I'm very familiar with the visual cue of a link launching a new website as is used in wikipedia:
However I'm not sure of how this works on mobile apps, for example I have this situation:
What is the custom for this on mobile?
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What I understand from your question is: What should be the behavior for "open in new tab" feature in Mobile applications?
First of all, It is not good to compare a browser functionality with an app(google map). You can do the same thing with Chrome in Mobile as well.
Assuming a general question about multitasking, it totally depends on the implements. For example,
Scenario 1: You click a button and third party app is appended inside your app and control goes there.(Pressing back button may gives back the control)
Scenario 2: You click a button and third party app opens with some passed inputs to that and you still able to switch back to your application.
Totally depends on apps behavior.
Hope this helps.