Wingman Arrows

La Douleur Est Temporaire, La Victoire Est Toujours


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01. Intro – Igneous Petrology

The Earth’s Interior

Crust:

  • Oceanic crust: Thin: 10 km, Relatively uniform stratigraphy. ophiolite suite: Sediments, pillow basalt, sheeted dikes, more massive gabbro, ultramafic (mantle)
  • Continental Crust: Thicker: 20-90 km average ~35 km, Highly variable composition, Average ~ granodiorite

image Mantle: Peridotite (ultramafic)

  • Upper to 410 km (olivine ® spinel), Low Velocity Layer 60-220 km
  • Transition Zone as velocity increases ~ rapidly, 660 spinel -> perovskite-type SiIV –> SiVI
  • Lower Mantle has more gradual velocity increase

Core: Fe-Ni metallic alloy

  • Outer Core is liquid, No S-waves
  • Inner Core is solid

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Deformation of Rocks

1. Stress and Strain

Stress is a force applied over an area. One type of stress that we are all used to is a uniform stress, called pressure. A uniform stress is a stress wherein the forces act equally from all directions. In the Earth the pressure due to the weight of overlying rocks is a uniform stress, and is sometimes referred to as confining stress.

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If stress is not equal from all directions then we say that the stress is a differential stress. Three kinds of differential stress occur.

· Tensional stress (or extensional stress), which stretches rock;

· Compressional stress, which squeezes rock; and

· Shear stress, which result in slippage and translation.

When rocks deform they are said to strain. A strain is a change in size, shape, or volume of a material. Continue reading


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Continental Drift and Plate Tectonics

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From the time maps of the globe became available, people wondered about the arrangement of the continents and oceans. Hundreds of years later, valid explanations were constructed.

Early Observations

Leonardo da Vinci and Francis Bacon wondered about the possibility of the American and African continents having broken apart, based on their shapes. This thinking continued up into the early 20th century, to a meteorologist named Alfred Wegener. Continue reading


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Skema Klasifikasi Batuan Beku

Batuan beku memiliki skema klasifikasi dua kali lipat, berdasarkan mineralogi batuan dan paragenesis nya, yaitu bagaimana batuan terbentuk.

Mineral yang ditemukan dalam batuan dibagi menjadi 5 kelompok untuk tujuan klasifikasi:

Q – kuarsa

P – plagioklas

A – feldspar alkali

F – feldspathoids

M – mafik dan mineral lainnya

Sangat penting untuk memahami asal-usul dari batuan beku, sehingga mineralogi hanya diperhitungkan setelah terlebih dahulu menentukan dalam kondisi apa batuan itu terbentuk. Artinya, perlu untuk menentukan apakah batu adalah

• plutonik – berbutir kasar, terbentuk didalam, intrusi utama

• vulkanik – berbutir halus, aliran lava ekstrusif

• hypabyssal – menengah sampai berbutir halus, dangkal, intrusi kecil

• piroklastik – batuan vulkanik terbentuk dari endapan jatuhan udara

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EKSPLORASI GEOFISIKA – 6. Seismik Refraksi

6. Seismik Refraksi

Jika gelombang seismik melewati dua medium yang mempunyai kecepatan rambat yang berbeda, maka gelombang tersebut akan terbiaskan (refraksi). Jika gelombang yang datang membentuk sudut i1 dan dipantulkan dengan sudut i2 dari garis normal (Gambar 19A), maka :

clip_image002 , dimana V1 dan V2 adalah kecepatan rambat pada masing-masing media.

Jika V2 lebih besar daripada V1, maka sudut refraksi lebih besar daripada sudut normal, dan disebut sebagai sudut ic.

clip_image004.

Jika gelombang rambat bergerak di sepanjang bidang pantul, maka sudut yang dibentuk disebut dengan sudut kritis (lihat Gambar 19B)

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