Chapter 16: Accretion and Hot Spots

Definition of Accretion:
- Accretion refers to the collision and coalescence of material, leading to the accumulation of matter. This process plays a critical role in geological formations and tectonic dynamics.
Accretionary Wedge:
- An accretionary wedge is defined as the material that is added to a continental plate during the process of subduction. This occurs when one tectonic plate moves under another and is forced, or subducted, into the mantle.
Geographical Context of Accretion:
- The Coastal Ranges, particularly those found in the western United States, contain numerous accreted terranes, which are fragments of crust that have been added to the continent through accretion.

Wrangellia Terrane:
- A significant example of an accreted terrane found within the Coastal Ranges.
Types of Accreted Terranes:
  - Island Arc:
    - Volcanic islands formed from subduction processes, a classic example of accretion.   - Submarine Deposits:
    - Sediments that have accumulated underwater, also contributing to accretion processes.   - Ancient Ocean Floor:
    - Remnants of previous oceanic crust that can be involved in accretionary processes when plates interact.   - Displaced Continental Fragments:
    - Sections of continental crust that have been shifted and added to other landmasses during tectonic activities.
Geographical Distribution:
- The text mentions important geographical locations involved in this process. These include regions in Canada and the United States, near the Craton of the United States, and areas extending into Mexico.

Mantle Plumes:
- Defined as plumes of magma that originate from deep within the Earth. Unlike some volcanic regions, these plumes are not always located at tectonic plate boundaries.
Hot Spots:
- Hot spots are regions demonstrating volcanic activity that occur above mantle plumes. They are characterized by persistent and localized volcanism.

Notable Hot Spots:
- The Hawaiian Islands are highlighted as a significant hot spot island chain, showcasing volcanic activity related to a mantle plume underneath the Pacific Plate.
Geographical Locations of Hot Spots:
- Other examples of hot spots around the globe include: - Cobb Seamount - Yellowstone National Park - Iceland - Eifel - Azores - Hawaii - Canary Islands - Cape Verde - Afar - Galápagos - Samoa - Pitcairn Islands - St. Helena - Reunion Island - Easter Island - Prince Edward Islands - Tristan da Cunha - Amsterdam Island - Bouvet Island - Balleny Islands

Age of Hawaiian Islands:
- Detailed ages of some islands in the Hawaiian chain are provided in millions of years: - Kauai: Approximately 3.8 to 5.6 million years old. - Oahu: Approximately 2.2 to 3.3 million years old. - Molokai: Approximately 1.3 to 1.8 million years old. - Maui: Less than 1 million years old.
Direction of Plate Motion:
- The motion of the tectonic plates influences the Hawaiian island chain's formation and positioning relative to the underlying hot spot.
The Emperor Seamount Chain:
- This chain is formed from the same mantle plume that created the Hawaiian islands, illustrating the historical volcanic activity and the trend of plate movement.

Lo'ihi Submerged Volcano:
- Located near Hawai'i, Lo'ihi is an underwater volcano that is part of the ongoing volcanic activity in the Hawaiian hot spot region. - Depth Information:
- The text provides elevation information for specific geographical locations around Lo'ihi, indicating a diverse underwater topography.

Submergence Process:
- Eventually, volcanic islands such as those in the Hawaiian chain may become submerged due to various geological processes, including erosion and plate tectonics. - Example:
- The emperor seamounts, which illustrate this process of submergence over geological timescales.