In the example below I set the maximum zoom level to 5% of the chart. Drag and pan with a left mouse button to zoom in; use a right mouse click to zoom out again. The functionality is available in other core charts as well, such as line, column and bar charts. For more configuration options of the explorer settings visit the Google documentation.
Add to the list of options
and you get crosshair navigation lines as well.
R version 3.1.1 (2014-07-10)
Platform: x86_64-apple-darwin13.1.0 (64-bit)
attached base packages:
 stats graphics grDevices utils datasets
 methods base
other attached packages:
loaded via a namespace (and not attached):
 RJSONIO_1.3-0 tools_3.1.1