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What is a “tectonic analog”?

What is a “tectonic analog”?. Figure A13–1. (1) Mmax implies large L, W . Most SCRs are best examined with regional geologic and tectonic maps (1:2,500,000 – 1:10,000,000 scale) (2) Large tectonic elements (rifts, passive margins, orogens, cratons) are easiest to identify on regional maps.

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What is a “tectonic analog”?

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  1. What is a “tectonic analog”? Figure A13–1 • (1) Mmax implies large L, W. • Most SCRs are best examined with regional geologic and tectonic maps (1:2,500,000 – 1:10,000,000 scale) • (2) Large tectonic elements (rifts, passive margins, orogens, cratons) are easiest to identify on regional maps. • (1) + (2): Do any kinds of large tectonic elements have characteristic fault styles that favor large rupture L, W? • (Most useful if represented in CEUS and adjacent Canada) • Mmax = large Mo release on large faults

  2. Figure A13–2

  3. Characteristic fault styles Figure A13–3 • Extensional plate motions (rifts, passive margins) • Rift-parallel & margin-parallel faults are long • Steep dips, deep penetration (alkaline igneous rocks) • Large L, W: large Mo • Thick, restricted sandstones, then widespread limestones • Contractional plate motions (orogens) • Low-dip thrust faults, long, wide, above most seismicity • Faults steepen into hot cores (healing, folding, offsetting faults) • Large L, W, where low dips; smaller W where steeper: smaller Mo? • Sandstones, shales, limestones; thicker closer to rising mountains • Precambrian plate motions (cratons) • Old: rifting, folding, thrusting overprinted on each other repeatedly • Faults of all L and orientations, older faults can be healed and deformed; small effective L, W: smaller Mo • Tectonically quiet: few associated sedimentary, igneous rocks

  4. Figure A13–4

  5. Analogs Figure A13–5 • Rifts & margins have distinctive fault styles and associated igneous and sedimentary rocks. • Ditto for orogens. Ditto for cratons. • Rifts & margins are recognizable from one SCR to another, ditto for orogens, cratons • Rifts & margins, orogens, cratons are distinguishable from each other within same SCR • Differences within an SCR >> differences between SCRs • Faults heal so faulting age matters

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