How to create a $navigation main menu with target="_blank" on specific page.tpl.php pages
There are many ways to do this

A quick way would be to use jQuery to rewrite the anchor tags in the menu with the target attribute

$( '.page--landing [menu link selector] ).attr( 'target','_blank' );


Using the Drupal API 

function MODULE/THEMENAME_menu_link_alter(&amp;$item)
{
   if (some logic that sets it only for the desired paths/context)
   {
     $item['options']['attributes']['target'] = '_blank';
   }
}


an example from the documentation for function hook_menu_link_alter

function MODULE/THEMENAME_menu_link_alter(&amp;$item)
{
  if($item['link_path']=="admin/tutorial14333")
  {
  $item['options']['attributes']['target'] = '_blank';
  }
}