side has oceanic (denser) material. Modern examples: Andes, Cascades Kenampakan utama: Palung, explosive volcanoes

Another subduction zone—this one with oceanic material on both sides. Modern example: Japan

Earthquake depth indicates subduction zones