26. Using the chart below, write a brief geologic history of the Sandia Mountain

Question

26. Using the chart below, write a brief geologic history of the Sandia Mountains area based on the cross section in Figure 7, using your knowledge of relative and absolute dating. Tell a story, by starting with the oldest recorded event and give your relative and/or absolute reasoning for its place in time. Events include rock names (as labeled on the diagram such as Sandia Granite, Zia Sandstone), formation of unconformities (referred to by specific type), and rock deformation (e.g. tilting or metamorphism during "x" time period). If some relative-age relationships seem ambiguous, then explain the different optional interpretations. Please use the space below to write out your answer. Time OLDEST Event (e.g. Madera Limestone) Absolute and/or Relative Reasoning YOUNGEST

Explanation / Answer

Time                             Event                                                               Absolute and/or Relative Reasoning

Oldest                     

                        Metamorphic rocks                                      All of the metamorphic rocks of the sandia’s                                                    

                                                                                                 are very old. They range in age from 1.4 to  

                                                                                                 1.7 billion years. This means that they represent

                                                                                                  parent rocks ( The original rocks Prior to      

                                                                                                  Metamorphism that are even older than the                       

                                                                                                   Sandia granite date 1.4 billion years old.

                      Sandia Granite                                                 Sandia granite is one of the oldest rocks visible at

                                                                                                 the surface. It is around 1.4 billion years old.

Aplite Dikes                                                        These are thinner than pegmatite dikes and are

                                                                                                  filled by fine, sugary crystals of Quartz and

                                                                                                  Feldspar.

                    Fault Zone                                                           They represent a complex of the ancient

                                                                                                 sedimentary and volcanic rocks and a very long

                                                                                                 and complicated geologic history involving faults.

                  Madera Limestone                                             About 300 million years ago

                                                                                               All limestone you find in the sandias will contain                                 

                                                                                                 marine fossils

                   Zia Sandstone                                                     Sandstone were formed about 290 million to 200

                                                                                                 million years ago during the geologic periods

                                                                                                 known as the Permian and Triassic.

                   Sierra Ladrones formation                               It preserves fossils dating back to the Neogene                        

                                                                                                 Period ( 23 million years old –present)

YOUNGER

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